Alla Tereshchenko

Viktoriia Fedorenko

Valentyn Smyntyna

Igor Konup

Anastasiya Konup

Martin Eriksson

Rositsa Yakimova

Arunas Ramanavicius

Sebastien Balme

Mikhael Bechelany

Keywords: ZnO, Atomic layer deposition, Photoluminescence, Optical Biosensor, Grapevine virus A-type

This thesis manuscript presents the investigations and potential applications as a (bio)sensor platform of the conform thin layers of ZnO and/or Al 2 O 3 /ZnO nanolaminates, deposited by atomic layer deposition (ALD) on the various substrates. First, a study of the optical properties of ZnO thin films (20 and 50 nm) deposited by ALD technique on the large areas of ordered silicon nanowires (SiNWs), produced by combining nanosphere lithography and metal-assisted chemical etching, was performed. These methods allowed the morphology and the organization control of SiNWs on a large area. The detailed study of structural and optical properties of core-shell SiNWs/ZnO heterostructure was done by utilizing XRD, SEM, reflectance and photoluminescence spectroscopy, respectively. Integration of SiNWs arrays as core and ZnO as shell can have a strong impact on the development of sensing elements with improved properties. In the further investigations, ZnO films formed by ALD as an optical biosensor platform for the detection of Grapevine virus A-type proteins (GVA-antigens) were represented. The GVA-antigen detection was performed using the changes in the GVA related PL band behavior. The biosensor selectivity has been proved. The possibility to detect GVAantigens without additional labels has been demonstrated. Thus, label free and sensitive photoluminescence based biosensor for GVA-antigens has been developed. Another part of our study is a specific control of protein anchoring by the development of multifunctional surface with large-scale array of polystyrene spheres (PSS), which produced by nanosphere lithography and further blocking the unspecific adsorption of protein on the surface of the PSS by PEG SAMs. The epifluorescence microscopy was used to confirm that after immersion of sample on target protein (avidin and anti-avidin) solution, the latter are specifically located on polystyrene sphere. These results are meaningful for exploration of devices based on large-scale nanoarray of PS spheres and can be used for detection of target proteins or simply to pattern a surface with specific proteins. Our research also includes the tuning of structural properties and the enhancement of electronic and optical properties of 1D PAN ZnO/Al 2 O 3 nanolaminates designed by atomic layer deposition (ALD) and electrospinning. The structural and optical properties of Al 2 O 3 / ZnO determined from the XPS, TEM, FTIR, XRD and PL analysis. The enhancement of electronic and optical properties would allow application in different fields such sensors and biosensors.

I am very thankful to my supervisor Prof. Valentyn Smyntyna and co-supervisors Dr.

Roman Viter and Dr. Igor Iatsunskyi from the home university, thanks to their efforts to establish this collaboration, the opportunity to come and to do joint French-Ukrainian PhD became possible for me.

I would like to say great thanks to my director thesis Dr. Sebastien Balme and cosupervisor Dr. Mikhael Bechelany from the host university, who always were ready to help with any challenges, for their immense support, fruitful scientific discussions and for their great experience, which they shared with me during the whole period of my PhD study at IEM. Thanks to them the work atmosphere was really nice, and it was to pleasure to work at IEM, and this thesis became a result of this work.

I would like to show my gratitude to Dr. Vincent Rouessac, who provided the attestation for the utilization oxygen plasma reactor to me. I would like to thank all the team, who work at IEM. I am very grateful to the reviewers of this thesis, Prof. Arunas Ramanavicius and Dr.

Fabien Picaud, for their effort to revise this thesis and for their contribution to improve the work. I am very thankful to the Erasmus Mundus Action 2, Backis program for the great opportunity to do my PhD in France, at IEM. The mobility gave me great experience not only in improving my scientific skills, but also in case of communication and work in team. It was pleasure to discover Montpellier and the region Languedoc-Roussillon. I had really a pleasant and fruitful continuation of my mobility at IEM. Si wafer with a trench structure [START_REF] Ritala | Perfectly conformal TiN and Al2O3 films deposited by atomic layer deposition[END_REF]………………………………………………………..……6 ZnO nanowires after the removal of PS; c) top view, the inset is a higher magnification, and d) tilted view (708). The inset is a high-magnification SEM image of the top of a nanowire grown at the top of the urchin-like structure. e,f) Cross-sectional SEM images of two urchin-like structures treated by FIB at different magnifications. g,h) High-magnification SEM images of a mechanically scratched structure for cross-section and internal surface observations, respectively [START_REF] Elias | Hollow UrchinYlike ZnO thin Films by Electrochemical Deposition[END_REF]……………………………………………………………………………………………….45 nm pore and (c) 2 nm pore. Black squares and gray rounds show signal with and without gA in the pores, respectively [START_REF] Abou Chaaya | Enhanced ionic transport mechanism by gramicidin a confined inside nanopores tuned by atomic layer deposition[END_REF]……………………………………………………………………….57 reported, representative values from the entire tested temperature range are displayed instead (The table is adopted from [START_REF] Tynell | Atomic layer deposition of ZnO: a review[END_REF])…………………………………………………………………11 Atomic layer deposition (ALD) is an attractive method to deposit thin films for advanced technological applications such as microelectronics and nanotechnology [START_REF] Kim | Atomic layer deposition of metal and nitride thin films: Current research efforts and applications for semiconductor device processing[END_REF]. ALD is generally well-suited for the deposition of oxide thin films and overlayers for various applications [2]. The oxides may be insulating, semiconducting, conducting or even superconducting. They can also be used as catalysts, light-emitting phosphors, or gas sensors. Among various methods used to form ZnO thin films, atomic layer deposition (ALD) is an innovative technique, which allows the deposition of ultrathin metal oxide films with controlled thickness, grain size, chemical composition, texture, surface morphology and defect concentration. The mentioned structural parameters make a strong impact on optical, electrical and mechanical properties [3].

List of figures

List of tables

Different studies report the growth of Al 2 O 3 /ZnO nanolaminates as well as the incorporation of Al doping in ZnO using ALD [START_REF] Abou Chaaya | Enhanced ionic transport mechanism by gramicidin a confined inside nanopores tuned by atomic layer deposition[END_REF][START_REF] Cabello-Aguilar | Slow translocation of polynucleotides and their discrimination by α-hemolysin inside a single track-etched nanopore designed by atomic layer deposition[END_REF][START_REF] Raghavan | Nanocrystalline-to-amorphous transition in nanolaminates grown by low temperature atomic layer deposition and related mechanical properties[END_REF][START_REF] Elam | Growth of ZnO/Al2O3 alloy films using atomic layer deposition techniques[END_REF][START_REF] Elam | ZnO/Al 2 O 3 nanolaminates fabricated by atomic layer deposition: growth and surface roughness measurements[END_REF]. Using ALD methods, ZnO grows as a conducting, polycrystalline film with a rough surface topography resulting from the individual crystallites. In contrast, Al 2 O 3 grown by ALD is an excellent insulating, amorphous film that deposits with high conformality. The wide disparity in physical properties between ZnO and Al 2 O 3 suggests that nanolaminates formed from alternating ZnO/Al 2 O 3 layers may possess properties that span a wide range in surface roughness and conductivity. The advanced properties of the nanolaminates such as biocompatibility, easy surface modification, and enhanced photoluminescence at room temperature could provide good capacity for the development of nanolaminates-based optical sensors and biosensors.

Research objectives

The objectives of this study are the following: Ø Optimization of the procedures for the preparation of silicon nanowires (SiNWs) by combining metal-assisted chemical etching (MACE) and nanosphere lithography (NSL) to fabricate large areas of ordered SiNWs. After the properties of the SiNWs will be improved by utilizing ALD for the deposition of ZnO thin films. Control of the morphology and organization of SiNWs on a large area by the above-mentioned techniques.

Ø Development of the novel, label free and sensitive photoluminescence based biosensor for GVA-antigens. The direct immobilization of anti-GVA antibodies was performed on the ZnO surface and resulted in the formation of biosensing structure (ZnO/anti-GVA) Ø Specific control of protein anchoring by the development of multifunctional surface with large-scale array of polystyrene spheres (PSS), which produced by nanosphere lithography and further blocking the unspecific adsorption of protein on the surface of the PSS by PEG SAMs.

Ø Tuning of structural properties and the enhancement of electronic and optical properties of 1D PAN ZnO/Al 2 O 3 nanolaminates designed by atomic layer deposition (ALD) and electrospinning. The enhancement of electronic and optical properties will allow application in different fields such sensors and biosensors.

Study plan

To achieve the above objectives, the following topics were investigated:

Ø

CHAPTER II

Literature review

General introduction

ALD is known as a unique among thin-film deposition techniques, offering conformal deposition of ultra-thin films on high-aspect-ratio nanostructures at temperatures below 100 °C.

The recently investigations in the area of ALD of ZnO, Al 2 O 3 , and Al 2 O 3 /ZnO nanolaminates, and potential applications of ALD in various research fields are overviewed in this chapter. As ALD is a thermally activated process in order to produce self-limiting reactions on the surface of a substrate, the processing temperature range for ALD -"ALD window" is represented as well.

In this chapter, the key features of ALD are described. In summary, the collected information about ALD technology is emphasized with the advantages and limitations. Finally, at conclusion part of this chapter the prospects of the ALD are presented. With devices becoming ever smaller and increasingly structured into complex three dimensional shapes, the need for controllable and conformal thin films has never been greater. ALD, with its sequential self-limiting reactions, is able to meet these demands in one of the most effective methods possible.

Introduction to ALD: brief history

Atomic layer deposition (ALD), a thin film deposition process, was first emerged as atomic layer epitaxy (ALE) and introduced in 1970s by Suntola and Antson in Finland [9]. The motivation for the development of ALD was the desire to make thin-film electroluminescent (TFEL) flat-panel displays.

From the beginning of ALD development, its applications were limited to the deposition of epitaxial layers of II-VI or III-V semiconductors, mainly for display devices, as inherently low growth rate was considered as a major obstacle for other applications [START_REF] Nishizawa | Molecular layer epitaxy[END_REF][START_REF] Bedair | Atomic layer epitaxy of IIIYV binary compounds[END_REF].

The transition from ALE to ALD occurred as a result of the fact that most films grown using sequential, self-limiting surface reactions were not epitaxial to their underlying substrates.

Moreover, amorphous films were most preferred for dielectric and diffusion barrier applications.

Consequently, the use of ALD grew in preference and now dominates with the practitioners in the field.

In Table 2-1 some mostly used names of ALD technique are presented. The name "atomic layer deposition (ALD)" dates back to the early 1990s.

Since the mid-1990s, an increasing interest to ALD has originated from the silicon-based microelectronics. This increase is a consequence of the ever decreasing device dimensions and increasing aspect ratios in the integrated circuits (IC), which require the introduction of new materials and thin-film deposition techniques. In addition, the required thickness of the films has decreased, in many cases, to the order of a few nanometers and therefore the main drawback of ALD, the low deposition rate, is becoming less important.

Currently, ALD is considered as one of the most promising thin film deposition techniques for enabling nanoscale device fabrication [START_REF] Kim | Atomic layer deposition of metal and nitride thin films: Current research efforts and applications for semiconductor device processing[END_REF]. The benefits of ALD include thickness control at the atomic scale, production of highly conformal films, low temperature growth, and wide-area uniformity. Due to these benefits, ALD is finding ever more applications.

Distinguished from other deposition techniques such as chemical vapor deposition (CVD), physical vapor deposition (PVD), and other solution-based methods, ALD as a chemical vapor method operates with a unique mechanism relying on two gas-solid half-reactions to produce an ultimate material [2]. The reactions of ALD feature the characteristics of surface-controlled and self-terminating nature. In return, ALD performs the deposition of films in a layer-by-layer mode and it is especially superior in controlling films at the atomic level. As a result, ALD provides the deposited films with excellent uniformity and unrivalled conformality. In essence, ALD works with a temperature lower than the decomposition of the used precursors typically lower than 400 ºC even down to room temperature. In addition, ALD requires no catalysts and has no needs on solvents. All the aforementioned characteristics contribute ALD to be a unique but precise deposition technique. [9]

[14]

[15]

[16]

[17]

[18]

[19]

[20] [START_REF] Malygin | CHEMICAL-COMPOSITION OF CHROMIUM AND PHOSPHORUS-CONTAINING SILICA[END_REF] In an ideal ALD growth process, different precursors are pulsed alternately onto the substrate surface in different steps. The non-reacted reactants and the reaction by-products are removed by the following inert gas purge step. This feature keeps the precursors strictly separated from each other in the gas phase. As a result, there is only the reaction of a gaseous compound reactant with the solid surface in the ALD process, which is defined as the gas-solid reaction. A general ALD process is illustrated in Figure 2 Because the GPC is fixed, a desired film thickness can be deposited simply by adjusting the number of reaction cycles. As the reactions are self-terminating, no tuning of reactant dose or flux is necessary provided that the dose is sufficient for the complete saturation of surface sites.

This surface control is responsible for ALD's inherent characteristics of extreme film thickness controllability and uniformity.

In addition, ALD has the capability to coat complex shapes with a conformal material layer of high quality, as illustrated by the cross-sectional scanning electron microscopy (SEM) image in Figure 2-2. Furthermore, ALD can make accuracy thickness control, facile doping, large area uniformity, and pinhole free film [START_REF] Leskelä | Atomic layer deposition (ALD): from precursors to thin film structures[END_REF]. ALD processes have been developed to manufacture many types of solid inorganic materials for a wide range of applications, such as oxides, nitrides, sulphides, selenides, tellurides and pure elements (Figure 2-3). Among these materials, oxides have been the type most often investigated. Typically, Al 2 O 3 can be used as a dielectric, protective or ion barrier layer in electronic and optoelectronic devices [START_REF] Puurunen | Surface chemistry of atomic layer deposition: A case study for the trimethylaluminum/water process[END_REF].

Over the past ten years, research advances have expanded the use of ALD technology to include deposition of films on materials for microelectronics applications (e.g. large area silicon substrates), materials for medical device applications and biologically derived materials. A variety of materials, such as metal oxides, metal nitrides, metal sulphides, metals, polymers and inorganic-organic hybrid materials, have been successfully grown using ALD [START_REF] George | Atomic layer deposition: an overview[END_REF]. Si wafer with a trench structure [START_REF] Ritala | Perfectly conformal TiN and Al2O3 films deposited by atomic layer deposition[END_REF].

Reactants (precursors) for ALD

Precursor chemistry plays an important role in a successful design of an ALD process [START_REF] Leskelä | Atomic layer deposition (ALD): from precursors to thin film structures[END_REF].

Several requirements are taken into consideration when choosing a chemical precursor. They must be volatile to produce a high enough vapor pressure (at least above 0.1 Torr) so they can easily be transported into the reaction zone of the process chamber. However, many precursors are low vapor liquids or even solids at room temperature and therefore require higher temperatures to raise their vapor pressure. The evaporating pressure of the precursor is an important parameter. The temperature will affect the precursor vapor pressure, which will influence the dose optimization together with pulsing length and methods. Due to various precursor states such as gas, solid and liquid, different pulsing methods should also be considered. Gas precursors are easy to pulse to the reactor. Liquid and solid precursor can be heated to achieve higher vapor pressure. If the vapor pressure is not possible to increase with raising temperature, different pulse methods can be applied to improve the precursor dose.

Precursors must be thermally stable in that they do not decompose in the source or on the substrate. Reactions due to the decomposition of reactants are likely to produce non-self-limited reaction with higher growth rates and possible film contamination of C, H, N or halide atoms depending on the precursor used.

Precursors also must react rapidly and aggressively with surface groups from the previous exposure and not with its own adsorbates in order to achieve a saturated self-limiting surface in a short time (usually < 1s). The aggressive reaction requirement is contrary to traditional CVD precursors.

Figure 2-3. Overview of the materials grown by ALD [START_REF] Miikkulainen | Crystallinity of inorganic films grown by atomic layer deposition: Overview and general trends[END_REF].

It is also preferable if the reactants are small in size to avoid reduced surface coverage due to steric hindrance. Finally, the choice of reactants has economic implications, as some are expensive and synthesis can be time consuming. Unfortunately, there are no perfect reactants, so the choice of reagents typically involves making trade-offs between cost, availability, safety, volatility and reactivity.

Different precursors have been employed for the deposition of an oxide ALD chemistry including metal halides and several types of organometallics for the metal containing precursor and water, O 2 plasma, and ozone for some of the more common oxidizers. Halides have been the most widely studied of all the metal containing precursors, however, their main drawback lies in the corrosive nature of the HCl byproduct that is often produced causing etching of the deposited films and the encasing reactor. Several organometallic precursors have been investigated

including metal alkyls, amides, alkoxides, and cyclopentadienyls, however, growth rates are usually low due to the steric hindrance associated with the large ligands attached to the molecules.

Typical metal precursors used in ALD are halides, especially chlorides, alkyl compounds, and alkoxides. Organometallic compounds, such as cyclopentadienyl complexes and alkyl and silyl amides have gained more attention recently. The nonmetal precursors used are: water, hydrogen peroxide, and ozone for oxygen; hydrides for chalcogens; ammonia, hydrazine, and amines for nitrogen; hydrides for group V elements.

The precursors should be safe and easy to handle, preferably non-toxic and noncorrosive towards the substrate and the reactor materials. For industrial use, price is also an issue. High purity is needed for some applications. While it in principle does not matter whether the reactants are gases, liquids, or solids at room temperature, the phase affects the reactor construction: Solids and low-vapor-pressure liquids require special source designs. The list of preferred properties is long, and it is evident that not many reactants in actual use fulfill all the criteria. Compromises often need to be made regarding, for example, the reactivity and corrosiveness of the by-products One of the major advantages in ALD precursor chemistry compared with CVD, for instance, is the fact that because ALD is based on surface saturation exact precursor dosage is not needed. The only requirement is that there are enough precursor molecules to cover the adsorption sites on the surface; the excess will be blown away by the inert gas purge. This makes it possible to use in situ-generation of the precursors and thus have a fresh supply of otherwise instable precursor molecules onto the substrate surface.

Synthesis of ZnO from DEZ and H 2 O

In general, metal oxides offer a variety of interesting properties for technical applications.

The oxides may be insulating, semiconducting, conducting or even superconducting. They can also be used as catalysts, light-emitting phosphors, or gas sensors. By doping, the properties can be changed or enhanced. ALD is generally well-suited for the deposition of oxide thin films and overlayers for various applications [2].

Zinc oxide (ZnO) has been widely studied since 1935 [START_REF] Bunn | The lattice-dimensions of zinc oxide[END_REF]. ZnO is a semiconductor with a wide band gap (3.37 eV) and large exciton binding energy (60 meV), making it an attractive optoelectronic material with unique optical, electronic, catalytic and photoelectrical properties [START_REF] Yang | Controlled growth of ZnO nanowires and their optical properties[END_REF]. It is one of few oxides showing confinement effects in an accessible size range [START_REF] Koch | Photochemistry of semiconductor colloids. Preparation of extremely small ZnO particles, fluorescence phenomena and size quantization effects[END_REF].

Many of the technological applications of ZnO thin films rely on producing films with high optical quality. ZnO has been commonly used for different applications, such as optical coatings [START_REF] Tonon | Degradation of the optical properties of ZnO-based thermal control coatings in simulated space environment[END_REF], light emitting diodes [START_REF] Chen | ZnO-based ultra-violet light emitting diodes and nanostructures fabricated by atomic layer deposition[END_REF], sensors [START_REF] Chaaya | ZnO 1D nanostructures designed by combining atomic layer deposition and electrospinning for UV sensor applications[END_REF], photovoltaics [START_REF] Elias | Urchin-inspired zinc oxide as building blocks for nanostructured solar cells[END_REF][START_REF] Elias | Hollow UrchinYlike ZnO thin Films by Electrochemical Deposition[END_REF][START_REF] Elias | Electrochemical growth of ZnO nanowires on atomic layer deposition coated polystyrene sphere templates[END_REF], and biosensors [START_REF] Viter | Application of room temperature photoluminescence from ZnO nanorods for salmonella detection[END_REF]. Recent approaches in nanotechnology allow one to fabricate ZnO nanostructures with high surface-tovolume aspect ratios, which is significantly important for sensor and biosensor applications.

First ALD process of ZnO was based on zinc acetate and H 2 O [START_REF] Tammenmaa | Zinc chalcogenide thin films grown by the atomic layer epitaxy technique using zinc acetate as source material[END_REF]. More recently, processes based on zinc alkyls (dimethylzinc = DMZn and diethylzinc = DEZn) have been developed [START_REF] Lujala | Atomic layer epitaxy growth of doped zinc oxide thin films from organometals[END_REF]. Because of the reactivity of the organometallics, the processes based on DMZn and DEZn and water can be operated at relatively low temperatures (below 200 °C) [START_REF] Yousfi | Study of atomic layer epitaxy of zinc oxide by insitu quartz crystal microgravimetry[END_REF].

Zinc oxide as deposited by ALD is a polycrystalline n-type semiconductor material that despite having a large band gap possesses low resistivity [START_REF] Ellmer | Resistivity of polycrystalline zinc oxide films: current status and physical limit[END_REF][START_REF] Özgür | A comprehensive review of ZnO materials and devices[END_REF].

The most studied precursor combination for ZnO ALD is DEZ-water. The deposition temperature range lies from around 100 to 350°C. Zinc oxide thin films are typically crystalline even when deposited at low temperature. Amorphous zinc oxide films can be deposited only as very thin films on certain substrate materials [START_REF] Libera | Conformal ZnO coatings on high surface area silica gel using atomic layer deposition[END_REF][START_REF] Shvareva | Thermochemistry of nanoparticles on a substrate: Zinc oxide on amorphous silica[END_REF][START_REF] Park | Preparation of one dimensional Bi 2 O 3-core/ZnO-shell structures by thermal evaporation and atomic layer deposition[END_REF].

ALD can be used to deposit ZnO by subsequently exposing a substrate to DEZ, Zn(C 2 H 5 ) 2 )

and deionized water vapor.

ZnOH* + Zn(C 2 H 5 ) 2 → ZnOZn(C 2 H 5 )* + C 2 H 6 (2-1) Zn(C 2 H 5 )* + H 2 O → ZnOH* + C 2 H 6 , (2-2)
where asterisks denote surface species [START_REF] Elam | Properties of ZnO/Al2 O 3 Alloy Films Grown Using Atomic Layer Deposition Techniques[END_REF]. Between the exposure to the precursor and the deionized water vapor, purge steps are applied to remove excess gases and reaction products.

Each ALD cycle consists therefore of a precursor step, a purge step, a deionized water vapor step, and another purge step. A Zn-O Lewis acid-base complex is formed during each half reaction, with ethane formed as a reaction byproduct with the surface alternating between being ethyl-terminated and hydroxyl terminated.

The simplified DEZ/H 2 O reaction can be generalized with the following reaction equation:

Zn(CH 2 CH 3 ) 2 (g) + H 2 O(g) → ZnO(s) + 2CH 3 CH 3 (g), (2-3)
where (g) is the gas phase of byproducts.

In the Table 2-2 some overview of the ZnO deposited by ALD technique is demonstrated. [ [START_REF] Sang | Growth of transparent conductive oxide ZnO films by atomic layer deposition[END_REF][START_REF] Yamada | Atomic layer deposition of ZnO transparent conducting oxides[END_REF][START_REF] Saito | Photo atomic layer deposition of transparent conductive ZnO films[END_REF] [53]

[38]

[8]

[54]

[55] [START_REF] Lee | Structural and optical properties of high quality ZnO films on Si grown by atomic layer deposition at low temperatures[END_REF] [57]

Zn(C 2 H 5 )

Zn(C 2 H 5 ) Zn(C 2 H 5 ) Zn(C 2 H 5 ) Zn(C 2 H 5 ) Zn(C 2 H 5 ) Zn(C 2 H 5 ) Zn(CH 3 ) 2 , Zn(C 2 H 5 ) Zn(CH 3 ) 2 , Zn(C 2 H 5 ) H 2 O H 2 O H 2 O N 2 O H 2 O H 2 O O 2 plasma H 2 O H 2 O Sapphire (0001) Glass, Si (100)
Si ( 100 1.8, 1.9 [START_REF] Lim | Effects of substrate temperature on the microstructure and photoluminescence properties of ZnO thin films prepared by atomic layer deposition[END_REF] [59]

[60]

[61]

[62]

[63]

[64]

[65]

[66]

Zn(CH [105]

[106]

[107]

[108] EDX measurements were done for the evaluation of ZnO films (Figure 2-4b). An analysis of the results show a monotonous decrease of the O/Zn ratio with a growth of the film while remaining greater than unity, which points to an oxygen-rich stoichiometry of the studied samples.

GIXRD diffraction patterns of thin ZnO films are shown in Figure 2-4c. The structure of ZnO ALD films strongly depends on the thickness. The ZnO samples obtained by 100 cycles were amorphous, had a smooth surface, and did not exhibit any XRD peaks. The increase of the film thickness was assisted by the growth of vertically oriented columns with well-defined boundaries, an improvement of the crystalline structure (narrowing of XRD peaks), a crystalline growth and an alleviation of lattice strain, and an enhancement of the surface roughness and the texture coefficient (Figure 2-4d). The same group of scientists proposed that the unusual behavior of the energy gap (Figure 2-5b) with thickness reflected by optical properties was attributed to the improvement of the crystalline structure resulting from a decreasing concentration of point defects at the growth of grains. Compared with the bulk ZnO crystals, the values of the energy gap of the films are lower due to structural defects. In summary, the authors concluded that the ultra-thin ZnO ALD films could be attractive for optical sensor/biosensor applications due to their high oxygen to zinc ratio and variable optical properties. In addition, the presence of hydroxyl terminals leads to the hydrophilicity of the films and improves the immobilization of selected kinds of bio-molecules, thus increasing the suitability for biosensor applications. The authors also overviewed a number of works with deposition of ZnO by ALD on different substrates (and influence of the substrate on the growth of ALD films) such as polyethylene-terephthalate (PET), polyethersulfone (PES) substrates, carbon nanotubes (CNTs), an organic polymer sublayer, and PAN (which was studied in their work).

The amorphous-to-crystalline phase transition in ZnO nanolayers deposited on Si and PAN nanofiber substrates, the authors explained by the higher value of nucleation sites on PAN nanofiber surfaces and the surface strain of PAN nanofibers. and the surface switches between methyl-terminated and hydroxyl-terminated.

During the first TMA half reaction (2)(3)[START_REF] Abou Chaaya | Enhanced ionic transport mechanism by gramicidin a confined inside nanopores tuned by atomic layer deposition[END_REF], TMA molecules are exposed to the surface and will adsorb on the active ligands present on the surface, in the case of TMA and water these are hydroxyl -OH* groups. A thermally activated reaction will occur splitting the (Al(CH 3 ) 3 )

molecules on the surface. The CH 3 ligands will combine with the hydroxyl surface groups and form a volatile organic compound, such as methane CH 4 , which will desorb from the surface.

The remaining part of the molecule chemisorbs to the surface chemically bonding the aluminum atom with either one or two oxygen atoms on the surface in order to deposit a stoichiometric Al 2 O 3 film. This reaction is referred to as a ligand exchange reaction. When all the hydroxyl active sites that are physically accessible to the (Al(CH 3 ) 3 ) molecules then the surface is considered saturated and the half cycle is complete. Excess TMA molecules that could not react on the surface as well as desorbed reaction by-products are purged out of the reactor. For the 2nd half cycle, for this case water, water molecules will bind to the methyl groups through another ligand exchange reaction causing the release of more CH 4 molecules.

The net effect of one (2-4)- (2)(3)[START_REF] Abou Chaaya | Enhanced ionic transport mechanism by gramicidin a confined inside nanopores tuned by atomic layer deposition[END_REF][START_REF] Cabello-Aguilar | Slow translocation of polynucleotides and their discrimination by α-hemolysin inside a single track-etched nanopore designed by atomic layer deposition[END_REF] The calculated band gap values E g are presented in Table 234. The band gap increased with the decrease of the bilayer thickness in the nanolaminates. The obtained E g values can be affected by structural defects (interstitials, vacancies, etc.) and impurities.

Table 234 The study of PL of nanolaminates was also performed (Figure 2 -11). The UV peak corresponds to free exciton emission, and the VIS peak was observed due to defect level emission.

The intensity of UV peak increased with the increase of the bilayer thickness in the nanolaminates.

The intensity of the VIS band does not follow the same tendency. The ratio of UV/vis emission could be a parameter of the crystalline structure quality of ZnO inside the nanolaminates.

It was mentioned that UV/vis intensity of nanolaminates did not increase monotonically with the increase of the single layer thickness (Figure 2

Temperature window of the ALD process

ALD is a thermally activated process in order to produce self-limiting reactions on the surface of a substrate [167]. The processing temperature range for ALD or the so-called "ALD window" is the region of nearly ideal ALD behavior between the non-ideal regions. The ALD temperature window is presented in Figure 2-12, which indicated the temperature range where thin film growth proceeds by the self-limiting reaction in an ALD mode [121]. At lower temperatures, the reactants could condense on the surface or the surface reactions may not have enough thermal energy to reach completion. At higher temperature, the surface species could decompose and allow additional reactant adsorption. This behavior is similar to CVD by unimolecular decomposition. The surface species needed for ALD could also desorb from the surface at higher temperatures and be unavailable for additional surface reactions. This desorption would lead to the decrease of the ALD growth per cycle at higher temperatures. This behavior is observed for Al 2 O 3 ALD [START_REF] Puurunen | Surface chemistry of atomic layer deposition: A case study for the trimethylaluminum/water process[END_REF]. One system that displays dramatic non-ideal ALD behavior is TiN ALD using tetradimethylaminotitanium (TDMAT) and NH 3 . Although this ALD system was initially presented as a working ALD process, additional studies revealed that the surface reactions did not reach completion, impurities were left in the resulting films, and the films had significant porosity that led to their easy oxidation [168,169]. TiN ALD using TDMAT and NH 3 has no "ALD window" where the ALD process is reasonable. In contrast, TiN ALD using TiCl 4 and NH 3 is a well-defined ALD process that occurs at higher temperatures and produces HCl as a reaction product [170]. showing the "ALD" window [START_REF] George | Atomic layer deposition: an overview[END_REF].

Outside the temperature window at lower temperatures there occurs either less growth due to insufficient thermal energy for reactions to occur or more growth due to condensation of precursor(s). At higher temperatures, if the material is volatile, desorption can occur which results in a reduced GPC. Alternatively, at sufficiently high temperatures reactant decomposition can occur which will cause an enhancement of growth. It is important to recognize that for true ALD growth all reactants have to be operating within their respective temperature windows. This requirement has the important consequence of restricting reactant pairs and thus potentially materials, particularly if strictly ALD growth is desired. It is however worth recognizing that operating outside of the temperature window may be tolerable as the non-ALD growth components may be sufficiently small. For example, the reactant pair of TMA and NH 3 may appear unsuitable candidates for ALD of AlN due to a mismatched temperature window between the two reactants.

TMA starts decomposing at a temperature of 600 K which is below the necessary temperature for reasonable reactivity of NH 3 . Nevertheless, one can still achieve reasonable ALD-like growth if the decomposition rate is sufficiently low.

The above considerations imply that with proper reactor design and careful process tuning one can achieve high quality ALD-like layers. On the low end of the temperature spectrum, the effects of condensation and poor reactivity can be mitigated with sufficiently long purges and reactant exposure times, respectively. There can be a considerable departure from the ideal ALD window.

Within the temperature window, the GPC is often not fixed due to temperature influencing available reactive surface sites, migration of admolecules, or even change in the favored reaction mechanism. growth rate at high pressure results primarily from gas transport mechanisms that are not strongly temperature dependent, whereas at higher temperatures, thermally activated processes also become important allowing the growth rates nearly convergence at T > 250 C for Al 2 O 3 ALD. A reasonable explanation is that the excess growth results from additional physisorbed water at high pressure, and the water desorbs more readily at T > 150 C, decreasing the growth rate difference. This is consistent with previous studies that show that large water doses produce additional growth per cycle during alumina ALD.

ALD applications in nanotechnology

ALD coatings have been widely used for different nanotechnology applications (Figure 2 -14).

They worked as supporting layers and as principal elements of the developed nanostructures.

Applications of ALD coatings as active functional layers for different areas

Chaaya et al. [109, 165] and Iatsunskyi et al. [173,174] proposed methodologies for integration of ALD deposited ZnO, TiO Calcination at high temperatures (T>650 0 C) was performed to remove the organic core and initiate phase transitions. SEM images of the obtained hollow nanotubes are shown in Figure 2-16. Elias et al. [START_REF] Elias | Urchin-inspired zinc oxide as building blocks for nanostructured solar cells[END_REF][START_REF] Elias | Electrochemical growth of ZnO nanowires on atomic layer deposition coated polystyrene sphere templates[END_REF] and Guerin et al. scratched structure for cross-section and internal surface observations, respectively [START_REF] Elias | Hollow UrchinYlike ZnO thin Films by Electrochemical Deposition[END_REF].

ALD is a powerful tool for modification of porous structures [START_REF] Abou Chaaya | Enhanced ionic transport mechanism by gramicidin a confined inside nanopores tuned by atomic layer deposition[END_REF]187]. Due to high reactivity, the internal surface of pores (Si, polymer, etc.) can be coated with metal oxide nanolayers. It was shown good coating of pores with Al 2 O 3 and ZnO/Al 2 O 3 nanolayers. The ALD coated pores were used for single pore biosensor [START_REF] Abou Chaaya | Enhanced ionic transport mechanism by gramicidin a confined inside nanopores tuned by atomic layer deposition[END_REF]187,188].

Thus, ALD technique fits well with micro-and nanofabrication and shows a number of useful applications.

ALD applications in

ALD applications for biosensors

The applications of ALD metal oxides for biosensor devices are not well studied. A number of published papers on ALD metal oxides for biosensors is not compatible with the number of reports on the other techniques [197,198]. Application of metal oxide ALD nanolayers for FET sensing devices were reported by Nakashima et al. and Sultan et al. [199,200] nm pore and (c) 2 nm pore. Black squares and gray rounds show signal with and without gA in the pores, respectively [START_REF] Abou Chaaya | Enhanced ionic transport mechanism by gramicidin a confined inside nanopores tuned by atomic layer deposition[END_REF].

The advanced approaches were also shown on single pore, modified with ALD technique for a-hemolysin capturing at the entrance of a long biomimetic nanopore of diameter 5 nm [START_REF] Cabello-Aguilar | Slow translocation of polynucleotides and their discrimination by α-hemolysin inside a single track-etched nanopore designed by atomic layer deposition[END_REF].

Similarly, to the study of Chaaya et al. [4] pore conductivity was measured at different concentrations of a-hemolysin.

Advantages and limitations of ALD

Summarizing the collected information about ALD technology we can emphasize following advantages:

1. Conformal coating on the surface;

2. Compatibility with non-standard (optical fibers, capillaries, etc.) substrates;

3. Tailored structure, electronic and optical properties of deposited ALD layers.

Compatibility with electrospinning and lithography for deposition of 1D nanostructures

with high surface-to-volume aspect ratio;

5. Wide range of applications (sensors, protective coatings, photodetectors, solar cells, etc.)

6. Good potential for development of novel materials.

While ALD has many promising features, it also suffers from slow deposition rates, usually only a fraction of a monolayer is deposited in one cycle. Because of the long cycle times involved in pulsing and purging precursors and the layer-by-layer nature of the deposition, most ALD rates are on the order of 100-300 nm/h [234,235]. This rate is strongly dependent on the reactor design and the aspect ratio of the substrate. As the surface area and volume of an ALD reactor increase, so does the time needed for pulsing and purging. High aspect ratio substrates also require longer pulse and purge times to allow for the precursor gas to disperse into trenches and other three dimensional features. To combat this shortcoming, spatial ALD has emerged as a promising technique that may significantly improve throughput [236][237][238]. Spatial ALD operates by eliminating the traditional pulse/purge chamber and replacing it with a spatially-resolved head, which exposes the substrate to a specific gas precursor based on location. In one design, as the head translates around the substrate, it alters the exposed precursor, resulting in film growth.

Alternatively, spatial ALD has also been demonstrated in which the substrate moves past stationary precursor nozzles, which are arranged so that by passing by them, precursor cycling is achieved and the film is grown. Overall, with spatial ALD techniques, deposition rates around 3600 nm/h are possible [235].

It is not very practical to grow micrometer-thick films by ALD. The slow growth rate can be compensated by processing large batches of substrates in one process, as is done in TFEL production. In microelectronics, however, single-wafer processing is preferred. Fortunately the films needed for future-generation ICs are very thin and thus the slowness of ALD is not such an important issue.

Another limiting factor in the application of ALD to thin film processing includes:

processing of ternary and more complicated compounds requires the constituent precursors to volatilize and then react at a common temperature ('ALD window') because during the growth process the reactor temperature cannot be changed.

As a chemical process, ALD has a risk of impurities. The impurities can come from gas precursors and/or a carrier gas, the process requires material with a high degree of cleanliness.

Impure chemicals can lead to the incorporation of impurities and to the growth of poor quality films [234].

Prospects of ALD

With devices becoming ever smaller and increasingly structured into complex three dimensional shapes, the need for controllable and conformal thin films has never been greater.

ALD, with its sequential self-limiting reactions, is able to meet these demands in one of the most effective methods possible. Comparable techniques, such as CVD and PVD, cannot always provide the same level of uniformity, conformality and thickness control at the Angstrom level.

Because of the advantages of ALD, ALD processes have been developed for a wide variety of materials, ranging from metals to metal oxides to complex ternary materials, allowing ALD to become incorporated into industrial procedures.

Atomic layer deposition (ALD) provides a unique tool for the growth of thin films with excellent conformity and thickness control down to atomic levels. The deposition of noble metals by ALD technique is one of the perspective directions of ALD method [239][240][241][242][243][244][245][246][247][248][249].

Research on thermal ALD of noble metal thin films has been very active since the first reports (2003). Noble metals, which include ruthenium, osmium, rhodium, iridium, palladium, platinum, silver, and gold, have proven to be of wide technological importance. A group of authors headed by Hamalainen has reviewed a thermal ALD of noble metals and their oxides [250]. In this review, reaction mechanisms in various types of processes were discussed and issues in nucleation were addressed. Deposition temperatures, film growth rates, and purities as well as evaporation temperatures used for noble metal precursors were tabulated for comparison.

The authors summarized the selected properties of the noble metal oxides in Table 2- The polymer solution (Polyacrylonitrile (10 wt % PAN) was dissolved in dimethylformamide (DMF)) is electrospuned in ambient air atmosphere under a high voltage ( 25kV) using a syringe connected to the positive output of the generator. A fix collector was placed 25 cm from the tip of the syringe and was related to the negative output of the generator. The droplet is transformed to a Taylor cone due to the electrostatic field applied between the syringe and the collector. The evaporation of the solvent during the process induces the formation of a net of submicron fiber. The excitation of luminescence was performed by a solid state laser source (Nd:YAG, 355 nm, 13 mW cm -2 ).

In the present work, we used a simple method based on metal-assisted chemical etching (MACE) in combination with nanosphere lithography (NSL) to produce highly ordered silicon nanowires (SiNWs) arrays [257].

These methods have a number of advantages. MACE is a simple, inexpensive process, and able to control various parameters of the etched nanostructures, such as cross-sectional shape, diameter, length, and crystallographic orientation. In parallel, the main advantages of NSL consist of a short preparation time, a high level of hexagonal structure orientation and a possibility of application of large, monolayered masks directly onto any kind of surfaces.

Nanosphere

H 2 O 2 + 2H + + 2e -→ 2H 2 O (2-11)
Electrons are taken from the gold that dissolved in ions following the dissolution reaction

Au → Au 3+ + 3e - (2-12)
Au is more electronegative than Si, so Au ions are able to recover into gold by catching electrons from Si bulk. That involves an injection of positives charge carriers, called holes. They are locally injected underneath the gold layer. On this weakness site, Si is oxidized into SiO 2 and the attack by HF occurs afterward, and the SiO 2 becomes an aqueous byproduct.

SiO 2 + 6HF → 2H 2 O + H 2 SiF 6 (2-13)
The Au layer sinks into the tracks around the PS and the SiNWs appear in this way.

Conclusion

Atomic layer deposition (ALD) is a vapour-phase deposition technique capable of depositing high quality, uniform and conformal ultra-thin films at relatively low temperatures (below 100 °C). In this chapter we report the synthesis of multifunctional surface with polystyrene spheres and selective functionalization ability. We aim to attach specifically the protein directly to the PS spheres and to limit its unspecific adsorption. In our work we use a silicon wafer coated with a thin adhesion layer of chromium ( 15 In order to confirm that the fluorescence comes from the dyes we performed some additional experiments. And we proved that our strategy allows designing a large scale of monolayer of PS spheres and that our strategy of functionalization is relevant to functionalize PS spheres surface and gold surface with different functions.

In order to prove that the large-scale nanoarrays are suitable for antibody detection, different samples were functionalized with PEG-biotin and unlabeled avidin.

Using epifluorescence microscopy, we confirmed that after immersion of sample on target protein (avidin and anti-avidin) solution, the latter are specifically located on polystyrene sphere. Thus, in this chapter we present the fabrication of large-scale nanoarrays which permit to control protein grafting and limit the unspecific adsorption. These results are meaningful for exploration of devices based on large-scale nanoarray of PS spheres and can be used for detection of target proteins or simply to pattern a surface with specific proteins.

Abstract

A simple synthetic route based on nanosphere lithography has been developed in order to design a large-scale nanoarray for specific control of protein anchoring. This technique based on two-dimensional (2D) colloidal crystals composed of polystyrene spheres allows the easy and inexpensive fabrication of large arrays (up to several centimeters) by reducing the cost. A silicon wafer coated with a thin adhesion layer of chromium (15 nm) and a layer of gold (50 nm) is used as a substrate. PS spheres are deposited on the gold surface using the floating-transferring technique.

The PS spheres were then functionalized with PEG-biotin and the defects by self-assembly monolayer (SAM) PEG to prevent unspecific adsorption. Using epifluorescence microscopy, we

show that after immersion of sample on target protein (avidin and anti-avidin) solution, the latter are specifically located on polystyrene sphere. Thus, these results are meaningful for exploration of devices based on large-scale nanoarray of PS spheres and can be used for detection of target proteins or simply to pattern a surface with specific proteins.

Keywords: Nanosphere, Avidin, Large-scale nanoarrays, Biosensor applications.

Introduction

In the area of biosensing and bioengineering, one of challenges is to produce large-scale patterning for specific anchoring of target protein. This challenge requires an ability to manipulate nano-objects, to order them on large surface areas and to control the location of protein attachment.

One of the strategies for the deposition of a large-scale array is the nanosphere lithography using two-dimensional (2D) colloidal crystals that is composed of microscale polystyrene spheres (PS spheres). This technique as introduced by Deckman and Dunsmuir [259] allows the synthesis of large arrays (several millimeters) [260,261]. This method is fascinating because it is rather easy in comparison to the traditional lithographical methods. Using this process, well-ordered and controlled micro/nanostructures could be designed on a large-area substrate using a mono or several layers of PS spheres.

Polystyrene is one of the most extensively used types of plastic, and the number of its applications is growing over the past 20 years. It is an aromatic polymer obtained by polymerization of styrene monomers [262]. It is also biocompatible and is not expected to adversely affect interactions of nanoparticles with biological systems. Polystyrene nanoparticles have been used to fashion large-scale nanoarray for various applications, such as biosensors [263], photonics [264],

and self-assembling of nanostructures [265]. Specifically surface-modified polystyrene nanoparticles are homogeneous, exhibit a low polydispersity index, and form stable colloids in biological fluids [266]. Because polystyrene nanoparticles can be easily synthesized in a wide range of sizes with distinct surface functionalization, they are perfectly suited as model particles to study the effects of the particle surface characteristics on various biological parameters. The protein micro/nano patterning using PS spheres has been previously reported. In most of case, the strategy consists to remove the sphere in order to adsorb the proteins [267-269]. There are several limitations for this strategy because the adsorption is an unspecific process which is not suitable to develop specific biosensor. This process does not allow controlling the protein orientation and denaturation.

Thus, the development of large-scale nanoarray requires an effort to control the protein location, integrity, and selectivity; this includes preventing the unspecific adsorption and the grafting of specific probe on the surface. The adsorption process is regulated by the properties of the protein as well as those of the surface of the material, the environmental conditions, and the kinetics of the process [270,271]. In the case of biosensor, unspecific protein adsorption may limit the effectiveness of the surface that provides the active component of the biosensors. This induces a low signal from the sensor and often causes a high background (noise) signal. Thus, control of the adsorption process is even more critical for applications that use nanostructured substrates with large relative surface areas, such as nanoparticles, microchannels, and thin porous membranes, due to their large surface.

There are different strategies to prevent unspecific adsorption of proteins, such as coating by bovine serum albumin (BSA), grafting of phospholipids, and use of non-ionic detergents like

Tween 20 or of polymeric materials like polyethylene glycol (PEG), as well as combinations of these elements [272,273]. PEG is one of the most studied materials used in order to obtain antibioadherent coatings, especially in the pharmaceutical, cosmetic, and biomedical fields [274][275][276]. The interest of this polymer is due to its unique physical and chemical properties. Indeed, it is highly hydrophilic and has a significant chain flexibility [277]. It has also excellent solubility in aqueous and organic and has a low toxicity to living cells [278]. Preventing unspecific adsorption via its strong hydration layer and its steric stabilization effect is one of the most widespread applications of PEG [278,279]. This coating by PEG is used to control the interaction of biological molecules with the surface of biosensors. This functionalization is commonly done by thiol-PEG self-assembled monolayers (SAM) on gold surface [280][281][282].

The SAMs produced on various substrates have been extensively investigated for the surface functionalization with active molecules or for protecting them from adsorption of species present in the environment [283,284]. The SAM formation is induced by the strong chemisorption between the substrate and the head group of the selected organic molecules. This allows making stable ultrathin organic films with controlled thickness [285,286]. These advantages make the SAMs particularly suited to the development of applications in the field of biosensors [287].This makes them an ideal model in many areas such as bioanalytical, organometallic, physical organic, bioorganic and electrochemistry [284,285,288]. Usually, SAMs formed on gold material or surface are attached using thiol-modified molecules. The self-assembled monolayers of alkanethiols on gold are probably one of the best surfaces currently available to obtain the functionalization and the patterning of biosensors with advantages such as flexibility and stability. The gold-thiol monolayers are stable when exposed to air, to water or to ethanolic solutions for several months [289]. They are also quite easy to produce, quickly assembled and well ordered.

This work aims to produce a large surface of nanoarray functionalized with proteins for antibody detection. Herein, we report the synthesis of multifunctional surface with polystyrene spheres and selective functionalization ability. We aim to attach specifically the protein directly to the PS spheres and to limit its unspecific adsorption. In our work we used a silicon wafer coated with a thin adhesion layer of chromium (15 nm) and a layer of noble metal (50 nm). PS spheres are deposited on the gold surface using the floating-transferring technique. We design a multifunctional surface with array of polystyrene spheres. We used PEG SAMs to block the unspecific adsorption of protein on the surface of these polystyrene spheres. Another interesting point is relative to the stability of PS sphere layer regarding the multistep functionalization which could create defects on the surface. The nanoarrays of polystyrene spheres were designed using the following procedure. A deposition of 15 nm of Cr and 50 nm of Au were performed on p-type Si (100) wafers (2x2 cm 2 pieces of boron doped (8 -25 Ω cm)). The substrates were treated by O 2 plasma using a pressure of 0.6 mbar and a power supply at 0.15 A in order to eliminate all the organic matters from the surface.

The polystyrene spheres (PS spheres) were then deposited using the floating-transferring technique.

Typically, the monolayers of spheres were prepared using monodisperse polystyrene particles with the diameter of 1 μm. Forty microliters of the polystyrene solution (10 wt%) diluted by an equal amount of ethanol. The solution was applied onto the Si substrate and displayed over the Si surface. The Si substrate was maintained stationary for few seconds in order to allow a good dispersion of the PS spheres. The Si wafer was then slowly immersed into a glass vessel filled with deionized water (80 ml). A non-ordered monolayer of PS spheres was formed on the water surface.

A droplet of 10% sodium dodecyl sulfate (SDS) solution was added to the water in order to modify the surface tension. This step targets to consolidate the PS spheres. A large monolayer of PS spheres was transferred to our target substrate (Si/Cr(15 nm)/Au(50 nm)). After drying, the Si substrate covered with the PS was heated at 100 °C for 10 min in order to sinter the PS spheres and to improve their adhesion into the Si substrate. After sintering, the diameter of the PS spheres was reduced with etching by O 2 plasma for different times: 1, 5, 10 and 15 min. In this experiment, the utilized pressure of O 2 plasma is 0.6 mbar and the power supply is 0.15 A.

Functionalization of nanoarrays

The PEGylating of gold surface by SAMS The nanoarray was placed into 1 ml of solution of thiol PEG, (mPEG-SH) (4 mg) in unmodified ethanol for 2 days. Then, the samples were rinsed with ethanol.

Polystyrene sphere biotinylation After PEGylation by SAMS, the nanoarrays were placed in a solution of 0.5 mg mL -1 PEG-biotin-NH 2 , 2 mg mL -1 EDC, and 1 mg mL -1 NHS for 24 h. After this period, the sample is rinsed with ethanol to remove the absorbed PEG.

mPEG-NHS and Cy5-PEG-NHS grafting on polystyrene sphere

In order to link mPEG-NHS or Cy5-PEG-NHS on the polystyrene surface, we have firstly grafted ethylenediamine on COOH groups as follows:(i) the nanoarrays were immersed in 1 ml ethanol solution which contained 2 mg mL -1 EDC and 1 mg mL -1 NHS for 2 h. (ii) Then, the sample is rinses with ethanol and it is placed in solution of mPEG-NHS or Cy5-PEG-NHS (0.2 mg mL -1 ) for 1 h. (iii) Finally, the samples were rinsed with ethanol.

Protein attachment assays For protein attachment assay, we used Avidin, Avidin labeled with Alexa Fluor 647 NHS (noted Avidin*), and Anti-Avidin labeled with Alexa Fluor 488 TFP ester (noted Anti-Avidin*). The nanoarrays were immersed for 30 min in 1 ml of protein (10 µg ml -1 ) in PBS (0.01 M phosphate buffer, 0.0027 M potassium chloride, and 0.137 M sodium chloride, pH 7.4, at 25°C). Then, the samples were rinsed with PBS.

Microscopy

The morphology of the samples was observed with scanning electron microscopy (SEM, Hitachi S-4800). Fluorescence images were performed using an epifluorescence microscope DM6000. The Alexa Fluor 647 and 488 were detected using CY5 and FTIC cube respectively.

Results and discussion

The present work aims to produce large-scale nanoarrays which permit to control protein grafting and limit the unspecific adsorption. The large-scale nanoarrays can be produced by nanospheres lithography using the floating-transferring technique of polystyrene sphere. These spheres can serve as anchor site for protein attachment. However, the main limitation comes from the unspecific adsorption between the spheres. In order to tackle this limitation, one way is the functionalization of these free spaces with a high density of PEG molecules. This can be achieved by thiol PEG SAM strategies on gold surface since it is a well-known strategy to limit the nonspecific adsorption of protein. The overall process for nanoarrays design is presented in the schematic diagram (Figure 3-1). This time permits to decrease the PS spheres diameter from 956 nm to 933 nm. After the plasma etching, the sample is composed by zone. The first one is the gold metallic surface which is uncovered by polystyrene spheres. The second one is the surface of PS spheres with exhibits COOH group. These two parts of the sample could be functionalized differently because we expect to graft protein and antibodies specifically on PS spheres. This imposes to prevent the absorption between the PS spheres. To do it, the gold surface between PS spheres was functionalized by SAMS of PEG-thiol.

After this step, we are able to have two different functionalizations on spheres and between them on the gold surface. We attached on polystyrene spheres PEG-Cy5 following two steps. The first one consists to link ethylene diamine on carboxyl groups using EDC/NHS and the second one is the addition of NHS-PEG-Cy5. Figure 3-3 shows a fluorescence microscopy image of the prepared sample. We can observe that fluorescence came only from the spheres and there is no fluorescence between them. The diameter of spheres around 0.9 µm is in good agreement with the one determined by SEM.

Several additional experiments were performed as blank to confirm that the fluorescence comes from the dyes. PS spheres do not exhibit self-fluorescence under excitation wavelength of 590-650 nm provided by Cy5 cube. In addition, the images performed after each step of functionalization (after reduction by plasma, gold coating and PEG-biotin grafting) do not reveal fluorescence emission under the same condition. A weak autofluorescence of PS sphere was only observed under excitation wavelength lower than 450 nm (using Hoeechst and CFT cubes).

According to that, we can conclude that the PEG-Cy5 is attached on PS spheres. Between the PS spheres, we observe some defects. However, PS spheres cover the majority of the surface of the sample (here the 90.48 x 67.6 µm 2 ). At this step, our results prove that our strategy allows designing a large scale of monolayer of PS spheres and that our strategy of functionalization is relevant to functionalize PS spheres surface and gold surface with different functions. We wanted to use similar strategy to attach the protein directly to the spheres, but not between them. To do it, we have done a variety of experiments using the avidin-biotin strategy. The latter is commonly used to design biosensor devise. The first step consists to graft PEG-biotin on PS spheres. This was performed using PEG-biotin-NH 2 and EDC/NHS. In the second step, the avidin labeled with Alexa-647 was added and their localization was investigated by epifluorescence spectroscopy (Figure 34). As expected, the fluorescence comes specifically from the PS spheres.

The lake of fluorescence between the spheres proves that there is no protein. Thus, the functionalization of gold surface is efficient to prevent the unspecific adsorption of protein. In order to prove that the avidin is on PS spheres due to the presence of biotin, a similar functionalization with mPEG on PS spheres was performed. After immersion, under labeled avidin, the epifluorescence reveals a weak fluorescence. Since the PS spheres and the functionalization do not reveal fluorescence emission using the CY5 cube, we can admit that the signal is due to avidin likely adsorbed on sphere. Actually, this is not surprising because PEG layer has to be dense to prevent the protein adsorption. In the case of PS spheres, the PEGs are grafted on carboxylate group. Thus, the density of these groups is likely too weak to induce a dense layer of PEG. In this case, proteins could be adsorbed on the defects and/or between the PEG chains. In order to prove that the large-scale nanoarrays are suitable for antibody detection, different samples were functionalized with PEG-biotin and unlabeled avidin. After this first step, no fluorescence can be detected under excitation wavelength of 460-500 nm as well as 590-650 nm.

Then, they were immersed in solution containing Anti-Avidin* labeled with Alexa Fluor 488. As expected, the epifluorescence image shows that anti-avidin is specifically located on PS spheres (Figure 345). The functionalization with SAMs of PEG prevents the antiboby as well as the avidin adsorption. We can observe that some microspheres have different intensity of green fluorescence.

This could be explained by the following: (i) the number of dyes on antibodies is not homogeneous or (ii) the number of antibodies attached on microspheres is different.

The Figure 3

Conclusion

In summary, we have presented a novel method based on nanosphere lithography in order to design a large-scale protein patterning. This technique based on two-dimensional (2D) colloidal crystals (polystyrene sphere (PS spheres)) allows the fast synthesis of large arrays (up to several centimeters) by reducing the cost. The nanoarrays are formed by a monolayer of polystyrene sphere deposit by floating-transferring technique on gold surface. On the one hand, the gold surface between spheres was functionalized with SAMs of PEG to prevent the unspecific adsorption. On the other hand, the PS spheres were functionalized with PEG biotin. After addition of avidin and anti-avidin, the proteins are located only on PS spheres confirming that our strategy is suitable to control their location. Our results are meaningful for exploration of devices based on large-scale protein patterning on PS spheres. Regarding the versatility of avidin/biotin system, this strategy can be extended for biosensor development as well as for other applications which require large-surface patterning of proteins.

In this chapter, we performed the novel optical biosensor based on thin films of ZnO deposited by ALD for the determination of Grapevine virus A-type (GVA) proteins (GVAantigens).

GVA is a plant vitivirus that is the most regularly detected virus in grapevine. In summary, label free and sensitive photoluminescence based biosensor for GVA-antigens has been developed. The decrease of the deposition time of immobilized layers has been achieved.

Optical properties of ZnO films obtained by ALD method were applied for the detection of GVAantigens. The GVA-antigen detection was performed by the evaluation of changes and behavior of corresponding luminescence band. The changes in the photoluminescence of ZnO/anti-GVA caused by the formation of complex between immobilized anti-GVA antibodies and GVA-antigens were interpreted as analytical signal. Thus, a good performance and simplicity of the described immunosensor ZnO-modified substrates could be applied as a platform for the development of other immunosensors based on immobilized antibodies, which would be sensitive to selected analyte.

Introduction

Grapevine virus A-type (GVA) is a plant vitivirus that is the most regularly detected virus in grapevine. Such viruses are easily transmitted from infected to healthy plants during grafting and by insect pests common in vineyards. Vine-grapes infected with GVA have poor health, poor quality and low-yielding fruit [293][294][295]. Even if GVA virus was identified more than 30 years ago, it is still common in vineyards worldwide. In addition, its origin is relatively unknown and it has negative economic impact on vineyard productivity. Up to date the monitoring and diagnostics of GVA are based on the study of its genome, genomic organization and replication mechanism [294,295]. For example, complete genome sequence of a natural mutant of GVA was determined by Goszczynski et al. However, up to date, the determination of GVA is based on serological methods (e.g. ELISA tests) and nucleic acid-based methods (variety of PCR-based approaches). These methods provide high sensitivity, up to 100 % detection, however they are time consuming, laborintensive and relatively expensive. Therefore, there is a need to develop rapid, sensitive, inexpensive and simple in use biosensor for the determination of GVA.

Advances in Zinc Oxide (ZnO) growth technology allow the formation of nanostructures with desired optical, structural, morphological and electrical properties that are exploited in the range of biosensors [296,297]. Due to its high isoelectric point (~ 9.5), biocompatibility, high chemical stability, strong adsorption ability, high catalytic efficiency along with nontoxicity and abundance in nature, ZnO is suitable for the immobilization of biomaterials, which are applied as biological recognition parts in biosensors [296,297]. As a wide and direct band gap (3.37 eV) semiconductor that has intense photoluminescence at room temperature, ZnO is widely applied in optical biosensors [298][299][300][301][302] particularly photoluminescence based biosensors [303][304][305]. In this type of biosensors, the changes in the photoluminescence signal of nanostructured material are used for the detection of analyte and the determination of its amount by the characterization of photoluminescence spectra. Therefore recently, a wide range of photoluminescence biosensors based on ZnO nanostructures have been developed [296,[303][304][305].

Among various methods used to form ZnO thin films, atomic layer deposition (ALD) is an innovative technique, which allows the deposition of ultrathin metal oxide films with controlled thickness, grain size, chemical composition, texture, surface morphology and defect concentration.

The mentioned structural parameters make a strong impact on optical, electrical and mechanical properties [109]. In previous studies [109,110,[306][307][308], we investigated the tuning of the optical and the structural properties of ultrathin ZnO films deposited by ALD along with their potential applications in sensors and biosensors [109].

In the wide range of studies, the influence of adsorption and immobilized proteins on the optical properties of ZnO was investigated [302][303][304][305][309][310][311]. The majority of results reports on the changes in photoluminescence intensity and peak positions of near band emission (NBE) and/or deep level emission (DLE) of ZnO after interaction with biomolecules. In rare cases, the immobilized proteins induce new photoluminescence peak or line in the spectra [302,310] but the photoluminescence caused by protein adsorption was not strong enough to be used as a biosensor response. In the present work, the influence of immobilized GVA-antibodies (against GVAantigens) on the photoluminescence spectra of ZnO was investigated for the first time. The direct immobilization of anti-GVA antibodies on the ZnO surface was performed and resulted in the formation of biosensing structure (ZnO/anti-GVA), which was characterized by increased intensity of the main NBE peak of ZnO and photoluminescence band appearance in the range around 425 nm. The changes in the photoluminescence of ZnO/anti-GVA caused by the formation of complex between immobilized anti-GVA antibodies and GVA-antigens were interpreted as analytical signal.

In this way, novel, label free and sensitive photoluminescence based biosensor for GVA-antigens has been developed.

Materials and Methods

ZnO thin film synthesis and characterizations

ZnO layers of 57 and 110 nm thicknesses were synthesized by ALD method using lab-made ALD reactor at the same conditions as described elsewhere. ALD was performed using sequential

Chemical and physical characterizations of ZnO thin films

Structural properties of ZnO films were characterized by Scanning Electron Microscopy (SEM), Ellipsometry and Grazing Incidence X-ray Diffraction (GIXRD). Optical properties were characterized by photoluminescence (PL) study of ZnO films that was used further as a biosensor signal.

In order to investigate the photoluminescence of the studied samples, they were excited by a solid state laser with a wavelength of 355 nm. The exited ZnO photoluminescence entered a spectrometer with the slit entrance of 1 by 1 mm, a focal length of 550, a 600 gr/mm grating and a liquid nitrogen cooled CCD as the detector. The large, 0.4 mm wide, excitation area was produced in order to obtain an average photoluminescence of each sample. The spot size on the sample was a diameter of roughly 1 mm. The laser power was 1.2 mW. All photoluminescence experiments were recorded at room temperature, with a spectral resolution of 3.3 nm, using the spectrometer TRIAX 550 made by Jobin Yvon (New Jersey, USA). The laser was blocked by a 364 nm long pass filter after the sample, with full transmission from 368 nm.

Functionalization of ZnO thin films

The biological samples used in the experiment were provided by National Scientific Centre "Institute of Viticulture and Wine Making named after V. Ye. Tairov" (Odesa, Ukraine). The used proteins were part of the immunoassay-based KIT for the determination of GVA produced by Agritest (Valenzano, Italy) and consisted from anti-GVA antibodies containing serum, which in deed was a real sample extracted from GVA-infected grape plants; control sample of GVAantigens, containing extract of GVA-infected grape plants (further in the text it is marked as 'Ag+') and real sample of non-infected plant extract, which does not contain any proteins of GVA virus capsid (further in the text it is marked as 'Ag-'). The molecular weight of GVA capsid proteins, which were present in Ag+ sample is ~ 27 kDa (Monette and Green, 1992).

The anti-GVA antibody immobilization procedure was the following: 5 μl of anti-GVA antibodies containing sample was diluted by [START_REF] Sang | Growth of transparent conductive oxide ZnO films by atomic layer deposition[END_REF]100,200,400,600,800, 1000 times that corresponds 1/50, 1/100, 1/200, 1/400, 1/600, 1/800, 1/1000 respectively, were dissolved in 0.01 mol/l PBS (pH=7.4) and this solution was equally distributed on the surface of as grown ZnO film modified substrates with the size 5×5 mm, and it was kept for 1 hour in humid environment at room temperature. After this, the samples were washed with PBS and with deionized water and then they were dried in air for 1 hour at room temperature. By above mentioned procedure biosensing structure (ZnO/anti-GVA) was formed. After all, the photoluminescence signal of ZnO/anti-GVA was recorded.

Evaluation of biosensor performance

The procedure for the determination of GVA-antigens was following: 5 μl of GVA-antigens containing samples of different concentrations from 1 pg/ml to 1 μg/ml dissolved in PBS (pH=7.4) and this solution was equally distributed on the surface of ZnO film modified substrates (ZnO/anti-GVA) and it was kept for 1 hour in humid environment at room temperature. After this, the samples were washed with PBS and with deionized water and then they were dried in air for 1 hour at room temperature. After all, the photoluminescence signals of ZnO/anti-GVA/GVA-antigen samples were recorded.

Before biosensor test, optical properties (absorbance and PL) of anti-GVA-based substrates were studied. The absorbance spectra were recorded with UV-VIS spectrophotometer Shimadzu UV-1700 (Kyoto, Japan) in the range of 250-600 nm. The photoluminescence spectra were registered using setup described above.

Results and Discussion

The In order to investigate the possibility of application of ZnO films, which were deposited by ALD method, as an optical transducer of immunosensor and to determine the optimal surface concentration of anti-GVA antibodies immobilized in the biosensitive layer, anti-GVA solutions of different concentrations were deposited on the surface of ZnO-modified substrates. For both ZnO110nm and ZnO57nm samples, the immobilization of anti-GVA has resulted in appearance of PL band in the range from 400 to 550 nm along with the intensity increase of the NBE peak in the average by 35% (Fig. 4-4a). The shift of NBE peak was not observed and no significant difference in the PL spectra after the immobilization of the same anti-GVA concentration on the surface of ZnO110nm and ZnO57nm modified substrates was observed (the spectra are not shown here).

Considering the fact that the PL signal from the ZnO110nm films was much more intense than the signal from ZnO57nm the films with the layer thickness of 110 nm were chosen for the further immunosensor design. ZnO films was varying from 16000 to 19000 arbitrary units. Thus, the PL spectra (Fig. 4-4b) were normalized in order to eliminate the fluctuation of this varying initial signal and to compare the were normalized and the response of the biosensor was based on the change in the intensity of PL band at 425 nm corresponding to the luminescence of anti-GVA (Fig. 4-5a). The response of the as formed immunosensor was observed at the Ag+ concentrations from 1 pg/ml to 10 ng/ml, where the intensity of protein related PL line decreased with the increase of the Ag+ concentration (Fig. 456).

The further increase of the Ag+ concentrations leaded to the increasing PL intensity and full saturation of the PL signal at the 1 µg/ml.

The biosensor response (S) was calculated using the equation 4-1 [304, 305, 309]:

S = " # $% &"# $%'$( # $% ; (4-1)
where: IAb is a PL intensity at 425 nm of ZnO110nm with immobilized anti-GVA; IAb-Ag is the PL intensity at 425 nm of ZnO110nm with immobilized anti-GVA and GVA-antigen (Ag).

The sensitivity of obtained biosensor to the GVA Ag+ is in the range from 1 pg/ml to 10 ng/ml (Fig. 4-6, inset). The sensitivity of here proposed immunosensor cannot be compared directly with the one of already known and widely applied methods for GVA-antigen detection, which are based on enzyme linked immune-sorbent assay (ELISA) or real time polymerase chain reaction (RT-PCR) tests. Both (ELISA and RT-PCR) methods are providing very efficient detection of GVA, which is close to 100%, but these methods are based on a number of chemical/biochemical reactions and another analytical signal detection principles. Therefore both (ELISA and RT-PCR) methods in comparison with action of here proposed immunosensor are time-consuming, needs initial sample preparation and requires much more advanced equipment. In addition by both (ELISA and RTPCR) methods the quantitative determination of concentration of GVA-antigens is not very easy and is technically complicated. The detection of GVA-antigens using optical properties of ZnO film formed by ALD method proved to be relatively sensitive and selective analytical approach, which could be applied as an express method for the diagnosis of GVA infection, because it does not applies any additional labels, such as enzymes, which are used in ELISA, fluorescent-dyes, which are used in RT-PCR.

Therefore here proposed immunosensor is simpler in use and much cheaper as well.

In order to check the selectivity of the biosensor, the control specimen -Ag-, which was isolated from the non-infected grapevine plants and not contained any GVA proteins, was deposited and incubated on the biosensitive layer of immunosensor that was formed using 1/200 diluted sample of initial anti-GVA sample. Therefore in the latest specimen no proteins that could specifically bound to the anti-GVA were present. The incubation of ZnO/anti-GVA-based immunosensor with control-specimen Ag-resulted in the decrease of NBE peak intensity and PL emission in the region of 400-500 nm (Fig. 4-5b). However, unlike the case of Ag+ specimen, PL lines, which are related to the GVA emission, have overlapped with each other and intersected at wavelength around 425 nm. Unlike the covalent binding, which is known as a 'strong' binding between protein and substrate that provides a significant structure of the bioselective layer and improves the bio-recognition, however it involves a cross-linking agent between ZnO surface and anti-GVA molecules forming the bioselective layer, which significantly complicates the general procedure, increases the cost of the experiment and partly damages immobilized anti-GVA antibodies. Therefore, in the absence of GVA-antigens no specific biosensor response was observed (Fig. 4-6b).

In the case of direct adsorption of biosensitive layer (anti-GVA antibodies) the binding between ZnO and biomolecules occurs due to Van der Waals forces and hydrogen bonds [296,305].

The increase of PL intensity of NBE peak after the formation of biosensitive layer results from the charge transfer between anti-GVA molecules and conductance band of ZnO [296,302,305,309,310]. The phenomenon is known as an adsorption assisted increase of exciton-phonon interaction, which is evident from the change of NBE-related peak of ZnO. After 'biofunctionalization' of ZnO thin film surface, the PL emission increases since the molecular complexes can supply extra free electrons, which can participate in transitions between different surface energy levels [310].

The quenching of the main ZnO peak and the decrease of PL intensity related to anti-GVA antibodies (which are proteins) after their interaction with target-analyte (GVA antigen), which is present in Ag+ specimen, may be induced by several reasons. The surface reaction with a quencher may introduce non-radiative surface defects. In addition, the charge transfer from a radiative material to a quencher can also be one of the main mechanisms of the PL quenching [296]. Sodzel The appearance of protein related luminescence band in the range of 400-500 nm can be caused by radiative transitions from defect states in the forbidden gap to valance band of ZnO. Zn interstitial states (~2. 97 eV [312, 313]) and Zn vacancies (3.09 eV [304]) can play the role of adsorption centers for the immobilized proteins. From the other side, the increase of PL peak at 425 nm, which is observed at high concentrations of anti-GVA antibodies, is in the same region as the blue emission peak of ZnS [314,315]. This fact indicates that during the adsorption process the disulfide bonds, which are formed between the chains of anti-GVA, at least partly dissociates [316][317][318][319][320][321] and forms strong complexes (-OZn-S-anti-GVA) with Zn atoms, which are present in ZnO structure. The quenching of both NBE (378 nm) and protein related (425 nm) PL peaks after antigen-antibody interaction of ZnO/antiGVA with target analyte can be related to the partial elimination and/or weakening of interactions between anti-GVA and ZnO, which were formed during the immobilization of anti-GVA molecules on the ZnO surface.

Conclusions

Optical properties of ZnO films obtained by ALD method were applied for the detection of GVA-antigens for the first time. The detection of GVA-antigens was performed through direct immobilization of anti-GVA antibodies on the ZnO thin film surface, forming the biosensitive layer.

The immobilization of anti-GVA antibodies resulted in new PL band appearance in the region of 400-550 nm that can be caused by the formation of Zn-S bound during the anti-GVA adsorption process. The GVA-antigen detection was performed using the changes in the GVA related PL band behavior. The sensitivity of obtained biosensor is in the range from 1 pg/ml to 10 ng/ml of protein.

The biosensor selectivity has been proved by test based on the application of control specimen -Ag-, which was isolated from the non-infected grapevine plants and not contained any GVA proteins (antigens). The possibility to detect GVA-antigens without additional labels (e.g. enzymes, which are used in ELISA, or fluorescent dyes, which are used in RT-PCR) has been demonstrated.

The decrease of the deposition time of immobilized layers has been achieved. The general duration of the experiment procedure is few times shorter than ELISA and RT-PCR. Due to good performance and simplicity of here described immunosensor ZnO-modified substrates could be applied as a platform for the development of other immunosensors based on immobilized antibodies, which would be sensitive to selected analyte.

In this chapter we represent the optimization procedures for the preparation of large areas ordered silicon nanowires (SiNWs) by combining metal-assisted chemical etching (MACE) and nanosphere lithography (NSL) techniques.

The aim of this study was to control the morphology and organization of SiNWs on a large area by the above-mentioned techniques, and to improve the properties of the SiNWs by utilizing ALD for the deposition of ZnO thin films. In summary, the conformal deposition of ZnO by ALD technique was done on highly-ordered vertical SiNWs array. The detailed study of structural and optical properties of core-shell SiNWs/ZnO heterostructure confirmed the highly uniform deposition of ZnO by ALD and the low optical reflection of the deposited thin films.

Abstract

Nowadays one dimensional silicon nanowires (SiNWs) are of great interest due to their abilities to scatter and trap incident light, large surface to volume ratio, and other special electronic and optical properties that make possible utilizing SiNWs as a promising blocks for a range of applications including electronic devices, energy storage devices, thermoelectrics, and biosensors.

In this research, SiNWs were produced by combination of nanosphere lithography and metalassisted chemical etching (MACE). After they were coated with ZnO layer by ALD method. These methods allow the morphology and the organization control of SiNWs on a large area. The structural and optical properties of the obtained nanostructures will be discussed. Structural properties of ZnO/SiNWs were studied by XRD and SEM. Optical characterization was performed by reflectance and photoluminescence spectroscopy.

The X-ray diffraction analysis revealed that all samples have hexagonal wurtzite structure.

The grain sizes as measured using XRD data are found to be in the range of 7 -14 nm. In order to confirm the composition of silicon nanowires covered by ALD ZnO, Raman spectroscopy have been used. The study of photoluminescence (PL) spectra of SiNWs/ZnO showed the domination of defect emission bands, which points to deviations of stoichiometry of the prepared 3D ZnO nanostructures. We observed also the reduction of the PL intensity of SiNWs/ZnO with the etching time for 7 minutes corresponding to a higher light scattering with the increase of the nanowire length.

Keywords: Silicon nanowires (SiNWs), metal-assisted chemical etching (MACE), nanosphere lithography (NSL), atomic layer deposition (ALD), ZnO.

Introduction

Since decades, silicon (Si) continues to be the most widely used semiconductor. Such great interest to this material is due to its beneficial features as high stability and non-toxicity, quantum confinement effects, high carrier mobility and well-established fabrication technique [322]. Because of morphological and energetic feature, silicon nanomaterials, known as one of the most important types of nanomaterials. Nowadays, one dimensional (1D) silicon nanostructures, i.e., silicon nanowires (SiNWs) and Si nanopillars, are of great interest because of their abilities to scatter and trap incident light, large surface to volume ratio, and other special electronic and optical properties that make possible utilizing SiNWs as a promising blocks for a range of applications including electronic devices [323][324][325], energy storage devices [326,327], thermoelectrics [328][329][330], and biosensors [331][332][333][334].

The first preparation of Si whiskers with <111> orientation, or filamentary Si crystals with macroscopic dimensions was reported in 1957 by Treuting and coworkers [335]. to control various parameters of the etched nanostructures, such as cross-sectional shape, diameter, length, and crystallographic orientation [258,344,345]. The main advantages of NSL consist of a short preparation time, a high level of hexagonal structure orientation and a possibility of application of large, monolayered masks directly onto any kind of surfaces [291,346,347].

Integration of SiNWs arrays as core and Zinc oxide (ZnO) as shell can have a strong impact on the development of sensing elements with improved properties. Si is an attractive substrate because of its low cost, good thermal conductivity, high crystalline quality, and availability of large size substrates with different types of conductivity (doping). In addition, silicon is the best candidate for miniaturized electronic devices for the development of modern nanoelectronic technology.

In parallel, ZnO is a wide bandgap (3.4 eV) II-VI compound semiconductor, that has a stable wurtzite structure with lattice spacing a = 0.325 nm and c = 0.521 nm [348]. It has attracted intensive research effort for its unique properties such as a thermal and chemical stability, optical transparency, piezoelectricity, etc. [349]. The attractiveness of ZnO is increased also due to its simplicity and the ease by which it can be synthesized as thin-film layer using a variety of techniques, including atomic layer deposition (ALD) [109,350]. ALD is a special modification of chemical vapor deposition (CVD) method, capable of angstrom resolution, layer-by-layer growth of compound films [159]. The reaction between the incoming precursors and surface species is selfterminating. As a result, atomic level control of film growth can be achieved. Nowadays it is becoming a promising deposition method for growing uniform thin and ultra-thin films, especially in the cases when precise film thickness control (should be determined by the number of reaction cycles), high reproducibility, thickness uniformity and excellent conformity are required [351].

In the present work, the silicon nanowires produced by utilizing gold-assisted chemical etching in combination with nanosphere lithography and after coated with ZnO layer by ALD method, were investigated. The structural and optical properties of the obtained nanostructures were discussed.

Materials and methods

Materials

Micro particles based on polystyrene, size 1 μm, 10 wt% aqueous solution (89904), sodium dodecyl sulfate (436143), Hydrofluoric acid HF 40% (47590), Perdrogen H 2 O 2 30% (31642), Nitric acid (30709), Hydrochloric acid (258148), Diethyl zinc (DEZ) (Zn(CH 2 CH,) 2 , 95% purity, CAS:

557-20-0) were purchased from Sigma Aldrich. Boron doped (8-25 Ω cm) p-type (100) crystal orientation, Si wafers were used as substrates.

Synthesis of SiNWs

The organized silicon nanowires were produced by utilizing gold-assisted chemical etching in combination with nanosphere lithography [290]. For this experiment, the monolayers were prepared using monodisperse polystyrene particles with the diameter of 1 μm.

The 1x1 and 2x2 cm 2 pieces of Si wafers are cleaned sequentially with deionized water (18.2 MΩ cm), ethanol and acetone by ultrasonication for 15 min each. Then the substrates were treated by O 2 plasma to have a hydrophilic surface. After the pretreatment, an ordered monolayer of polystyrene spheres (PSS) was prepared by self-assembly. The floating-transferring technique was utilized to deposit PSS on Si substrate. The polystyrene solution (40 µl) diluted by an equal amount of ethanol, was applied onto the modified substrate, which spread all over the substrate. After holding the substrate stationary for a while to obtain good dispersion of the suspension, the wafer was then slowly immersed into the glass vessel filled with deionized water and PSS started to form an unordered monolayer on the water surface. Then, one drop of 10% sodium dodecyl sulfate (SDS) solution was added to the water to change the surface tension and to consolidate the particles. The addition of SDS solution was an important step to produce 2D ordered colloidal array [352]. As a result, a large monolayer with highly ordered areas was obtained. Then this monolayer of PSS was transferred to the target substrate.

The quality of the PSS monolayer mask can be assessed right away by looking at the uniformity of the color throughout the whole area. The reflected color of the pattern varies with the size of the spheres and its quality.

After the sample was dried in air at room temperature and the spheres were self-assembled into a close-packed, two-dimensional ordered lattice via attractive capillary forces [353,354]. Then The samples with organized SiNWs were then placed into the ALD chamber for the synthesis of SiNWs/ZnO coating material.

Synthesis of ZnO coating Si nanowires arrays

A custom-made ALD reactor was used for the synthesis of ultrathin ZnO films. ALD was performed using sequential exposures of DEZ and H 2 O separated by a purge of Argon with a flow rate of 100 standard cubic centimeters per minute (sccm). The deposition regime for ZnO consisted of 0.2 s pulse of DEZ, 40 s of exposure to DEZ, 60 s of purge with argon followed by 2 s pulse of H 2 O, 40 s of exposure to H 2 O, and finally 60 s purge with argon. Thus, 20 and 50 nm thick ZnO layers were deposited on silicon nanowires using 100 and 250 ALD cycles, respectively. The deposition was performed at 100°C. The typical growth rate for ZnO coating during these cycles is found to be 0.2 nm per cycle.

Characterization

Structural and chemical compositions of the SiNWs/ZnO were analyzed by the scanning electron microscopy (SEM, S-4800, Hitachi), and the X-Ray diffraction (PANAlyticalXpert-PRO diffractometer equipped with a X'celerator detector using Ni-filtered Cu-radiation). From the latter, the grain size was calculated by Debye-Scherer equation.

The crystallographic structure of the films has been studied by X-ray diffraction (XRD). The analysis was performed using PANAlyticalXpert-PRO diffractometer equipped with a X'celerator detector using Ni-filtered Cu-radiation. The XRD spectra were measured in the 2θ angular region between 10° and 60°.

Structural properties of silicon nanowires covered by ALD ZnO were investigated by SEM and transmission electron microscopy (TEM) (JEOL ARM 200F high-resolution transmission electron microscope (200 kV) with an EDX analyzer). The cross-sections and lamellas for TEM investigations were prepared by Focused Ion Beam (FIB) by procedures described elswhere. [356].

The FIB milling was carried out with a JEOL, JIB-4000.

Raman scattering measurements were performed using a Renishaw micro-Raman spectrometer equipped with a confocal microscope (Leica). The samples were measured in backscattering geometry with a spectral resolution of 1.0 cm -1 . The incident light was not polarized and also the light detector contained no polarization filters. The Raman scattering spectra were excited by a 488 nm laser. The beam was focused on the samples with a 50 x microscope objective with a numerical aperture of 0.4. The incident optical power was changed by using neutral density filters in the beam path.

Optical properties of the samples have been studied by diffuse reflectance spectroscopy (the spectral range 200-1400 nm). The diffuse reflectance spectroscopy has been performed using standard Shimadzu UV-3600 spectrophotometer with scanning step of 1 nm.

Photoluminescence spectroscopy was studied in spectral range of 350-800 nm. The measurements were performed at standard fluorometer (FS5 Spectrofluorometer (Edinburg instruments Ltd, 2 Bain Square, Kirkton Campus, EH54 7DQ, UK)). The excitation of luminescence was performed at wavelength of 280 nm. plasma for 1 to 10 minutes permits to decrease the PSS diameter from 960±10 nm to 610±10 nm. The respective positions of ZnO diffraction peaks show that all the films are polycrystalline with ZnO hexagonal wurtzite structure. The XRD patterns consists of the diffraction peaks of ZnO at 2θ values of 31.78°, 34.35°, 36.25° and 56.69° attributed to (100), ( 002), ( 101) and ( 110) planes, that have been observed for both ZnO thickness spectra (but with rather low intensity). The increase of the ZnO thickness (50 nm) led to the appearance of XRD peaks at 2θ = 47.46° corresponding to (102) reflections of ZnO.

Results and discussion

The grain sizes (D) of the deposited films are estimated using the following formula [350]:

) = " 0.9*" + cos,-/ where λ is the wavelength of X-ray used (λ = 0.154 nm), β is the full width at half maximum intensity in radians, and θ is the Bragg angle. The average value of grain size is found to be 7.5±0.45 nm and 14±6.5 nm for samples etched for 7 minutes and covered with 20 and 50 nm ZnO, respectively. ZnO coating is seen to always be near the thickness of around 20 nm. It is clearly seen that the distance between the nearest wires is narrowed to the bottom from 150 to 300 nm. We can notice that the diameter of the wires is about 450 nm on the top and 850 nm at the bottom. Thus, wires have the shape of a truncated trapezoid. That would come from the longer exposure time of the top part to the etching solution according to Dawood et al. [358]. Macroporous structure of the wires could be also observed (Fig. 5 In order to confirm the composition of silicon nanowires covered by ALD ZnO, Raman spectroscopy have been used. Figure 5-6 shows the Raman spectra of Si nanowires (7 min. etching) with 20 and 50 nm ZnO layer. Raman spectra of the as-prepared ZnO-Si nanowires showed no significant peaks of ZnO in the background of the strong spectrum of the Si (520 cm -1 ), indicating the small amount and/or the polycrystalline/amorphous phase of ZnO. However, increasing the number of accumulations allowed us to observe the Raman peak at about 432±2 cm -1 (E 2 high mode), corresponding to the wurzite phase of ZnO, associated with the motion of oxygen atoms (inset of PL of 3D ZnO nanostructures with different thicknesses is plotted in Figure 5-9. The PL spectra showed strong peaks in the range of 410-450 nm with long PL tail to higher wavelengths.

Deconvolution of the PL spectra on separate lines has been performed using Gauss fitting in Origin software (see supporting information, Figure SI3-1). The spectra deconvolution showed peaks, centered at 376-379, 411-415, 434-437, 447-480, 490-540, 570-640 nm, 660-740 nm related to free exciton, Zn interstitials, Zn vacancies, neutral oxygen vacancies, single charged oxygen vacancies, double charged oxygen vacancies and surface defects, respectively [109,165,176,177].

Domination of defect emission bands points to deviations of stoichiometry of the prepared 3D ZnO a b

nanostructures. The decrease of PL intensity for ZnO samples, deposited on 7 min etched Si nanowires could be related to higher light scattering with the increase of the nanowire length.

Conclusion

In summary, we have demonstrated a simple and inexpensive method for the fabrication of ordered aligned SiNWs. The method utilizes 2D non-close-packed polystyrene sphere template for metal deposition in metal-assisted chemical etching of silicon. Here conformal deposition of ZnO was done on highly-ordered vertical SiNWs array by ALD technique. The ordered SiNWs readily produced by the present method may find myriad applications in array devices, such as field-effect transistors, sensors, electrodes, and two-dimensional photonic crystals. The high aspect ratio, antireflective characteristics inherent to nanowires structure can be exploited for fabricating future nanoelectronic and optoelectronic devices. The detailed study of structural and optical properties of core-shell SiNWs/ZnO heterostructure was represented.

The X-ray diffraction analysis revealed that all samples have hexagonal wurtzite structure.

The grain sizes as measured using XRD data were found to be in the range of 7 -14 nm, and confirmed by TEM measurement. The TEM and SEM images demonstrated the ability to produce highly uniform layers of ZnO covered silicon nanowires by the ALD processes. The optical reflectance spectra for SiNWs/ZnO confirmed the low optical reflection of thin films. Layer of ZnO on SiNWs can work as antireflection coating. The study of photoluminescence (PL) spectra of SiNWs/ZnO showed the domination of defect emission bands, which points to deviations of stoichiometry of the prepared 3D ZnO nanostructures. We observed also the reduction of the PL b a intensity of SiNWs/ZnO with the etching time for 7 minutes that could be due to the higher light scattering with the increase of the nanowire length.

Supporting information

Introduction

Nanolaminates are new class of promising nanomaterials with well-tailored properties. These materials are obtained by alternating layers with an individual thickness on the nanometer scale of different materials [165]. They manifest outstanding advanced mechanical [START_REF] Raghavan | Nanocrystalline-to-amorphous transition in nanolaminates grown by low temperature atomic layer deposition and related mechanical properties[END_REF], electrical, and optical properties [165] which depend from the constituent materials forming these nanolaminates. Zinc Oxide (ZnO) which can be incorporated in the nanolaminate material is a n-type semiconductor with wide band gap value (3.3 eV) and high exciton binding energy (0.06 eV). It also exhibited room temperature photoluminescence in UV-vis region [109,165]. Among the different techniques to elaborate oxides based nanolaminates, atomic layer deposition (ALD) is a powerful tool to fabricate different oxide materials [159,307]. It is based on two self-limiting surface reactions which allow growing continuous, smooth, and conformal ultrathin film on high aspect ratio and complex substrates such as the 1D nanotructures with a precise dimensional control. This paper deals with the investigation of electronic and optical properties of ZnO/Al 2 O 3 nanolaminate coated electrospun nanofibers.

The design of Al 2 O 3 /ZnO nanolaminates as well as ZnO thin film doped with Al was widely investigated by ALD [4-6, 8, 164] Previously, we have reported on the fabrication of three-dimensional polyacrylonitrile/ZnO material prepared by the combination of electrospinning and atomic layer deposition (ALD) as new material with large surface area to enhance the optical properties [START_REF] Chaaya | ZnO 1D nanostructures designed by combining atomic layer deposition and electrospinning for UV sensor applications[END_REF]110]. The study of room temperature photoluminescence (PL) spectrum exhibits peak intensity which enhance by a factor of 2000 compared to a flat Si substrate [110]. In the present work, we report on the enhancement of electronic and optical properties of 1D organic core with ZnO/Al 2 O 3 nanolaminates shell nanostructures. The influence of structure parameters of ZnO/Al 2 O 3 nanolaminates (thickness, grain size, number of bilayers, defect concentration) on the main electronic (work function) and optical (photoluminescence and band gap) properties will be discussed. The enhancement of electronic and optical properties will allow application in different fields such sensors and biosensors.

Materials and methods

Polyacrylonitrile (PAN) nanofibers have been elaborated by electrospinning technique to be a template for the nanolaminates design by ALD.

Electrospinning of PAN Nanofibers.

Polyacrylonitrile PAN (Mw = 150 000) and dimethylformamide (ACS reagent, ≥99.8%) were purchased from Sigma-Aldrich. Polyacrylonitrile (10 wt % PAN) was dissolved in dimethylformamide (DMF). The electrospinning solution was maintained under agitation for 1 h and then heated in an oil bath at 80 °C for 10 min. The used electrospinning machine was a homemade device using an HPx 600 605 generator (physical instruments) and a KDS 100 syringe pump. The polymer solution was electrospuned in ambient air atmosphere under an applied voltage of 25 kV with a flow rate of 3 mL h-1 using a 0.7 mm diameter syringe connected to the positive output of the generator. A fix collector was placed 25 cm from the tip of the syringe and was related to the negative output of the generator. The droplet was transformed to a Taylor cone due to the electrostatic field applied between the syringe and the collector. The evaporation of the solvent during the process induces the formation of a net of submicron fiber. 6-1). The deposition temperature was fixed to 100 °C. We note here that, in contrast to the deposition of thin films on flat surfaces, the reactants had to diffuse into the high-aspect-ratio structures. Therefore, an exposure time should be added and adapted in order to ensure the conformal coating of the PAN nanofibers. GPC of !0.2 nm/cycle has been observed for Al 2 O 3 and ZnO. These values are consistent with what has been reported elsewhere by Karvonen et al. [164] FTIR spectra were obtained with the Bruker VERTEX 70v vacuum spectrometer using the RT-DLaTGS detector (spectral resolution of 4 cm -1 ). X-ray diffraction measurements were performed with PANAlytical Xpert-PRO diffractometer equipped with a X'celerator detector using 002) planes (Figure 6-1a and b insets). Using ImageJ software, the grain size and the interplane distances for ( 101) and (002) lattice planes were calculated (insets of Figure 6-1a-c). The grain size was calculated using elliptical shape fitting and the longer axis was used as the grain size.

The average grain size for 20 nm, 10 and 5.2 nm bilayer thicknesses were 9.8 ± 2.5 nm, 6.5 ± 1.5 nm and 5.3 ± 2.1 nm, respectively. For 2 and 1.2 bilayer thicknesses, the grain size was not determined due to the quality of the image and the resolution of TEM. We suppose that the in case of 20, 10, and 5.2 nm bilayer thicknesses, the grains were elongated and limited by the layer thickness. The TEM analysis provided evidence that the Al 2 O 3 layers are amorphous for all samples. The ZnO layers are in a polycrystalline phase. The TEM images demonstrate the ability to produce highly uniform layers of nanolaminates covered PAN fibers by the ALD processes. 35 eV, respectively [383, 384].

Fermi level E F position in each component of the nanolaminates was estimated:

E 1 = 2 3 4 (6-1)
where Φ is the work function.

The conductance band and valence band gap offsets could be calculated as (Table 6-2): The built in potential V bi between two altering ZnO and Al 2 O 3 layers was calculated due to (Table 6-2): V <> ? = E 17 3 E 18 where q is an electron charge, and E F1 and E F2 are Fermi level positions in Al 2 O 3 and ZnO, correspondently.

To estimate potential drops in ZnO and Al 2 O 3 , the Debye lengths in the altering materials were estimated: where k, T, ε, and ε 0 are the Boltzmann's constant, absolute temperature, dielectric permittivity of The potential drops in ZnO and Al 2 O 3 could be calculated as V JKM = L @JKM V <> L @NO7MP Q L @JKM V NO7MP = V <> 3 V JKM Based on eqs 6-5 and 6-6, the potential drop in ZnO was 10 -4 eV.

L @ = A BCDD F G H I (
Therefore, the band bending in ZnO at the interface between ZnO and Al 2 O 3 is significantly small and the potential drop will be mostly faced in Al 2 O 3 layer. The estimated values of ZnO work function are strongly affected by the surface band bending in the upper ZnO layer. The later could be estimated from eq 6-7:

V R = 2 8<O 3 2 7T<O [START_REF] Raghavan | Nanocrystalline-to-amorphous transition in nanolaminates grown by low temperature atomic layer deposition and related mechanical properties[END_REF][START_REF] Elam | Growth of ZnO/Al2O3 alloy films using atomic layer deposition techniques[END_REF] where Φ 1bl and Φ 20bl are the work function of ZnO in 1 bilayer and 20 bilayer samples, respectively. The obtained V s value was 0.64 eV. The depletion width in ZnO could be calculated from eq 6-8

[387]:

W = A 7U X DD F IG H (6-8)
The estimated W value was around 50 nm. Therefore, the upper ZnO layer will be fully depleted vacancies and interstitials [109, 110, 165]. According to that, the observed peaks at 473, 520, and 580 nm could be assigned to neutral, single charged and double charged oxygen vacancies, respectively [109,110,165]. However, the peak at 473 nm could also be related to Zn vacancies [109,110,165]. Measuring only room temperature luminescence, we cannot discriminate the observed peak at 473 nm between two different defect states. However, this fact does not change the nature of the emission. In our previous works [109,165], we observed similar results when no excitonic peaks were found for thin layers due to band bending and low grain size. This will result from the high concentration of defects, the low grain size (compatible with exciton Bohr radius for ZnO (2.6 nm)), and the surface band bending. Therefore, domination of defect level emission and low rate of exciton formation are observed.

The ZnO layers were polycrystalline with small grain size. We suppose that the grain boundaries will have the following effects in the optical properties of the nanolaminates: (i)

Quantum confinement effect: due to the low grain size, the blue shift of the band gap is observed.

(ii) Defects are formed on the grain boundaries [390]: XPS showed the higher concentration of the defects for low ZnO thickness, which enhanced visible photoluminescence. (iii) Grain boundaries influence light absorption, particularly, the Urbach tail [390]: a higher Urbach tail value is observed for low ZnO thickness due to the increasing of the grain boundaries active surface (more defects).

In the present study, we have shown that the ZnO work function significantly decreased with the decreasing of the bilayer thickness. We explain this observation by band bending. It is well-known fact that grain boundaries can induce localized energy states within the band gap, leading to trapped, localized charges. These will form an electrostatic potential barrier, band bending, for the

Conclusion

Summarizing, the structural and optical properties of Al 2 O 3 / ZnO determined from the XPS, TEM, FTIR, XRD and PL analysis provide an important information about crystalline structure of nanolaminates on the 1D PAN substrate. The amorphous-to crystalline transition has been observed

for ZnO nanolayers at the thickness of 2.6 nm on the 1D PAN nanotemplate. In particular, strong influence of the bilayer thicknesses on the crystallinity of ZnO nanolayers has been found. Due to the quantum confinement effect, the shift of XPS peaks to higher energies has been observed. Work Photoluminescence of the nanolaminates corresponded to emission bands in ZnO nanolayers.

Due to low grain size, high defect concentration, and surface band bending, no excitonic peaks were observed. The defect emission band was affected by the band bending and defect concentration. The observed XPS and PL data are in good correlation. The enhanced PL of the nanolaminates could be used for optical (bio)sensing.

Supporting information

CHAPTER VII

General conclusion

General conclusion

ALD is considered as one of the most promising thin film deposition techniques for enabling nanoscale device fabrication. In this study, we used the ALD technique for the deposition of ZnO and Al 2 O 3 /ZnO nanolaminates thin films on the different substrates, reached some interesting results and performed some tasks, as following:

(i) In this research, a simple and inexpensive method for the fabrication of ordered aligned SiNWs was proposed, which concluded the combination of nanosphere lithography and metal-assisted chemical etching. To improve the properties of the prepared highly-ordered vertical SiNWs array, it was coated with ZnO thin films (20 and 50 nm) by ALD method. These methods allow the morphology and the organization control of SiNWs on a large area. Structural properties of ZnO/SiNWs were studied by XRD and SEM. Optical characterization was performed by reflectance and photoluminescence spectroscopy. The X-ray diffraction analysis revealed that all samples have hexagonal wurtzite structure. The grain sizes as measured using XRD data were found to be in the range of 7 -14 nm. In order to confirm the composition of silicon nanowires covered by ALD ZnO, Raman spectroscopy have been used. The study of photoluminescence (PL) spectra of SiNWs/ZnO showed the domination of defect emission bands, which points to deviations of stoichiometry of the prepared 3D ZnO nanostructures. We observed also the reduction of the PL intensity of SiNWs/ZnO with the etching time for 7 minutes corresponding to a higher light scattering with the increase of the nanowire length. The high aspect ratio, anti-reflective characteristics inherent to nanowires structure can be exploited for the fabricating future nanoelectronic and optoelectronic devices.

(ii) ZnO films formed by ALD as an optical biosensor platform for the detection of Grapevine virus A-type proteins (GVA-antigens) were represented. The detection of GVAantigens was performed through direct immobilization of anti-GVA antibodies on the ZnO thin film surface, forming the biosensitive layer. The immobilization of anti-GVA antibodies resulted in new PL band appearance in the region of 400-550 nm that can be caused by the formation of Zn-S bound during the anti-GVA adsorption process. The GVA-antigen detection was performed using the changes in the GVA related PL band behavior. The sensitivity of obtained biosensor was in the range from 1 pg/ml to 10 ng/ml of protein. The biosensor selectivity has been proved by test based on the application of control specimen -Ag-, which was isolated from the noninfected grapevine plants and not contained any GVA proteins (antigens). The possibility to detect GVA-antigens without additional labels (e.g. enzymes, which are used in ELISA, or fluorescent dyes, which are used in RT-PCR) has been demonstrated. The decrease of the deposition time of immobilized layers has been achieved. The general duration of the experiment procedure was few times shorter than ELISA and RT-PCR. Due to good performance and simplicity of the described immunosensor, ZnO-modified substrates could be applied as a platform for the development of other immunosensors based on immobilized antibodies, which would be sensitive to selected analyte.

(iii)

We have presented a simple synthetic route based on nanosphere lithography to produce large-scale protein patterning. This technique based on two-dimensional (2D) colloidal crystals (polystyrene sphere (PS spheres)) allows the fast synthesis of large arrays (several millimeters) with low cost. The nanoarrays were formed by a monolayer of polystyrene spheres deposit by floating-transferring technique on gold surface. On one hand, the gold surface between spheres was functionalized with SAMs of PEG to prevent the unspecific adsorption. On the other hand, the PS spheres were functionalized with PEG biotin. After addition of avidin and anti-avidin, the proteins are located only on PS spheres confirming that our strategy is suitable to control their location. The epifluorescence microscopy was used to confirm this finding.

Regarding the versatility of avidin/biotin system, this strategy can be extended for biosensor development as well as for other applications which require large surface patterning of proteins. • Fedorenko, V., Viter, R., Iatsunskyi, I., Nowaczyk, G., Graniel, O., Załęski, K.,

I

  photoluminescence spectroscopy, XRD, TEM, and Raman spectroscopy. I am also thankful to the research staff from the NanoBioMedical Centre at Adam Mickiewicz University, Poznan, Poland (Dr. Igor Iatsunskyi, Dr. Mateusz Kempinski, Dr. Grzegorz Nowaczyk, Dr. Karol Załęski, and Prof. Stefan Jurga), University of Latvia, Riga (Dr. Donats Erts, and Dr. Roman Viter), and State Research Institute Center for Physical Sciences and Technology, Vilnius, Lithuania (Dr. Saulius Tumenas, Dr. Zigmas Balevicius, and Prof. Arunas Ramanavicius), who participated in discussion of experimental results and writing of scientific papers.

Figure 2 - 1 . 5 Figure 2 - 2 .

 21522 Figure 2-1. Schematic illustration of one ALD reaction cycle [12]……………………………...5 Figure 2-2. Cross-sectional SEM image of an Al 2 O 3 ALD film with a thickness of 300 nm on a

Figure 2 - 3 . 7 Figure 2 19 Figure 2

 2372192 Figure 2-3. Overview of the materials grown by ALD [25]……………………………………...7 Figure 2-4. a) SEM images of a cross section of ZnO ALD films deposited on Si substrates by 200, 500, and 1000 cycles; b) EDX; c) GIXRD of ZnO ALD films deposited by 100, 200, 500, and 1000 cycles; d) grain size and lattice strain in ZnO ALD films of different thickness [109].19 Figure 2-5. a) Transmittance spectra, and b) band gap and Urbach energies of ZnO ALD films of different thickness [109]………………………………………………………………………....20 Figure 2-6. (a) SEM image of 1D ZnO NSs obtained with 300 s electrospinning time and coated with 50 cycles ALD ZnO at 100 °C. (b) XRD spectra of the obtained 1D NSs. (c) TEM image of 1D ZnO NSs [110]……………………………………………………………………………….21

Figure 2 - 7 .

 27 Figure 2-7. SEM images of ZnO thin film of 100 nm thickness and Al 2 O 3 /ZnO nanolaminates with different sequences (a), EDX of Al 2 O 3 /ZnO nanolaminates (b), and GIXRD of ZnO thin film of 100 nm thickness and Al 2 O 3 /ZnO nanolaminates with different sequences (c) [165]…..33

Figure 2 - 8 .Figure 2 - 9 .Figure 2 - 10 .Figure 2 - 11 .Figure 2 - 12 .

 2829210211212 Figure 2-8. Blue square, roughness vs the film thickness of single layer of ZnO; black square, roughness vs the top layer of ZnO in the Al 2 O 3 /ZnO nanolaminates [165]…………………..…34 Figure 2-9. Transmittance spectra of Al 2 O 3 /ZnO nanolaminates with different bilayer thickness and single ZnO thin film [165]………………………………………………………………..…34 Figure 2-10. Refractive index (real part) of Al2O3 single thin film and Al 2 O 3 in Al 2 O 3 /ZnO nanolaminates with different bilayer thicknesses [165]…………………………………………35 Figure 2-11. Photoluminescence spectra of 50 nm thick single ZnO film and Al 2 O 3 /ZnO nanolaminates with different bilayer thicknesses [165]…………………………………………36 Figure 2-12. Schematic of possible behavior for the ALD growth per cycle versus temperature showing the "ALD" window [23]……………………………………………………………….38

Figure 2 -Figure 2 - 14 .

 2214 Figure 2-13. ALD growth per cycle for Al 2 O 3 (a) and ZnO (b) as a function of deposition temperature for reactor pressures of 2 and 760 Torr. The gas pulse conditions used for deposition are identified in the figure [92]……………………………………………………………….…39Figure 2-14. Potential applications of ALD in various research fields [172]………………..….40

Figure 2 - 41 Figure 2 - 43 Figure 2 - 17 .

 241243217 Figure 2-15. Cross-sectional view SEM image of a) macroporous silicon surface fabricated by MACE, b) mesoporous layer of PSi, c) mesoporous silicon surface (high magnification); d) cross-sectional view of as-prepared PSi/TiO 2 nanostructure after 150 ALD cycles, e) plane view SEM image of the individual macropore in the PSi/TiO 2 nanostructure after 150 ALD cycles, f)

Figure 2 -

 2 Figure 2-18. a,b) SEM images of a self-assembled monolayer of PS microspheres on a TCO substrate; a) tilted (458) low magnification and b) top view. The lower inset of (a) presents the digital image of the same sample. c,d) SEM images of an ordered hollow urchin-like structure of

Figure 2 - 47 Figure 2 - 56 Figure 2 - 21 .Figure 2 - 22 .

 247256221222 Figure 2-19. PL sensitivity test of ethanol vapor (150 ppm of ethanol) using 1D ZnO NSs obtained with 300 s electrospinning time and coated with 50 cycles ALD ZnO at 100 °C [110]…………………………………………………………………………………….……....47 Figure 2-20. Schematic process for hybrid membrane synthesis [4]………………….…….….56 Figure 2-21. Measurement scheme of ALD-based pore biosensor……………………….….…56 Figure 2-22. Evolution of nanopore conductance with and without confined gA under NaCl symmetrical concentration in ALD-based pores with different diameters :(a) 10 nm pore (b) 6

Figure 2 - 23 . 61 Figure 2 - 24 .

 22361224 Figure 2-23. Atomic layer deposition reactor…………………………………………………...61 Figure 2-24. Schematic diagram of set up of electrospinning apparatus [255]………………….62

Figure 2 - 25 .

 225 Figure 2-25. The scheme of floating-transferring technique…………………………………….72

Figure 2 - 26 .

 226 Figure 2-26. Scheme of processes involved in metal-assisted chemical etching………………..73

Figure 3 - 1 .

 31 Figure 3-1. The schematic diagram of overall process for protein immobilization…………….81

Figure 3 - 2 . 82 Figure 3 - 3 .Figure 3 - 4 .Figure 3 - 5 . 85 Figure 3 - 6 .

 32823334358536 Figure 3-2. Diameter of PS spheres as the function of the O 2 plasma etching: The insets show PS spheres with different O 2 plasma etching times: 1 (a), 5 (b), 10 (c) and 15 (d) min, respectively, as determined by SEM (scale bars 500 nm)…………………………………………………….82 Figure 3-3. Fluorescent images of Cy5-PEG-NHS-modified polystyrene spheres (the inset indicates a zoom)……………………………………………………………….………………..83

Figure 4 - 93 Figure 4 - 2 .Figure 4 - 3 .

 4934243 Figure 4-1. a) SEM cross section images and b) GIXRD of ZnO ALD films deposited on Si substrates by different numbers of cycles (250 and 500)………………………………………..93 Figure 4-2. PL spectra of the ZnO samples with 57 and 110 nm layer thicknesses (a), PL spectra of anti-GVA deposited on glass (b)…………………………………………….……………..…94 Figure 4-3. The scheme of PL based immunosensor……………………………………………95

Figure 4 - 4 .

 44 Figure 4-4. PL spectra of bare ZnO110nm and ZnO110nm functionalized with anti-GVA using 1/100 diluted initial anti-GVA solution (a), PL spectra (normalized intensity) of bare ZnO110nm and ZnO110nm functionalized with anti-GVA using solutions containing different concentrations of anti-GVA (b), PL intensity at 425 nm as a function of concentration of anti-GVA solutions used for the modification of ZnO-based substrates (c), absorbance spectra of anti-GVA deposited on glass from two solutions containing different concentrations of anti-GVA antibodies (d)……..96

Figure 4 - 5 .Figure 4 - 6 .

 4546 Figure 4-5. The dependence of ZnO110nm/anti-GVA/Ag+ PL spectra (normalized intensity) after incubation of ZnO110nm/anti-GVA-based imunosensor in different GVA-antigen concentrations containing specimens (specimens -Ag+) (a), PL spectra dependence (normalized intensity) of ZnO110nm/anti-GVA-based immunosensor under different concentrations of proteins separated from healthy vine grape plants, which not contains antigen for anti-GVA (specimens -Ag-) (b)……………………………………………………………………………………………...…98 Figure 4-6. PL intensity at 425 nm as a function of GVA-antigen concentration in Ag+ specimen, insetbiosensor response (S) as a function of GVA-antigen concentration in Ag+ specimen (a), PL intensity at 425 nm as a function of different concentrations of proteins separated from healthy vine grapes, which not contain any antigen capable to bind with anti-GVA (specimens -Ag-), inset -biosensor response (S) as a function of Ag-specimen concentration (b)……….…99

Figure 5 - 1 .

 51 Figure 5-1. The schematic diagram of overall process for the synthesis of SiNWs by combining MACE and NSL techniques……………………………………………………………………106

Figure 5 - 2 .Figure 5 - 3 .Figure 5 - 4 .Figure 5 - 5 .Figure 5 - 6 .Figure 5 - 7 .

 525354555657 Figure 5-2. Diameter of PSS as the function of the O 2 plasma etching: Inset consists of SEM images of the PSS as-prepared by floating transferring technique (a) and with different O 2 plasma etching times: 1 (b), 5 (c) and 10 (d) min, respectively. And photographs of the

Figure 5 - 8 . 113 Figure 5 - 9 .Figure 6 - 1 .Figure 6 - 2 .Figure 6 - 3 .Figure 6 - 4 .Figure 6 - 5 .

 58113596162636465 Figure 5-8. Band gap estimation of SiNWs covered with 20 (a) and 50 nm ZnO (b) by ALD, respectively…………………………………………………………………………………….113 Figure 5-9. Photoluminescence spectra of SiNWs prepared at different etching time -2, 5 and 7 minutes, and after ALD of 20 (a) and 50 nm ZnO (b), respectively…………………………...114 Figure SI5-1. Deconvolution of PL peaks spectra of SiNWs prepared at different etching time -2, 5 and 7 minutes, and after ALD of 20 and 50 nm ZnO……………………………………...115 Figure 6-1. TEM images of PAN-Al 2 O 3 /ZnO nanolaminates with different bilayers thicknesses: (a) 20 nm, (b) 10 nm, (c) 5.2 nm, and (d) 2 nm. Insets show the corresponding highmagnification images…………………………………………………………………………..121 Figure 6-2. (a) Absorbance spectra and (b) XRD spectra of PAN-Al 2 O 3 /ZnO nanolaminates at various bilayers thicknesses. Spectra are shifted for clarity……………………………………122 Figure 6-3. XPS survey spectra of ZnO/Al 2 O 3 nanolaminates coated polymer fiber with different bilayer thicknesses: (a) 1.2 nm, (b) 2 nm, (c) 5.2 nm, (d) 10 nm, and (e) 20 nm. Main core levels are labeled. Data are normalized to each O 1s peak maximum and separated vertically………123 Figure 6-4. XPS survey spectra of ZnO/Al 2 O 3 nanolaminates coated polymer fiber with different bilayers thicknesses: (a) 1.2 nm, (b) 2 nm, (c) 5.2 nm, (d) 10 nm, and (e) 20 nm. Main core levels are labeled. Data are normalized and separated vertically…………………………………..…124 Figure 6-5. O 1s energy-loss spectra for band gap determination of Al 2 O 3 of ZnO/Al 2 O 3 nanolaminate coated polymer fiber with different bilayers thicknesses………………………..125

Figure 6 - 6 .Figure 6 - 7 .Figure 6 - 8 .

 666768 Figure 6-6. UPS results of work function measurements of ZnO/Al 2 O 3 nanolaminate coated polymer fiber with different bilayer thicknesses……………………………………………….126 Figure 6-7. Zone diagram of Al 2 O 3 /ZnO nanolaminate formation: (a) single layers before contact, (b) 1 bilayer, and (c) n bilayers………………………………………………………..127

  Overview of the recently investigations in the area of atomic layer deposition (ALD) of ZnO, Al 2 O 3 , and Al 2 O 3 /ZnO nanolaminates, and potential applications of ALD in various research fields (Chapter 2). Ø Study of the optical properties of ZnO deposited by atomic layer deposition (ALD) on Si nanowires (Chapter 3). Ø ZnO films formed by ALD as an optical biosensor platform for the detection of Grapevine Virus A-type Proteins (Chapter 4). Ø Large-scale protein/antibody patterning with limiting unspecific adsorption (Chapter 5). Ø Enhancement of electronic and optical properties of ZnO/Al 2 O 3 nanolaminate coated electrospun nanofibers (Chapter 6).

- 1 .

 1 The typical two-reactant ALD process is characteristically consists of four steps: Pulse step of the first reactant (A) and subsequent self-terminating gas-solid reaction. Then the second step is the purge step with an inert carrier gas (typically N 2 or Ar) to remove excess reactants and gaseous reaction byproducts. Pulse step of the second reactant (B) and subsequent self-terminating gas-solid reaction. And the last step is purge of the unreacted precursor B and of the byproducts. During each reaction cycle a fixed amount of material having a corresponding nominal thickness is deposited, known as growth per cycle (GPC), due to the self-limiting nature of the reactions.

Figure 2 - 1 .

 21 Figure 2-1. Schematic illustration of one ALD reaction cycle [12].

Figure 2 - 2 .

 22 Figure 2-2. Cross-sectional SEM image of an Al 2 O 3 ALD film with a thickness of 300 nm on aSi wafer with a trench structure[START_REF] Ritala | Perfectly conformal TiN and Al2O3 films deposited by atomic layer deposition[END_REF].

Figure 2 -

 2 Figure 2-4. a) SEM images of a cross section of ZnO ALD films deposited on Si substrates by 200, 500, and 1000 cycles; b) EDX; c) GIXRD of ZnO ALD films deposited by 100, 200, 500, and 1000 cycles; d) grain size and lattice strain in ZnO ALD films of different thicknesses [109].

Figure 2 -

 2 Figure 2-5. a) Transmittance spectra, and b) band gap and Urbach energies of ZnO ALD films of different thicknesses [109].

Viter

  et al.[110] investigated for the first time the ability of a three-dimensional polyacrylonitrile (PAN)/ZnO material -prepared by a combination of electrospinning and atomic layer deposition (ALD) as a new material with a large surface area -to enhance the performance of optical sensors for volatile organic compound (VOC) detection. The photoluminescence (PL) peak intensity of these one dimensional nanostructures has been enhanced by a factor of 2000 compared to a flat Si substrate. In addition, a phase transition of the ZnO ALD coating from amorphous to crystalline has been observed due to the properties of a PAN nanofiber template surface strain, roughness, and an increased number of nucleation sites in comparison with a flat Si substrate. The greatly improved PL performance of these nanostructured surfaces could produce exciting materials for implantation in VOC optical sensor applications.

Figure 2 - 6 .

 26 Figure 2-6. (a) SEM image of 1D ZnO NSs obtained with 300 s electrospinning time and coated with 50 cycles ALD ZnO at 100 °C. (b) XRD spectra of the obtained 1D NS and (c) TEM image of 1D ZnO NSs [110].

Chaaya

  et al. reported on the tuning of optical and structural properties of Al 2 O 3 /ZnO nanolaminates designed by atomic layer deposition (ALD). The SEM images (Figure 2-7a) indicate a conformal coating by ALD of the Si substrate in case of ZnO thin film of 100 nm thickness as well as for Al 2 O 3 /ZnO nanolaminates with different sequences. The SEM cross-section proves as well that the sequence of alternating Al 2 O 3 and ZnO interlayers was achieved throughout the total film thickness of the nanolaminates. The SEM images show that the single layer of ZnO developed a rough surface of columnar growth where the nanolaminates consist of alternating layers of amorphous Al 2 O 3 and nanocrystalline ZnO [6, 90]. The EDX of nanolaminates Al 2 O 3 /ZnO 10 (10/10 nm) consisting of alternating ZnO/Al 2 O 3 films (Figure 2-7b) grown at 100 °C by ALD showed the presence of Al, Zn, and O. GIXRD patterns of Al 2 O 3 /ZnO 50 (2/2 nm) nanolaminates with the thinnest bilayer thickness showed weak broad X-ray diffraction peak at 34.26° (Figure 2-7c) which can result from their amorphous structure or their crystalline size below 2 nm. The increase of the bilayer thickness in the nanolaminates, Al 2 O 3 /ZnO 10 (10/10 nm), led to the appearance of XRD peaks at 2θ = 31.82° and 34.35° and a weak peak at 2θ = 36.1° corresponding to (100), (002), and (101) reflections of ZnO, respectively. A change in the preferential growth orientation (strong (002) and negligible (101) XRD peaks) is observed when comparing the thicker nanolaminates Al 2 O 3 /ZnO 2 (50/50 nm) to the single ZnO film (100 nm).

Figure 2 - 7 .

 27 Figure 2-7. SEM images of ZnO thin film of 100 nm thickness and Al 2 O 3 /ZnO nanolaminates with different sequences (a), EDX of Al 2 O 3 /ZnO nanolaminates (b), and GIXRD of ZnO thin film of 100 nm thickness and Al 2 O 3 /ZnO nanolaminates with different sequences (c) [165].

Figure 2 - 8 .

 28 Figure 2-8. Blue square, roughness vs the film thickness of single layer of ZnO; black square, roughness vs the top layer of ZnO in the Al 2 O 3 /ZnO nanolaminates [165].

Figure 2 - 9 .

 29 Figure 2-9. Transmittance spectra of Al 2 O 3 /ZnO nanolaminates with different bilayer thicknesses and single ZnO thin film [165].

  . Band gap of Al 2 O 3 /ZnO nanolaminates with different bilayer thicknesses and ZnO single thin film of 50 nm thickness [165] The authors proposed three physical phenomena for the determination of the observed blue shift, such as quantum confinement effect of small nanograins, doping of ZnO by Al, and improvement of crystalline quality of the single layer.

Figure 2 -

 2 Figure 2-10. Refractive index (real part) of Al 2 O 3 single thin film and Al 2 O 3 in Al 2 O 3 /ZnO nanolaminates with different bilayer thicknesses [165].

Figure 2 - 11 .

 211 Figure 2-11. Photoluminescence spectra of 50 nm thick single ZnO film and Al 2 O 3 /ZnO nanolaminates with different bilayer thicknesses [165].

  -11). It could be affected by structural changes during the layer growth and/or doping by Al. Blue shift of band gap and excitonic peak position of ZnO single layers were explained by quantum confinement effect and the improvement of crystalline quality of ZnO layer.The advanced properties of the nanolaminates such as biocompatibility, easy surface modification, and enhanced photoluminescence at room temperature could provide good capacity for the development of nanolaminates-based optical sensors and biosensors.Viter et al. reported on the optical and structural properties of ultrathin Al 2 O 3 /ZnO nanolaminates (lower than 20 nm) deposited by ALD technique[166]. The one of the proposed way to explain amorphous nature of ultrathin nanolaminates is the minimum thickness required to allow crystallization in a thin film. The proposed crystallization model for ultrathin layers and superlattices was taking into account the interface energies, the thickness of the layers, the melting point of the system, and the bulk amorphous crystallization temperature. It was shown that exponential increase of the crystallization temperature leads to the decrease of the minimal thickness at which crystallization occurs.Mechanisms of growth of ultrathin ZnO/Al 2 O 3 nanolaminates were studied using AFM and ellipsometry. On the basis of the analysis of optical methods such as transmission, spectroscopic ellipsometry and photoluminescence of ultrathin nanolaminates, the amorphous nature of them has been proven. These results allowing not only to determine optical properties of Al 2 O 3 /ZnO nanolaminates but also to get some inside on the formation processes of ultrathin films of Al 2 O 3 /ZnO[166].

Figure 2 - 12 .

 212 Figure 2-12. Schematic of possible behavior for the ALD growth per cycle versus temperature

  For example, the Al 2 O 3 process based on TMA and H 2 O displays a progressive decrease in GPC from 175 to 300 °C due to dehydroxylation.Mousa et al. investigated an effect of temperature and gas velocity on growth per cycle duringAl 2 O 3 and ZnO atomic layer deposition at atmospheric pressure[START_REF] Mousa | Effect of temperature and gas velocity on growth per cycle during Al2O3 and ZnO atomic layer deposition at atmospheric pressure[END_REF].

Figure 2 -

 2 Figure 2-13. ALD growth per cycle for Al 2 O 3 (a) and ZnO (b) as a function of deposition temperature for reactor pressures of 2 and 760 Torr. The gas pulse conditions used for deposition are identified in the figure [92].

Figure 2 - 14 .

 214 Figure 2-14. Potential applications of ALD in various research fields [172]

  photoluminescence were achieved. Mechanisms of physical properties in such structures have been proposed[110, 177].

Figure 2 -

 2 Figure 2-15. Cross-sectional view SEM image of a) macroporous silicon surface fabricated by MACE, b) mesoporous layer of PSi, c) mesoporous silicon surface (high magnification); d) cross-sectional view of as-prepared PSi/TiO 2 nanostructure after 150 ALD cycles, e) plane view SEM image of the individual macropore in the PSi/TiO 2 nanostructure after 150 ALD cycles, f) surface of the macropore in the PSi/TiO 2 nanostructure (high magnification).

Figure 2 -

 2 Figure 2-16. SEM images of co-centric hollow nanotubes with different contents of ZnO and Al 2 O 3 .

Figure 2 - 17 .

 217 Figure 2-17. Photodegradation of Methylorange by double, triple and quadruple cocentric nanotubes of ZnO/ZnAl 2 O 4 .

  [181] used ALD ZnO nanolayers as seed layers on polystyrene microspheres for further growth of urchin-like ZnO nanostructures (Figure2-18). The developed urchin-like ZnO nanostructures have been applied for hybrid solar cells. ALD deposited metal oxides and nanolaminates are also used in barrier applications for food packaging and electronics[182][183][184]. It was found that nanolaminate materials showed higher resistance to oxygen and applied strain rather than single layers.ALD deposited metal oxide and metal oxide nanolaminates such as Al 2 O 3 , HfO 2 and HfO 2 /Al 2 O 3 are used as gates in MOSFET transistors[185, 186].

Figure 2 -

 2 Figure 2-18. a,b) SEM images of a self-assembled monolayer of PS microspheres on a TCO substrate; a) tilted (458) low magnification and b) top view. The lower inset of (a) presents the digital image of the same sample. c,d) SEM images of an ordered hollow urchin-like structure of ZnO nanowires after the removal of PS; c) top view, the inset is a higher magnification, and d) tilted view (708). The inset is a high-magnification SEM image of the top of a nanowire grown at the top of the urchin-like structure. e,f) Cross-sectional SEM images of two urchin-like structures treated by FIB at different magnifications. g,h) High-magnification SEM images of a mechanically

  core/shell PAN/ZnO nanostructures[110]. The UV and visible emission bands of ZnO were studied before and after ethanol adsorption. Good sensitivity was found to 150 ppm of ethanol. Modeling of the surface properties was performed[196]. Tailoring of structure, electronic and sensor properties of 1D ZnO nanostructures was proposed.

Figure 2 -

 2 Figure 2-19. PL sensitivity test of ethanol vapor (150 ppm of ethanol) using 1D ZnO NSs obtained with 300 s electrospinning time and coated with 50 cycles ALD ZnO at 100 °C [110].

For

  single molecule sensing, Al 2 O 3 was the most used. It increases the detection capabilities of the nanopore by adjusting precisely its surface properties [219], by reducing the noise [220, 230], and by neutralizing the surface charges to increase the capture rate of DNA [231] or other negative poly-electrolyte. Using alternate bilayers of Al 2 O 3 /ZnO on PET nanopores creates a low roughness of the deposited layers. Using this functionalization, completed by a cover by trimethyl silane, it have been show how the surface charge of nanopore influence the polynucleotide translocation [232, 233].The scheme of preparation of nanopore biosensors is shown in Figure2-20. A periodic mask was formed on a polymer (poly(ethyleneterephthalate) (PET)) using UV lithography. The film was etched in KOH solution to form pores. The pores were coated with Al 2 O 3 /ZnO nanolaminates. Gramicidin (gA), solved in methanol, was added to pure water (pH=8) to reach a final concentration of 10 -4 M. Then, the porous PET/nanolaminate was filled with gA solution.The gA incubation procedure was performed during 72 h at 6 °C. A gA confinement throughout in PET/nanolaminate pores was achieved.Measurement scheme of the ALD pore-based nanostructures is shown in

Figure 2 -

 2 Figure 2-20. Schematic process for hybrid membrane synthesis [4].

Figure 2 -

 2 Figure 2-21. Measurement scheme of ALD-based pore biosensor.

Figure 2 -

 2 Figure 2-22. Evolution of nanopore conductance with and without confined gA under NaCl symmetrical concentration in ALD-based pores with different diameters :(a) 10 nm pore (b) 6

7 .

 7 photovoltaics[253].

Figure 2 - 23 .

 223 Figure 2-23. Atomic layer deposition reactor.

Figure 2 -

 2 Figure 2-24. Schematic diagram of set up of electrospinning apparatus [255].

  lithography is a powerful fabrication technique to produce nanoparticle arrays with controlled shape, size, and interparticle spacing. The need for monodisperse, reproducible, and materials general nanoparticles has driven the development and refinement of the most basic NSL architecture as well as many new nanostructure derivatives. In this technique the submicron latex particles self-organized into hexagonal pattern, which was used as template to create ordered 2D array of desired materials.

Figure 2 - 25 .

 225 Figure 2-25. The scheme of floating-transferring technique.

Figure 2 - 26 .

 226 Figure 2-26. Scheme of processes involved in metal-assisted chemical etching [258].

  Currently, ALD is considered as one of the most promising thin film deposition techniques for enabling nanoscale device fabrication. The recently investigations in the area of ALD of ZnO, Al 2 O 3 , and Al 2 O 3 /ZnO nanolaminates, and potential applications of ALD in various research fields were overviewed in this chapter. With devices becoming ever smaller and increasingly structured into complex three dimensional shapes, the need for controllable and conformal thin films has never been greater. ALD, with its sequential self-limiting reactions, is able to suit to these demands. The requirements, which have to be taken into consideration for choosing a chemical precursor for ALD process, were presented. The precursors for the ALD deposited ZnO and Al 2 O 3 thin films were overviewed and presented in the Tables2-2 and 2-3, respectively. The applications of ALD metal oxides for biosensor devices are not well studied. Some recent investigations of ALD biosensor applications were presented in the Table 2-6. The collected information about ALD technology was emphasized with the advantages and limitations. Finally, at conclusion part of this chapter the prospects of the ALD are presented. In this thesis, the ALD technique was used for the deposition of ZnO and Al 2 O 3 /ZnO nanolaminates thin films on the different substrates. The following tasks were performed: -Improvement of the properties of SiNWs, which were prepared by the combination of NSL and MACE techniques, by the ALD deposited ZnO thin films (20 and 50 nm); morphology and the organization control of SiNWs on a large area; -ZnO films formed by ALD as an optical biosensor platform for the detection of Grapevine virus A-type proteins (GVA-antigens); -A specific control of protein anchoring by the development of multifunctional surface with large-scale array of polystyrene spheres (PSS), which produced by NSL and further blocking the unspecific adsorption of protein on the surface of the PSS by PEG SAMs -The tuning of structural properties and the enhancement of electronic and optical properties of 1D PAN ZnO/Al 2 O 3 nanolaminates designed by atomic layer deposition (ALD) and electrospinning.

  nm) and a layer of noble metal (50 nm) as a substrate. PS spheres are deposited on the gold surface using the floating-transferring technique. The PS spheres were then functionalized with PEG-biotin and the defects by self-assembly monolayers (SAMs) PEG to prevent unspecific adsorption. The schematic diagram of overall process for protein immobilization is represented in Figure a.

Figure .

 . Figure. The schematic diagram of overall process for protein immobilization (a), fluorescent images of Cy5-PEG-NHS-modified polystyrene spheres (the inset indicates a zoom).

Figure b shows a

  Figure b shows a fluorescence microscopy image of the prepared sample.

3. 3 .

 3 Materials and method 3.3.1. Materials Avidin from egg white (A9275), Poly(ethylene glycol) 2-aminoethyl ether biotin (PEG) M n = 5300 g mol -1 (757772), N-Hydroxysuciinimide (NHS) Mw = 115.09 g mol -1 (130672), Ethylenediamine Mw = 60.10 g mol -1 (E26266), Anti-Avidin, antibody produced in rabbit (A5170), Ethanol (absolute alcohol, without additive (02860)), phosphate buffered saline (P4417) and Micro particles based on polystyrene, (size 1 μm, 10 wt% aqueous solution (89904)) were purchased from Sigma Aldrich. Thiol PEG, mPEG-SH Mw = 2000 g mol -1 (PG1-TH-2k), Cy5-PEG-NHS Mw = 5000 g mol -1 (PG2-NSS5-5k) and Succinimidyl PEG, mPEG-NHS Mw = 2000 g mol -1 (PG1-SC-2k) were purchased from Nanocs. N-(3-Dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride (EDC) Mw = 191.70 g mol -1 (03449) was purchased from Fluka Analytical. Alexa Fluor 488 TFP ester (A37570) and Alexa Fluor 647 NHS (A37573) were purchased from ThermoFisher Scientific.3.3.2. Protein labelingAvidin was labeled with Alexa Fluor 647 NHS. Typically, 100 μL of protein solution(1 mg Avidin and 100 µl PBS pH = 8.3) was added to dry fluorophore Alexa-647 and allowed to react for 0.5 h at 20 °C. Anti-Avidin was labeled using Alexa Fluor 488 TFP ester. One hundred microliters of protein solution (5 μL Anti-Avidin and 100 µl PBS pH = 8.3) was added to dry fluorophore Alexa-488 and allowed to react for 0.5 h at 20 °C. Then the unreacted dyes and proteins were separated by centrifugation (16000 g, 1 min) using filter (Biospin P6) according to the supplier of the kit. 3.3.3. Polystyrene sphere deposition on the Si/Cr/Au surface

Figure 3 - 1 .

 31 Figure 3-1. The schematic diagram of overall process for protein immobilization.

Figure 3 - 2 .

 32 Figure 3-2. Diameter of PS spheres as the function of the O 2 plasma etching: The insets show PS spheres with different O 2 plasma etching times: 1 (a), 5 (b), 10 (c) and 15 (d) min, respectively, as determined by SEM (scale bars 500 nm).

Figure 3 - 3 .

 33 Figure 3-3. Fluorescent images of Cy5-PEG-NHS-modified polystyrene spheres (the inset indicates a zoom)

Figure 3 - 4 .

 34 Figure 3-4. Fluorescent images of PS spheres functionalized with biotin-PEG-NH 2 (a) and mPEB (b) after addition of avidin (labeled with Alexa Fluor 647).

  -6 depicts the fluorescence image of a sample where both avidin* and antiavidin* are labeled with Alexa Fluor 647 and 488 respectively. The first one is characterized with CY5cube and the second one with FTIC cube. The perfect superposition of both images confirms that both avidin and anti-avidin are located on PS spheres.

Figure 3 - 5 .

 35 Figure 3-5. Fluorescent images of PS spheres functionalized with biotin-PEG-NH 2 and avidin (unlabeled) after Anti-Avidin*(labeled with Alexa Fluor 488).

Figure 3 - 6 .

 36 Figure 3-6. Fluorescent images of PS spheres functionalized with biotin-PEG-NH 2 and avidin (labeled with Alexa Fluor 647) after Anti-Avidin (labeled with Alexa Fluor 488) addition recorded with FTIC cube (a) Cy5 cube (b).

  Figure a represents the vine-grapes infected with GVA. Such vine-grapes have poor health, poor quality and low-yielding fruit. Among a large variety of biosensors, immunosensors are based on specific interaction between antibodyantigen couple. The scheme of PL based immunosensor, which was used in the present work, is shown in Figure b. ZnO is suitable for the immobilization of biomaterials, which are applied as biological recognition parts in biosensors. The detection of GVA-antigens was performed through direct immobilization of anti-GVA antibodies on the ZnO thin film surface, forming the biosensitive layer.

Figure

  Figure. Vine-grapes infected with Grapevine virus A-type (GVA) (a), and the scheme of PL based immunosensor (b).

  exposures of Diethyl Zinc (DEZ) (Zn(CH 2 CH 3 ) 2 , 95% purity, CAS: 557-20-0) and H 2 O separated by a purge of Argon with a flow rate of 100 sccm. The deposition regime for ZnO consisted of 0.2 s pulse of DEZ, 30 s of exposure and 30 s of purge with Argon followed by 2 s pulse of H 2 O, 30 s of exposure to H 2 O and finally 40 s purge with Argon. ZnO ultrathin films with different numbers of cycles were deposited at 100 °C.

  SEM images of ALD ZnO thin films deposited on Si substrates with different numbers of cycles are represented in figure 4-1a. The SEM images show a conformal coating of the Si substrate by the ALD formed the ZnO films. With increasing thickness of ZnO films, a rough surface with colomnar growth has been observed. Ellipsometry-based measurements confirmed that ZnO films of 57 and 110 nm thickness (these films in the further text are noted as ZnO57nm and ZnO110nm) were obtained respectively by 250 and 500 ALD cycles, which correspond to a growth of 2.2 Å per one cycle. GIXRD diffraction patterns of ZnO thin films are shown in figure 1b. It demonstrates the diffraction peaks at 2θ = 31.80°, 34.54° and 36.16°, which are corresponding to (100), (002), and (101) reflection planes of hexagonal wurtzite structure of ZnO respectively.

Figure 4 - 4 . 4 . 1 .

 4441 Figure 4-1. a) SEM cross section images and b) GIXRD of ZnO ALD films deposited on Si substrates by different numbers of cycles (250 and 500).

Figure 4 - 2 . 4 . 4 . 2 .

 42442 Figure 4-2. PL spectra of the ZnO samples with 57 and 110 nm layer thicknesses (a), PL spectra of anti-GVA deposited on glass (b)

Figure 4 - 3 .

 43 Figure 4-3. The scheme of PL based immunosensor

Figure 4 -

 4 Figure 4-4b presents the PL spectra of the ZnO110nm films with immobilized anti-GVA antibodies (ZnO110nm/anti-GVA) from the solutions with different concentrations of anti-GVA, which are ranging from the lowest concentration (at 1/1000 dilution of initial anti-GVA containing solution) to the highest concentration (at 1/50 dilution). The initial PL signal intensity among all

Figure 4 - 5 .

 45 Figure 4-5. The dependence of ZnO 110nm /anti-GVA/Ag+ PL spectra (normalized intensity) after incubation of ZnO 110nm /anti-GVA-based imunosensor in different GVA-antigen concentrations containing specimens (specimens -Ag+) (a), PL spectra dependence (normalized intensity) of ZnO 110nm /anti-GVA-based immunosensor under different concentrations of proteins separated from healthy vine grape plants, which not contains antigen for anti-GVA (specimens -Ag-) (b).

Figure 4 - 6 .

 46 Figure 4-6. PL intensity at 425 nm as a function of GVA-antigen concentration in Ag+ specimen, insetbiosensor response (S) as a function of GVA-antigen concentration in Ag+ specimen (a), PL intensity at 425 nm as a function of different concentrations of proteins separated from healthy vine grapes, which not contain any antigen capable to bind with anti-GVA (specimens -Ag-), insetbiosensor response (S) as a function of Ag-specimen concentration (b).

  photon with energy close to the ZnO band gap (!3.3 eV) for NBE emission or alternatively through the level defects with energies !2.9 eV for the protein related emission[304].

  Figure a shows the scheme of metal-assisted chemical etching of Si wafer covered with polystyrene spheres, and the SEM image of SiNWs (etching time is 5 min) with 50 nm ZnO ALD layer. The TEM and SEM investigations confirmed the ability to produce highly uniform layers of ZnO covered SiNWs. The detailed study of structural and optical properties of core-shell SiNWs/ZnO heterostructure was done by utilizing XRD, SEM, reflectance and photoluminescence spectroscopy, respectively. The X-ray diffraction analysis revealed the hexagonal wurtzite structure of all samples. The optical reflectance spectra for SiNWs/ZnO confirmed the low optical reflection of thin films. The study of photoluminescence (PL) spectra of SiNWs/ZnO showed the domination of defect emission bands, which points to deviations of stoichiometry of the prepared 3D ZnO nanostructures.

Figure .

 . Figure. Scheme of metal-assisted chemical etching of Si wafer covered with PSS (a), and the SEM image of SiNWs/ZnO, 50 nm (b).

  Thereafter, in 1964 by Wagner and Ellis performed the illuminating work and established the vapor-liquid-solid (VLS) mechanism of the Si whisker growth [336]. These pioneer studies open exciting possibilities for fabrication and investigation of SiNWs. In 2002, Peng and coworkers introduced a HF-etchingassisted nanoelectrochemical strategy to synthesize wafer-scale aligned SiNWs [337]. To date, there are a lot of different techniques to produce silicon nanowires such as chemical vapor deposition using the VLS (Vapor-Liquid-Solid) mechanism [338], laser ablation [339], molecular beam epitaxy [340], chemical etching [341], and solution growth [342]. Among various preparation methods, the metal-assisted chemical etching (MACE) of silicon substrates in combination with nanosphere lithography (NSL) has recently emerged as a promising method to fabricate large areas of ordered SiNWs [290, 343]. The combination of MACE and NSL techniques is under increasing attention, especially because MACE is a simple, inexpensive process, and able

  the diameter of spheres was decreased by O 2 plasma etching for 5 min to expose the surface of wafer for metal deposition. Plasma etching is capable of uniform and fast modification of nanospheres, and it can control the sphere diameter by adjustment the etching time[355]. It is a convenient and efficient etching method. In order to stick the PS spheres at the Si surface, a heat treatment at 100 °C for 30 min was performed. On the next step a thin Au film was deposited by physical vapor deposition (PVD). The sputtering was carried out at a discharge of 25 mA in a vacuum with a pressure below 0.1 mbar. After the samples covered by Au were etched with the solution consisting of H 2 O/H 2 O 2 /HF in the volume ratio 1:0.15:0.3 respectively, at room temperature for 1, 2, 5 and 7 minutes. The metal was removed with aqua regia solution; the PS spheres were etched by O 2 plasma.

Figure 5 -

 5 Figure 5-1 represents the overall process for the synthesis of SiNWs.

Figure 5 - 1 .

 51 Figure 5-1. The schematic diagram of overall process for the synthesis of SiNWs by combining MACE and NSL techniques.

Figure 5 -

 5 Figure 5-2 represents a dependence of the diameter of PSS as the function of different etching times (insets: 1 (b), 5 (c) and 10 (d) min, respectively) by O 2 plasma. The etching of PSS by O 2

Figure 3 -

 3 Figure 3-2a demonstrates the SEM image, which confirms the possibility to obtain a relatively large area, close-packed, hexagonal polystyrene monolayer, produced by floating-transferring technique.

Figure 3 -

 3 Figure 3-2f shows a photograph of a monolayer pattern of PSS prepared by the mentioned before technique on 2x2 cm 2 silicon wafer. The color of the substrate observed in this photograph is due to the diffraction of light.

Figure 5 - 2 .

 52 Figure 5-2. Diameter of PSS as the function of the O 2 plasma etching: Inset consists of SEM images of the PSS as-prepared by floating transferring technique (a) and with different O 2 plasma etching times: 1 (b), 5 (c) and 10 (d) min, respectively. And photographs of the monolayer of PSS on the water surface (e) and 2x2 cm 2 silicon wafer covered with monolayer built from 1 µm PS latex beads by the mentioned before technique (f).

Figure 5 -

 5 Figure 5-3 shows the final structure after depositing 50 nm ZnO film on SiNWs array. The SEM images indicate a conformal coating by ALD of the Si substrate.

Figure 5 - 3 .

 53 Figure 5-3. SEM images of SiNWs (etching time is 5 min) with 50 nm ZnO ALD layer.

Figure 5 - 4 .

 54 Figure 5-4. XRD spectra of SiNWs/ZnO with different thicknesses (20 and 50 nm) ZnO layers on SiNWs with 7 min etching.

Figure 5 -

 5  shows the XRD spectra of 20 and 50 nm ZnO films deposited on the silicon nanowires substrate with 7 minute etching. All peaks in the recorded range were identified[109, 165, 357].

Figure 5 - 5 .

 55 Figure 5-5. Cross-sectional view TEM image of ZnO-Si nanowires with different ZnO layer thicknesses: (a) 20 nm and (b) 50 nm.

Figure 5 -

 5 Figure 5-5 shows the high-resolution TEM image of ZnO-Si nanowires with different ZnO layer thicknesses. Silicon nanowires coated with 20 nm of ZnO by ALD is presented in Fig 5-5a.

  -5 a). It can be explained by the lateral transport of the charge carriers [290].

Figure 5 -

 5 Figure 5-5b shows a TEM image of individual silicon nanowires covered by 50 nm ALDZnO layer. The total thickness of the layer is approximately 50 nm, having the maximum value on the top (55 nm). For both samples, the ZnO layers are in a polycrystalline phase. The size of nanocrystallites was estimated using elliptical shape fitting and the longer axis was used as the nanocrystallite size. The average grain size for 50 nm and 20 nm layer thicknesses was almost the same, 11.8±2.5 nm and 10±2.5 nm, respectively. These results confirmed the data obtained by XRD. The TEM images demonstrate the ability to produce highly uniform layers of ZnO covered silicon nanowires by the ALD processes.

Figure 5 - 6 .

 56 Figure 5-6. The Raman spectra of the Si NWs as-prepared (etching time is 7 min) and after deposition of ZnO 20 nm and 50 nm, respectively.

Figure 5 - 6 )

 56 Figure5-6) [359-361]. It is typical of the wurzite ZnO phase, but the peak is broader (full width half maximum -FWHM, is about 20 cm -1 ) with respect to the bulk value (FWHM is less than 10 cm -1 ) and blue-shifted[359][360][361]. This broading and shifting could be explained by the quantum confinement effects in ZnO nanocrystals[360][361][362].

Figure 5 - 7 .

 57 Figure 5-7. The reflection spectra of the SiNWs prepared at different etching times (2, 5 and 7 min) and after deposited of ZnO 20 nm (a) and 50 nm (b), respectively.

Figure 5 -Figure 5 - 8 .

 558 Figure 5-7 shows the reflectance of Si nanowires arrays etched for 2, 5 and 7 minutes and covered with 20 (a) and 50 nm (b) of ZnO, respectively. It was found that the reflectance decreases with increasing of etching time, for longer Si nanowires. This may be explained by the more effective light trapping and more absorption of longer nanowires. We observe that the reflectance is less than 5% and 8% for the SiNWs (etching time is 5 minutes) covered with ZnO 20 and 50 nm, respectively. Such low reflectance could be explained by the energy band structure of the sample. Various band gaps in the system causes a variety of near band-edge absorption from sunlight in different frequency ranges, reducing reflectivity. Also the change of the refractive indexes of the materials may effect on the reflection reduction [363]. The optical reflectance spectra for SiNWs/ZnO presented in Figure 5-7 confirm the low optical reflection of thin films. Layer of ZnO on SiNWs can work as antireflection coating.

Figure 5 - 9 .

 59 Figure 5-9. Photoluminescence spectra of SiNWs prepared at different etching times -2, 5 and 7 minutes, and after ALD of 20 (a) and 50 nm ZnO (b), respectively.

Figure SI5- 1 .

 1 Figure SI5-1. Deconvolution of PL peaks spectra of SiNWs prepared at different etching time -2, 5 and 7 minutes, and after ALD of 20 and 50 nm ZnO.

Figure 1 .

 1 Figure 1. Schematic diagram of set up of electrospinning apparatus (a), and TEM image of the end face of PAN fiber coated by the nanolaminates (b).

  . The ZnO deposited on Al 2 O 3 thin films in the Al 2 O 3 /ZnO nanolaminates demonstrated a different growth direction in comparison to single ZnO thin film[364]. ZnO demonstrates as well a change from amorphous to nanocrystalline with the increase of the bilayers thickness where Al 2 O 3 layer remains amorphous[START_REF] Raghavan | Nanocrystalline-to-amorphous transition in nanolaminates grown by low temperature atomic layer deposition and related mechanical properties[END_REF]. The change of the growth direction, the crystallinity, and the Al doping influence the optical[165, 166], electrical[101], and mechanical properties[START_REF] Raghavan | Nanocrystalline-to-amorphous transition in nanolaminates grown by low temperature atomic layer deposition and related mechanical properties[END_REF] of the deposited thin films. Recently, we investigated the optical and the structure properties of ZnO/Al 2 O 3 nanolaminates deposited on Si substrates by ALD[165]. We demonstrated the amorphous-to-crystalline phase transitions of ZnO in ZnO/Al 2 O 3 nanolaminates as well as the quantum confinement and size dependent room temperature photoluminescence [165]. It was shown a correlation between structure (grain size and layer thickness) and optical (extinction coefficient and refractive index), pointing to the influence of growth conditions on the fundamental properties of the nanolaminates [165]. Different 1D nanostructures such as carbon nanotubes (CNTs) and polymer fibers have been investigated in order to design core/shell nanostructures using ALD of metal oxides [365-369]. Different studies were performed for the growth of oxides of Carbon nanotubes. Stano et al. reported the influence of CNTs type and the defect concentration on the ALD coating [369]. For low defect concentration, ALD coating cannot be realized. The functionalization of CNTs surface is needed to promote the nucleation of the oxide film. Carboxyl and hydroxyl groups are formed on the CNTs surface to initiate the ALD growth. Kemnade et al. showed that conformal growth of ALD ZnO layer on CNTs requested the modification of the CNTs with aromatic linking agents [366]. Lin et al. reported on the importance of CNT functionalization before deposition of ZnO nanolayers by ALD [367]. Kayaci et al. reported that ALD ZnO layers provided a conformal coating of nylon fibers [365]. However, Oldham et al. demonstrated that TMA and DEZ precursors could chemically react with polyamide-6 (PA-6) nylon nanofibers destroying their physical properties [368]. Therefore, the conformal and uniform ALD coating on 1D nanostructures could be achieved by the right choice of the core chemical composition and surface state of the 1D nanostructures. PAN nanofibers are good chemically stable material for 1D core/ shell nanostructure design [256]. PAN nanofibers have been successfully used for chemical deposition of different metal nanoparticles on their surface. It was shown that PAN nanofibers have good mechanical and thermal stability. The adsorption sites present on the surface of the PAN fibers would facilitate the nucleation of the metal oxide layers by ALD. Thus, integration of metal oxide ALD technique and PAN nanofibers has a good perspective.

6. 3 . 2 .

 32 ALD Deposition of Nanolaminates. Diethyl zinc (DEZ) (Zn(CH 2 CH 3 ) 2 , 95% purity, CAS: 557-20-0) and trimethylaluminum (TMA) ((CH3)3Al) 98% purity, CAS: 75-и24-1) were purchased from Sigma-Aldrich. A custom-made ALD reactor was used for the synthesis of ultrathin Al 2 O 3 /ZnO nanolaminates. ALD was performed using sequential exposures of TMA (DEZ) and H 2 O separated by a purge of Argon with a flow rate of 100 sccm. The deposition regime for ZnO and Al 2 O 3 consisted of 0.2 s pulse of TMA (DEZ), 30 s of exposure to TMA (DEZ), 30 s of purge with argon followed by 2 s pulse of H 2 O, 30 s of exposure to H 2 O, and finally 40 s purge with argon. Al 2 O 3 /ZnO ultrathin nanolaminates with different numbers of cycles were deposited on electrospun PAN nanofibers (Table

  Ni-filtered Cu-radiation. Surface structural and chemical properties of PAN-nanolaminates were analyzed by means of the XPS/UPS technique mounted within the Omicron Nanotechnology multiprobe UHV system, using a monochromatized Al Kα X-ray as the excitation source (hν = 1486.6 eV) and choosing C 1s (284.6 eV) as the reference line. XPS was conducted under ultrahigh vacuum(10 -7 Pa). CasaXPS software was used to analyze the XPS data. Optical properties of ultrathin nanolaminates have been studied by photoluminescence spectroscopy (in the spectral range of 370-800 nm). The excitation of luminescence was performed by a solid state laser source (Figure6-1d). Lattice fringes seen in high-resolution TEM images reveal ZnO nanocrystals with (101) and (

Figure 6 -

 6 Figure 6-2. (a) Absorbance spectra and (b) XRD spectra of PAN-Al 2 O 3 /ZnO nanolaminates at various bilayers thicknesses. Spectra are shifted for clarity.

Figure 6 - 3 .

 63 Figure 6-3. XPS survey spectra of ZnO/Al 2 O 3 nanolaminates coated polymer fiber with different bilayer thicknesses: (a) 1.2 nm, (b) 2 nm, (c) 5.2 nm, (d) 10 nm, and (e) 20 nm. Main core levels are labeled. Data are normalized to each O 1s peak maximum and separated vertically.

Figure 6 - 4 .

 64 Figure 6-4. XPS survey spectra of ZnO/Al 2 O 3 nanolaminates coated polymer fiber with different bilayers thicknesses: (a) 1.2 nm, (b) 2 nm, (c) 5.2 nm, (d) 10 nm, and (e) 20 nm. Main core levels are labeled. Data are normalized and separated vertically.

Figure 6 - 5 .

 65 Figure 6-5. O 1s energy-loss spectra for band gap determination of Al 2 O 3 of ZnO/Al 2 O 3 nanolaminate coated polymer fiber with different bilayers thicknesses.

Figure 6 - 6 . 6 . 4 . 3 .

 66643 Figure 6-6. UPS results of work function measurements of ZnO/Al 2 O 3 nanolaminate coated polymer fiber with different bilayer thicknesses.

Figure 6 -

 6 6 shows the UPS spectra of PAN-ZnO/Al 2 O 3 nanolaminates. The calculated values of Φ are shown in the image. The Φ of ZnO decreases gradually from 5.86 eV (20 nm bilayer thickness) to 5.19 eV (1.2 nm bilayer thickness), which is possibly due to the morphology changes of the top ZnO layers in nanolaminates. The structure of ZnO layer in the 20 nm bilayer thickness sample is polycrystalline (TEM results; Figure 6-1); thus, the energy barriers presenting at the border of disorientated ZnO nanocrystallites increase the value of the Φ. The small peak corresponding to Al 2 O 3 is also present in Figure 6-6. The average value of WF for Al 2 O 3 is approximately 4.7 eV, and it changes insignificantly. Work functions of ZnO and Al 2 O 3 layers are plotted in Figure 6-6. The work function of Al 2 O 3 was insignificantly changed whereas the ZnO work function significantly decreased with the bilayer thickness.

Figure 6 - 7 .

 67 Figure 6-7. Zone diagram of Al 2 O 3 /ZnO nanolaminate formation: (a) single layers before contact, (b) 1 bilayer, and (c) n bilayers.

ZnO (ε = 8 . 5 )

 85 , and electric constant (ε 0 = 8.85 × 10 -12 F m -1 ), respectively. The donor concentrations in ZnO and Al 2 O 3 were taken as 10 23 and 10 16 m -3 , respectively [385, 386]. The estimated Debye lengths were 10 -8 and 5 × 10 -5 m for ZnO and Al 2 O 3 , respectively.

6 . 4 . 4 .

 644 photogenerated holes and electrons as the equilibrium holes concentration is too low. PL depends on the defects concentration. The visible PL intensity increases with the decrease of the layer thickness due to the growth of defects number. It was shown that PAN, as a template, induces the nucleation of pure ZnO during the growth affecting the optical properties[110]. However, in the present work, PAN template did not influence the PL of ZnO as since Al 2 O 3 layer was the first layer deposited over PAN in all the analyzed samples. It is known that PL of ZnO is sensitive to surface band bending and grain size dimensions[109]. Due to the depleted layer, no exciton emission was observed in the samples with 20, 10, and 5.2 nm bilayers thicknesses. Moreover, the strong visible emission has been observed for all samples. The intensity of the measured emission was 1000-fold higher than the PL emission of the nanolaminates, deposited on Si substrates[110, 165]. The significant increase of the PL was found with the increase of the bilayer numbers. It has been reported that visible PL in ZnO nanostructures is resulted from defects, mostly from Zn and O

Figure 6 - 8 .

 68 Figure 6-8. Room temperature PL spectra of PAN-Al 2 O 3 /ZnO nanolaminates with different bilayer thicknesses; Al 2 O 3 /ZnO nanolaminate 50 (2 nm × 2 nm) deposited on silicon was added for comparison.

  photogenerated carriers, thus increasing the PL what we can observe on the PL spectra. Many other authors have shown that the formation of a nanocrystalline structure decreases the electron work function [391, 392].

  function of Al 2 O 3 was mostly independent of the bilayers number whereas the ZnO work function decreased with an increase of the bilayer number. The observed phenomenon indicate surface band bending on the upper layer of ZnO and further charge "screening" by Al 2 O 3 layers in internal ZnO layers of the nanolaminates.

Figure SI6- 1 .

 1 Figure SI6-1. EDS mapping of PAN-nanolaminates. Blue color -Zn and green color -Al.

Figure SI6- 3 .

 3 Figure SI6-3. De-convolution of XPS peaks using CasaXPS software.

Figure SI6- 4 .

 4 Figure SI6-4. De-convolution of PL peaks spectra of PAN-Al 2 O 3 /ZnO nanolaminates with different bilayers thicknesses.

  structural properties and the enhancement of electronic and optical properties of 1D PAN ZnO/Al 2 O 3 nanolaminates designed by atomic layer deposition (ALD) and electrospinning were performed in our research study as well. The structural and optical properties of Al 2 O 3 /ZnO determined from the XPS, TEM, FTIR, XRD and PL analysis provide important information about crystalline structure of nanolaminates on the 1D PAN substrate. The amorphous-to crystalline transition has been observed for ZnO nanolayers at the thickness of 2.6 nm on the 1D PAN nanotemplate. In particular, strong influence of the bilayer thicknesses on the crystallinity of ZnO nanolayers has been found. Due to the quantum confinement effect, the shift of XPS peaks to higher energies has been observed. Work function of Al 2 O 3 was mostly independent of the bilayers number whereas the ZnO work function decreased with an increase of the bilayer number. The observed phenomenon indicate surface band bending on the upper layer of ZnO and further charge "screening" by Al 2 O 3 layers in internal ZnO layers of the nanolaminates. Photoluminescence of the nanolaminates corresponded to emission bands in ZnO nanolayers. Due to low grain size, high defect concentration, and surface band bending, no excitonic peaks were observed. The defect emission band was affected by the band bending and defect concentration. The observed XPS and PL data are in good correlation. The enhanced PL of the nanolaminates could be used for optical (bio)sensing.

Table 2 -

 2 1. Different names of ALD [12]……………………………………………………..…..4

Table 2 -

 2 2. ALD processes reported for the growth of ZnO thin films. The growth per cycle (GPC) values displayed in the table are from inside the ALD window; if no ALD window is

Table 2 -

 2 3. ALD processes reported for the growth of Al 2 O 3 thin films………………………....24

Table 2 -

 2 4. Band gap of Al 2 O 3 /ZnO nanolaminates with different bilayer thicknesses and ZnO single thin film of 50 nm thickness [165]………………………………………………………..35

Table 2 -

 2 5. Deposition sequences of Al 2 O 3 and ZnO cycles on the PAN nanofibers…………....42

Table 2 -

 2 6. ALD for biosensors applications…………………………………………………….50

Table 2 -

 2 7. Selected properties of the most common noble metal oxides………………………..60

Table 2 -

 2 8. The process list for the ZnO ALD……………………………………………………62

Table 2 -

 2 [START_REF] Suntola | Method for producing compound thin films[END_REF]. The experimental tools used for the study of the samples prepared at the present thesis……………………………………………………………………………………………..64 Table 5-1. Band gap of SiNWs covered with 20 and 50 nm ZnO……………………………...113

Table 6 -

 6 1. Al 2 O 3 /ZnO Ultrathin Nanolaminates Synthesis by ALD…………………………...120

Table 6 -

 6 2. Electronic parameters of Al 2 O 3 /ZnO Ultrathin Nanolaminate Synthesis by ALD…127

	1.1. Background

Table 2 -

 2 1. Different names of ALD[START_REF] Puurunen | Surface chemistry of atomic layer deposition: A case study for the trimethylaluminum/water process[END_REF].

	Name	Abbreviation	Refs.
	Atomic layer deposition	ALD	[13]
	Atomic layer epitaxy	ALE
	Atomic layer evaporation	ALE
	Atomic layer growth	ALG
	Chemical assembly
	Molecular deposition
	Molecular lamination
	Molecular layer epitaxy	MLE
	Molecular layering	ML
	Molecular stratification

Table 2 -

 2 2. ALD processes reported for the growth of ZnO thin films. The growth per cycle (GPC) values displayed in the table are from inside the ALD window; if no ALD window is reported, representative values from the entire tested temperature range are displayed instead (The table is adopted

	from [45])

2.3.2. Synthesis of Al 2 O 3 from TMA and H 2 O

	Aluminum oxide (Al 2 O 3 ) is one of the most widely studied and used material grown by
	ALD. Al 2 O 3 is a well-behaved ALD system that can be accomplished with a variety of
	precursors and relatively short cycle times. The deposition is usually performed using
	trimethylaluminum (Al(CH 3 ) 3 , TMA) and water as precursors [111-115]. This is almost an ideal
	self-limiting ALD process and considered as a model system for ALD [12]. The first report dates
	back to late 1980s [116] but since then the process has been extensively studied and
	characterized in detail. Aluminum oxide is probably the most extensively studied ALD material
	for numerous diverse applications. ALD Al 2 O 3 films are widely used as protective, barrier, and
	dielectric layers as such or as component in nanolaminates [117, 118].
	The surface chemistry during Al 2 O 3 ALD can be described as the following binary reaction
	sequence [119, 120]:
	AlOH* + Al(CH 3 ) 3 → AlOAl(CH 3 ) 2 * + CH 4	(2-4)
	AlCH 3 * + H 2 O → AlOH* + CH 4	(2-5)
	where the surface species are designated by asterisks.
	The Al 2 O 3 ALD growth occurs during alternating exposures to TMA and H 2 O. Al 2 O 3 ALD
	is a model system because the surface reactions are very efficient and self-limiting. The main
	driver for the efficient reactions is the formation of a very strong Al-O bond. An Al-O Lewis
	acid-base complex is formed during each half reaction, with methane as a reaction byproduct,

Table 2 -

 2 3. ALD processes reported for the growth of Al 2 O 3 thin films.

	cycles is to deposit one monolayer of Al 2 O 3 on the

2.3.3. Al 2 O 3 /ZnO nanolaminates produced by ALD

	nanolayers show a transition from amorphous to nanocrystalline phases when bilayer spacing
	increased [6]. Thin amorphous Al 2 O 3 layers work as stopping layers for ZnO crystal growth [164]. Atomic layer deposition (ALD) is a powerful tool to fabricate different oxide materials [159]. The ZnO ALD films are deposited using alternating exposures to DEZ and H 2 O. The recent ALD oxide studies have often dealt with growth mechanism investigations, but also the structural properties of the films have been of interest. One important material type of ALD oxides The (2-7) and (2-8) surface reactions that define the cycle can be written as:
	is nanolaminates. Nanolaminates are unique nanocomposites that allow various thin film properties ZnOH* + Zn(CH 2 CH 3 ) 2 → ZnOZn(CH 2 CH 3 )* + C 2 H 6 (2-7)
	to be tuned by changing the composition and interfacial density. Nanolaminates are composite films comprised of alternating layers of different materials, which have individual layer thicknesses on Zn(CH 2 CH 3 )* + H 2 O → ZnOH* + C 2 H 6 , (2-8)
	the nanometer scale [160-162]. The multilayered structure often imparts unique properties to the where the asterisks designate the surface species.
	nanolaminates film. In some cases, the nanolaminates may have physical properties that are The Al 2 O 3 ALD films are deposited using alternating TMA and H 2 O exposures.
	superior to those of the constituent materials. The (2-9) and (2-10) surface reactions that define the cycle for Al 2 O 3 ALD are:
	In addition, surface reactions can be devised that promote good nucleation and adhesion between the different nanolayers. Once the physical properties of the nanolaminates have been AlOH* + Al(CH 3 ) 3 → AlOAl(CH 3 ) 2 * + CH 4 (2-9)
	optimized, ALD allows objects with diverse sizes and shapes to be coated with the desired AlCH 3 * + H 2 O → AlOH* + CH 4 , (2-10)
	nanolaminates film. The ALD methods allow the tailoring of structural and optical parameters of the
	The ALD of nanolaminates and alloys has many applications in semiconductor device
	fabrication and nanostructure engineering. The first report of nanolaminates fabricated using ALD
	examined HfO 2 /Ta 2 O 5 nanolaminates as low leakage dielectric films [163].
	In nanolaminates the advantageous properties of each component can be retained, for example, in
	insulators: high permittivity, low leakage current density, and high charge storage capacity.
	The Al 2 O 3 /ZnO NLs can be grown by alternating between the trimethylaluminum (TMA) and
	H 2 O reaction cycles for Al 2 O 3 ALD and the DEZ and H 2 O reaction cycles for ZnO ALD [8].
	Different studies report the growth of Al 2 O 3 /ZnO nanolaminates as well as the incorporation of Al
	doping in ZnO using ALD [4-8].
	Using ALD methods, ZnO grows as a conducting, polycrystalline film with a rough surface
	topography resulting from the individual crystallites. In contrast, Al 2 O 3 grown by ALD is an
	excellent insulating, amorphous film that deposits with high conformality. The wide disparity in
	physical properties between ZnO and Al 2 O 3 suggests that nanolaminates formed from alternating
	ZnO/Al 2 O 3 layers may possess properties that span a wide range in surface roughness and
	conductivity.
	Although there are nucleation issues upon initiating the Al 2 O 3 ALD cycles following the ZnO
	ALD cycles, the relative number of Al 2 O 3 ALD and ZnO ALD cycles can be changed to define a
	wide range of alloy compositions [7]. Since Al 2 O 3 ALD films are insulating and ZnO ALD films
	are conducting, variable resistivity films can be fabricated using Al 2 O 3 /ZnO alloys. Al 2 O 3 thin films
	deposited by ALD are amorphous in nature independently of their thickness, whereas ZnO

nanolaminates, including single layer thickness, grain size, band gap, and PL

[165]

.

  Nasr et al. used ZnO and ZnO/Al 2 O 3 to form novel ZnO/ZnAl 2 O 4 multi co-centric nanotubes for photocatalytic application [178]. Electrospun PAN nanofibers were used as template for deposition of ALD layers. Altering ZnO and Al 2 O 3 layers were deposited as shown in Table 2-5.

Table 2 -

 2 5. Deposition sequences of Al 2 O 3 and ZnO cycles on the PAN nanofibers. Double 20 nm Al 2 O 3 /40 nm ZnO/20 nm Al 2 O 3 Triple 20 nm Al 2 O 3 /40 nm ZnO/20 nm Al 2 O 3 /40 nm ZnO/20 nm Al 2 O 3 Quadruple Al 2 O 3 /40 nm ZnO/20 nm Al 2 O 3 /40 nm ZnO/20 nm Al 2 O 3 /40 nm ZnO/20 nm Al 2 O

3 Due to a temperature induced phase transitions, new phase of ZnAl 2 O 4 has been formed. The presence of new phase was confirmed using XRD measurements. PL quenching of ZnAl 2 O 4 /ZnO nanotubes was observed with the increase of ZnAl 2 O 4 content. The developed ZnO/ZnAl 2 O 4 nanotubes showed good photocatalytic performance for organic pollutants degradation. Particularly, the increase of ZnAl 2 O 4 content supported charge separation. Clear increase of photocatalytic performance was observed for samples with high ZnAl 2 O 4 content (Figure 2-17).

sensors and biosensors 2.6.1. ALD applications for gas and optical sensors

  Jędrzejewska-Szczerska et al. developed new fiber-optic Fabry-Perot interferometer supplied with ALD thin ZnO layer as an active medium for temperature measurements [102]. Interference fringes in ZnO layer depended on optical thickness of the film. Due to thermal expansion of the ZnO the fringes position shifted. The developed sensor was tested in the range of temperatures of 50-300 0 C. It showed sensitivity of 0.05 nm/ 0 C. Improvement of sensitivity and selectivity of ALD layers, decrease of operation temperature and reduction of time constants of the sensors within doping, deposition of catalyst and forming hybrid structures are discussed in details.ZnO nanofibers was enhanced by a factor of 250 compared to the same ZnO layers, deposited on Si substrate.[START_REF] Shao | Flexible, thorn-like ZnO-multiwalled carbon nanotube hybrid paper for efficient ultraviolet sensing and photocatalyst applications[END_REF] showed high efficiency of UV detection by hybride carbon nanotubes/ZnO paper[195]. Combination of 1D organic fibers and ZnO ALD layers showed good prospects due to high surface-to-volume aspect ratio of the developed 1D nanostructures.Viter et al. reported on photoluminescence sensors for ethanol vapours, based on 1D

	ZnO based ALD nanostructures have good prospects for applications in optical sensors [189].
	Due to conformal coating of ALD layer, combination of ZnO ALD nanolayers with optical fibers
	and 1D templates had a significant impact for sensor development.
	Due to unique optical properties such as room temperature photoluminescence and optical
	absorption edge in UV region, ZnO-based ALD nanocoatings could be applied of optical sensing
	[109, 110, 165, 176, 177].

Majchrowicz et al.

reported on application of 200 nm ZnO ALD layers on optical fibers for measurement of the refractive index of following chemical substances: cyclohexane, benzene, toluene, issue oil, paraffin

[190]

. The developed ALD optical sensor showed different responses to the target analytes.

ZnO ALD nanostructures have been applied for gas sensors. Humayun et al. reported on resistive sensors, based on carbon nanotubes/ZnO for methane detection

[191]

. ZnO nanoparticles were deposited on the surface of carbon nanotubes with ALD method at 175 0 C. Room temperature sensitivity tests showed repeatable sensor response towards 2-10 ppm of methane.

Boyadjiev et al.

demonstrated performance of ZnO thin films, formed by ALD on quartz microbalance crystal to nitrogen oxide detection

[192]

. The sensor showed high sensitivity to 150-500 ppm of NO 2 at room temperature.

Yun et al.

showed that deposition of ZnO layer by ALD technique over thin-film transistor transducer enhanced sensor performance to ammonia

[193]

. Recent advances in ZnO ALD sensors were summarized by

Marichy et al. [194]

.

Novel 1D core/shell polyacrylonitrile/ZnO nanofibers have been applied as UV detectors

[START_REF] Chaaya | ZnO 1D nanostructures designed by combining atomic layer deposition and electrospinning for UV sensor applications[END_REF]

. ZnO layers were deposited over dielectric organic core by ALD technique. Current measurements were performed in dark and under UV excitation. The measured photocurrent of 1D

  . Nakashima et al. reported on use of HfO 2 as a gate in carbon nanotubes (CNT)-FET biosensor device [199]. Sultan et al. reported on ALD ZnO FET sensitivity to oxygen and possible applications in biosensors [200]. Ramesh et al. reported on ALD Al 2 O 3 , used in capacitance biosensors for protein sensing The developed ALD sensitive layers were compatible with the silane-based surface chemistry for covalent binding [207]. Watanabe et al. showed the application of ALD deposited ZrO 2 nanolayers for biosensor applications. Similarly to the methodology, reported by Cha et al., the shift of the lasing was observed due to DNA adsorption on the ZrO 2 surface which was deposited over

	GaInAsP emitting system [208]. The developed sensor showed also good sensitivity to pH changes
	[208].

[201]. Couniot et al. developed on an advanced label free microfluidic capacitance biosensor, based on ALD Al 2 O 3 nanolayers for the whole-cell bacteria detection [202]. Bajpai et al. reported on ALD ZnO nanorod resonators, used as mass biosensors [203]. Guo et al. reported on Al 2 O 3 , TiO 2 , and SiO 2 ALD nanolayers, coated over GaN nanowires [204]. Protein adsorption was studied by dye-label fluorescence spectroscopy. SiO 2 nanolayer showed the best properties for protein adsorption due to the high content of hydroxyl groups on their surface [204]. The ALD deposited Al 2 O 3 nanolayer was used to enhance the sensitivity of optical fiber cladding mode to surrounding refractive index (SRI) variation [205]. Applications in chemical sensors were discussed [205]. Purniawan et al. reported on TiO 2 ALD nanolayers as evanescent waveguides for biomedical sensing applications [206]. ALD-SiO 2 nanolayers have been used for biosensor applications [207]. The developed silica layers were deposited on InGaAsP lasing system, and a lasing shift was observed after adsorption of the biomolecules on the silica surface [207]. ALD deposited Al 2 O 3 nanolayers were combined with plasmonic nanostructures to work as an active biosensor surface [115]. Another application of the Al 2 O 3 nanolayer was to enhance the SERS signal [115].

Table 2 -

 2 [START_REF] Raghavan | Nanocrystalline-to-amorphous transition in nanolaminates grown by low temperature atomic layer deposition and related mechanical properties[END_REF]. ALD for biosensors applications. important application in nanopore biosensors[START_REF] Abou Chaaya | Enhanced ionic transport mechanism by gramicidin a confined inside nanopores tuned by atomic layer deposition[END_REF]. The latter methods permit to detect single object such as protein, DNA or nanoparticle. ALD, it is a powerful technique to fashion nanostructure with complex shapes and high aspect ratio[159]. These methods have several advantages. Indeed, they permit (i) a perfect control of the final diameter, (ii) an increase of the reactivity of the surface and (iii) a homogenous coating inside a nanopore with high aspect ratio.ALD permits to deposit different oxide or non-oxide materials which broaden the scale of nanopore functionalization. In the area of nanopore, ALD was used to tuneSiN [218, 219], with oxide metals such as Al 2 O 3 [220], Al 2 O 3 /ZnO bilayers [221, 222], TiO 2 . HfO 2 [223], Al 2 O 3 /ZnO were deposited on alumina pores [224]. For polymeric materials Al 2 O 3 [220, 225], Al 2 O 3 /ZnO[222, 226], can be used, however, the processes have been done at low temperature (60°C). In order to limit the roughness due to the crystallinity, Al 2 O

	Type of materials	Applications	References
	ZnO	nanorod resonators, used as	[203]
		mass biosensors
	SiO 2	study of protein adsorption	[204]
	HfO	gate in carbon nanotubes	[199]
		(CNT) field effect transistors
		(FET) biosensor device
	TiO 2	evanescent waveguides for	[206]
		biomedical sensing applications
	ZnO	the effects of oxygen	[200]
		adsorption by measuring FET
		characteristics
	Al 2 O	capacitance biosensors for	[201]
		protein sensing
	Al 2 O	enhancement of the sensitivity	[205]
		of optical fiber cladding mode
		to surrounding refractive index

3 /ZnO nanolaminates are used to reduce the diameter of the nanopore up to 1 nm in PET nanopores

[227]

. Another advantage from metal oxide-deposition by ALD is the possible functionalization of the surface, thanks to the -OH function, by silanisation in gas phase for instance

[222]

. However, the functionalization is not only located inside the nanopore. This permit to obtain a homogeneous functionalisation inside and outside the nanopore

[228, 229]

.

Table 2 -

 2 8. The process list for the ZnO ALD

	Index Process Time	Duration	Action	Gas	Mass Flow
	0	00:00:00,00	00:00:00,20	Pulse Precursor3	DEZ	25,0
	1	00:00:00,20	00:00:40,00	Exposure	DEZ	0,0
	2	00:00:40,20	00:01:00,00	Purge (Carrier Gas)	Argon	100,0
	3	00:01:40,20	00:00:02,00	Pulse Precursor2	H 2 O	25,0
	4	00:01:42,20	00:00:40,00	Exposure	H 2 O	0,0
	5	00:02:22,20	00:01:00,00	Purge (Carrier Gas)	Argon	100,0

Table 5 -

 5 1) are lower than the value typical of a ZnO single crystal (E g = 3.37 eV). As was reported before, this difference should be due to the concentration of point defects (such as vacancies and interstitials of Zn and O)[109]. We can also observe a small increase of the band gap value with ZnO thickness, which could be associated with improvement of the crystalline structure of deposited samples[109].

  on ZnO/Al 2 O 3 nanolaminates. The difference between the GPC of Al 2 O 3 reported on single Al 2 O 3 layers and the ZnO/Al 2 O 3 nanolaminates has been attributed to the higher surface area of the rough crystalline ZnO interfaces [164].

Table 6 -

 6 1. Al 2 O 3 /ZnO Ultrathin Nanolaminates Synthesis by ALD

	samples	cycles of	cycles of	no. of	bilayer
		Al 2 O 3	ZnO	bilayers	thickness (nm)
	Al 2 O 3 /ZnO 20	3	3	20	1.2
	(0.6/0.6 nm)
	Al 2 O 3 /ZnO 10	5	5	10	2
	(1/1 nm)
	Al 2 O 3 /ZnO 4	13	13	4	5.2
	(2.6/2.6 nm)
	Al 2 O 3 /ZnO 2	25	25	2	10
	(5/5 nm)
	Al 2 O 3 /ZnO 1	50	50	1	20
	(10/10 nm)
	6.3.3. Structural, Chemical, and Optical Characterizations. Structural and chemical
	compositions of all PAN-nanolaminates were analyzed by transmission electron microscopy
	(TEM). Images were obtained with a JEOL ARM 200F high-resolution transmission electron
	microscope (200 kV) with an EDX analyzer (JED2300, at least 30 accumulations, matrix 512 × 512
	points in STEM mode). Dark and bright field detectors were used.

6.4.2. Band Gap Energy Determination.

  It is well-known that the difference between the onset of inelastic electron losses (E loss ) energy and the core level peak (e.g., oxygen peak, E O 1s) allows one to estimate the energy gap (E g ) of the material[382]. The intersection of the linear-fit line of the measured electron loss spectra near the core level peak and the background "zero" level gives us the onset of inelastic losses occurring in Al 2 O 3[149]. Then we can calculate the band gap energy of Al 2 O 3 using the formula: E g = E loss -E O . Applying this theory, we have calculated E g of Al 2 O 3 for PAN-nanolaminate samples (Figure6-5). The following values were obtained: 5.37 ± 0.06, 5.78 ± 0.09, 5.88, and 6.01 ± 0.08 eV for PAN-nanolaminate samples with 0.6, 1, 2.6, and 5 nm Al 2 O 3 layer thickness, respectively. Unfortunately, it was impossible to calculate the E g of Al 2 O 3 for PAN-Al 2 O 3 /ZnO (10 nm Al 2 O 3 layer thickness) due to the thick top layer of ZnO under the Al 2 O 3 layer.

Our obtained value of about 6 eV is low compared to the one reported for amorphous Al 2 O 3

(8.8 eV) [382]

. This observation might be explained by the highly defected structure of Al 2 O 3 layer in nanolaminates. Upon increasing the Al 2 O 3 layer thickness in PAN-nanolaminates, the E g gradually increases and tends to bulk value.

Table 6 -

 6 2. Electronic parameters of Al 2 O 3 /ZnO Ultrathin Nanolaminate Synthesis by ALD a 5E : = E ;8 3 E ;7 3 5E 6 (6-3) where E g1,2 and χ 1,2 are band gap values of Al 2 O 3 and ZnO and electron affinity values of ZnO and Al 2 O 3 , respectively.

		electron affinity (eV)	band gap (eV)	work function (eV)	ΔE c (eV)	ΔE v (eV)	V bi (eV)
	Al 2 O 3 ZnO	1.35 [384] 4.35 [383]	6 ± 0.1 3.3 [383]	4.8 ± 0.1 5.8 ± 0.1	3	0.3 ± 0.1	2 ± 0.1

a Numbers in square parentheses are references.

  Jurga, S., Smyntyna, V., Miele, P.,Ramanavicius, A., Balme, S., Bechelany., M., Optical properties of ZnO deposited by atomic layer deposition (ALD) on Si nanowires, Materials Science and Engineering B -Submitted ALD on 3D Si substrates for optical biosensors applications, The 8-th NanoSchool "Application of Nanolaminates for Biosensors Design", October 6-8, 2015, Vilnius, Lithuania.• Synthesis of silicon nanowires by metal-assisted chemical etching combined with nanosphere lithography for optical biosensors applications, II-éme Journée des doctorants de l'IEM, May 3, 2016, Montpellier, France.• Structure and optical properties of ZnO deposited by atomic layer deposition (ALD) on Si nanopillars, formed by sphere lithography, COST action, workshop, ALD nanotechnology: advances, prospects and applications,May 22-23, 2017, Riga, Latvia.

	Participation in conferences
	Oral communications
	•

Acknowledgments

This thesis is a result of the international collaboration between European Membrane Institute (IEM), University of Montpellier, Montpellier, France (host university) and Experimental Physics Department, physical faculty, Odessa National I.I. Mechnikov University, Ukraine (home university).

List of abbreviations

ALD

Atomic layer deposition Some of the recent investigations of ALD in biosensors applications are represented in the adsorption sites present on the surface of the PAN fibers would facilitate the nucleation of the metal oxide layers by ALD. Thus, integration of metal oxide ALD technique and PAN nanofibers has a good perspective.

The study of the prepared samples, which were mentioned above, was done in European Membrane Institute (IEM), University of Montpellier, (Montpellier, France), Adam Mickiewicz University (Poznan, Poland), University of Latvia (Riga) and Vilnius University (Lithuania). The details of the performed investigations are represented in the Table 23456789.

CHAPTER III

Large-scale protein/antibody patterning with limiting unspecific adsorption

This chapter has been published in Journal of Nanoparticle research as:

Viktoriia Fedorenko

CHAPTER IV

ZnO Films Formed by Atomic Layer Deposition as an

Optical Biosensor Platform for the Detection of Grapevine

Virus A-type Proteins influence of protein adsorption on ZnO. Such immobilization of anti-GVA has resulted in the appearance of PL emission in the range from 400 to 550 nm. This intensity increases with the increase of surface-concentration of anti-GVA adsorbed from solutions containing different antiGVA concentrations (Fig. 4-4b). For low surface-concentrations of anti-GVA (adsorbed from initial anti-GVA solutions diluted by 1/1000 to 1/400 times), the PL caused by protein adsorption looks like PL band, which intensity increases with anti-GVA surfaceconcentration. In the ZnO110nm/anti-GVA films, which were formed by immobilization of anti-GVA from 1/200 diluted initial anti-GVA solution, the PL emission turns to the formation of PL peak, which is centered at 425 nm, with the intensity increasing proportionally to the immobilized anti-GVA surface concentration. For the ZnO110nm/anti-GVA films formed from the highest concentration (1/50 diluted initial anti-GVA sample) of anti-GVA containing sample, a redistribution of the peak intensities was observed between the PL peak atributed to the protein emission and the peak related to NBE of ZnO. The dependence of PL intensity vs anti-GVA concentration at the λ=425 nm (protein attributed PL) is shown in figure 4-4c. This dependence indicates that the saturation of the PL signal of ZnO110nm/anti-GVA films appears for the films formed from 1/100 diluted initial sample of anti-GVA. Therefore, the optimal concentration of anti-GVA for the formation of biosensitive layer was in the 1/200 diluted sample.

Optical properties of anti-GVA were investigated by PL and optical absorbance measurements. The PL spectra of anti-GVA deposited on glass substrates are shown in figure 4-2b.

No PL line around 425 nm was observed for the samples formed using solutions with highest antiGVA concentrations from 1/200 and 1/50 diluted samples. The spectra of optical absorbance of the same samples (Fig. 4-4d) demonstrate that anti-GVA antibodies do not have optical activity by themselves in the UV-VIS range of spectra. Therefore, the PL line at 425 nm is caused by the luminescence, resulted from the interaction of anti-GVA with ZnO.

Performance of immunosensor

The sensitivity of immunosensor was tested using ZnO110nm film modified by anti-GVA (ZnO110nm/ anti-GVA) formed using 1/200 diluted initial anti-GVA sample. The target analyte used in the experiment was GVA-antigen (Ag+) that is specifically bounding to the immobilized anti-GVA, because both, immobilized anti-GVA and GVA-antigen, which is present in Ag+ specimen, are complementary to each other and by interaction they are forming an 'immune complex'. The concentration of GVA-antigen in Ag+ specimen was in the range from 1 pg/ml to 1 µg/ml (Fig. 4-5a). The interaction between ZnO110nm/anti-GVA and GVA-antigen, which is present in Ag+ sample, resulted in the decrease of the NBE peak intensity by 20 % in average for all ZnO110nm/anti-GVA/Ag+-based structures. However, the initial variation of NBE peak intensity for all ZnO110nm samples disabled the application of NBE intensity changes as a sensor signal. Therefore, the spectra

CHAPTER V

Optical properties of ZnO deposited by atomic layer deposition (ALD) on Si nanowires

This chapter is in preparation for publication as:

Viktoriia Fedorenko 1,2 , Roman Viter