The thesis is made up of 5 chapters. Chapter 1 gives a general introduction about latest literature in the field of carbon nanotechnology and carbon nanomaterials. The state of the art aims at the electrochemical surface modification of SWCNT and graphene-based electrodes through two different approaches: the diazonium chemistry reaction and the covalent surface modification of SWCNT with BDYT. Chapter 2 introduces the characterization techniques used during this work. It will sum up important aspects in our field; i.e. Raman spectroscopy as an important key when working with carbon nanotubes and graphene. Chapter 3 explains the preparation of SWCNT-based electrodes starting from solutions of HiPCO and CoMoCAT-SWCNTs. Preparation of solutions and films, selection of substrates and characterization are described. Chapter 4 describes the state of the art on this thesis work and will show the results obtained for the electrochemical surface modification of SWCNT-based electrodes via covalent surface modification by: (a) diazonium chemistry (followed by click chemistry reaction) and (b) the electrophylic addition of 1, 3-BDYT molecules.

Chapter 5 is dedicated to GICs and graphene-based electrodes. Synthesis of graphite intercalation compounds (GICs) with particular stoichiometry, GIC solutions, deposition on glass are explained along the chapter. Graphene films are tested as electrode material. Its performance for surface modification is described.

Titre : Electrochemical surface modification of Single walled carbon nanotubes and graphene-based electrodes for (bio) sensing applications

Résumé :

Les capteurs sont des dispositifs ayant montré une utilisation répandue, allant de la détection des molécules en phase gazeuse au suivi de signaux chimiques dans les cellules biologiques. En général, un capteur est réalisé à partir d'un élément actif de détection et d'un signal transducteur produisant un signal de sortie qui peut être électrique, optique, thermique ou magnétique. Les électrodes à base de nanotubes de carbone à simple paroi et les électrodes à base de graphène se sont révélées être un matériau excellent pour le développement des biocapteurs électrochimiques, puisqu'ils montrent des propriétés électroniques remarquables et la capacité de se comporter en tant que nano-électrodes individuelles, un excellent transport de porteur de charge à faible dimension, et permettent de l'électrocatalyse de surface.

Le travail présenté vise à la préparation et à l'étude d'électrodes de nanotubes de carbone à simple paroi et d'électrodes de graphène modifiées par voie électrochimique pour des applications dans le domaine des biocapteurs. Nous avons d'abord étudié les films de nanotubes de carbone à simple paroi et nous nous sommes intéressés à leur topographie, à leur composition de surface, et leurs propriétés électriques et optiques. Nous montrons que ces films sont homogènes avec une conductivité d'environ 200-300 Ω/□, et une transparence d'environ 40%. En parallèle aux nanotubes de carbone à simple paroi, des films de graphène ont été étudiés. Des valeurs de résistance plus élevées en comparaison avec les films de nanotubes ont été obtenues. La modification de surface par voie électrochimique des deux types d'électrodes a été étudiée en suivant deux voies, (i) l'électro-greffage de sels d'aryl diazonium, et (ii) l'addition électrophile de 1, 3-benzodithiolilyum tetrafluoroborate (BDYT). Les caractéristiques qualitatives et quantitatives de la surface modifiée des électrodes ont été étudiées, comme le degré de fonctionnalisation et la composition de surface. La combinaison de spectroscopie Raman, et de photoelectrons X-(XPS) de microscopie à force atomique (AFM), d'électrochimie et d'autres techniques, a montré que des précurseurs particuliers peuvent être ancrés de façon covalente à la surface des électrodes de nanotubes et de graphène, grâce à la formation de nouvelles liaisons carbone-carbone. Dans le premier cas (i), leur post-modification par des réactions de « clickchemistry » mène finalement à l'immobilisation sur la surface de l'électrode des groupes fonctionnels souhaités, comme des sondes/shuttles redox (e.g., un groupe ferrocenyl) ou des groupements catalytiques (e.g., une enzyme). L'enzyme HRP (horse-radish peroxidase) a été, par exemple, immobilisée sur des surfaces de nanotubes de carbones à simple paroi modifiées par un groupe aryl, et l'étude voltammétrique a montré une réponse catalytique avec l'augmentation de la concentration de peroxyde d'hydrogène en solution, en suivant le « shuttle » redox hydroquinone/benzoquinone à la surface de l'électrode.

Dans le second cas (ii), l'addition électrophile de radicaux BDYT électro-générés a été étudiée pour la première fois sur des électrodes de nanotubes de carbone à simple paroi ou sur les électrodes de graphène. La combinaison de différentes techniques complémentaires a montré l'attachement covalent de BDYT aux électrodes de nanotubes de carbone à paroi simple. Une telle modification mène à la formation de rubans torsadés qui ont pu être observés et analysés par AFM et par microscopie électronique à balayage. Aucune preuve de la formation de rubans torsadés n'a pu être mise en évidence pour les électrodes modifiées à base de graphène.

Mots clés : capteurs, nanotubes de carbone, graphene, électrochimie

Title : Electrochemical surface modification of Single walled carbon nanotubes and graphene-based electrodes for (bio) sensing applications

Abstract :

Sensors are devices that have shown widespread use, from the detection of gas molecules to the tracking of chemical signals in biological cells. In general, a sensor is made of an active sensing element and a signal transducer producing an electrical, optical, thermal or magnetic output signal. Single walled carbon nanotube (SWCNT) and graphene based electrodes have demonstrated to be an excellent material for the development of electrochemical biosensors as they display remarkable electronic properties and the ability to act as individual nanoelectrodes, display an excellent low-dimensional charge carrier transport, and promote surface electrocatalysis.

The present work aims at the preparation and investigation of electrochemically modified SWCNT and graphene-based electrodes for applications in the field of biosensors. We initially studied SWCNT films and focused on their topography and surface composition, electrical and optical properties. We show that these films are homogeneous with thickness around ̴ 60-70 nm, resistance values around ̴ 200-300 Ω/□, and transparency around ̴ 40%. Parallel to SWCNTs, graphene films were investigated. Higher resistance values were obtained in comparison with nanotubes films.

The electrochemical surface modification of both electrodes was investigated following two routes (i) the electrografting of aryl diazonium salts, and (ii) the electrophylic addition of 1, 3-benzodithiolylium tetrafluoroborate (BDYT). Both the qualitative and quantitative characteristics of the modified electrode surfaces were studied such as the degree of functionalization and their surface composition. The combination of Raman, X-ray photoelectron spectroscopy, atomic force microscopy, electrochemistry and other techniques, has demonstrated that selected precursors could be covalently anchored to the nanotubes and graphene-based electrode surfaces through novel carbon-carbon formation.

In route (i), their post-modification by click-chemistry reactions finally leads to the immobilization at the electrode surface of desired functional groups, such as redox probes/shuttles (e.g., a ferrocenyl group) or catalytic moieties (e.g., an enzyme).

HRP has been for instance immobilized on SWCNT-aryl-modified surfaces, and its voltammetric study showed catalytic response with the increasing concentration of hydrogen peroxide in solution upon monitoring the redox shuttle hydroquinone/benzoquinone at the electrode surface.

In route (ii), the electrophylic addition of electrogenerated BDYT radicals was There is a plenty of room at the bottom in a meeting of the American Physical Society. [START_REF] Feynman | There Is Plenty of Room at the Bottom[END_REF] The lecture provided inspiration for the field of nanotechnology with an emergence in the 80s where the convergence of experimental advances, as the invention of the scanning tunneling microscope (STM), took off. Along with the years the concept has shifted, up to now, where nanotechnology gives rise to lots of contributions in the field.

Nature has always attracted attention and it is a fact that the majority of biological processes occurs at the nanometer scale. DNA chains, building blocks of the human life are only 2 nm in diameter. Proteins, enzymes, and other biomolecules in charge of important processes in the human body are only 5 nm in diameter.

Carbon, being an inexpensive raw material, has shown to be an ideal candidate as a source of fantastic nanomaterials with noticeable properties. The use of such unique nanomaterials for the investigation of biological processes is an exciting challenge in the field of nanotechnology.

. CARBON NANOTUBES AND GRAPHENE

Carbon Nanotubes

The discovery of carbon nanotubes is credited to S. Iijima back in 1991, [START_REF] Iijima | Helical Microtubules of Graphitic Carbon[END_REF] where he described the preparation of a new type of finite carbon structures (later named carbon nanotubes) consisting in needle-shape tubes obtained by arcdischarge evaporation (similar to that used for fullerenes).

Carbon nanotubes, here-after CNTs, are tubular shape structures composed mainly of carbon atoms in sp 2 hybridation upon hexagonal honey-comb lattices as it is showed in figure 2. They are described as individual graphite sheets that have been wrapped into themselves forming a tube. These tubes are closed defining two regions, the a Picture from Internet.

Chapter 1: Introduction 8 nanotube body and the cap, being this last half-fullerene with topological defects as pentagons. [START_REF] Rivas | Carbon Nanotubes for Electrochemical Biosensing[END_REF] Structure and properties associated to CNTs have been shown to be the most diverse and rich among nanomaterials. [START_REF] Dai | Carbon Nanotubes: Synthesis, Integration, and Properties[END_REF] Carbon nanotubes can be classified into single-walled nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). The difference between them remains in the number of sheets of carbon forming the final tube. MWCNTs are concentric single graphitic tubes, while a SWCNT is a single graphitic layer rolled forming a cylinder of 1-2 nm in diameter. The way to roll up is defined by specific chiral angles, resulting in a specific nanotube electronic behavior (metallic or semiconducting) upon definition of the n and m indices. Being n and m two natural numbers, and a and b two primitive translation vectors (see figure 2) where the chiral vector of a specific CNT can be describe as,

= +

Kataura and co-workers published in 1999, SWCNT characterization upon the study of the optical absorption spectra and transmission electron microscopy observations (TEM) obtaining what is known as Kataura's plot showed in figure 3. [START_REF] Kataura | Optical Properties of Single-Wall Carbon Nanotubes[END_REF] Chapter 1: Introduction properties of single-walled carbon nanotubes. [START_REF] Kataura | Optical Properties of Single-Wall Carbon Nanotubes[END_REF] This plot helps to individualize precise (n, m) SWCNT under specific excitation energy. Many efforts have been done in CNT synthesis controlling the CNT growth resulting in specific nanotubes with desired (n, m) indices. Pure metallic or pure semiconducting CNT samples are very important in many electronic applications, but unfortunately synthesis methods used up to now, produce mixtures of CNTs with random indices. [START_REF] Ajayan | Nanotubes from Carbon[END_REF] SWCNTs are produced mainly by arc-discharge, laser ablation, and chemical vapor deposition (CVD) methods. CVD was described to be a method for potential industrial scale up on CNT synthesis upon controlled morphology and structure of the produced SWCNTs.

Chapter 1: Introduction 10

• High-pressure carbon monoxide (HiPCO) is a SWCNT synthesis process where high-pressure carbon monoxide is used as carbon source. The iron catalyst formed in the reactor form clusters upon decomposition where the SWCNTs undergo nucleation and grow. This was originally developed by Smalley's group in Rice University. [START_REF] Bronikowski | Gas-Phase Production of Carbon Single-Walled Nanotubes from Carbon Monoxide via the HiPco Process: A Parametric Study[END_REF] • Cobalt-Molybdenum catalyst process (CoMoCAT) is attributed to

Resasco group in Oklahoma University, [START_REF] Bachilo | Narrow (n,m)-Distribution of Single-Walled Carbon[END_REF] being an important advance on scale up synthesis of SWCNTs.

The work by R.E. Smalley and coworkers in 1997 showed a STM study to explore the local electrical characteristics of SWCNTs. It was the first publication for a nanotube nanodevice. 10 SWCNTs are interesting materials to be used in electrochemical devices from the point of view of surface area availability, as well as high conductivity and excellent mechanical properties. 11 The electroactivity of SWCNTs has been widely studied and some works concluded by the attribution of electroactivity to reacting groups on the tube's surface. Later ab-inito calculations have demonstrated that this observed improvement in the electron transfer was due to the inherent curvature of the CNTs. [START_REF] Ajayan | Nanotubes from Carbon[END_REF] Chapter 1: Introduction In the present study, two different sources of SWCNTs were studied, HiPCO and CoMoCAT, as starting materials for the prep electrode devices. Specific characteristics at their final state will be shown along with the redaction. Here it is shown (see above, figure 5) SEM images for raw powder material of HiPCO and CoMoCAT SWCNTs.

Graphene

The concept of graphene appears for the first time in 1947 but the scientific community of carbon was relatively small and they worked separately. concept of graphene appears for the first time in 1947 but the scientific community of carbon was relatively small and they worked separately. 12 The first International Conference on Intercalation Compounds was in France, in irst important event in which carbon researchers were brought together. In the 80s Materials Research Society (MRS) meetings and other conferences started including carbon nanostructure sessions.

Graphene it is defined as a single sheet of sp forming a net of hexagons. An infinite number of graphene layers stabilized upon π-π stacking interactions, as it is showed in figure 6, results in graphite structures.

Fig. 6: Graphene sheet and derivate structures. From: Geim an 2004. 13 The synthesis of a monolayer graphene was published in 2004 by Geim and Novoselov, of this new material. Since then, an exponential growth o contributions in the field occured.

awarded to Geim and Novoselov for their innovative experiments on these 2D materials. 17 nanoelectronic devices.

Chapter 1: Introduction

Graphene it is defined as a single sheet of sp 2 hybridatio forming a net of hexagons. An infinite number of graphene layers stabilized π stacking interactions, as it is showed in figure 6, results in graphite structures.

Fig. 6: Graphene sheet and derivate structures. From: Geim an

The synthesis of a monolayer graphene was published in 2004 by Geim and Novoselov, 13 and many experimental efforts were done for the understanding of this new material. Since then, an exponential growth o contributions in the field occured. 14,15,16 In 2010, the Nobel prize in Physics was awarded to Geim and Novoselov for their innovative experiments on these 2D

17 Graphene was announced to be an interesting material for nanoelectronic devices.

12 hybridation carbon atoms forming a net of hexagons. An infinite number of graphene layers stabilized π stacking interactions, as it is showed in figure 6, results in graphite The reactivity of graphene is described to be reduced compared to the reactivity of SWCNTs because of a lack of local strain or misalignment of the π orbitals. 22 In 2008, E.R. Margine showed a theoretical paper for the study of the thermal stability of covalently functionalized graphene and CNTs. 23 Haddon and coworkers communicated experimental data of modified epitaxial graphene (EG)

with aryl diazonium salts as shown in figure 7. 24 Here it is shown an example of using the spontaneous grafting of aryl diazonium salts. It will be introduced later on as one of the reactions selected in this work for the functionalizatio graphite intercalation compounds (GICs). A nice review on chemical functionalization of graphene and its further applications was published by J.

H. Lee in 2012.

GRAPHITE INTERC (GICS)

The CNT group at CRPP for the reductive dissolution of CNTs: by electrostatically charging nanotube bundles polyelectrolytes are formed that spontaneously disso solvents. 26 spontaneous dissolution of a graphite intercalation compound (KC (see figure 8).

Chapter 1: Introduction

Fig. 7: EG surface modification upon spontaneous grafting of aryl diazonium

Here it is shown an example of using the spontaneous grafting of aryl diazonium salts. It will be introduced later on as one of the reactions selected in this work for the functionalization of carbon materials as SWCNTs and graphite intercalation compounds (GICs). A nice review on chemical functionalization of graphene and its further applications was published by J.

H. Lee in 2012. 25

GRAPHITE INTERCALATION COMPOUNDS )

The CNT group at CRPP-CNRS, Pessac, developed in 2004 an original method for the reductive dissolution of CNTs: by electrostatically charging nanotube bundles polyelectrolytes are formed that spontaneously disso 26 Graphene solutions were analogously 27 spontaneous dissolution of a graphite intercalation compound (KC (see figure 8).

ace modification upon spontaneous grafting of aryl diazonium

Here it is shown an example of using the spontaneous grafting of aryl diazonium salts. It will be introduced later on as one of the reactions selected n of carbon materials as SWCNTs and graphite intercalation compounds (GICs). A nice review on chemical functionalization of graphene and its further applications was published by J. This approach was recently reviewed in ref.

ALATION COMPOUNDS

of pristine nanocarbon opens a roadmap to SWCNT/graphene for many applications.

GICs were firstly synthesized in 1841 by Schaffäutl, but it was the introduction of X-ray diffraction techniques which showed the stage index of these compounds in the 30s. This stage index is determined by the number of layers of graphite between the intercalate species set. Mildred Dresselhaus and coworkers determined in the 70s the related properties of GICs (see figure 9). This approach was recently reviewed in ref. 28 The availability of real solutions of pristine nanocarbon opens a roadmap to SWCNT/graphene-based devices GICs were firstly synthesized in 1841 by Schaffäutl, but it was the introduction ray diffraction techniques which showed the stage index of these compounds in the 30s. This stage index is determined by the number of layers ite between the intercalate species set. Mildred Dresselhaus and coworkers determined in the 70s the related properties of GICs (see figure 9). 29 The present thesis work will focus on the s modification of electrodes made from solutions of pristine SWCNTs and GICs.

The functionalization of nanoscale material surface (addition of specific moieties for specific purposes) is well reported and some of the appli from drug delivery to electronic devices. In the present work we describe the Chapter 1: Introduction The present thesis work will focus on the study of the electrochemical surface modification of electrodes made from solutions of pristine SWCNTs and GICs.

The functionalization of nanoscale material surface (addition of specific moieties for specific purposes) is well reported and some of the appli from drug delivery to electronic devices. In the present work we describe the 16 The functionalization of nanoscale material surface (addition of specific moieties for specific purposes) is well reported and some of the applications go from drug delivery to electronic devices. In the present work we describe the electrochemical surface modification of electrodes made entirely of SWCNTs or graphene, aimed to the obtainment of bio-sensing devices. The modification of electrode surfaces for analytical or catalytic purposes has attracted much attention along the years. In this section, some literature about diazonium chemistry and carbon surface modification will be introduced remarking pros and cons on using this functionalization chemistry.

J. Pinson, J.M. Savéant and co-workers showed in 1992 a first approach for carbon surface modification upon the reduction of diazonium salts. Until this time, the modification of carbon surfaces underwent upon surface oxidation with formation of oxygenated species on the surface like ketones, hydroxilic groups, and so on, that would react with selected molecules to be attached.

The resulting oxygenated functional groups were difficult to control and besides, the corrosion of the carbon surface was often observed.

Instead, the covalent attachment of aryl radicals precursors onto carbon surfaces upon electrochemical reduction of diazonium salts 32 leads to non corrosive covalent attachment upon one through (see figure 10) absorption spectra of pristine and derivatized tubes show clear differences (in terms of loss of structure) consistent with a covalent functionalization rather than a strong adsorption (see figure 12). the preferential derivatization of small diameter SWCNTs for the enhanced reactivity of these tubes (0.7 nm) for aryl diazonium compounds. 34 The absorption spectra of pristine and derivatized tubes show clear differences (in onsistent with a covalent functionalization rather than a strong adsorption (see figure 12). In 2009, Joyeux, Mangiagalli, and Pinson showed an approach (see figure 14), to place CNTs in trenches through chemical attachment using ethylene dianiline (EDA) as a linker. 37 Route A, describes the electrografting of EDA on the surface of a selected substrate followed by the transformation of the remaining amino group in a second diazonium moiety which grafted spontaneously to the SWCNT-surface.

Fig
Route B, follows the opposite approach binding firstly to the SWCNT surface followed by the transformation of the amino free groups which bind to the selected substrate.

The in-situ formation of the diazonium salt was already shown in 2006 by D.

Bélanger and J. Lyskawa, 38 where the electrochemical surface modification of gold substrates with p-Phenylenediamine (PhDA) moieties was reported. They remarked that one equivalent of sodium nitrate was the optimal amount to obtain a compact layer of aryl groups; above that value the amount of moieties grafted was diminished.

In the present study following the same strategy EDA moieties were used for the electrochemical surface modification of SWCNT-based electrodes. SWCNT devices were prepared from a spontaneous dissolution of a SWCNT salt. 26 The process will be explained in detail in chapter 3: SWCNT-transparent conductive films. Likewise 4-[(Trimethylsilyl) ethynyl] aniline (TMS) and p-Phenylenediamine (PhDA) (Figure 15) were selected as precursors for the present study. 39,40,41 Chapter 1: Introduction The remaining reactive groups after the grafting process (amines and internal azides) are suitable to anchor electroactive probes and set up a bioconjugation protocol for the final preparation of bio-sensing surfaces based on carbon materials. Among the chemical methods for post-functionalization of CNTs and graphene films, bio-conjugation amidation and copper catalyzed cycloaddition (click) reaction have been widely used. Most of the reactions which satisfy click chemistry to occur are now wellstudied and the preparation of a specific set of conditions is simple [54][55][START_REF] Hein | Click Chemistry, a Powerful Tool for Pharmaceutical Sciences[END_REF] . The ability of modifying a surface through a click-chemistry reaction offers the possibility of designing nanomaterials with targeted response to the environment. An example of construction of bio-conjugated materials using click-chemistry was reported by J-F. Lutz and Z. Zarafshani. [START_REF] Lutz | Efficient Construction of Therapeutics, Bioconjugates, Biomaterials and Bioactive Surfaces Using Azide-Alkyne "Click[END_REF] This approach can be used for surface modification of CNTs, fullerenes, or graphene.

The experimental demonstration for changes on the electronic and optical properties of the non-covalently surface modified SWCNTs was reported by S.

Campidelli, M. Prato and coworkers in 2006. [START_REF] Campidelli | Dendrimer-Functionalized Single-Wall Carbon Nanotubes: Synthesis, Characterization, and Photoinduced Electron Transfer[END_REF] SWCNTs were efficiently noncovalently functionalized with porphyrin dendrons via click chemistry reaction. 40 In 2011, G. Clavé and S. Campidelli reviewed advances using clickchemistry for the preparation of CNT-functional materials. 39 An example combining surface modification with diazonium chemistry followed by click-chemistry was reported by C. Mangeney and coworkers (see figure 17). 59

Chapter 1: Introduction

Scheme for the preparation of gold modified surfaces as platforms for immobilization of nanoparticles by click-chemistry. [START_REF] Gehan | A General Approach Combining Diazonium Salts and Click Chemistries for Gold Surface Functionalization by Nanoparticle Assemblies[END_REF][START_REF] Boudou | Multiple Functionalities of Polyelectrolyte Multilayer Films: New Biomedical Applications[END_REF] In order to modify materials by click-chemistry reactions, complementary for the reaction must be present on the surface (see figure 18) Notice than BDYT is a precursor of tetrathiafulvalenes (TTF). TTF and its derivatives have been widely studied over the years. Some examples of its applications are Langmuir-Blodgett films, molecular switches or building blocks, as many other contributions in the field. [START_REF] Blodgett | Films Built by Depositing Successive Monomolecular Layers on a Solid Surface[END_REF][START_REF] Bendikov | Oligoacenenes, and Their Buckminsterfullerene Derivatives: The Brick and Mortar of Organic Electronics[END_REF][START_REF] Naraso | High-Performance Organic Field-Effect Transistors Based on Pi-Extended Tetrathiafulvalene Derivatives[END_REF][START_REF] Gao | A Facile Synthesis of Linear Benzene-Fused Bis(tetrathiafulvalene) Compounds and Their Application for Organic Field-Effect Transistors[END_REF] The strategy followed is based on the electrochemical surface modification of SWCNT and graphene-based electrodes upon formation of benzodithiolilyum Four-points-conductivity measurements will determine the surface conductivity of the films depending on the amount of nanotubes used for film preparation (Ω/□).

Fig
Contact-angle measurements were useful to determine the wettability of the surface of films. For instance, it was used to characterize SWCNT-based electrodes before and after electrochemical surface modification.

To quantify (and qualify) such modification X-Ray photoelectron spectroscopy (XPS) was used. Elements present on the film surface were determined; for Chapter 2: Characterization techniques 32 instance, in the C1s spectrum of a SWCNT film there is an intense band at ˜284 eV related to sp 2 carbon atoms while at higher binding energies bands related to oxygenated carbon atoms are observed (-COOH,-C=O,-COH).

Raman Spectroscopy was used to observe the characteristic bands of carbon related materials. During the present study the IG/ID ratio (intensity of the Graphite band (G band) over the intensity of the defect band (D band)) before and after surface modification will be studied as a degree of functionalization.

Other features in the spectra will be explained when needed. The Piezo electric scanner is made of ceramic materials which extend or contract in the presence of a voltage gradient, developing an electrical potential in response to mechanical pressure, i.e. close to the sample surface.

V-shaped cantilevers are the most used providing low mechanical resistance values to vertical deflection and high resistance values to lateral torsion. For the detection of the displacement of the cantilever, a laser is reflected on the cantilever and is collected in a photodiode.

Modes of Tip-Surface interaction

Three different modes are available for working with an AFM. First AFM operated in contact mode where the tip scans the surface of the sample following the Cartesian axis. In this case the deflection of the cantilever is kept constant.

Non-contact mode was introduced in 1987 for the scanning of fragile samples as biological samples. In this mode, the cantilever oscillates close to its resonant frequency at a small distance from the sample surface. Compared to contact mode, forces on the sample are lower avoiding damage during the measurements.

Tapping mode is defined as somewhere between both, contact and noncontact modes. All AFM images acquired during this study have been performed with tapping mode. Forces governing when the tip is brought close to the surface lead to a deflection of the cantilever according to Hooke's law of elasticity. So, if the tip is brought close enough to the sample surface and the cantilever is deflected, this deflection will be function of the tip-sample interaction being measured at many points of the 2D surface and can be mapped spatially resulting in three dimensional images.

While the topographic image is registered the phase image is collected being possible to observe at once the topographic and material properties.

Lateral resolution depends on tip sharpness

The tip and the cantilever determine the lateral resolution of the system and the magnitude of force applied to the sample surface being critical components of the AFM.

If the tip sharp is not selected properly common artifacts are observed. That is known as the fat-tip effect and is showed in figure 2.

SCANNING ELECTRON MICROSCOPY (SEM)

Electromagnetic lens were firstly developed in 1926 by Hans Busch. These lenses were used for focusing or deflecting charge particles in movement as electrons or ions under electro and magnetic fields by using the Lorentz force.

H. Busch has laid the theoretical basis for the electron microscope, but it was the German physicist E. Ruska and the electrical engineer M. Knoll who constructed the prototype of the electron microscope in 1931.

In a scanning electron microscope an electron beam is focused into the sample and is rastered across the surface of the sample. The beam-sample interaction results in emitted electrons or photons collected with an appropriate detector

Chapter 2: Characterization techniques yielding valuable information about the material. The resolution of an SEM image depends on the beam diameter. The principle follows the same than for optical microscopes with the difference that in this case electron beams are used instead of light and the lens are magnets instead of optical materials (see figure 3).

Fig. 3: Scanning Electron Microscope cartoon representation showing its principle.

The optics of scanning electron microscopes include condenser lens to focus the electron beam on the sample surface determining the size of the interaction, and electromagnetic coils which drive the deflection on the electron beam.

Sample and sample holder sizes are in orders of centimeters, and can be rotated at the three different directions axis (x, y, and z).

Chapter 2: Characterization techniques 37 yielding valuable information about the material. The resolution of an SEM image depends on the beam diameter. The principle follows the same idea than for optical microscopes with the difference that in this case electron beams are used instead of light and the lens are magnets instead of optical

Microscope cartoon representation showing its

The optics of scanning electron microscopes include condenser lens to focus the electron beam on the sample surface determining the size of the interaction, and electromagnetic coils which drive the raster scanning upon deflection on the electron beam.

Sample and sample holder sizes are in orders of centimeters, and can be rotated at the three different directions axis (x, y, and z).

Chapter 2: Characterization techniques 38

The conductivity of the sample is required to obtain an image, so for nonconductive samples a metallic coating is needed.

Detectors can be made of a semiconductor transducer or by a scintillation device. In both cases there is a response (increase of conductivity or cascade of visible photons) when is bombarded by electrons.

The signal produced upon electron beam-sample surface interaction contains information about topography, composition, and other properties such as electrical conductivity. Signals registered by an SEM include among other characteristic X-rays, secondary electrons and back-scattered electrons (BSE).

Upon a strong relation between the intensity of the signal and the atomic number of a species, BSE images can provide an elementary analysis of elements present in the surface of the sample.

In conclusion, SEM is adapted for scanning any kind of sample surface. In case of non-conducting samples previous coating is needed in order to ensure a clear image. As it is based on surface interactions, it is not a pre-requisite to work with electron transparent samples as for example, in transmission electron microscopes (TEM).

In the present study a high resolution SEM was used from CREMEM laboratory, Pessac.

Chapter 2: Characterization techniques 39

SURFACE RESISTIVITY MEASUREMENTS

The surface resistivity of a material can be described as the surface resistance to a flow of current. It does not depend on the physical dimensions of the material. According to Ohm's law, the resistance (R, ohms) of a specific material is determine by the applied voltage (V, volts) divided by the current flow (I, amperes) across the material as is showed as follows

= =

The electrical resistance is proportional to the length of the sample (L), and inversely proportional to the sample's cross section area (S).

Surface resistivity is expressed in Ohms (Ω), and usually is given in terms of Ω/□ (ohms/square). The surface resistivity of a tested sample with thickness equal to the unit is expected to show equal resistance in square dimensions independently of its in-plane dimensional resistance value. The expression surface resisbvity (Ω/□) is the value of these calculabons. Here we described methods for determination of surface resistivity values using techniques as the Van der Pauw method and the four point's method.

VAN DER PAUW AND FOUR-POINT METHODS

Van der Pauw method is widely used in semiconductors industry to determine the resistivity values of uniform samples. The original device is showed below where a thin plate sample contains small ohmic contacts placed on the periphery, in this case, on the corners. Measuring the resistivity will determine the sheet resistance R S . Van der Pauw demonstrates that two characteristic resistances are associated with the corresponding terminals as is expressed in figure 4.

Fig. 4: Schematic determination of the two characteristic resistances R

The method used to measure SWCNT and graphene films was measurement. This pattern to the sample surface he method used to measure SWCNT and graphene films was measurement. This method uses electrodes aligned linearly or i pattern to the sample surface (see figure 5).

: Two-and four-point set up techniques. Arrows show direction of current flow.

In the case of two-point method, the voltage between the two ele measured upon the passage of a flow of electrons. The expresion that results

for the calculation of the surface resisitivity on this method contains a parasitic contact resisitance due to electrode-surface contact. In contrast to this method, the addition of two more electrodes as it is showed for the four-point method eliminates the parasitic resistance due to contact and spread.

Since the measurements are done under finite sizes areas, corrections factors are needed. These factors are sample thickness dependent, among others. Many methods for measuring the contact angle are explained in literature.

CONTACT ANGLE

One of the most studied techniques is the static or sensile drop method, where the contact angle is measured for the advancing and receding contact angle as shown below in figure 6. When there is no interaction with the surface the contact angle tends to 180°, high interaction contact angle values go close to zero : Different wetabilities form different contact angles.

A sequence of the contact angle characterization of SWCNT showed below (see figure 8). During the present study a contact angle equipment from CRPP was used. The static drop method with water was used to measure the contact angle of SWCNT devices before and after chemical treatment of the surface.

X-RAY PHOTOELECTRON SP (XPS)

This spectroscopic technique was developed in the fifties by K. Siegbahn, which received the novel prize for this work in 1981.

XPS analysis allows the measurement of binding energies variation resulting

from the chemical environment present on the advantages of XPS lead to chemical nat information for most elements except hydrogen.

Matter is made of atoms, and these around them with defined orbits. Each electron carries unique information regarding its nucleus. The goal on XPS is to collect them in order to identify from which atom they proceed. For t During the present study a contact angle equipment from CRPP-CNRS, Pessac, was used. The static drop method with water was used to measure the contact CNT devices before and after chemical treatment of the surface.

RAY PHOTOELECTRON SPECTROSCOPY

This spectroscopic technique was developed in the fifties by K. Siegbahn, which received the novel prize for this work in 1981.

s the measurement of binding energies variation resulting from the chemical environment present on the sample surface. The chemical nature and electronic state of elements information for most elements except hydrogen.

is made of atoms, and these are made of nuclei and electrons moving around them with defined orbits. Each electron carries unique information regarding its nucleus. The goal on XPS is to collect them in order to identify from which atom they proceed. For that purpose, it is nessesary to separate

Chapter 2: Characterization techniques 44 them from the attractive nucleus force upon excitation with an X-ray source.

The energy will be sufficient to free them from the nucleus and they will travel through the matter reaching the surface and furthermore, leaving the solid matter to the surrounding vacuum. Once there, they will be collected by the analyzer and classified according to their unique informations.

The binding energy expressed in the spectra is the binding energy of collected electrons before leaving the atom. Each energy is related to a specific atom, as for example carbon: 286 eV, Oxygen: 532.5 eV, and so on. The peak area is proportional to the number of atoms present on the surface and a chemical composition analysis can be calculated in therms of atomic percentage (%).

Sample needs to be prepared before data aquisition ranging from few milimeters up to few centimeters depending on the equipment used.

After its preparation, the sample is introduced in a preparation chamber where the vacuum values reached are below 10 -7 mbar and usually is left overnight to reach such values. After successful vacuum is achieved, the sample is transferred to a second chamber called the analysis chamber, where vacuum reaches limits ~ 10 -11 mbar.

While the electron leaves the matter it can suffer interactions (shocks) which change its energy. This effect contributes to the background noise to grow up.

On the other hand, the electrons who leave the matter without suffering an inelastic interaction form the collection of peaks. This effect of background noise is related to the thickness of matter crossed by the electron.

Scan aquisitions allow to identify different chemical components and bonding

nature on the sample surface. To obtain this last information about chemical Here it is shown an aquisition window for C, O, S, and F obtaining quantitavite and qualitative information of sample surface.

XPS analysis of SWCNT and graphene

Institut de Chimie de la matière condensée de Bordeaux (ICMCB), Pessac. As we worked with conducting samples no coating was needed. Sample size was ~ 1 cm 2 and was usually left overnight in the first chamber before being introduce in the analyzer chamber were the dat In Raman scattering the energy of the incident photon and the energy of the resulting one are different.

The difference can be higher in energy upon electron gain of energy from the molecule, or lower upon electron loss of energy from the molecule. These are described as Stokes and Anti-Stokes lines in the Raman spectra situated at higher and lower energy respectively in respect to Rayleigh scatter (see figure 10). The elastic scattering of light has been observed since the nineteenth century.

The inelastic scattering instead, was not observed until 1930 by C. Raman and his fellow, receiving the Nobel Prize in physics for such discovery named since then, the Raman Effect. [START_REF] Raman | The Molecular Scattering of Light[END_REF] But Raman spectroscopy took off with the introduction of the first lasers.

The scattering of light is not a dipole phenomenon as observed in infrared spectroscopy. Instead of that, it requires the presence of an electric field which induces polarization in atoms or molecules. The polarizability in atoms is described to be isotropic resulting in an elastic scattering of light or Rayleigh scattering. In molecules, the polarizability must be anisotropic and is dependent on the rotational and vibrational coordinates to be Raman active.

By this selection rule, symmetric molecules can be studied by Raman spectroscopy. In fact, both techniques, IR and Raman, are complementary.

Radial Breathing Modes (RBMs)

They are observed at small Raman shifts and are the low energy modes observed in SWCNTs. They range from ~ 150 to ~250 cm -1 and are observed upon elastically scattered laser light in tubes ranging ~ 1-2 nm in diameter.

They are called breathing modes because all carbon atoms of the tube structure vibrate radially in phase as the act of breathing. The frequency of these modes is dependent on tube diameter, and independent on the chirality of the tube (n, m). The dependence with tube diameter [START_REF] Dresselhaus | Raman Spectroscopy on Isolated Single Wall Carbon Nanotubes[END_REF] can be described as,

= +

Being A and B two constants determined experimentally. This relation is not valid for tubes diameter smaller than 1 nm or higher than 2 nm. In the case of < 1nm tubes, the dependence is not valid due to distortions in the tube structures resulting in a chirality dependence. For tubes with diameters > 2 nm the intensity of RBMs is not easily observed resulting in weak bands.

M. Strano and coworkers were pioneers in their work for the selective surface modification of SWCNTs and Raman characterization by characterizing changes on the RBMs (see figure 11).

Fig. 11: RBM Raman spectra for pristine and surface modified SWCNTs showing differen

At the same time, the grafting of aryl diazoniu metallic nanotubes rather than for semiconducting.

Tangential modes

Tangential modes of SWCNT include the G feature (see figure 12 cm -1 .

For graphite, a high cm -1 ; in a SWCNT, this mode results in a multi metallicity or semiconducting behavior of tubes. An analysis can be done At the same time, the grafting of aryl diazonium salts shows to be selective for metallic nanotubes rather than for semiconducting.

Tangential modes-G band

Tangential modes of SWCNT include the G-band. It results a widel feature (see figure 12). G comes from Graphite, typically observed at ~ For graphite, a high-intense Raman-active tangential mode is observed at 1582

; in a SWCNT, this mode results in a multi-peak feature depending on metallicity or semiconducting behavior of tubes. An analysis can be done than for SWCNTs, is not an enhancing resonant process, but used as a measure of the functionalization degree. carbon atoms) on the surface of the tubes. [START_REF] Fantini | Two-Phonon Combination Raman Modes in Covalently Functionalized Single-Wall Carbon Nanotubes[END_REF] In 2010, M.S. Strano and coworkers probed electrochemically modified graphene with aryl diazonium salts upon Raman spectroscopy. [START_REF] Sharma | Anomalously Large Reactivity of Single Graphene Layers and Edges toward Electron Transfer Chemistries[END_REF] It was explained that graphene, opposite than for SWCNTs, is not an enhancing resonant process, but instead could be sure of the functionalization degree. During the present study an Xplora confocal Raman microscope from HORIBA scientific has been used for all samples characterization (see figure 13). All the measurements were done using an excitation laser of 532 nm, otherwise it will be specified along with the text.

Chapter 2: Characterization techniques All measurements showed were performed at CRPP-CNRS, Pessac. Three different excitation laser were available: 532, 638 and 785 nm wavelength with respectively.

ELECTROCHEMICAL TECHNIQUES

Electrochemistry has its historical derivation from the studies of Alessandro , a brilliant physicist of the University of Pavia, which in 1800 invented the electric battery. The inspiration of his studies probably came from the famous frog leg experiments of Luigi Galvani (1737-1798), physician and anatomist of the University of Bologna (see figure 14). From his studies on the effects of electricity on frogs, the scientist of Bologna L.

Galvani derived his hypothesis that animal electricity that is involved in fundamental physiological processes such as From his studies on the effects of electricity on frogs, the scientist of Bologna L.

Galvani derived his hypothesis that animal tissues are endowed with intrinsic electricity that is involved in fundamental physiological processes such as nerve conduction and muscle contraction in his main work, Viribus electricitatis in motu musculari (1791) [START_REF] Galvani | Viribus Electricitatis in Motu Musculari[END_REF] summarizing and discussing more than 10 years of research on the effect of the electricity on frogs mostly. Rudolph Marcus (b. 1923) won the Nobel Prize in Chemistry for his theory of electron transfer in chemical systems in 1992. [START_REF] Marcus | Electrostatic Free Energy and Other Properties of States Having Nonequilibrium Polarization[END_REF][START_REF] Marcus | On the Theory of Oxidation-Reduction Reactions Involving Electron Transfer. II. Applications to Data on the Rates of Isotopic Exchange Reactions[END_REF][START_REF] Marcus | On the Theory of Oxidation-Reduction Reactions Involving Electron Transfer. III. Applications to Data on the Rates of Organic Redox Reactions[END_REF][START_REF] Marcus | Theory of Oxidation-Reduction Reactions Involving Electron Transfer. Part 4.-A. Discuss[END_REF][START_REF] Marcus | On the Theory of Oxidation-Reduction Reduction Reactions Involving Electron Transfer. V. Comparision and Properties of Electrochemical and Rate Constants[END_REF][START_REF] Marcus | On the Theory of Electron-Transfer Reactions. VI. Unified Treatment for Homogeneous and Electrode Reactions[END_REF] Today electrochemistry is a rigorous science concerned with the quantitative relations among the chemical, surface, and electrical properties of systems that greatly profited from the huge advances in material science and technology.

In electrochemical systems, processes and factors that affect the transport of charge across the interface between an electrode and an electrolyte are studied. This electrode/electrolyte interface and the events that occur when an electric potential is applied and a current flows, will be explained in the following. Later on, the electrochemical techniques used for the characterization of samples during this study will be explained.

ELECTRODE PROCESSES

Charge (q) is expressed in units of Coulombs (C), where 1 C is equivalent to 6,24 X 10 18 electrons. It is transported through the electrode upon electrons movement and holes. Typical electrodes include solid and liquid metals, semiconductors, and carbon. In the case of electrolytic phase, the charge is Besides Faradaic processes the electrochemical interface is also characterized by a capacitive behavior.

At a given potential, there will exist a charge on the metallic electrode q M , and a charge in the solution q S , respecting that at any time q M = -q S . This entire array of charged species and oriented dipoles existing at the metal-solution interface is named the <<electrical double layer>> (see figure 15).

CYCLIC VOLTAMMETRY

The potential of a stationary working electrode changes lineary with time.

Starting from a potential where no electrode reaction occurs, it will be driven to potentials where reduction or oxidation of a solute occurs (see figure 16).

Chapter 2: Characterization techniques . [START_REF] Evans | Cyclic Voltammetry[END_REF] After traversing the potential region in which desired reactions take place, the direction of the linear sweep is reversed and the electrode reactions of intermediates or products (formed during the forward scan) can be detected.

The time scale of the experiment is controlled by the scan rate and the total potential traversed can be varied over the range of 10 electrolyte maintains the migration of charged reactants and products.

The anodic and cathodic peak curre The measurements can be done over a wide range of frequencies: (10 4 to 10 -6 s or 10 -4 to 10 6 Hz, as 1 Hz = 1 s -1 ).

Electrochemical Impedance Spectroscopy (EIS) is a technique where the cell or electrode impedance is plotted versus the frequency. It is a technique frequently used for evaluation of heterogeneous charge-transfer parameters and for the study of the double layer.

During the present thesis work, electrochemical measurements have been set

in an electrochemical cell of three electrodes (see figure 17).

Fig. 17: Electrochemical cell used during the present study.

White was the reference electrode, red was the counter electrode, and green the working electrode made of SWCNTs or Graphene.

A CHI-potentiostat Instrument has been used during this study, being able to collect cyclic voltammograms and impedance spectra in both laboratories when needed.

Connection of the potentiostat to inert atmosphere was already set at CRPP-CNRS, Pessac, allowing measurements of air-sensitive species with no need of degas.

CHAPTER 3: SWCNT TRANSPARENT CONDUCTIVE FILMS SWCNTs are carbon-based nanomaterials used in many field applications, for example composites, energy conversion and storage, sensors, and so on, but process them and/or prepare CNT solutions/dispersions is still a challenge for some of these applications. [START_REF] Baughman | Carbon Nanotubes--the Route toward Applications[END_REF] As raw materials SWCNTs are agglomerated forming bundles upon high van der Waals forces. Those forces are difficult to counteract for separating them into individual tubes. Bundles can alter important properties in composites or SWCNT-based films so, a complete exfoliation before their use in material preparation is necessary. [START_REF] Pénicaud | Concentrated Solutions of Individualized Single Walled Carbon Nanotubes[END_REF] In 2004, at the CRPP-CNRS, Pessac, a spontaneous dissolution of a SWCN-salt in DMSO was prepared. 26 Thermodynamically stable solutions of unmodified and uncut SWCNT soluble without any sonication, surfactants or functionalization was reported.

Such polyelectrolyte salt can be filtered and deposited on alumina membranes

obtaining what is defined as a film of SWCNTs; transparency will depends on the quantity of material deposited. After controlled re-oxidation, the film is handled under ambient conditions. The dissolution of the alumina in a strong Chapter 3: SWCNT transparent conductive films 66 NaOH medium results in a free-standing SWCNT film that floats on the bath surface upon hydrophobic interactions.

At this moment, the deposition can be on any selected substrate, taking into account adhesion forces between the nanotubes and the substrate (higher the hydrophobicity of the substrate, higher will be the adhesion with carbon nanotubes). The result returns ready-to-use SWCNT-conductive films that will be tested as SWCNT-based electrodes.

INTRODUCTION OF THE STUDY

Previously to this study, transparent conductive films were produced and studied at CRPP-CNRS with the purpose of producing novel conducting devices which could replace actual ones like Indium Tin Oxide (ITO). Transparency was an important factor to respect as well as conductivity values.

What if we combine mechanical and electrical properties of SWCNTs with specific properties of anchored groups to create a multifunctional device? (See figure 1).

SOLUTIONS OF SWCNTS

The preparation of solutions of CNTs is an air-sensitive process. During the study an Innovative Technologies Glove box was used.

Chapter 3: SWCNT transparent conductive films 68 SWCNT-salt preparation requires the preparation of a naphthalene salt in THF upon intercalation with metallic sodium. Naphthalene shows high reduction potential to reduce SWCNTs. After obtaining the naphthalene salt, nanotubes can be add stoichiometrically, replaced by naphthalene and resulting in a polyelectrolyte salt of nanotubes. 26,[START_REF] Petit | Tuning and Monitoring the Electronic Structure of Carbon Nanotubes[END_REF] The stoichiometry chosen was NaC 10 and naphthalene was added with 5% excess.

C 1D D $ 7 + C @E+ FGH IC 1D D & C J K (@E+) L
Sodium was cut in small pieces after removal of the oxidized layer, added to a bottom flask and covered with some mL of THF. Then, naphthalene was added and dissolved in ~250 mL THF. A stirring magnet was added and the solution was left under reflux. After 2 hours the solution turns dark green in color due to naphthalene charges. Sodium was still visible so it was left react overnight.

The day after sodium was not reacted completely (still some traces floating on the bath) and we decided to replace it by potassium.

KC 10

Metallic potassium was cut in small pieces and made it react with naphthalene in ~250 mL of THF. A black cloud formation around potassium pieces upon reaction of the metal surface with naphthalene moieties was observed after 30 minutes of reaction. The reaction is showed below:

C 1D D $ 7 + M @E+ FGH IC 1D D & M J K (@E+) L

Chapter 3: SWCNT transparent conductive films 69

The solution becomes dark-green after two hours under reflux as expected for the successful reaction between potassium and naphthalene moieties but, in any case, was left overnight to be sure all the potassium reacted. The obtained grams of solution (KC 10 ) contain one positive charge per potassium atom, hence one negative charge per 10 carbon atoms (KC 10 ).

C M N O #P %#$Q *#7 = "#$(M J ) O &' = C 9 '5

Single-walled carbon nanotube (SWCNT) sources

During the present study three sources of SWCNTs have been tested in order to compare properties of the resulting films. Early with the study, CoMoCAT (labeled CG200) and HipCo SWCNT (lot 0556), announced to be richer in metallic nanotubes, were used. HiPCO SWCNT commercially available from Unidym-carbon for electronics was introduced during last step of the study.

50 mg of single-walled carbon nanotubes were chosen to prepare the corresponding nanotube salt. Calculating number of mol of carbon (N C ) and the grams of naphthalene solution need for the salt preparation, carbon nanotubes were added to the naphthalene solution and covered with Aluminum foil to avoid light contact. Photochemical processes could be in competition during the reaction time.

RC 1D D & M J S (@E+) L + 9C@% → RM J 9C@% & S(@E+) T + C 1D D $ 7

The solution was filtered in a polyvinylidene difluoride membrane (PVDF) of 0.45 μm in pore size and the remaining powder was rinsed with distilled THF until filtration remains colorless. The product obtained is the SWCNT-salt.

Normally the salt is placed in the antichamber overnight for the elimination of

SWCNT FILMS

On Alumina membranes

For the preparation of SWCNT films, the SWCNT-salt solution in DMSO (stable in the glove box) was centrifugated in order to eliminate the insoluble part (4000 rpm/1 hour; rtc~2800). The SWCNT solution remains on the top.

The centrifuge tubes were sealed accurately to avoid oxidation of the solution when carrying them outside the glovebox. After centrifugation time, the tubes were placed back in the box and the insoluble part was eliminated. There was a partial lost into the aggregates during centrifugation for CoMoCAT SWCNTs.

H-SWCNT showed higher concentration values compared with C-SWCNT films.

It can be possible due to higher dissolution of HiPCO tubes vs CoMoCAT.

The concentration of the SWCNT solution was calculated by dry extract where 2.5 mL were left overnight for solvent evaporation. C-SWCNT or H-SWCNT solution concentration (mol/mL) was calculated by the relation

7(M9 '5 ) = "O M9 '5 UV(M9 '5 ⁄ )

Chapter 3: SWCNT transparent conductive films

Whatman Anodisc Filter Membranes (0.02 from Fisher Scientific were used to prepare films of carbon nanotubes. The equipment used is shown below (see figure 2). After that, the box containing SWCNT films is opened (two valves: one left and one right) and connected slowly to the dry air column. The control in the flow of air will control films not to be damaged. Films are left to dry for at least 2 hours until complete drying.

Transfer of SWCNT films on selected substrates

The dissolution of the alumina membrane results in films made exclusively of SWCNTs. Here we used a bath of sodium hydroxide (1.5 M). The alumina takes 8-9 minutes to get dissolved. Time should not exceed 12 minutes otherwise SWCNTs could be damaged. After complete dissolution, the bath should be neutralized by rinsing with deionized water until pH~7. After that, the substrate must be placed at the bottom of the bath and by removing it SWCNTs will be deposited on any selected substrate. They will dry overnight in the oven at 40-50 °C protected from dust with a glass cover.

Substrates: problems of the study Following precedent studies on SWCNTs film deposition, the substrates selected were Glass slides and thin film of polyethylene terephthalate (PET). • Glass slides. The adhesion of the nanotube film onto glass leads to detachment and loss. Silanization of the glass substrate results in the improvement on the adhesion forces but resulted in a significantly longer procedure, deciding to keep going with PET samples.

Due to problems detected in

• PET. It was the perfect substrate in terms of adhesion, thickness and manipulation as well as for its resistivity to organic and non organic solvents. Polyethylene terephthalate displays Raman bands in the same region of SWNTs under specific excitation laser. At this moment of the study performed in Bologna a less-interacting substrate was need for continuing with the study of the SWCNT surface modification.

• Polystyrene. After collecting some candidates, Raman spectra for each material was measured at different wavelength. Polystyrene bands at 532 and 638 nm lasers showed not to overlap with the bands under study. The polystyrene used for this study was Polystyrene foil (0.25 mm thick) from Goodfellow Inc (see figure 3). In order to compare original solution of SWCNTs with the filtered solution, samples were sealed with liquid parafilm (to avoid self oxidation) and left for sedimentation for three weeks. Angles from 40° to 70° were measured. It was not possible to measure bigger angles than 70° because the solution was too diluted to obtain enough results for statistics. Other method was to dropcast the filtered solution on a clean mica surface. The resulting deposition was observed by AFM but no presence of tubes was observed.

Chapter 3: SWCNT transparent conductive films After drying the resulting films in the oven (overnight at <50 °C) their aspect became homogeneous. Further characterization with AFM confirmed it.

Apparently, during the drying process there is a reorganization of the material.

CoMoCAT SWCNT films did not show any of these particularities. The aspect of the films did not change at any moment along the process.

Chapter 3: SWCNT transparent conductive films Near-Infrared absorption spectra of both films on PET were measured for the study of the characteristic spectral signatures corresponding to the respective electronic transitions of HiPCO tubes after dissolution and film preparation (see figure 5). Chapter 3: SWCNT transparent conductive films 78 This characterization will be important for the subsequent surface modification. Cleaner will be the surface easier would be to detect modifications. The roughness and thickness of the films was revealed by Atomic force microscopy (see figure 7). HiPCO-SWCNT solutions. In that case, the films are homogeneous and they can be described like a mat of nanotubes. The deeper zones could be formed during dissolution of the alumina membrane where tubes are partially lost.

The thickness of H-SWCNT films was measured ~60-70 nm for films prepared with 0.58 mg of tubes.

Contact angle measurements will show changes in the wettability of SWCNT film surface before and after surface modification. In figure 8, it is shown a SWCNT film on glass where it is possible to observe the advancing and receding angle measured for the pristine material. Higher contact angles were found with CoMoCAT-SWCNT films.

Chapt

Four-point conductivity prepared (see table 1).

Table. 1: Different SWCNT so resistivity values ( dilutions express in quantities of tubes (

The presented values result from an average value of several R film prepared. The corrective factor provided for these measurements was 4.53 (numerical value of compared to large surfaces (~1 An X-ray photoelectron spectroscopy an atomic percentage (%) of differ (see table 2). We considered the purification of raw HiPCO Unidym because the presence of catalyst was higher than for previous sources (HiPCO-0556).

Chapter 3: SWCNT transparent conductive films point conductivity shows surface resistance values for the six films prepared (see table 1).

Table. 1: Different SWCNT solution concentrations and corresponding surface resistivity values (Ω/□) measured for the respective 400, 600, and 1000 dilutions express in quantities of tubes (mg).

The presented values result from an average value of several R film prepared. The corrective factor provided for these measurements was .53 (numerical value of X $7 ) accepted when measuring thin (< 1 compared to large surfaces (~1 cm 2 ).

% = 9 Y Z ; 9 \. 6
ray photoelectron spectroscopy analysis of the film surface can give us an atomic percentage (%) of different elements present in the sample surface (see table 2). We considered the purification of raw HiPCO Unidym because the presence of catalyst was higher than for previous sources 0556). 2). We considered the purification of raw HiPCO-SWCNTs from Unidym because the presence of catalyst was higher than for previous sources Chapter 3: SWCNT transparent conductive films For HiPCO-0556 SWCNT films the amount of iron catalyst was 0.82%. The atomic % of iron on the film surface was 1.22% for films prepared with non purified SWCNTs versus the 0.33% when the film tubes. We consider that, compared to the time consumed for purifying the tubes using procedures that implies manipulation of large quantities of strong acids, was better to prepare SWCNT solutions starting from the non purified SWCNTs.

It is a fact that the preparation of the solution itself cleans the nanotubes resulting in lower atomic quantities of oxygen and iron after film preparation. 0556 SWCNT films the amount of iron catalyst was 0.82%. The atomic % of iron on the film surface was 1.22% for films prepared with nonpurified SWCNTs versus the 0.33% when the film was prepared with purified tubes. We consider that, compared to the time consumed for purifying the tubes using procedures that implies manipulation of large quantities of strong acids, was better to prepare SWCNT solutions starting from the non purified It is a fact that the preparation of the solution itself cleans the nanotubes resulting in lower atomic quantities of oxygen and iron after film preparation.

The presence of sulfur could be due to reaction with DMSO during disolution At this point, we considered that non-purified HiPCO-SWCNT films were the best candidates to continue with the study of the electrochemical surface modification of SWCNT-based electrodes. The Raman spectrum of an HiPCO-SWCNT film prepared on polystyrene substrate is shown in figure 9. SWCNT solutions and films from Rice University tubes available at CRPP were prepared (Figure 10). Here is reported the Raman spectra of these films Unexpected results were obtained and analyzed. We will try to explain them and present all data obtained ongoing with the experiments.

Chapt

Before introducing the results obtained, it is important to explain that the electrochemical surface modification of SWCNT electrodes is not resulting in the formation of mono-to-few layers of organic molecules on the surface of the electrode material, but in more complicated polymeric structures with ramifications already introduced in chapter 1. In this case, more complicated structures can be observed. These can often show different electrochemical properties and may be useful, as in this study, in applications as sensors.

Processes that can occur at modified electrodes are shown in figure 1, selected as previously explained.

Chapter 4: Electrochemical surface modification of SWCNT

Chapter 4: Electrochemical surface modification of SWCNT-based electrodes

Movement of A through a pinhole or chanel in the film to the substrate, where it can be reduced can occur. P and Q represent reducible and oxidative species in a film electrode surface and A, species in solution.

ELECTROCHEMICAL SURFACE MODIFICATION WITH DIAZONIUM CHEMISTRY 4.1.1. REDUCTION OF ARYL DIAZONIUM SALTS

The experimental conditions for performing the electrochemical reduction of phenyl diazonium salts on SWCNT electrodes were reproduced from literature (D. Bélanger in 2006). 38 The three precursors (see figure 2) were selected as previously explained. 37,41 The contact angle measured for the electrode surface after modification with EDA (and PhDA) moieties was smaller compared to the unmodified material in both cases (see figure 5). This was expected after introducing hydrofilic moieties on the film surface. Opposite to that, TMS modified film shows higher contact angle due to the contribution of hydrophobic moieties (-Si(CH 3 ) 3 ). X-ray photoelectron spectroscopy (XPS) surface analysis of modified films shows the presence of Nitrogen groups as well as the presence of Trimethylsilyl moieties as expected. Observing the C1s spectra for EDA and TMS samples (see figure 7), there is an increase of the intensity on the signal at 286 eV related to sp 3 carbons in accordance with the formation of covalent bonds on the surface. Besides, there is a decrease in the intensity of bands related to oxygenated carbon on the surface (~288 eV).

Chapter 4: Electrochemical surface modification of SWCNT-based electrodes 97

This is in accordance with Raman spectroscopy where an increased D-band related to sp 3 carbon atoms is observed after surface modification in comparison with the spectrum of the pristine material (see figure 6).

TRANSFORMATION OF THE REMAINING ACTIVE MOIETIES

SWCNT modified films were treated chemically in order to prepare the reactive functional groups for the subsequent cycloaddition reaction. In the case of EDA and PhDA moieties, the remaining amine groups need to be transformed in azide groups while TMS molecules need to be unprotected to obtain a final alkyne.

Such transformations will allow the cycloaddition reaction to occur between those groups and ferrocene complementary moieties synthesized for this purpose. The amine to azide transformation was obtained upon formation of a second diazonium salt with 0.1 M NaNO 2 and reaction with 0.2 M solution of sodium azide (NaN 3 ). The formation of bubbles indicates production of nitrogen molecules. First experiments were performed upon dropcasting the solution on the film surface but the amount and size of nitrogen bubbles formed hindered the reaction.

As an alternative, films were softly stirred in the solution for two hours, insuring contact between film surface and solution at any moment. After the reaction, the films were washed with distillated water.

Deprotection of TMS moieties to obtain the alkyne requires the use of TBA + F - solution. This strong chemical dissolves polystyrene substrates. We were In parallel infrared spectra were measured for the three different modified surfaces at any single step, but unfortunately, the amount of material deposited was too small compared with SWCNT film and substrate (PS) making it difficult to observe any significant change of the best spectra obtained.

Anyhow, here it is presented the best obtained (see figure 9). The small change in the orange spectra may be related to the formation of N 3 moieties that are known to display a strong band at ~ 2100 cm -1 . No significant change in the spectrum is observed except for the band at ~2800 cm -1 , related with aryl modified substrates.

The presence of aryl moieties on a modified surface was recently shown to contribute with a band between ˜2800 and 3100 cm -1 . This is in fact observed in the spectra displayed in figure 12, and the small shoulder in the final spectrum can be attributed to the formation of the triazolic ring. The analysis of the scan rate dependence of the peak current indicates that the redox species is immobilized at the electrode surface (see figure 13 b) with calculated value of Γ=2x10 15 molecules cm -2 . This value is significantly higher than for monolayers where Γ=~10 12 molecules cm -2 . Such value is in accordance with functionalized polymeric films. As introduced in chapter 1, the electrografting of aryl-diazonium salts leads to the formation of polymeric films. In consequence, the number of species immobilized should be significantly higher as observed. The modified electrode surface was characterized by cyclic voltammetry studying the evolution in the current in response to an increasing concentration of hydrogen peroxide in the presence of 1 mM Hydroquinone in PBS (see figure 14a and14b). HRP, in the presence of hydrogen peroxide, will oxidize hydroquinone which will get reduced at the electrode surface (as shown in scheme 3).

-180 i / µA E / V NO H 2 O 2 1 µM H 2 O 2 5 µM H 2 O 2 10 µM H 2 O 2 20 µM H 2 O 2 30 µM H 2 O 2
h i R S j + R S
resulting in a K M value of 1.238 μM and V max equal to 1.38x10 -4 μmol cm 2 s -1 .

The obtained i max = 26.7 μA has been transformed into μmol/s by k ∝ lmn n k!op &q ) lm!orst &q ) u

where n are the number of electrons involved in a single process (as shown in scheme 3) and F is the Faraday constant.

Scheme 3: HRP Immobilized on a SWCNT-based electrode modified with

PhDA. Redox shuttle Hydroquinone/benzoquinone used for monitoring catalytic activity of HRP while increasing concentration of hydrogen peroxide.

Chapter 4: Electrochemical surface modification of SWCNT-based electrodes 110

The resulting detection limit is 1.2 μM. After such value the curve reach Plato.

The K M obtained is smaller than values reported. [START_REF] Cosnier | A Composite Clay Glucose Biosensor Based on an Electrically Connected HRP[END_REF][START_REF] Shan | Zn-Cr-ABTS] Redox Clay-Based Biosensor: Design and Optimization for Cyanide Detection[END_REF][START_REF] Tertis | Carbon Based Electrodes Modified with Horseradish Peroxidase Immobilized in Conducting Polymers for Acetaminophen Analysis[END_REF] This may be related to small values of enzyme loading on the electrode surface.

ELECTROCHEMICAL SURFACE MODIFICATION WITH 1, 3-BENZODITHIOLILYUM TETRAFLUOROBORATE

The electrochemical covalent adsorption of 1, 3-Benzodithiolilyum tetrafluoroborate molecules (here on, BDYT) on SWCNTs was an alternative approach for surface modification. The inspiration came along with two articles found in literature. [START_REF] Sohee | Adsorption of 1,3-Benzodithiolylium Tetrafluoroborate (1,3-BDYT) on the Carbon Nanotubes[END_REF][START_REF] So | Selective Suppression of Conductance in Metallic Carbon Nanotubes[END_REF] Since this molecule was shown to react with SWCNTs (with higher reactivity with metallic tubes) resulting in a covalent bond formation, we investigated the surface modification of SWCNT-based electrode through the electrochemical generation of radical species at the electrode surface. This study is preliminary to the possibility of surface functionalization according to the scheme shown in figure 15. In addition, the electrochemical surface modification would represent an advantage with respect to thermal reactions since it is a more controlled process. After setting up the reaction conditions the electrografting on SWCNT films was performed by cycling the potential from the OCP towards reductive potentials. HiPCO and CoMoCAT SWCNT based electrodes were tested to react with BDYT moieties in acetonitrile and TBA + PF 6 -as a supporting electrolyte.

Depending on the SWCNT starting material, films with different conductivities were obtained.

Upon performing several potential cycles, formation of a white thin layer was observed on the electrode surface (see figure 17).

Chapter 4: Electrochemical surface modification of SWCNT The sample was characterized by SEM (see figure 18) showing the presence of bright spots on the surface of the SWCNT film when scanning at high resolutions. In agreement with these results atomic force microscopy also showed the formation of spots grown onto the nanotubes. The sample was characterized by SEM (see figure 18) showing the presence of bright spots on the surface of the SWCNT film when scanning at high resolutions. In agreement with these results atomic force microscopy also formation of spots grown onto the nanotubes. In order to identify the composition of the layer formed on the surface of the SWCNT film the sample was characterized by XPS. The resulting modified surface shows an evolution of bands with respect to the pristine material in the C1s and S2p spectra (see figure 19). Notice that the dropcast solution do not shows a peak at this position. The images obtained gave unexpected results (see figure 23b). The resulting modified surface shows unexpected twisted ropes, and the ropes grow in number with the number of cycles. The AFM analysis of the ropes showed heights around 10-15 nm and width around 0.5 μm that are confirmed by SEM and optical microscopy.

The image 23c shows the cyclic voltammetries, AFM images and C1s XPS spectra when increasing the number of potential cycles. The XPS analysis shows in accordance to that an evolution of the C1s band at ~284.83 eV (related to sp2 carbons) to higher energy bindings at ~285.53 eV with higher number of potential cycles (10 cycles) related to sp3 carbons. This intensity still diminishes when increasing the number of potential cycles to 70, leading to the formation of new bands at ~287-290 eV.

The hypothesis that such patterns would form because of capillary effects during the drying process was discarded by exposing the film to the BDYT solution without application of any potential.

Chapter 4: Electrochemical surface modification of SWCNT-based electrodes 124

After removing the solution and rinsing the film AFM analysis was performed that did not show the presence of any deposit (see figure 24).

Fig. 24: SWCNT film after being in contact with BDYT moieties in acetonitrile.

No potential was applied.

At this point we were able to say that those twisted ropes formed in the surface are electrochemically generated.

To get chemical and structural information about the material formed a MALDI-TOF experiment was performed (70 potential cycle sample).

Experiments were run in order to identify a mass distribution of the material electrochemically generated at the electrode surface. Unfortunately (see figure 25) only features characteristic of carbon nanotubes film were observed. Therefore in order to perform a mass spectrometry analysis of the material formed the substrate should be removed.

In order to identify possible ordered structures the modified samples observed under polarized light in an optical microscope. Upon polarization of light generated film was described as ordered system thus an X (XRD) analysis was performed.

XRD is a non-destructive analytical technique resulting in a un (Bragg reflections) associated with a crystal structure. A crystal structure is a construction of layers or planes acting as a semi transparent mirror. A source of x-rays with a wavelength similar to that distance between crystal planes ca be reflected. The angle of such reflection is equal to the incident angle. Therefore in order to perform a mass spectrometry analysis of the material formed the substrate should be removed.

In order to identify possible ordered structures the modified samples were observed under polarized light in an optical microscope. Upon polarization of light generated film was described as ordered system thus an X-ray diffraction destructive analytical technique resulting in a unique fingerprint (Bragg reflections) associated with a crystal structure. A crystal structure is a construction of layers or planes acting as a semi transparent mirror. A source rays with a wavelength similar to that distance between crystal planes can be reflected. The angle of such reflection is equal to the incident angle.

Chapter 4: Electrochemical surface modification of SWCNT-based electrodes 126

The diffractogram shows an amorphous behavior in the case of SWCNT film surface (red line), but after electrochemical surface modification with BDYT sharp reflections appear being related to a highly ordered deposit (see figure 26a). Although the results are very encouraging, an identification of the crystalline phases has not still been possible. However, some of the reflections are in agreement with those reported in films of TTF derivatives (see figure 27a). [START_REF] Naraso | High-Performance Organic Field-Effect Transistors Based on Pi-Extended Tetrathiafulvalene Derivatives[END_REF]102 The formation of tetrathiafulvalene (TTF) derivatives was already proved by XPS analysis (see above). The probability of dimerization of BDYT moieties was quite high resulting in dibenzo-TTF (here on, DB-TTF). There is no evidence of electrochemical formation of TTF molecules at the electrode surface scanning to oxidative potentials. After the formation of BDYT radical species at the electrode surface upon reductive potentials, the potential was driven to positive potentials and a oxidation peak was observed at E ap = 0.6 V (related to DB-TTF moieties). [START_REF] Naraso | High-Performance Organic Field-Effect Transistors Based on Pi-Extended Tetrathiafulvalene Derivatives[END_REF] The formation of DB-TTF species could not occur at the electrode surface, but instead, the formation of the BDYT cationic radical species leads to formation of DB-TTF moieties in solution. DB-TTF molecules are widely studied as semiconducting materials for the performance of highlyoriented field effect transistors (OFETs) [START_REF] Naraso | High-Performance Organic Field-Effect Transistors Based on Pi-Extended Tetrathiafulvalene Derivatives[END_REF][102][103][104] and its crystals showed an XRD spectra in accordance to the spectra obtained, thus indicating that apparently we have obtained a thin film made of DB-TTF crystals (see figure 26b). Graphite is described as a semi-metal and shows a complex electronic band structure. 29,107 Its thermoconductivity is highly anisotropic resulting in a material that is highly conductive in plane but almost insulating in perpendicular to it. Intercalated compounds may be obtained from graphite with different stage index, determined by the number of layers of graphite between the intercalate species layer. Intercalation allows the modulation of the free carrier concentration in compounds, being possible to control the electrical, thermal, and magnetic properties of the graphitic material.

Intercalation with alkali metals is one of the most studied, like KC 8 compounds.

These are classified as donor-type compounds, where the metal atom transfers its charge to the graphite conduction band resulting in a large increase of the As we mentioned in chapter 1, the surface modification of carbon-based materials is well studied. 108,109,110 Over the present chapter, the synthesis, solutions and depositions of GIC solutions has been investigated. Likewise, the electrochemical surface modification of graphene films (from GIC solutions) has been studied. These films are suitable to be used as electrodes for performing surface modification, as in the case of SWCNTs.

In our laboratory three different sources of graphite were used during the study: natural graphite from Sigma-Aldrich, graphite from Brazil (labeled as G4), and from Madagascar.

GICs prepared with natural graphite (Sigma-Aldrich) resulted in a mixture of different stages of KC 8 ; when prepared with natural graphite from Brazil (G4) the stage obtained was mostly one.

Chapter 5: Transparent conductive films from GICs 137

SYNTHESIS AND SOLUTIONS OF KC8 COMPOUNDS

To prepare KC 8 compounds the two-zone vapour transport method was used.

In this method the intercalant (potassium) is heated up to some temperature T i and the graphite, some distance away is heated to a higher temperature T g .

The sublimation of the metal leads to the formation of the intercalated compound.

Tubes were filled with the corresponding calculated amounts of natural graphite and metallic potassium. An excess of potassium is added to ensure a complete intercalation between graphite flakes. This preparation takes place under inert atmosphere reaching pressure ~8.3x10 -4 mbar. Overnight reaction gave high quality stage-one graphite intercalation compound with a nice gold color. The resulting compound was placed back to an inert environment and preserved from oxidation.

Procedures for the preparation of Graphene solutions have been set up at CRPP-CNRS, Pessac, over the last years. 27 Deposition from such solutions showed large graphene flakes under TEM (see figure 1).

Chapter 5: Transparent conductive films from GICs 138 Fig. 1: Route representation to produce graphene solutions (above). Multifolded graphene flake image by high resolution TEM (below). 28 Solutions of graphite intercalated compounds gives "graphenide" solutions. 28 The term "graphenide" was introduced in 2012 during ChemOnTubes2012 conference in Arcachon to describe negatively graphene sheets.

The dissolutions of GICs were performed using distilled methyltetrahydrofuran (M-THF) and distilled cyclopentyl methyl ether (CPME) (2 mg of KC 8 per milliliter of solvent). They were covered with aluminum foil and mildly stirred for 48 hours. The resulting solution was centrifuged (2000 r.p.m.

per 10 minutes at room temperature) and the supernatant was collected.

Chapter 5: Transparent conductive films from GICs

139

A first attempt to prepare films from the above solutions was made by dropcasting on glass substrates. Deposition was performed following two different strategies, (i) dropcasting on glass under inert conditions followed by dry air oxidation, or (ii) dropcasting on glass directly in air.

FROM SOLUTIONS TO GRAPHENE FILMS

In order to produce thin films of graphene, two different routes were followed: a) dropcasting of the solution under inert atmosphere before oxidation of the flakes (by dry oxygen) b) dropcasting of the solution in air from deareated solutions.

In both cases glass slides (A= 1.5 cm 2 ) were used as substrates.

Starting from route (a), solutions of methyl tetrahydrofuran (M-THF) and cyclopentyl methyl ether (CPME) were spincoated in the glove box. The resulting deposits were re-oxidized using dry air and labeled as DN 2 -MTHF and DN 2 -CPME meaning deposit under nitrogen atmosphere with the respective solvent.

For the preparation route (b), samples of the corresponding M-THF and CPME solutions were taken by air-tight syringes under inert atmosphere and spin coated in air, obtaining DO 2 -MTHF and DO 2 -CPME deposits that were characterized by high-resolution-SEM (see figure 2). Samples were characterized at the CREMEM institute, Pessac, after metallization with gold.

While for DN 2 -CPME and DO 2 -CPME there is no evidence of their presence Further studies would be necessary in order to procedure. However, the following study was concentrated on films prepared according to a method set up by Y. Wang, Ph.D. student Briefly, the GIC solutions were filtrated preparing SWCNT films, obtaining graphene films supported on PS (see figure 3). Further studies would be necessary in order to optimize the film preparation procedure. However, the following study was concentrated on films prepared according to a method set up by Y. Wang, Ph.D. student at CRPP-CNRS, Pessac.

Briefly, the GIC solutions were filtrated following the same protocol used for ng graphene films supported on PS (see figure on polystyrene (PS) substrate.

Chapter 5: Transparent conductive films from GICs 142 These are transparent and conductive films that resulted to be composed mainly by single-to-few layers graphene d suitable to be used as electrodes for performing surface modification as in the case of SWCNTs. AFM (introduced in chapter 2) was used for the characterization of the films.

GRAPHENE-BASED ELECTRODES

Firstly, polystyrene substrate was analyzed (Figure 4). Some origami-folded graphene flakes show different contrast that may be associated to various numbers of folds and layers. In any case, the deposition of GIC solutions is not yet resulting in a very clean deposit (see figure 5a). An XPS analysis of the surface gives information regarding such an issue. 6) shows an intense peak at ˜284.5 eV related to sp 2 carbon and a small peak at 532.4 eV related to oxygen.

The Raman spectrum of a graphene film on PS is reported in figure 7. The main information that can be obtained by Raman is crystallinity /orientation of the sample (stage index of the compound) by analysis of the Dband, and the number of graphene layers by analysis of the width of the band at ~2700 cm -1 . An increase of the D-band intensity in Raman spectroscopy determines break in the symmetry of carbon nanomaterials. The modified material will show hybridization changes from sp 2 to sp 3 carbons resulting in a symmetry break and it will be reflected on the D-band situated ~1300 cm -1 .

1 5 0 0 2 0 0 0 2 5 0 0

Mapping of the surface gives an average value of these bands and their intensities. Raman spectrum of a graphene film displays (see figure 7) three characteristic bands: the D-band (ca. at 1300 cm -1 ), the G-band (ca. at 1600 cm - 1

), and the G'-or 2D-band (ca. at 2700 cm -1 ). The sharpness of the G'-band indicates uncorrelated graphene layers, i.e. exfoliated material.

The electrochemical surface modification with aryl diazonium salt onto graphene films was performed. In parallel, surface modification with 1, 3 -BDYT was also investigated. For both reactions, the film was placed in the electrochemical cell (figure 8), where the surface area of the film in contact with the solution during measurements is fixed and equal to A= 0.21 cm 2 . In the first approach, the reaction takes place in aerated solutions while for the second reaction inert conditions are needed, due to high reactivity of the electrogenerated radical with oxygen in solution. In our laboratory (CRPP-Bordeaux), we had the possibility to carry out such reactions in the glove box.

Chapter 5: Transparent conductive films from GICs A starting potential of 0.55 V (OCP) was chosen that ensured that no current flew before starting the scan. The potential was cycled 15 times from 0.55 V to -0.25 V leading to formation of a visible layer on the surface of the film (see figure 9).

Chapter 5: Transparent conductive films from GICs The transformation of the immobilized amines in azide groups was performed.

The resulting film was rinsed with distilled water and dried under a flow of argon.

The cycloaddition reaction with ferrocene containing probes (previously introduced in chapter 4) was investigated. 1 mg of alkyne-ferrocene was dissolved in 400 μL of distillated water resulting in a 10 μM solution concentration. In parallel, copper sulfate penthydrate and (+) sodium Lascorbate were calculated in excess respect to the alkyne-ferrocene solution.

The mixture was stirred and dropcasted onto the reactive film surface.

Samples were placed on an ice bath during reaction. After 2 hours the film was rinsed and sonicated for a short time (<1 minute) for the removal of adsorbed/trapped species on/in graphene film. The anodic peak at 0.26 V and its cathodic partner at 0.18 V were also attributed to ferrocene species in a different environment. The peak separation in this case (80 mV) is closer to the theoretical value.

In order to attribute the two redox processes a model compound (FcMeOH)

was investigated with pristine graphene films (see figure 12a). Signal associated to ferrocene species was still observed after rinsing the electrode and placing it in a fresh PBS solution (see figure 12b). The comparison of the CV curves in figure 11a with those of the model compound allows to formulate a hypothesis for the two redox processes observed:

1. The main peak with E 1/2 = 0.36 V is related to the ferrocene probe covalently anchored to the film surface upon the click reaction. Its redox potential is compatible with that of FcMeOH in solution (vs.

Ag/AgCl reference electrode) E 1/2 =0.34 V.

2. The minor peak at E 1/2 =0.21 V is instead related to ferrocene moieties strongly interacting with graphene (physically adsorved). This explains the anticipation of the redox process with respect to the model. This is in agreement with figure 12b. Furthermore, the faster kinetics associated to this peak is in line with the strong interaction between ferrocene and graphene film (Π-Π stacking).

SURFACE MODIFICATION THROUGH ELECTROPHYLIC ADDITION OF 1, 3-BDYT

The electrochemical adsorption of 1, 3-BDYT moieties on graphene film, was performed following studies done for SWCNT films. After 15 cycles of potential the system leads to an increase of current values, and after twenty, the process leads to a steady state values. The resulting surfaces were analyzed by Raman spectroscopy, atomic force microscopy (AFM) and photoelectron spectroscopy (XPS).

Raman spectra after normalization by the G-band would show an increase of the D-band intensity, as expected in the case of covalent functionalization.

However, the strong increase of fluorescence makes this observation less conclusive with respect to the previous systems (figure 14). These oxygen species could be related to the formation of oxygenated groups on graphene flakes (probably edges) during film re-oxidation. Fluorine atoms were also present on the film surface in amounts of ~1% related to the In this case, the pristine material shows highest point at ~23 nm while the modified material appears to be at ~4.5 nm. The topography is noticeably changed in comparison with the pristine graphene film.

Chapter 5: Transparent conductive films from GICs 160 However, no presence of twisted ropes formation, as in the case of SWCNT films, was observed. An explanation for such an observation may be the lower reactivity of graphene films in comparison with SWCNT films, lacking of any intrinsic curvature of the pristine material.

CONCLUSIONS

We have presented the synthesis and dissolution of some prepared GICs. Its deposition on glass has been investigated by SEM. Only for solutions prepared with CPME graphene flakes were observed.

Graphene films e are transparent conductive films that can be used as electrode devices (as seen for SWCNTs in chapter 4). AFM shows well-defined, folded, and corrugated graphene flakes. XPS analysis shows clean surfaces with the presence of carbon and oxygen mostly. Raman spectra showed well defined bands related to graphitic material. adsorption of material on the film surface; thus is detected as a fast electron transfer where the oxidation of ferrocene species is facilitated by the graphene film surface.

Likewise, BDYT moieties were electrochemically investigated to react with graphene films as studied with SWCNT films. Its characterization by Raman spectroscopy, XPS and AFM has been shown. In contrast to SWCNT films, no formation of twisted ropes was observed.

  investigated for the first time at either SWCNT-or graphene-based electrodes. The combination of different techniques has demonstrated the covalent attachment of BDYT to SWCNT-based electrodes. Such modification leads to the formation of twisted ropes observed and analyzed by AFM and scanning electron microscopy. No CHAPTER 1: INTRODUCTION The early understanding and manipulation of nanostructured materials, as the colloidal ruby gold discovered by M. Faraday, demonstrated that gold nanoparticles produce different color light under different lighting conditions. The physicist R. Feynman, Nobel Prize in 1965, gave what is considered to be the first lecture based on the atomic scale under the title:

  figure1).

Fig. 1 :Fig. 1 : 7 1. 1

 1171 Fig. 1: Time coworkers Iijima 3 in 1991 (right).

Fig. 2 :

 2 Fig. 2: Graphite sheet (left) showing possible chiral angles for wrapping up resulting in (a) arm-chair, (b) zig-zag, and (c) intermediate conformations of CNTs (right) a .

Fig. 3 :

 3 Fig. 3: Kataura's plot showing specific resonant nanotubes (metallic or semiconducting) when excited at specific laser energy. From: Optical

Fig. 5 :

 5 Fig. 5: SEM images for HiPCO (left) and CoMoCAT (right) SWCNT raw powders.

Fig. 5 :

 5 Fig. 5: SEM images for HiPCO (left) and CoMoCAT (right) SWCNT raw

Fig. 6 :

 6 Fig. 6: Graphene sheet and derivate structures. From: Geim and Novoselov,

Fig. 7 :

 7 Fig. 7: EG surf salts.

Fig. 8 :

 8 Fig. 8: Left: Spectroelectrochemical experiment showing the absorption spectra of GICs in NMP upon air exposure (above) and electrochemical oxidation (below). Right: TEM images of graphene flakes obtained in NMP.

Chapter 1: Introduction 15 Fig. 8 :

 158 Fig. 8: Left: Spectroelectrochemical experiment showing the absorption ICs in NMP upon air exposure (above) and electrochemical oxidation (below). Right: TEM images of graphene flakes obtained in NMP. 27

Fig. 9 :

 9 Fig. 9: GIC representation (left) and Raman spectra (right) obtained for different stage index GICs in 1970s. From: Physica scripta,2012.

Fig. 9 :

 9 Fig. 9: GIC representation (left) and Raman spectra (right) obtained for different stage index GICs in 1970s. From: Physica scripta,2012.

Fig. 9 :

 9 Fig. 9: GIC representation (left) and Raman spectra (right) obtained for different stage index GICs in 1970s. From: Physica scripta,2012. 29

  Fig. 10: Arylation reaction: Meerwein Arylation.

Fig. 11 :Fig. 10 :

 1110 Fig. 11: Cyclic voltammetry for the surface modification of HOPG with aryl diazonium salts (left), and mechanism proposed for the covalent attachment (right).33

Fig. 11 :Fig. 11 :

 1111 Fig. 11: Cyclic voltammetry for the surface modification of HOPG with aryl diazonium salts (left), and mechanism proposed for the covalent attachment

Fig. 12 :

 12 Fig. 12: Absorption and Raman spectra of pristine (a) and surface modified SWCNTs (b). From: JACS, (2001), 123, 6536.

Fig. 12 :20

 12 Fig. 12: Absorption and Raman spectra of pristine (a) and surface modified-SWCNTs (b). From: JACS, (2001), 123, 6536.

Fig. 13 :

 13 Fig. 13: Electrochemical surface modification of SWCNTs with aryl radicalsshowing polymeric growth. From: New. J. Chem., 2004, 302.35

Fig. 14 :

 14 Fig. 14: Route selected for the covalent immobilization of EDA molecules on SWCNT-and graphene-based electrodes. From: Adv. Matter., 2009, 21, 4404.

Fig. 15 :

 15 Fig. 15: Precursors selected for the electrochemical surface modification of SWCNT and graphene-based electrodes. (A) 4, 4'-Ethylene dianiline (EDA), (B) p-Phenylenediamine (p-PhDA), and (C) 4-[(Trimethylsilyl) ethynyl] aniline (TMS).

Fig. 17 :Fig

 17 Fig. 17: Scheme the immobilization of nanoparticles by click

Fig. 19 : 1 .

 191 Fig. 19: Theoretical simulation for the covalent adsorption on carbon nanotubes. From: Journal of the Korean Physical Society, (2010) 57, 1.

Fig. 20 :

 20 Fig. 20: Selected strategy for SWCNT surface modification with BDYT.

Chapter 1 :

 1 Introduction 29 radicals directly on the electrode surface. This modification will have an effect on the relative intensities of the D-band (before and after the reaction) that is related with symmetry disruption on SWCNTs upon changes in the carbon hybridation ( → ) due to surface modification.

  this thesis study a significant number of techniques have been used for characterization. We will introduce the Atomic force microscopy and the Scanning electron microscopy useful to reveal a topography image of the nanocarbon films. It was possible to extract information about roughness of films and to observe differences between films produced with HiPCO and CoMoCat carbon nanotubes. It was possible to determine the thickness of the films, contamination of the samples in terms of remaining catalyst, determine aggregates and measure its diameters.

Chapter 2 :Fig. 1 :. 1 :

 211 Fig.1: Schematic representation of different components present in the AFM instrument. b

Chapter 2 :

 2 Characterization techniques 35Different composition in the sample surface will show different adhesive and mechanical properties resulting in a phase contrast. That was useful when observing SWCNT and graphene films making possible the interpretation of corrugations, estimated number of layers, chemical modification of tubes, and so on.

Fig. 2 :

 2 Fig. 2: Fat-tip effect upon collecting images with unapropiate tip.

Fig. 5 :

 5 Fig. 5: Two current flow.

Chapter 2 :

 2 Characterization techniques 40 resistances are associated with the corresponding terminals as is expressed in representation of a Van der Pauw configuration used in the and R B . he method used to measure SWCNT and graphene films was the four-point method uses electrodes aligned linearly or in a square point set up techniques. Arrows show direction of point method, the voltage between the two electrodes is measured upon the passage of a flow of electrons. The expresion that results for the calculation of the surface resisitivity on this method contains a parasitic Chapter 2: Characterization techniques 41

  Contact angle measurement characterizes the wettability of a surface upon measuring the surface tension of a drop of water (or other liquid) at the interface with a homogeneous surface. It is one of the most sensitive and cheap surface analysis techniques capable of measuring from 3 up to 20 amstrong (Å) deep in the surface. When the drop comes in contact with the sample surface it can happen a complete spread of the drop over the sample surface, or that the drop will establish a define angle with the surface, named the contact angle. Thomas Young is credited with the development of the theory of capillary phenomenon while Laplace is credited to put numbers of such effect.

Fig. 6 :

 6 Fig. 6: Contact angle cartoon representation showing different phase contacts (solid

Fig. 7 :

 7 Fig. 7: Different wetabilities form different contact angles.

Fig. 8 :

 8 Fig. 8: Contact angle measurement of a

Chapter 2 :

 2 Characterization techniques 43 Contact angle measurement of a SWCNT film deposited on glass.

Chapter 2 :

 2 Characterization techniquesbonds, it is necessary to define different a component. As it is showed in figure SWCNT-film surface, the adquisiton done in study for each element in particular and its chemical contributions.

Fig. 9 :

 9 Fig. 9: XPS analysis of a surface modified SWCNT the main aquisition spectra (left), oxygen 1s, and sulfur 2p (right).

Chapter 2 :

 2 Photons can be absorbed and emitted by molecules, but besides they may also be scattered. The molecular effect responsible of such phenomenon is explained as follows. Scattering means the deviation of light from its original (straight) trajectory. Most of this scattered light is being scattered elastically, also named Rayleigh scattering, and a tiny amount is inelastically scattered. This inelastic scattering is defined as the event where the energy of the incident radiation is transferred between the scattered phonon and a state of the molecule (rotational, vibrational, or a phonon in the crystal lattice). The dipole scattering was calculated by Lord Rayleigh to be inferior to the λ scatter by the relation 1/λ 4 .

Fig. 10 :

 10 Fig. 10: Scattering of light representation and different stokes and anti-stokes lines.

Chapter 2 :

 2 Characterization techniques 48 SWCNT Raman spectroscopy is a resonant process, where nanotube signals are enhanced by two main reasons: the incoming energy or the scattered radiation matches (or allows) electronic transitions in the sample. This intensity enhancement depends on the density of states (DOS) available for optical transitions in SWCNTs. As each individual SWCNT possess an inherent electron and phonon structure depending on the chiral vector ((n, m) indices, it is possible to determine electronic and phonon structures for specific (n, m) nanotube. Raman modes of metallic-SWCNT were published by M.S. Dresselhaus, Smalley, Pimenta and coworkers in 1998. 70 In 2003, M.S. Dresselhaus, et al. 71 reviewed Raman spectroscopy as an important tool for carbon material characterization. In 2005, M. Burghard reviewed electronic and vibrational properties of covalent and non-covalent modified SWCNTs. 72 R. Graupner have reviewed a year later the Raman spectroscopy of covalently modified SWCNTs. 73 C. Fantini, M.A. Pimenta, and M.S. Strano published in 2008 the Raman spectra of covalently functionalized SWCNTs where they showed an electron-phonon coupling responsible of the intensity enhancement observed in some features of the spectra.[START_REF] Fantini | Two-Phonon Combination Raman Modes in Covalently Functionalized Single-Wall Carbon Nanotubes[END_REF] A recent review on Raman spectroscopy of graphene and nanotubes was published in 2011 by Saito, Hofmann, Dresselhaus and coworkers summing up recent advances and some basics regarding the use of Raman spectra for the study of graphene and nanotubes materials.[START_REF] Saito | Advances in Physics Raman Spectroscopy of Graphene and Carbon Nanotubes[END_REF] CHARACTERISTIC FEATURES OF SWCNTS RAMAN SPECTROSCOPY AND VARIATION OF THE INTENSITIES UPON FUNCTIONALIZATIONSWCNTs have characteristic features in Raman spectroscopy. Here we will describe what these features represent and which are the variations observed after surface modification of the SWCNT-based electrodes.

Chapter 2 :

 2 Characterization techniquesM. Strano and coworkers were pioneers in their work for the selective surface modification of SWCNTs and Raman characterization by characterizing changes on the RBMs (see figure11).[START_REF] Strano | Probing Chiral Selective Reactions Using a Revised Kataura Plot for the Interpretation of Single-Walled Carbon Nanotube Spectroscopy[END_REF]

Fig. 11 :

 11 Fig. 11: RBM Raman spectra for pristine and surface modified SWCNTs showing differences in bands related to metallic nanotubes.

Chapter 2 :

 2 Fig. 11: RBM Raman spectra for pristine and surface modified SWCNTs ces in bands related to metallic nanotubes.[START_REF] Strano | Probing Chiral Selective Reactions Using a Revised Kataura Plot for the Interpretation of Single-Walled Carbon Nanotube Spectroscopy[END_REF]

Fig. 12 :

 12 Fig. 12: RBMs and tangential modes of SWCNTs. Arrows indicate direction of vibrations. From: New J. Phys., 2003, 5, 139.1

Chapter 2 : 75 :

 275 Characterization techniques 51 main peaks originated upon symmetry break of original Gband (graphene original sheet before wrapping up to form the nanotube). RBMs and tangential modes of SWCNTs. Arrows indicate direction of vibrations. From: New J. Phys., 2003, 5, 139.1-139.17. induced D band band has its origins in a double resonance process involving an inelastic ttering by a phonon, and an elastic scattering by a defect (observed at . The intensity of this feature increases with increasing structural disorder. It is usual to observe D-band over G-band integrated areas expresions, as a representation of the amount of defects (sp 3 hybridation

Chapter 2 :

 2 Characterization techniques 52For the case of non-modified graphene samples, the D-band at the edges of the sheet showed a strong dependence on the polarization of the incident light, which was irreversively lost after surface modification. This phenomenon indicated that defects created upon attachment of functional groups are the main contribution to the D-band in the spectra.D-band second-order overtone: 2D-band or G' bandThis feature appears in the range of 2500-2900 cm -1 and shows a strong dispersive behavior depending on the excitation energy, opposite to what is observed for RBMs or G-band. Opposite to what is observed for D-band features, the 2D-band do not requires an static defect scattering process to be observed. Experimental results have shown that, semiconducting and metallic CNTs in resonance with the incident photon exhibits a D-and 2D-band features in addition to RBMs and tangential modes.

Fig. 13 :

 13 Fig. 13: Xplora confocal Raman microscope. From HORIBA scientific.

Fig. 14 :

 14 Fig. 14: Plate II of the Commentarius (1791): The experiment with the stormy atmospheric electricity.

  nerve conduction and muscle contraction in his main work, Viribus electricitatis in motu musculari (1791) 10 years of research on the effect of the electricity on frogs mostly. Volta's experiments led to the invention of the electrical battery as well as the famous voltaic pile opening a pathway to tremendous development of the physical investigations of electricity, electrochemistry, electromagnetism and related phenomena. Galvan Electrophysiology. Alessandro Volta is immortalized in the unit nomenclature that dates back to 1881. Chapter 2: Characterization techniques : Plate II of the Commentarius (1791): The experiment with the stormy atmospheric electricity.

  olta's experiments led to the invention of the electrical battery as well as the famous voltaic pile opening a pathway to tremendous development of the physical investigations of electricity, electrochemistry, electromagnetism and related phenomena. Galvani, in the other hand, established the foundations of Electrophysiology. Alessandro Volta is immortalized in the unit nomenclature that dates back to 1881.Chapter 2: Characterization techniques 54 : Plate II of the Commentarius (1791): The experiment with the stormy From his studies on the effects of electricity on frogs, the scientist of Bologna L. tissues are endowed with intrinsic electricity that is involved in fundamental physiological processes such as nerve conduction and muscle contraction in his main work, Viribus summarizing and discussing more than 10 years of research on the effect of the electricity on frogs mostly. olta's experiments led to the invention of the electrical battery as well as the famous voltaic pile opening a pathway to tremendous development of the physical investigations of electricity, electrochemistry, electromagnetism and i, in the other hand, established the foundations of Electrophysiology. Alessandro Volta is immortalized in the unit volt, a Chapter 2: Characterization techniques 55 In 1820, Hans Christian Ørsted observed the magnetic effect of electric current, and following this contribution, A. M. Ampère contributed formulating his findings mathematically. The German physicist Georg Ohm introduced a law connecting voltage, current, and resistance in 1827, the Ohm's law which later on, was considered as fundamental importance in electrical circuit analysis.

Chapter 2 :

 2 Characterization techniques 56 carried by the movement of ions being the most used, liquid solutions containing ion species, either in water or in a non aqueous solvent. Solvent-Electrolyte system should be sufficiently low in resistance in order to be useful during the measurements. Instead of approaching the idea of events at a single interface which is not easy to deal with experimentally, one must study the properties of collections of interfaces called electrochemical cells, defined by two electrodes separated by at least one electrolytic phase.The overall chemical reaction in a cell is made up of two independent halfreactions describing the real chemical changes at the two electrodes surface, each of them, responding to the interfacial potential difference at the corresponding electrode. For the study of the reaction occurring at the working -or indicator -electrode, a three electrode configuration is usually adopted, where the secondary -or counter-electrode closes the circuit while the reference electrode, having constant composition, allows to decouple the potential difference across the electrochemical cell, and controls the working electrode potential.Driving the electrode to high enough negative potentials the energy of electrons is raised to the point of being able to transfer into vacant electronic states on electrolyte species resulting in a flow of electrons to the solution: a reduction current. Following the same principle, the energy of electrons can be low down imposing a positive potential which will present a more favorable energy state for electrons on the electrode and they will flow right there: an oxidation current. The critical potentials at which these processes occur are related to the standard potentials (E 0 ) for the specific chemical substances in the system.Chapter 2: Characterization techniques 57The number of electrons that cross an interface is related stoichiometrically to the extent of chemical reaction as the amount of product consumed and the product generated. The number of electrons is measured in terms of total charge, Q, which had passed in the circuit.The relationship between charge and amount of product formed is given by Faraday's law where the passage of 96,485.4 C causes one equivalent of reaction as consumption/production of 1 mole of reactant/product in a 1electron reaction. The current, i, is the rate of flow of electrons (coulombs) being a current of 1 ampere (A) equivalent to 1 C/s. When plotting the current as a function of the potential, a current-potential curve is obtained. It can be quite informative about the nature of the solution and the electrodes as well as about reactions that occur at the interfaces. Since these reactions are governed by Faraday's law they are called faradaic processes.

Fig. 15 := 58 :+

 1558 Fig. 15: Representation of the electrical double layer at the interface metal solution.

Fig. 16 :

 16 Fig. 16: Cyclic voltammograms showing main important parameters: the cathodic and anodic peak potentials (E peak currents (i pc and i pa ), the cathodic half wave potential (E 1/2 ).[START_REF] Evans | Cyclic Voltammetry[END_REF]

61 : 62 ν 1

 61621 Cyclic voltammograms showing main important parameters: the cathodic and anodic peak potentials (E pc and E pa ), the cathodic and anodic), the cathodic half-peak potential (E p/2 ) and the half-After traversing the potential region in which desired reactions take place, the direction of the linear sweep is reversed and the electrode reactions of intermediates or products (formed during the forward scan) can be detected. le of the experiment is controlled by the scan rate and the total potential traversed can be varied over the range of 10-10 -3 s. A supporting electrolyte maintains the migration of charged reactants and products.The anodic and cathodic peak currents are expressed by the relations is the scan rate of the reaction. Anodic and cathodic peak potentials are dependent on the half-wave potential E 1/2 as follows => 1 -> '/ = = '. '6 @ + the half-wave potential is expressed as,The peak current is directly proportional to the square root of the scan rate,* 1 ∝ √/ , and varies linearly with the value of concentration of the species in solution. The peak potential, do not depend on the concentration of electroactive species.Conventional cyclic voltammetry is especially informative about qualitative aspects of an electrode process.During the present study, chemically modified electrodes were prepared using cyclic voltammetry. The strong adsorption of species to the electrode surface will often change the electrochemical behavior of an electrode. Thick films can be formed on the electrode surface by irreversible adsorption, covalent attachment or as organized assemblies. The electrochemical surface modification with aryl diazonium salts and 1, 3-BDYT moieties will be discussed later on.Chapter 2: Characterization techniques63IMPEDANCE SPECTROSCOPYTo perturb the electrochemical cell with an alternating signal of small magnitude and observe the way in which the system follows the perturbation at steady state is another approach for studying electrode reactions. Some advantages of Impedance techniques are Experimental ability to perform precise measurements upon steady response which can be averaged to long term Treat the response theoretically by linearization of currentpotential characteristics, and

Chapter 3 : 67 Fig. 1 :

 3671 Fig. 1: Cartoon representation of modified SWCNT-based electrode.

Chapter 3 :

 3 SWCNT transparent conductive films 70 the remaining THF. The resulting salt contains THF molecules, probably coordinated to the alkali metal as described in literature.26 (@E+) L RM J 9C@% & S Upon stirring overnight in dry DMSO a homogeneous SWCNT-salt solution is obtained. The relation used was 2 mg of SWCNT salt per mL of DMSO.

Fig. 2 :

 2 Fig. 2: Glass equipment used for the preparation of SWCNT

Fig. 2 :

 2 Fig. 2: Glass equipment used for the preparation of SWCNT-based electrodes.

  Bologna when trying to characterize SWCNT surface modification by Raman spectroscopy, we were constricted to look for a new substrate that does not interact with the instrument. The flexibility was Chapter 3: SWCNT transparent conductive films 73 also an important factor to consider; rigid substrates when placed in the electrochemical cell can present problems in terms of lost of conductivity due to o-ring contact and possibility of micro-break formation. Many materials were tested with solvents, Raman spectrum at different wavelengths, transparency, flexibility, etc., and polystyrene was highlighted as the best candidate for the present study.

Chapter 3 : SWCNT transparent conductive films 74 Fig. 3 :Observations 1 .

 37431 Fig. 3: Raman spectra at 532, 638 and 785 nm excitation laser (green, red and black lines respectively) of: (A) Polystyrene (PS) and (B) Polyethylene terephthalate (PET).

75 2 .

 2 During the dissolution of the alumina there is a partial dissolution of SWCNT aggregates. The fact is in accordance with the idea of tubes trapped on the membrane pores during film preparation. Besides, the aspect of the film changes apparently upon formation of micro channels in the internal structure. The partial lost of nanotubes during alumina dissolution allows water to reach the surface of the SWCNT film (figure4).

Fig. 4 :

 4 Fig. 4: HiPCO-SWCNT film (left) during dissolution of the alumina membrane and (right) after deposition in PS and dried in the oven overnight.

76 3. 3 .

 763 SWCNT FILMS CHARACTERIZATIONCoMoCAT-SWCNT (C-SWCNT) and HiPCO-SWCNT (H-SWCNT) films were studied in parallel. Dilutions of 400, 600 and 1000 μL of the original SWCNT solution were prepared in 50 mL of DMSO respectively and the resulting films containing different quantities of tubes are shown. The techniques used and the information obtained is explained as follows.

Fig. 5 :Chapter 3 :

 53 Fig.5: Near infrared absorption spectra of (from black to blue line): 400, 600 and 1000 μL HiPCO-SWCNT films.

Fig. 6 :

 6 Fig. 6: Scanning electron microscopy of (a) HipCo-SWCNTs powder, (b-c) H-SWCNT film 1 μm and 100 nm scale, (d) CoMoCAT-SWCNTs powder, (e-f) C-SWCNT film 1 μm and 100 nm scale. Films were prepared with 1000 μL of the respective SWCNT solution.

Fig. 7 :

 7 Fig. 7: Atomic force microscopy images of (A) C-SWCNTs (1000 μL) on PET; (B) H-SWCNTs (1000 μL) on PET; (C) H-SWCNTs (400 μL) on PS.

Fig. 8 :

 8 Fig. 8: Advancing and receding angles measured for HiPCO-SWCNT film on glass.

er 3 :

 3 SWCNT transparent conductive films 80 shows surface resistance values for the six films lution concentrations and corresponding surface ) measured for the respective 400, 600, and 1000 μL The presented values result from an average value of several R s values of each film prepared. The corrective factor provided for these measurements was ) accepted when measuring thin (< 1μm) analysis of the film surface can give us ent elements present in the sample surface (see table

  surface modification. At low wavenumber, the main features of the Raman spectra of SWCNTs are the shifts situated between 150 and 350 cm ~1300-1400 nanotubes (sp a tangential mode related to the degree of orden in the sp streching). More details about this technique can b The Raman spectrum of an HiPCO substrate is shown in figure 9.

Fig. 9 :

 9 Fig. 9: Raman spectra of HiPCO used for the measurement was 532

Fig. 9 :

 9 Fig. 9: Raman spectra of HiPCO-SWCNT film on polystyrene. Excitation laser used for the measurement was 532 nm.

er 3 :Fig. 10 :

 310 Fig. 10: Raman spectra of Rice-SWCNT film on silanize glass measured at three different excitation lasers.

  Over this chapter we will explain the preparation and characterization of chemically modified SWCNT-based electrodes. Following the idea of setting up a sensing surface made of SWCNTs upon electrochemical modification, three precursors were chosen: EDA, PhDA, and TMS. Those molecules were selected in accordance with literature because they have been used with similar purpose of direct surface modification of carbonaceous materials through aryl diazonium chemistry. The three precursors have in common an amine group which is necessary for the formation of diazonium salts that will react with the surface of the carbon nanotubes creating new covalent bonds on the electrode surface. Moreover, the covalently linked organic moieties have a second reactive group (depending on the precursor selected) where Chapter 4: Electrochemical surface modification of SWCNT-based electrodes 86 further chemistries can be performed. As SWCNT-based electrodes were chosen for setting up a bioconjugation protocol with the objective of preparing biosensing surfaces based on carbon nanotubes, Cu(I)-catalyzed azide-alkyne cycloaddition or "click"chemistry was selected for anchoring selected probes on the electrode surface. As a first try, HRP enzyme was immobilized on the SWCNT electrode surface. Ongoing with the study, the surface modification of SWCNT devices with 1, 3-BDYT moieties was proposed. Getting inspiration from literature (see chapter 1) the present moiety shows to covalently link to the tubes. The possibility of performing a second substitution on the remaining carbocation and the removal of benzodithiol moiety with Nickel-Raney treatment would lead to a novel carbon-carbon bond formation on the surface of the carbon nanotube.

Fig. 1 :c where 1 . 2 . 5 .Chapter 4 : 87 Fig. 1 :Chapter 4 :

 112548714 Fig. 1: Schematic diagram of processes that can occur at a modified electrode. c

Fig. 2

 2 Fig.2: Aryl SWCNT based electrodes. (a) 4, 4' Phenylenediamine (p (TMS).

Fig. 2 :Chapter 4 :Chapter 4 :Chapter 4 : 91 Fig. 3 :

 2444913 Fig.2: Aryl-amines selected for the electrochemical surface modification of SWCNT based electrodes. (a) 4, 4'-Ethylene dianiline (EDA), (b) p Phenylenediamine (p-PhDA)., and (c) 4-[(Trimethylsilyl) ethynyl

Fig. 4a :Chapter 4 : 92 Fig. 4b :Chapter 4 : 93 Scheme 1 :

 4a4924b4931 Fig. 4a: Cyclic voltammetry of K x [Fe(CN) 6 ] 3-/4-at the electrode surface before (black line) and after (red line) electrochemical modification with 5 mM EDA in PBS; scan rate 100 mV s -1

Chapter 4 : 94 Fig. 5 :Chapter 4 : 95 Fig. 6 :Chapter 4 : 96 A

 49454956496 Fig. 5: Left: Contact angle measured before and after the electrochemical surface modification of SWCNT-based electrodes (on glass) with EDA moieties. Right: Pictures took after SWCNT-based electrodes (on polystyrene) surface modification with PhDA (above) and TMS (below).

Fig. 7 :

 7 Fig. 7: XPS C1s spectra of SWCNT-based electrodes with EDA (left) and TMS (right). The black arrows indicate changes observed. Blue and red lines are the signals obtained after surface modification with EDA and TMS respectively. Black line represents the pristine electrode surface of SWCNTs.

Chapter 4 : 91 Chapter 4 : 99 Fig. 8 :Chapter 4 :

 49149984 Fig. 8: Raman spectra of SWCNT films after chemical transformation of modified surfaces for the three different approaches (EDA, PhDA, and TMS molecules). Excitation laser used was 532 nm for the three measurements.

Fig. 9 :Chapter 4 :

 94 Fig. 9: FIT-IR spectra for the PhDA modified SWCNT film showing different steps of the reaction.

Fig. 10 :Fig. 11 :

 1011 Fig. 10: Alkyl-Ferrocene probe for click chemistry reaction on the modified films.

92

 92

Chapter 4 :Fig. 12 : 93 Chapter 4 :Chapter 4 :Fig. 13b :

 412934413b Fig.12: Zoom of Raman spectra from Figure 11, on the region of related aryl and aryl-triazolic modified surfaces (from black to pink lines: pristine film, PhDA modified surface, azide formation, and click reaction. Right image Sum Frequency generation spectra from: J. Am. Chem. Soc., 2012, 134, 20681.

Chapter 4 : 96 Scheme 2 :

 4962 Scheme 2: Catalytic cycle of HRP (left) and cartoon representation of the enzyme (right).

Fig. 14a :

 14a Fig. 14a: Cyclic voltammetry for the electron transfer of the redox shuttle HQ⇆BQ (1 mM Hydroquinone in PBS) at the SWCNT-modified electrode upon an increasing concentration of hydrogen peroxide. Reference electrode was Ag/AgCl.

Chapter 4 :Fig. 14b :Chapter 4 :

 414b4 Fig. 14b: Michaelis-Menten fitting obtained from curve showed in figure 14a.

Chapter 4 :Fig. 15 :

 415 Fig. 15: Schematic representation for the surface modification of SWCNT based electrodes with BDYT moieties.

Fig. 17 :

 17 Fig. 17: Cyclic voltammetry for CoMoCAT SWCNT based electrode with 10 mM solution of BDYT in acetonitrile. Scan rate: 50 mV s film formed during the process at different magnifications.

Chapter 4 :

 4 Electrochemical surface modification of SWCNT-based electrodes 113 for the electrochemical surface modification of CoMoCAT SWCNT based electrode with 10 mM solution of BDYT in V s -1 . Optical images for the resulting crystalline film formed during the process at different magnifications.This white material remains strongly attached on the SWCNT film after washing it repeatedly with acetonitrile. Optical images showed the presence of crystals/fibers on the electrode surface. As described for glassy carbon, the electrochemical surface modification of SWCNT-based electrodes with BDYT moieties leads to the formation of a thin layer that develops in big crystalline eyes (see figure17 right).

Chapter 4 :Fig. 18 :

 418 Fig. 18: SEM (above) and AFM (below) of the electrochemically modifiedCoMoCAT SWCNT based electrode with 10 mM of BDYT in acetonitrile.

Chapter 4 :Fig. 19 :Chapter 4 :Scheme 4 :

 41944 Fig. 19: C1s and S2p XPS spectra for the pristine (left) and electrochemically modified (right) SWCNT-based electrodes.

Chapter 4 :Fig. 20 :Chapter 4 :Fig. 21a :

 420421a Fig. 20: S2p XPS spectra for 10 mM BDYT dropcast on SWCNT surface.

Fig. 21b :Chapter 4 :

 21b4 Fig. 21b: XPS spectra (S2p) of SWCNT surface modified films with BDYT solution prepared with different number of potential cycles showing the evolution of the ~162 eV band.

Fig. 22 :Chapter 4 :

 224 Fig. 22: Raman spectra of BDYT powder (top left) and after interaction with SWCNT film (top right) with resulting quench in the fluorescence. Evolution of the D-band with the number of potential cycles (bottom).

Chapter 4 :Fig. 23b :

 423b Fig. 23b: AFM of SWCNT modified surfaces with BDYT prepared with different number of potential cycles.

Chapter 4 : 1 .Chapter 4 :

 414 Fig. 23c: CV, AFM, and C1s XPS analysis of (5 mM) electrochemically modified electrode with: 2 (above), 10 (center), and 70 (below) potential cycles. The scan rate was 50 mV s -1 .

Fig. 23d :

 23d Fig. 23d: Low scan sizes AFM images of HiPCO-SWCNT-BDYT electrochemically modified electrode showed in figure 23c. Polymeric material and fibers were observed after 70 potential cycles.

Fig. 25 :

 25 Fig. 25: MALDI-TOF spectra of pristine and modified HiPCO electrode.

Chapter 4 :

 4 Electrochemical surface modification of SWCNT-based electrodes 125 TOF spectra of pristine and modified HiPCO-SWCNT-based

Fig. 26a : 101 Chapter 4 :

 26a1014 Fig. 26a: XRD spectra of CoMoCAT-SWCNT-based electrode before (red line) and after (blue line) electrochemical surface modification with BDYT moieties. Small capture: X-ray diffraction of DB-TTF film deposited at room temperature. 101

Chapter 4 :

 4 Fig. 26b: (a) Diffraction patterns of evaporated DB-TTF film, (b) Out-of-plane diffraction patterns of DB-TTF film prepared by dropcasting (the λ used was 0.154 nm), and (c) crystal structure of the β-phase of DB-TTF along the molecular axis. Sulfur atoms are identified in yellow. 102

Fig. 27 :Chapter 4 :Fig. 28 :Chapter 4 :Fig. 29 :

 27428429 Fig. 27: Electrochemical adsorption of BDYT in ultraflat ITO electrode (left) and the electrochemical adsorption in gold electrode (right).

Chapter 4 :Chapter 4 :Chapter 4 :

 444 Electrochemical surface modification of SWCNT-based electrodes132 4.3. CONCLUSIONS SWCNT-based electrodes have been electrochemically modified following two routes: the electrochemical modification of aryl diazonium salts and the electrochemical surface modification with 1, 3-BDYT. Both approaches lead to successful covalent modification of the electrode surface characterized by Raman and XPS spectroscopy, among other techniques. SWCNT-modified electrodes with aryl diazonium salts undergo further transformation of the remaining active groups. A post cycloaddition reaction with complementary Ferrocene species results on the detection of those moieties on the electrode surface by cyclic voltammetry showing an electrochemical response related to species that have been immobilized in a non-uniform electrode surface explained by Marcus-Hush-Chidsey theory. 93 The electrochemical modification with 1, 3-BDYT was successfully characterized by Raman and XPS analysis (among other techniques) showing BDYT characteristic bands after the interaction with nanotubes. At the same time, fluorescence was quenched after interaction with the SWCNT surface. The growth of the band situated at 162 eV on XPS spectra with the number of potential cycles is related to the covalent attachment of BDYT moieties on the electrode surface. At the same time, there is a shift towards higher energy bindings with increasing potential cycles. Now that we have introduced the idea of DB-TTF moieties in the surface, it is relevant to look again to the spectra showed in figure 22b, where dynamics of the reaction on the electrode surface lead to the formation of a visible band at 164.0 eV (70 cycles). It has been found in literature the XPS spectra of DB-TTF-C 60 moieties showing an s2p band at 164.0 eV. 105 Electrochemical surface modification of SWCNT-based electrodes 133 The study of the reaction under inert atmosphere and a small number of potential cycles leads to the formation of patterns on the electrode surface. It has been characterized by AFM and SEM microscopy. In order to gain some information regarding the formation of these patterns further efforts should be done on an in situ AFM imaging SWCNT electrochemical surface modification experiment. Hypothesis formulated for the mechanism involving formation of twisted ropes patterns. At the same time, the hypothesis of producing DB-TTF molecules in solution during the electrode surface modification reaction (oxidative potential at 0.6 V corresponds with DB-TTF moieties as found in literature 67 ) it is being possibly responsible for the formation of helical structures by π-π stacking interactions between BDYT covalently linked to the surface and DB-TTF molecules in solution. Such interactions could result in a 3D modified electrode surface. Electrochemical surface modification of SWCNT-based electrodes 134 Helical structures were found in literature to be formed through π-π stacking interactions involving naphthyl rings for several TTF compounds. 106

Chapter 5 :

 5 Transparent conductive films from GICs 136 in-plane and c-axis conductivity. Many of the GICs are sensitive to air requiring encapsulation to ensure chemical stability. The sample color gives qualitative information on the stage index: for alkali compounds, yellow, gold, or red is characteristic of stage one compounds, steel blue for stage two, dark-blue for stage three and metallic black for higher stages.

Fig. 2 :Chapter 5 :

 25 Fig. 2: SEM images of GIC bottom: DO

Fig. 3 :

 3 Fig. 3: Graphene film on polystyrene

Fig. 4 :

 4 Fig. 4: AFM of polystyrene foil (height image). Polystyrene substrates are commercially available from Goodfellow.

Fig. 5 :

 5 Fig. 5: AFM image collection of Graphene film on a PS substrate.

Fig. 7 :

 7 Fig. 7: Raman spectrum of graphene film on polystyrene. Excitation wavelength used 532 nm.

Fig. 8 :

 8 Fig. 8: Electrochemical setup of the cell. Contacts were made with crocodile electrodes.

148 5 . 3 . 1 .

 531 SURFACE MODIFICATION UPON ELECTROGRAFTING WITH ARYL DIAZONIUM SALTSThe electrografting of aryl diazonium salts on graphene films was performed with PhDA moieties following the same procedure as for the surface modification of SWCNT films.The graphene film was placed in the electrochemical cell as the working electrode. The reference electrode was Ag/AgCl in a saturated solution of KCl and the acidic solution (HCl) ensured conductivity in solution acting as a supporting electrolyte. 5 mM of p-PhDA was prepared in a 0.5 M HCl, and parallel to that another solution 0.1 M NaNO 2 was prepared. The stoichiometry was calculated for the reactivity of only one amino group and the corresponding volumes were added to the cell. P-PhDA solution turns yellow upon addition of NaNO2 equivalents indicative for the formation of diazonium salts. Besides, formation of bubbles during the reaction (-N 2 ) is indicative for nitrogen elimination with the ongoing reaction.

Fig. 9 :

 9 Fig. 9: Cyclic voltammetry for the electrografting graphene-based electrodes. Scan rate of 100

Chapter 5 :Fig. 10 :

 510 Fig. 10: Raman spectra of graphene film before (black line) and after (red line) electrochemical surface modification with PhDA.

Chapter 5 :

 5 Transparent conductive films from GICs 151Taking advantage of redox properties of ferrocene containing species, cyclic voltammetries were run in a Phosphate buffered saline solution (PBS) to investigate the efficacy of the performed reaction (see figure11).

Fig. 11 :Chapter 5 :

 115 Fig. 11: Analysis of the voltammetric curve of click-modified graphene-based electrodes with ferrocene containing moieties. CV measured in PBS at a scan rate of 30 mV s -1 .

Fig. 12a : 2 .Chapter 5 :

 12a25 Fig. 12a: Analysis of the scan rate dependence with the voltammetric current of 1 mM FcMeOH in PBS on graphene-based electrode. The inset figure shows linear response of peak currents vs. v 1/2 .

Fig. 12b :Chapter 5 :

 12b5 Fig. 12b: Analysis of the scan rate dependence with the voltammetric current of rinsed graphene-based electrode (figure 12a) in PBS. The inset figure shows linear response of peak currents vs. scan rate.

  The graphene film was placed in the electrochemical cell and introduced inside the glove box. The reference electrode was prepared inside the box before the measurement being Ag/AgCl wire in 0.1 M tetrabutylammonium hexafluorophosphate (TBA + PF6 -) acetonitrile solution. The electrodeposition Chapter 5: Transparent conductive films from GICs 155 was carried out in 5 mM 1, 3-BDYT acetonitrile solution with 0.1 M TBA + PF6 -by performing a variable number of potential cycles between 2 and 20.As shown in figure13the radical species is formed starbng at ̴ 0.15 V. The efficiency of the process, measured by the passivation of the electrode surface, is lower than in the case of SWCNTs.

Fig. 13 :

 13 Fig. 13: Cyclic voltammetry for the electrochemical surface modification of graphene film with 5 mM 1, 3-BDYT in acetonitrile. Left: 2 cycles. Right: 20 cycles. Scan rate: 50 mV s -1 .

Chapter 5 :Fig. 14 :

 514 Fig. 14: Raman spectra of graphene film before (black) and after (red and blue lines: 2 and 20 potential cycles) surface modification normalized to the G-band.

Chapter 5 :Fig. 15 :(

 515 Fig. 15: XPS spectra of BDYT surface modified graphene film. The arrow shows peaks detected after surface modification attributed to sulfur atoms (2p and 2s).

Chapter 5 :

 5 Transparent conductive films from GICs 158 supporting electrolyte (tetrabutylammonium hexafluorophosphate) present during the performance of the reaction. Analogously, traces of fluorine and phosphor were also found in SWCNT-BDYT functionalized films. Atomic Force Microscopy images of the graphene film were obtained before and after electrochemical modification with BDYT moieties (see figure16a and 16b).

Fig. 16a: AFM images of graphene film before and after electrochemical surface modification with BDYT. Chapter 5 :

 5 Fig. 16a: AFM images of graphene film before and after electrochemical surface modification with BDYT.

Fig. 16b :

 16b Fig. 16b: AFM images of graphene film before and after electrochemical surface modification.

  The electrochemical surface modification of graphene films have been achieved following two different routes (i) electrografting of aryl diazonium salts and (ii) electrophylic addition of BDYT on the graphene film surface.The electrochemical surface modification with PhDA, transformation of the remaining amino groups and click-reaction leads to the formation of new triazolic rings containing ferrocene moieties which were detected by cyclic voltammetry. The immobilized species through a polymeric aryl film show slower electron transfer with higher peak separation; the strong interaction of ferrocene with electron rich systems, as graphene films, leads to a strong e Prepared by Ph.D. student Y. Wang, CRPP-CRNS, Pessac.

16: Copper (I) From: Direct evidence of a dinuclear copper intermediate in Cu (I) azide alkyne cycloadditions

	4,42,43,44 1.3.2. AZIDE-ALKYNE CU (I)-CYCLOADDITION REACTION: CLICK-CHEMISTRY The copper (I)-catalyzed azide-alkyne cycloaddition reactions, named click-chemistry" due to facility of conditions for high-yield reactions by simply was introduced in 2001 by Sharpless and coworkers opening a new pathway for versatile chemical reactions in synthetic chemistry. The mech Fokin and M.G. Finn autocatalytic systems. At that time, the precise nature of the binuclear copper system responsible for an effic Worrell, J.A. Mali dinuclear copper intermediate solving issues present at that time mechanism was introduced in 2001 by Sharpless and coworkers opening a new pathway for versatile chemical reactions in synthetic chemistry. 46,47 The mechanism of the in situ reaction was studied by V. O. Rodionov, V. V. Fokin and M.G. Finn 48 with the objective of developing new autocatalytic systems. At that time, the precise nature of the binuclear copper system responsible for an efficient catalysis was not resolved Worrell, J.A. Malik, and V.V. Fokin 51 showed evidence of an involvement of a dinuclear copper intermediate solving issues present at that time Fig. Chapter 1: Introduction mechanism (see figure 16).
	"clicking" the two reactive groups 45 is expected to provide in the future years
	excellent opportunities for the construction at the nano-scale. This concept

: Copper (I)-catalyzed azide-alkyne cycloaddition reaction mechanism. Direct evidence of a dinuclear copper intermediate in Cu (I) azide alkyne cycloadditions, Science,(2013),457.

	was introduced in 2001 by Sharpless and coworkers opening a new pathway
	V. O. Rodionov, V. V.
	with the objective of developing new ligands and
	autocatalytic systems. At that time, the precise nature of the binuclear copper
	ient catalysis was not resolved. 49 50 In 2013, B.T.
	showed evidence of an involvement of a
	dinuclear copper intermediate solving issues present at that time in the
	24

alkyne cycloaddition reaction mechanism. Direct evidence of a dinuclear copper intermediate in Cu (I) azide-

	Chapter 1: Introduction
	Click-chemistry in material science represents a big advantage for surface
	modification after the successful grafting of an organic layer. 52 Jean-François
	Lutz published a minireview showing the exponential growth publications
	using click-chemistry over the last few years. 53
	25

. 18: Schematic representation of click-chemistry reaction from: Sci., (2012), 27, 985-1003 (above) and Ferrocenes contai during the present study (below). 26 for the preparation of gold modified surfaces as platforms for 60

chemistry reactions, complementary (see figure

18

).

61 chemistry reaction from: Prog. Pol. (above) and Ferrocenes containing probes used

	Chapter 1: Introduction
	In this work, for setting up the immobilization procedure, ferrocene moieties
	were used as redox probes during click chemistry reactions. After reaction,
	probes are detectable by cyclic voltammetry. The Organic chemistry group at
	Bologna University has synthesized two different ferrocenes containing
	molecules as presented in figure 20.
	1.3.3. ELECTROPHYLIC ADDITIONS: 1, 3-
	BENZODITHIOLILYUM TETRAFLUOROBORATE
	A novel approach in SWCNT-based electrodes surface modification was
	inspired by a theoretical work by Y. Jaeyong ET. al. 62 describing an adsorption
	model of 1, 3-BDYT (BDYT) on SWCNT surface. Later on it was found that the
	reactivity of BDYT is selective for metallic rather than for semiconducting
	27

SWCNTs: Jeong-O Lee and Hyunju Chang,

[START_REF] So | Selective Suppression of Conductance in Metallic Carbon Nanotubes[END_REF]

proved the adsorption of BDYT derivatives on SWCNT surfaces leading to a highly enhanced D-band in Raman spectra (see figure

19

).

Table . 2: XPS analysis of HiPCO powder and HiPCO from purified and non purified sources.

 .

Table . 2: XPS analysis of HiPCO powder and HiPCO-SWCNT films resulting from purified and non purified sources.

 .

	er 3: SWCNT transparent conductive films
	The presence of sulfur could be due to reaction with DMSO during disolution
	of nanotubes. At this point, we considered that non
	films were the best candidates to continue with the study of the
	electrochemical surface modification of SWCNT
	81

XPS spectrum for graphene-based film. Carbon 1s and Oxygen 1s bands are shown as small captures. The arrows indicate the band position.

	Chapter 5: Transparent conductive films from GICs
	XPS shows the presence of nitrogen and silicon atoms (0.46 and 0.23 atomic %
	respectively) together with carbon (95.82 %) and oxygen (3.47 %) thus
	indicating there is no potassium residues (see figure 6 and table 1).
	Fig. 6: Name Peak BE	Height	FWHM	Area (P)	Area (N)	At. %
			Counts	eV	CPS.eV
	C1s	284,59	23218,71 1,1	36655,39 0,6	95,84
	N1s	403,62	132,79	0,37	303,97	0	0,46
	O1s	532,44	1152,81	2,98	3587,03	0,02	3,47
							145

Table 1 : XPS of graphene-based film shows the quantification of different atoms present in the surface.

 1

	Chapter 5: Transparent conductive films from GICs

Table 2 : Atomic values found for surface modified graphene-based film with BDYT.

 2

	C1s	284,46 27455,37	1,08 40290,75 0,66 94,52
	O1s	532,26 1077,83	2,76 3285,83 0,02 2,85
	F1s	686,1	492,24	3,15 1840,54 0,01 1,13

Nanotubes Grown Using a Solid Supported Catalyst. J. Am. Chem. Soc. 125, 11186-11187. (10) Collins, P. G.; Smalley, R. Nanotube Nanodevice. Science (80-. ). 1997, 278, 100-102. (11) McCreery, R. L. Advanced Carbon Electrode Materials for Molecular Electrochemistry. Chem. Rev. 2008, 108, 2646-2687. (12) Dresselhaus, M. Graphene: A Journey through Carbon Nanoscience. MRS Bull. 2012, 37, 1319-1320. (13) Novoselov, K.; Geim, A.; Morozov, S. Electric Field Effect in Atomically Thin Carbon Films. Science (80-. ). 2004, 306, 666-669. (14) Stankovich, S.; Piner, R. D.; Chen, X.; Wu, N.; Nguyen, S. T.; Ruoff, R. S. Stable Aqueous Dispersions of Graphitic Nanoplatelets via the Reduction of Exfoliated Graphite Oxide in the Presence of Poly(sodium 4-Styrenesulfonate). J. Mater. Chem. 2006, 16, 155-158. (15) Lee, Y.; Bae, S.; Jang, H.; Jang, S.; Zhu, S.-E.; Sim, S. H.; Song, Y. Il; Hong, B. H.; Ahn, J.-H. Wafer-Scale Synthesis and Transfer of Graphene Films. Nano Lett. 2010, 10, 490-493. (16) Xu, Y.; Liu, Z.; Zhang, X.; Wang, Y. A Graphene Hybrid Material Covalently Functionalized with Porphyrin: Synthesis and Optical Limiting Property. Adv. Mater. 2009, 21, 1275-1279. (17) Novoselov, K.; Geim, A.; Morozov, S. Two-Dimensional Gas of Massless Dirac Fermions in Graphene. Nature 2005, 1-6. Bibliography 165 (18) Niyogi, S.; Bekyarova, E.; Itkis, M. E.; McWilliams, J. L.; Hamon, M. a; Haddon, R. C. Solution Properties of Graphite and Graphene. J. Am. Chem. Soc. 2006, 128, 7720-7721. (19) Park, S.; Ruoff, R. S. Chemical Methods for the Production of Graphenes. Nat. Nanotechnol. 2009, 4, 217-224. (20) Gengler, R. Y. N.; Spyrou, K.; Rudolf, P. A Roadmap to High Quality Chemically Prepared Graphene. J. Phys. D. Appl. Phys. 2010, 43, 374015-374034. (21) Coleman, J. N.; Lotya, M.; O'Neill, A.; Bergin, S. D.; King, P. J.; Khan, U.; Young, K.; Gaucher, A.; De, S.; Smith, R. J.; et al. Two-Dimensional Nanosheets Produced by Liquid Exfoliation of Layered Materials. Science 2011, 331, 568-571. (22) Niyogi, S.; Hamon, M. a.; Hu, H.; Zhao, B.; Bhowmik, P.; Sen, R.; Itkis, M. E.; Haddon, R. C. Chemistry of Single-Walled Carbon Nanotubes. Acc. Chem. Res. 2002, 35, 1105-1113. (23) Margine, E. R.; Bocquet, M.-L.; Blase, X. Thermal Stability of Graphene and Nanotube Covalent Functionalization. Nano Lett. 2008, 8, 3315-3319. (24) Bekyarova, E.; Itkis, M. E.; Ramesh, P.; Berger, C.; Sprinkle, M.; de Heer, W. a; Haddon, R. C. Chemical Modification of Epitaxial Graphene: Spontaneous Grafting of Aryl Groups. J. Am. Chem. Soc. 2009, 131, 1336-1337. Bibliography 166 (25) Kuila, T.; Bose, S.; Mishra, A. K.; Khanra, P.; Kim, N. H.; Lee, J. H. Chemical Functionalization of Graphene and Its Applications. Prog. Mater. Sci. 2012, 57, 1061-1105. (26) Pénicaud, A.; Poulin, P.; Derré, A.; Anglaret, E.; Petit, P. Spontaneous Dissolution of a Single-Wall Carbon Nanotube Salt. J. Am. Chem. Soc. 2005, 127, 8-9. (27) Catheline, A.; Vallés, C.; Drummond, C.; Ortolani, L.; Morandi, V.; Marcaccio, M.; Iurlo, M.; Paolucci, F.; Pénicaud, A. Graphene Solutions. Chem. Commun. (Camb). 2011, 47, 5470-5472. (28) Pénicaud, A.; Drummond, C. Deconstructing Graphite: Graphenide Solutions. Acc. Chem. Res. 2013, 46, 129-137. (29) Dresselhaus, M. S. Fifty Years in Studying Carbon-Based Materials. Phys. Scr. 2012, T146, 014002. (30) Cohen, M. L. Nanotubes, Nanoscience, and Nanotechnology. Mater. Sci. Eng. C 2001, 15, 1-11. (31) Zhao, W.; Tan, P.; Liu, J.; Ferrari, A. Intercalation of Few-Layer Graphite Flakes with FeCl3: Raman Determination of Fermi Level, Layer by Layer Decoupling, and Stability. J. Am. Chem. Soc. 2011, 2-7. (32) Delamar, M.; Hitmi, R. Covalent Modification of Carbon Surfaces by Grafting of Functionalized Aryl Radicals Produced from Electrochemical Reduction of Diazonium Salts. Am. Chem. Soc. 1992, 114, 5884-5886. Bibliography 167 (33) Allongue, P.; Delamar, M. Covalent Modification of Carbon Surfaces by Aryl Radicals Generated from the Electrochemical Reduction of Diazonium Salts. J. Am. Chem. Soc. 1997, 119, 201-207. (34) Bahr, J. L.; Yang, J.; Kosynkin, D. V; Bronikowski, M. J.; Smalley, R. E.; Tour, J. M. Functionalization of Carbon Nanotubes by Electrochemical Reduction of Aryl Diazonium Salts: A Bucky Paper Electrode. J. Am. Chem. Soc. 2001, 123, 6536-6542. (35) Marcoux, P.; Hapiot, P.; Batail, P.; Pinson, J. Electrochemical Functionalization of Nanotube Films: Growth of Aryl Chains on Single-Walled Carbon Nanotubes. New J. Chem. 2004, 28, 302-307. (36) Kongsfelt, M.; Vinther, J. Combining Aryltriazenes and Electrogenerated Acids To Create Well-Defined Aryl-Tethered Films and Patterns on Surfaces. J. … 2011, 3788-3791. (37) Joyeux, X.; Mangiagalli, P.; Pinson, J. Localized Attachment of Carbon Nanotubes in Microelectronic Structures. Adv. Mater. 2009, 21, 4404-4408. (38) Be, D. Direct Modification of a Gold Electrode with Aminophenyl Groups by Electrochemical Reduction of in Situ Generated Aminophenyl Monodiazonium Cations. 2006, 4755-4763. (39) Clavé, G.; Campidelli, S. Efficient Covalent Functionalisation of Carbon Nanotubes: The Use of "click Chemistry."Chem. Sci. 2011, 2, 1887-1896. (40) Palacin, T.; Khanh, H. Le; Jousselme, B.; Jegou, P.; Filoramo, A.; Ehli, C.; Guldi, D. M.; Campidelli, S. Efficient Functionalization of Carbon Bibliography 168 Nanotubes with Porphyrin Dendrons via Click Chemistry. J. Am. Chem. Soc. 2009, 131, 15394-15402. (41) Wang, H.-X.; Zhou, K.-G.; Xie, Y.-L.; Zeng, J.; Chai, N.-N.; Li, J.; Zhang, H.-L. Photoactive Graphene Sheets Prepared by "Click" Chemistry. Chem. Commun. 2011, 47, 5747-5749. (42) Balasubramanian, K.; Burghard, M. Biosensors Based on Carbon Nanotubes. Anal. Bioanal. Chem. 2006, 385, 452-468. (43) Chen, B.; Flatt, A. K.; Jian, H.; Hudson, J. L.; Tour, J. M. Molecular Grafting to Silicon Surfaces in Air Using Organic Triazenes as Stable Diazonium Sources and HF as a Constant Hydride-Passivation Source. Chem. Mater. 2005, 17, 4832-4836. (44) Hauquier, F.; Pastorin, G.; Hapiot, P.; Prato, M.; Bianco, A.; Fabre, B. Carbon Nanotube-Functionalized Silicon Surfaces with Efficient Redox Communication. Chem. Commun. 2006, 4536-4538. (45) Such, G. K.; Johnston, A. P. R.; Liang, K.; Caruso, F. Synthesis and Functionalization of Nanoengineered Materials Using Click Chemistry. Prog. Polym. Sci. 2012, 37, 985-1003. (46) Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Click Chemistry: Diverse Chemical Function from a Few Good Reactions. Angew. Chemie Int. Ed. 2001, 40, 2004-2021. (47) Rostovtsev, V. V; Green, L. G.; Fokin, V. V; Sharpless, K. B. A Stepwise Huisgen Cycloaddition Process: copper(I)-Catalyzed Regioselective Bibliography 169 "Ligation" of Azides and Terminal Alkynes. Angew. Chem. Int. Ed. Engl. 2002, 41, 2596-2599. (48) Rodionov, V. O.; Fokin, V. V.; Finn, M. G. Mechanism of the Ligand-Free CuI-Catalyzed Azide-Alkyne Cycloaddition Reaction. Angew. Chemie 2005, 117, 2250-2255. (49) Bock, V. D.; Hiemstra, H.; van Maarseveen, J. H. CuI-Catalyzed Alkyne-Azide "Click" Cycloadditions from a Mechanistic and Synthetic Perspective. European J. Org. Chem. 2006, 2006, 51-68. (50) Kabalah-Amitai, L.; Mayzel, B.; Kauffmann, Y.; Fitch, A. N.; Bloch, L.; Gilbert, P. U. P. a; Pokroy, B. Vaterite Crystals Contain Two Interspersed Crystal Structures. Science 2013, 340, 454-457.

2003,

(51) Worrell, B. T.; Malik, J. a; Fokin, V. V. Direct Evidence of a Dinuclear Copper Intermediate in Cu(I)-Catalyzed Azide-Alkyne Cycloadditions. Science 2013, 340, 457-460. (52) Binder, W. H.; Sachsenhofer, R. "Click" Chemistry in Polymer and Materials Science. Macromol. Rapid Commun. 2007, 28, 15-54. (53) Lutz, J.-F. 1,3-Dipolar Cycloadditions of Azides and Alkynes: A Universal Ligation Tool in Polymer and Materials Science. Angew. Chem. Int. Ed. Engl. 2007, 46, 1018-1025. (54) Ganesh, V.; Sudhir, V. S.; Kundu, T.; Chandrasekaran, S. 10 Years of Click Chemistry: Synthesis and Applications of Ferrocene-Derived Triazoles. Chem. Asian J. 2011, 6, 2670-2694.

SUMMARY

Since the discovery of the new allotropes of carbon, modified carbon nanotubes and graphene surfaces have been proposed for several technological applications. Carbon nanotubes and graphene have been already proposed as excellent candidates to improve (bio) sensor performances as they display remarkable electronic properties and the ability to act as individual nanoelectrodes, display an excellent low-dimensional charge carrier transport, and promote surface electrocatalysis. Films are made from such nanomaterials that show chemical and electrochemical inertness, physical robustness as well as adjustable transparency and optical features. Their high surface area and wide versatility in functionalization can be exploited to covalently bind biomolecules, enzymes, antibodies and DNA fragments onto the nanostructured surface. In Chapter 4, the electrochemical surface modification of SWCNT films is described. Two routes have been investigated and the resulting modified surfaces were in both cases fully characterized. Both routes lead to the creation of novel covalent carbon-carbon bonds between the tube surface and the anchored moiety. In the first case, the well-known electrochemical grafting of aryl diazonium salts was exploited to anchor functional groups onto the SWCNT film surface suitable for their subsequent click-reaction with ferrocenecontaining moieties.

Summary 181

In the second case, the electrophylic addition of electrogenerated BDYT radicals was investigated for the first time.

The aryl-modified SWCNT surface was successfully reacted with an enzyme (HRP), to prove the viability of bioconjugation routes with the present modified nanocarbon surfaces.

In Chapter 5 the electrochemical surface modification of graphene films produced from GIC solutions are described. Earlier GIC synthesis, dissolution and deposition are described at the beginning of the chapter. The electrochemical surface modification of graphene films f , following the two routes explained for the electrochemical surface modification of SWCNT-based electrodes, is finally described.

f Prepared by Y, Wang, CRPP-CNRS, Pessac.