Ana Borras

Manuel Macias-Montero

Pablo Romero-Gomez

Agustin R Gonzalez-Elipe

Supported plasma-made 1D heterostructures: perspectives and applications

come

Introduction

Classical thin film deposition methods using vacuum based technologies, and particularly plasma related methods, are generally intended to get very compact thin films. This has been traditionally the case when dealing with mechanical (e.g., hard and friction resistant coatings), protective (e.g., corrosion resistant coatings) or optical (e.g., high refraction index materials) applications [1,2]. To get a high compactness, there are several experimental approaches with the common concept of energetically exciting the arriving particles to enhance their mobility and rearrangement within the bulk of the film. The ion beam assisted procedures are a clear example of this approach [3].

However, the advent of new applications based on the use of nanostructured and porous thin films or other surface nanostructures (e.g., superhidrophobic/superhydrophilic surfaces, dye synthesized and hybrid solar cells, photocatalytic devices, electrodes for electrochemical and photo-electrochemical cells, piezoelectric brushes, fluorescent devices and other examples in electronics and photonics has fostered the development of new deposition procedures or the modification of the existing ones with the purpose of getting efficient methodologies of surface and thin film nanostructuring [4][5][6] and the preparation of supported 1D nanostructures such as nanowires (NWs), nanofibres (NFs), nanoribbons, nanotubes (NTs), etc. [7][8][9][10][11][12]. Numerous examples are available in the most recent literature where different supported 1D nanostructures are prepared by using wet chemical and electrochemical routes [13], vapour phase condensation methods (e.g. vapour-liquid-solid, VLS methods) [14], solution-phase methods [15], template directed synthesis [16] or other evaporation based approaches [17,18], etc. An important advantage of the 1D over the 2D nanostructures and thin films is the facile fabrication of 1D defect-free heterostructures, and the tailored synthesis of multicomponent materials and heterojunctions with controlled 1D morphology (e.g., core@shell nanofibres, metal decorated CNTs and oxide nanowires, nanobrushes, segmented, cross junctions or branched 1D nanostructures) [10,[19][20][21].

On other hand, plasma deposition and, in general, plasma processing have been successfully used for the surface nanostructuring of materials and, to a much lesser extent, for the preparation of supported 1D nanostructures, although a deeper understanding of the physical phenomena involved in the development of these nanostructures is still needed [22]. For example, quite interesting plasma based methods have been developed for the preparation of oxide NFs and nanorodos [23,24], nanoparticles [25] or the formation of deposited vertically aligned carbon nanotubes (CNTs) [26][27][28][29]. In this case, the last achievements in the formation of these nanostructures have enabled the fabrication of devices like flat panel displays, X-ray sources, etc. A common feature for the plasma fabrication of carbon nano-structures is the need of supported metal particles. Besides other phenomena, the effect of the metal nanoparticles has been discussed in terms of a catalytic action favouring the arrangement and diffusion of the carbon species arriving to the surface from the plasma phase [28,29].

Plasma assisted methodologies present significant advantages over classical sol-gel, and other chemical and physical vapour deposition processes. Recent advances in this emerging topic of plasma-assisted fabrication of nanostructures are stressed in excellent reviews on the subject [30]. Among the advantages of plasma processes, it has been quoted that they are relatively low cost procedures, environmentally friendly (i.e., solventless method) and scalable at wafer scale for direct deposition onto electronic and photonic devices while providing a precise control over the composition of the deposited materials. Due to these advantages, during the last years plasma technology has being systematically used for the fabrication of 1D nanofibres and other heterostructures [25,[29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47]. As already mentioned, most works in this field deal with the fabrication of heterostructures formed by CNTs and carbon nanofibers where the metal particle acts as a catalyst of the growth process. Just as examples of this type of heterostructures let us mention the case of Co nanoparticles encapsulated in CNTs that were synthesised by a one-step PECVD method at high pressures and substrate temperatures [32], that of Ti-coated CNTs fabricated by inductively-coupled plasma enhanced chemical vapour deposition (ICP-CVD) and Ti sputtering for field emission applications [33][34][35] or Cu-C hybrid nanosystems produced by means of plasma deposition of carbon on copper metal seeds [28]. The results of Penza et al. about the decoration of CNTs with metal (Ag, Au, Pt and Ru) nanoparticles are also very promising in the field of nanosensor applications [36].

Less numerous are the examples of nanostructures of other materials formed by plasma deposition/processing. Thus, for example, Chen and co-workers [37] have shown the fabrication of metal nanoparticles embedded in dielectric nanofibres and core@shell nanofibres in a sandwich-like microreactor combining H 2 plasma with high microwave power and substrate temperatures of 530 ºC. Inorganic n-p heterojunctions based on GaN/InGaN 1D heterostructures have been fabricated by plasma-assisted molecular beam epitaxy and used for the development of light emitting diodes [41]. Formation of complex oxide semiconducting 1D heterostructures have been also recently reported [42]. In this case, a TiO 2 shell is deposited by plasma sputtering deposition onto ZnO nanorods previously deposited by a hydrothermal method. Particularly interesting in this context are also the formation of oxide NFs by the direct interaction of high density plasmas of oxygen on the surface of metals [31]. In previous publications we have also shown that supported Ag@TiO 2 NFs are formed at low temperatures when titanium oxide is plasma deposited on a silver metal foil previously treated with oxygen plasma [46,47].

Metal seeds are commonly used by many methods of preparation of supported NFs, particularly those based on chemical routes or the so called vapour-liquid-solid and vapour-solid methods (VS) [10][11][12]48]. It has been already discussed that metal nanoparticles are used for the plasma fabrication of CNTs and other carbon nanostructures [29]. A common feature of these procedures, usually carried out at relatively high temperatures, is that the metal nanoparticles participate actively in the NF formation through some catalytically induced phenomena (i.e., by inducing a chemical change in the incoming particles that favour their integration into the fibres) and/or by the dissolution of the nanofibre forming element within the seed particle forming an active alloy that favours the fibre growth [10-12, 30, 48, 49]. The case that we would like to deal with in detail in the present work is the use of metal seeds for the plasma formation of composite NFs where no catalytic effect has been detected. This was the case during the preparation of Ag@TiO 2 nanofibres mentioned above, where the NF growth mechanism was related with the surface mobilisation of the silver and the effect of inhomogeneities of the plasma sheath in inducing a preferential growth of the nanostructures. Recently, the idea that plasma sheaths inhomogeneities can be important in this kind of processes has been claimed to account for the pulsed laser deposition of Ga-doped ZnO NFs [50]. In the present work we aim to overview previous results in the area and extend the understanding of morphological features on the formation of oxide NFs by exploring the possibilities of the metal seed methodology for the fabrication of supported 1D heterostructures on processable substrates. For the sake of clarity, we have focussed this study on the morphology of the obtained nanostructures, although differences in crystallinity, density, and other properties have been also found. Examples are shown for metal seeds of Ag, Au and Pt and various oxides (SiO 2 , TiO 2 and ZnO). An extraordinary wealth of different kinds of supported NFs and, in general surface nanostructures, are obtained by modifying the characteristics of the metal seeds (size and percolation degree of particles, equivalent thickness of the metal layer, pretreatment with a plasma of oxygen, etc.) and the deposition temperature, always in ranges much lower than the usual processing temperatures utilize by other vapour or plasma based procedures [23][24][25][26][27][28][29][30]. We also try to give some explanations to account for the observed results where basic processes like stress relaxation, local confinement and deformation of the electric field associated to the plasma sheath, etc. are taken into account. Lacking of theoretical descriptions of these basic phenomena (some recent theoretical works have tried to account for the growth of NFs under plasma but not for their formation as an effect of metal seeds and plasma sheath inhomogeneities [51]), the proposed models are still qualitative and phenomenological, although they are able to account for the observed processes and predict new scenarios for the surface nanostructuring of deposited oxides by metal seedmediated plasma enhanced chemical vapour deposition (PECVD).

Experimental plasma processes used for the development of nanostructures

A full account of the experimental conditions used for the growth and characterization of the oxide nanostructures can be found in the supplementary information. Here we will comment on some basic aspects of the plasma conditions and metal substrate treatment used for the growth of the oxide nanostructures. TiO 2 , SiO 2 and ZnO were deposited at various substrate temperatures by PECVD in a plasma reactor with a downstream configuration and using pure O 2 or mixtures Ar+O 2 as plasma gas.

Titanium tetraisopropoxide (TTIP), hexamethyldisilazane HDMS, and diethyl Zinc (DEZ) were used as a titanium, silicon and zinc oxide precursor respectively. An important parameter for the development of NFs was the substrate temperature during deposition. A threshold temperature of 130º C or higher had to be used for NF formation on silver or silver/silicon substrates. Temperature was measured with a thermocouple placed besides the position of the samples.

In most experiments with silver foils or silver layer/particles deposited on silicon, the substrates were previously subjected to a plasma of oxygen in the same chamber used for the deposition of the oxides.

Silver and gold particles/layers were deposited onto the substrates by sputtering from a metal wire placed at 3 cm from the substrates in a chamber filled with Ar. In some cases substrate temperature during deposition was set a T > 200 ºC in order to increase the average size of the deposited metal particles. The Pt/Si(100) substrates were fabricated by chemical vapor deposition from a Pt(acac)2 precursor and posterior annealing at elevated temperatures.

A first step in the synthesis of metal@oxide nanofibres: Control on the micro/nanostructure of oxide thin films.

Formation of oxide thin films can be considered as a first step for the comprehension of the plasma processes leading to the synthesis of 1D heterostructures. This section is therefore dedicated to discuss some of the factors controlling the morphology of oxide thin films.

3.1Columnar thin films of TiO 2 and ZnO on flat and non-metal substrates

Previous studies on plasma deposited TiO 2 and ZnO thin films have shown that they may present different microstructures depending on deposition conditions and particularly on the plasma gas composition [52][START_REF] Barranco | Thin Sol[END_REF][54][55][56][57]. Thus, for example, either columnar or homogeneous TiO 2 thin films can be obtained by using pure O 2 or a mixture Ar+O 2 as plasma gas, respectively [55][56][57]. The formation of homogeneous thin film microstructures by PECVD has been associated with a growing mechanism where surface diffusion of ad-species is the controlling process [55][56][57], while the columnar growth has been related with the existence of shadowing effects and a high sticking coefficient of the ad-species coming from the plasma [55,56,60]. In connection with this columnar growth of thin films, it has been realized that in PECVD processes the particles arrive with a wide distribution of incoming angles and that the actual angular distribution is a key factor in determining the microstructure developed by the films [58,59]. Figure 1 shows as an example two cross-section scanning electron microscope (SEM) micrographs obtained for columnar amorphous TiO 2 (Fig. 1 a)) and lowcrystallinity columnar ZnO (Fig. 1 b)) thin films prepared at 130 ºC with an oxygen plasma and Ti-tetraixopropoxide (TTIP) and diethyl Zinc (DEZ) precursors for the TiO 2 and ZnO respectively as explained in the experimental section. For these two film preparations the highly oxidative character of the plasma ensures that the Zn or Ti containing ad-species impinging onto the growing film do not contain carbon in their structure [55,56] and therefore possess a high sticking coefficient. This reduces the relative importance of the diffusion processes of ad-species and favours the development of the observed columnar microstructures. We must note that the obtained films were either amorphous (i.e., TiO 2 ) or presented low crystallinity (i.e.

ZnO), so that crystallization-induced changes in the microstructure can be neglected.

This picture can be altered if a crystallization driven process occur during the thin film deposition by PECVD. In case that crystallization occurs (e.g., by increasing the substrate temperature), previous investigations on the PECVD growth of anatase have shown that the thin film microstructure is affected not only by shadowing, diffusion or other similar processes, but mainly by the dynamics of formation of crystallites [60].

Metal substrates and crystallinity of metal oxide films

By the depositions in Fig. 1 and, in general, in most works dealing with the formation of oxide thin films, the role of the substrate is usually overlooked, even if evidences exist that its chemical nature and, particularly its metal or insulator character, may have a great importance in determining the microstructure and crystallinity of the films deposited by PECVD. These differences are particularly important during the PECVD growth of crystalline thin films. A clear evidence of the importance of the metal character of the substrate in controlling the crystallinity of the deposited films is provided by the images in Figure 2a (see also ref. 60). This figure shows a SEM micrograph of the surface of a TiO 2 crystalline thin film deposited at 250 ºC on a silicon substrate that had been partially covered by a silver layer. The crystalline character of this film and the others films reported in Fig. 2 has been proved by X-ray diffraction (XRD) (data not shown). The micrograph has been taken at the limit of the silver layer to evidence that the film microstructure is completely different on the silver covered zone than on the bear silicon substrate. In the former case the TiO 2 crystallites are smaller in size and appear randomly oriented on the surface, while in the second they aggregate in certain zones forming well defined crystal columnar habits whose origin can be accounted for by the Kolmogorov model of crystal growth [56]. An enhanced crystallinity of the deposits is also evidenced in Fig. 2b) and c) showing a comparison of the normal view microstructure of ZnO thin films deposited at 130 ºC on a silicon wafer and on an Ag foil. In this latter case the crystal size is much higher, an observation that runs parallel with an increase in the size of crystal domains as determined by XRD (data not shown). The clear differences in crystal aspect constitute additional evidence on the effect of a metal on the growth of crystalline films.

Significant differences are also found when deposition is carried out on a metal thin layer deposited on a silicon substrate. Some micrographs exemplifying this situation are shown in Figures d) and e), corresponding to crystalline ZnO thin films deposited at 250 ºC on a silicon wafer and on a silicon wafer previously covered with a thin gold layer.

In both cases the thin film microstructure is columnar, but in the second the height of the columns and their aspect ratio are much higher than in the former. In summary, these experiments clearly show an enhanced tendency of the crystalline thin films (i.e.

anatase and wurtzite phases respectively) of the two oxides to form nanostructures when they are deposited on noble metal layers. Different processes can be tentatively proposed to account for such enhancement in the crystal development: i) a fast crystal development fostered by the crystalline surface of the metal substrate at the very first steps of the crystal growth, i.e. at the nucleation stage [60] and ii) a possible catalytic effect on the growth driven by the metal layer. As we will see in the next section this latter hypothesis must be discarded.

Metal islands and the preferential deposition of oxides

Additional changes in the thin film microstructure are obtained if, instead of a continuous metal layer, the metal deposit is formed by micro or nano-meter size islands that leave uncovered large zones of the substrate. In that case, it is found that the plasma deposition occurs preferentially on the metal particles that act as growing centres of the oxide nanostructures. This behaviour is illustrated in Figure 3 The facts that the deposition was carried out at relatively low temperatures as measured by a thermocouple placed at the porthole samples and that no catalytic effect is known for silver, gold or platinum towards the growth of titanium oxide, seem to discard that catalytic effects, similar to those claimed for the plasma formation of CNTs [25][26][27][28][29][30], are involved in the selective deposition of the oxides over the metal particles. This catalytic effect implies the excitation/chemical transformation of the plasma species arriving to the surface by the effect of the metal particles. The processes involved in the formation of the oxide nanofibres are different and must involve other effects likely related with the electrical conductive character of the metal particles. Tentatively, following previous suggestions by several authors [22,50,51], we propose that the electrical field of the plasma sheath developed over the substrate is locally modified by the metal particles in a way that it favors the selective impingement of charged plasma species of partially decomposed precursor molecules onto the metal particles. This would favour a selective drift of the positively charge particles and an increase of the local deposition rate on the nanoparticles. However, this simplistic model does not account for the fate of the neutral species of the plasma arriving to the substrate according to a large range of incoming angles [58]. In this case shadowing effects should be also claimed, particularly by the PECVD of oxides under oxygen rich plasma conditions where adparticles with a high sticking coefficient arrive to the substrate. A brief discussion of this situation for thin film growth has been included in section 2.

Formation of supported core@shell (metal/oxide (Ag@TiO 2 )) nanofibres

The use of bulk metal substrates with pronounced surface inhomogeneities favours the development of additional phenomena that contribute to the plasma deposition of oxide nanostructures. Ag@TiO 2 core@shell NFs have been prepared by TiO 2 deposition at 130 ºC over a silver metal foil that had been previously exposed to a plasma of oxygen [46,47]. Formation of gold-nanoparticle-embedded dielectric nanowires and other related "peapod" nanostructures is an active area of research because of their multiple applications in various fields [37,61,62]. In our previous works by plasma deposition it was shown that oxygen plasma treatments provoke the development of silver surface nanostructures and a high accumulation of mechanical stress at its surface because of the higher specific volume of silver oxide as compared with metal silver. On this plasma modified substrate, TiO 2 deposition induced the formation of NFs (Fig. 4a) which, according to their analysis by transmission electron microscopy (TEM) (Fig. 4b), are formed by a metal core made of a single crystalline silver wire (thickness around 20 nm) and an external layer of TiO 2 . Usually, the length of these fibres is in the range of 2-3 microns and its width depends on the deposition time. The TiO 2 shell can be either amorphous or crystalline and be characterized by a columnar or homogeneous microstructure depending on the deposition temperature and plasma composition. a) the surface of the bulk silver substrate is heterogeneous due to the oxygen plasma treatment. It is known that silver becomes oxidized when exposed to a plasma of oxygen [64] and that partial decomposition of the oxide into the metal or other oxide phases may occur locally without needing a substantial excitation energy [65,66]. In this locally heterogeneous surface, some "hot spots" favour the deposition of the TiO 2 which becomes enhanced by plasma sheath inhomogeneities as it happens onto the metal islands as referred in section 3.3.

b) The stress accumulated in the external layers of the oxygen plasma treated silver is released by the formation of a silver wire. The mechanism is similar to that involved in the formation of whiskers in tin plates used for welding conventional electronic components [67]. It is worthy of note that the NFs only develop when this experiment is carried out at T substrates ≥ 130 ºC, precisely the Huttig temperature of silver at which its atomic mobility is considerably high. c) As the silver wire is being formed it becomes covered by TiO 2 whose deposition occurs preferentially on the wire walls and significantly at its tip because of the plasma sheath effects already claimed in a). Some models existing in literature on the simulation of a coating growth on nanofibres [67,68] could help to describe this part of the process. Ag@TiO 2 -SiO 2 , where a mixture of SiO 2 and TiO 2 is obtained by simultaneously dosing Si and Ti precursors for the deposition, Ag@SiO 2 , Au@TiO 2 and Ag/ZnO. For the first three type of fibres, there are evidences by TEM that the core of the fibre consists of a metal thread. However, in the fourth system, silver seems to be also distributed onto the fibre tips, in a very similar way as metal seeds appear onto oxide fibers grown by the vapour VLS method [10][11][12]. It must also be noted that for Ag@SiO 2 and Au@TiO 2 there is a much smaller surface density of nanofibres than in Ag@TiO 2 and that the experiment with gold had to be carried out at T substrates > 250 ºC.

It is likely that this lesser efficacy of fiber formation is related with the lower atomic mobility of the metal substrate (Au) and/or because of a lesser efficiency of SiO 2 to induce NF growth. In any case, the point to be stressed here is that the mechanism of NF formation has a general character and that, provided that the right experimental conditions are found, it can be used for the formation of different composite NFs. The case of Ag/ZnO NFs in Fig. 5, even if grown by plasma deposition under conditions similar to those used in the other examples (i.e. a oxygen plasma treated metal foil and ZnO deposited by PECVD), presents as a peculiarity that metal nanoparticles seem to decorate the outer surface of the nanostructures. Tentatively we propose that the growth mechanism in this case is a mixture of the volcano type mechanism described in the previous section and an additional VLS processes. Further experimental studies are being carried out at present to understand the basic processes involved in this experiment and how they can be altered to get a tailored synthesis of composite NFs. where the metal core is easily appreciable. e) and f) SE and BSE SEM images respectively of Ag/ZnO NWs grown on an Ag foil by deposition at 135 ºC. Note that the silver particles seem to be on along the ZnO NW and that a homogeneous thread is not appreciable inside the nanostructure.

Towards processable substrates

The previous substrates consisting of a bulk or a very thick metal layer cannot be processed easily and its use for many practical applications is not straightforward. With the intention of developing a methodology suitable for application at an industrial scale for nanotechnological applications, we have carried out a set of experiments to get nanostructured metal-oxide supported nanofibres on conventional substrates (e.g., silicon wafers, floated glass or flat quartz plates, etc.) which are processed according to classical physical vapour deposition and/or plasma technologies. A way to achieve this goal is to play with the amount, percolation degree and type of the deposited metal particles and/or thickness of the thin metal film deposited onto conventional substrates.

The application of a previous plasma oxidation treatment to these modified substrates is another variable that can be also used. Thus, different kinds of metal nanoparticles/thin films were deposited on silicon or quartz and then subjected to oxygen plasma treatments for various periods of time prior to the PECVD deposition of ZnO or TiO 2 .

Oxide depositions were always carried out at the critical temperature of 130 ºC or above. Herein, to advance in the comprehension of the basic processes involved in the synthesis of the obtained nanostructures, we will concentrate on two examples. Fig. 6 shows the cross section SEM micrographs of TiO 2 and ZnO supported nanostructures deposited on a silicon substrate with silver on its surface. These two samples consists of perpendicular arrays of NFs of approximately 90 nm and 50 nm width, 900 nm and 600 nm long and with a surface density of approximately 8 x 10 8 NFs cm -2 and for the TiO 2 and 70 x 10 8 NFs cm -2 ZnO, respectively. It is clear in these micrographs that the oxide NFs grow out from the silver metal particles that act as a seed for the fibre development. However, in comparison with the experiments in Figs.

4 and 5, a significant difference of the microstructure of these supported NFs, besides their irregular character, is that they do not integrate a well defined metal thread in its core as it is shown in Figure 7. This difference suggests that formation of such metal wire requires a considerable supply of metal and that shortage in this supply occurs when using dispersed metal islands to act as a seed of NF formation.

nm

Ag core TiO 2 Nanocolumns Nevertheless, the most important result from this experiment is that oxide NFs are formed at relatively low temperatures on silver particles. Another important result is that silver nanoparticles become embedded within the NFs, a feature that opens the use of these nanostructures for many different applications in photonics and other fields [62,63].

Prospects and potential applications

The previous experiments have shown that noble metals can be efficiently used as seeds for the growth of hybrid oxide NFs and other deposited nanostructures. However, while the comprehension of the basic phenomena involved in the nanostructuring of PECVD oxide thin films in the absence of metals is relatively well understood [44][45][46][47][48][49], the effects induced by the presence of the metal are not yet clear and only phenomenological models exist to account for the development by plasma deposition of the NFs and related nanostructures [22,30,47,51]. In relation with the results reported here, we believe that a thorough description of the plasma sheath inhomogeneities induced by the presence of the metal seeds is a critical step in the comprehension of the plasma formation of core@shell metal/oxide NFs. We are convinced that the development of these models would help finding the experimental conditions required for a straightforward control of the formation of the final nanostructures. Despite this lack of theoretical interpretation, we have shown that on a trial and error basis well reproducible results can be obtained and different types of NFs and other supported oxide nanostructures formed by PECVD at relatively low temperatures. In addition, compared with other oxide nanostructures formed by very intense plasma treatments [24,31] and/or by catalytically driven processes [10][11][12], we have shown that our experimental protocols are based on relatively low temperature and mild plasma conditions. These are basic requirements for their use with sensitive substrate and an efficient control of the final process. Because of these reasons advances are foreseen in implementing modifications leading to the formation of other hybrid (organic-oxide) structures or the performance of well controlled lithographic depositions. The control of the electronic structure (i.e., doping) of the deposited nanostructures is another step required for the implementation of the deposited nanostructures for real applications.

In relation with that, and precisely at the present stage of development of the plasma methodology based on metal seeds, we think that it is quite pertinent to briefly discuss its potential practical applications. Thus, former studies have shown that the Ag@TiO 2 nanofibre surfaces described in section 3 are superhydrophobic (water contact angles (WCA) higher than 150º) but can be converted in superhydophilic (water contact angles virtually 0º) by UV light irradiation [69]. Changes in WCAs when TiO 2 and other oxides are subjected to UV irradiation are generally attributed to reversible modifications in the surface hydroxylation state and/or the removal by photo-oxidation of surface carbonaceous species [70]. The implications of this behaviour for microfiltration and, in general, microfluidic are obvious [71,72]. However, potential applications are not restricted to the interaction with fluids, the implementation of TiO 2 and ZnO nanostructures as sensors, luminescent devices, piezoelectric brushes, electrodes for electrochemical and photo-electrochemical cells, dye sensitized or hybrid photovoltaic solar cells, etc. are direct niches of application and their use could provide significant improvements of the present figure of merit of such devices [10-12, 19-21, 73]. We hope that future improvement in the PECVD processes and their understanding can contribute to a tailored synthesis of oxide directly usable in these fields. In our opinion, a very promising way for a versatile fabrication of core@shell nanostructures is the combination of conformal thin films or layers deposited by plasma methods onto previously grown 1D nanostructures [see also refs. 42-45]. Furthermore, the utilisation of low substrate temperature and remote plasma reactors for the fabrication of the shell materials make such methodology compatible with the deposition onto sensitive substrate, e.g. polymer nanofibres. Finally, owing to the ease change in composition of the oxide phase achievable by using plasma processes, the preparation of customized 1D nanostructures with p-n junctions or other interfaces is another option which would deserve further attention for their use in advanced applications.

Figure 1 .

 1 Figure 1. SEM cross sections micrographs of columnar TiO 2 (a) and ZnO (b) thin films deposited by PECVD of a silicon substrate without metal seeds. Both thin films were deposited at 130 ºC under pure oxygen plasma conditions.

Figure 2 .

 2 Figure 2. a) SEM micrograph of a crystalline layer of TiO 2 deposited on a silicon substrate partially covered by a silver layer (dash line has been included to guide the eyes). b) and c) Normal view SEM micrographs of the ZnO growth at 130 ºC on Si(100) and on Ag foil respectively. d) and e) Cross section SEM image of the ZnO growth at 250 ºC on Si(100) and on a gold film respectively. Note that: i) the length of the ZnO columns grown at 250 ºC on Au is almost a 125 % higher when compared with the same experiment on Si(100); and ii) the aspect ratio of the ZnO columns grown at 250 ºC is ∼5 for the experiments on Si(100) and ∼18 for the experiments on the Au surface.

Figure 3 .

 3 Figure 3. Cross section SEM micrographs of TiO 2 deposited at 130 ºC on Ag/Si(100) substrates (a) and b) recorded for secondary electrons (SE) and backscattered electrons (BSE) respectively); at 250 ºC on Pt/Si(100) substrates (c); and at 250 ºC on Au/Si(100) substrates (d) SE image and e) BSE image). In BSE micrographs the bright features correspond to the metal seeds.

1 .

 1 Although these and other fundamental questions are outside the scope of the present work they represent an open topic for the modelling of the plasma sheath, very likely by considering lateral inhomogneities in its electrical field distribution, and the random arrival of neutral particles onto the surface.

Figure 4 .

 4 Figure 4. a) Normal view SEM micrograph of the surface formed by a high density Ag@TiO 2 NFs; b) TEM micrograph of an individual Ag@TiO 2 NF showing that the core is formed by a silver thread surrounded by a nanocolumnar TiO 2 shell.

5 .

 5 Generalization of the formation of M@M'O x (M: Ag, Au; M':Si, Ti, Zn) nanofibres Plasma formation of M@M'O x nanofibres also occurs with different efficacy for other metal substrate/deposited oxide couples. Fig. 5 shows a series of SEM micrographs corresponding to different types of NFs. Examples are reported in this figure for

Figure 5 .

 5 Figure 5. a) SEM normal view micrograph of Ag@TiO 2 /SiO 2 NFs fabricated at 130 ºC by the simultaneous deposition on the Ag membrane of TiO 2 and SiO 2 ; b) Ag@SiO 2 NF deposited at 130 ºC. In both a) and b) experiments the substrates were subjected to the same oxygen plasma pre-treatment procedure used for the growth of Ag@TiO 2 NFs in Fig. 3; c) and d) SEM micrographs of Au@TiO 2 NFs fabricated on a gold film of thickness ∼ 500 nm at 250 ºC. The micrograph in panel d) shows a broken NF

Figure 6 .

 6 Figure 6. a) and b) SE cross section and BSE cross section images respectively of Ag@TiO 2 nanofibres deposited on a Si(100) wafer; c) and d) Idem of Ag/ZnO nanowires deposited on Si(100).

Figure 7 .

 7 Figure 7. a) TEM image of an individual Ag@TiO 2 NF fabricated on Ag/Si(100). The TiO 2 shell is amorphous and nanocolumnar.

Acknowledgments

This work was funded by the EU (project NMP3-CT-2006-032583), the Spanish MICINN (projects MAT 2007-65764, MAT2010-18447, MAT2010-21228 and Consolider CSD2008-00023) and JUNTA de Andalucía (projects P09-TEP-5283, CTS-5189).

Supplementary Information

Supported plasma made 1D heterostructures: perspectives and applications.

Ana Borras,* Manuel Macias-Montero, Pablo Romero-Gomez and Agustin R.

Gonzalez-Elipe

Materials Science Institute of Seville (CSIC-Universidad Sevilla), C/ Américo Vespucio 49 41092, Sevilla (Spain)

Experimental

TiO 2 , SiO 2 and ZnO were deposited at various substrate temperatures by PECVD in a plasma reactor with a downstream configuration. The experimental setup, described in a previous work [39][40][41], consists of a remote plasma source (SLAN from Plasma consult Gmbh, Germany) attached to a deposition chamber where the deposition is carried out.

The source was operated with a power of 400 W with either pure O 2 or mixtures Ar+O 2 (80% or 90% Ar) as plasma gas. Titanium tetraisopropoxide (TTIP), hexamethyldisilazane HDMS, and diethyl Zinc (DEZ) were used as a titanium, silicon and zinc oxide precursor respectively. Due to low vapor pressure of the titanium precursor at room temperature, it was placed in a heated stainless steel recipient while oxygen (10% of the total flow of gases) was bubbled through it. Both the bubbling line and the shower-type dispenser used to dose the precursor into the chamber were heated at 100 ºC to prevent any condensation in the tube walls. The zinc and silicon precursors, having enough vapor pressure at room temperature, were directly dosed into the deposition chamber by means of a mass flow controller and a heated gas line (at 100 ºC). An important parameter for the development of NFs was the substrate temperature during deposition. Generally a threshold temperature of 130º C or higher had to be used for NF formation on silver or silver/silicon substrates. The actual temperature used in each particular case is specified in the text.

Total pressure during deposition was ∼4x10 -3 Torr either with pure O 2 or Ar+O 2 mixtures as plasma gas. Films were deposited simultaneously on several substrates (approximately 1x1 cm 2 size) intended for different characterization tests and to control the development of NFs.

In some of the experiments with silver foils or silver layer/particles deposited on silicon, the substrates were subjected to a plasma of oxygen prior to the deposition of the oxides. For this treatment we used the same chamber used for the PECVD of the oxides, before deposition was carried out. For this pre-treatment the source was fed with oxygen at a pressure of ∼4x10 -3 Torr.

Pieces of silicon and fused silica substrates, silver foils and silicon covered with metal (Ag, Pt and Au) films or nanoparticles have been used depending on the intended experiment. Silver and gold were deposited onto the silicon substrates by sputtering from a metal wire placed at 3 cm from the substrates in a chamber filled with Ar (1.12 -1.5 Torr). A voltage of 400 V was applied for the metal sputtering. In some cases substrate temperature during deposition was set a T > 200 ºC in order to increase the average size of the deposited metal particles. The Pt/Si(100) substrates were fabricated by chemical vapor deposition from a Pt(acac)2 precursor at temperatures between 370-390 ºC, followed by annealing at 600 ºC in an Ar atmosphere.

Normal and cross-section SEM characterizations of the films/structures grown on silicon were carried out in a Hitachi S4800 and Hitachi S5200 instruments. TEM analysis of nanofibres was carried out in a Phillips CM200 set up.


V Ménoret

R Geiger

G Stern

N Zahzam

B Battelier

A Bresson

A Landragin

P Bouyer

Dual-wavelength laser source for onboard atom interferometry

We present a compact and stable dual-wavelength laser source for onboard atom interferometry with two different atomic species. It is based on frequency-doubled telecom lasers locked on a femtosecond optical frequency comb. We take advantage of the maturity of fiber telecom technology to reduce the number of free-space optical components which are intrinsically less stable, and to make the setup immune to vibrations and thermal fluctuations. The source provides the frequency agility and phase stability required for atom interferometry and can easily be adapted to other cold atom experiments. We have shown its robustness by achieving the first dual-species K-Rb magneto optical trap in microgravity during parabolic flights.

Atom interferometers have demonstrated excellent performances for precision acceleration and rotation measurements [1]. Many foreseen applications of these instruments such as tests of fundamental physics [2,3] or terrain gravimetry [4] require the setup to be transportable and able to operate in harsh environments. A lot of efforts have been made in the past few years to develop such transportable systems [5][6][7], and in particular to make the laser setup as compact and immune to perturbations as possible [8].

Atom Interferometers usually operate with alkali atoms by driving transitions in the near-infrared spectrum (852 nm for Cs, 780 nm for Rb and 767 nm for K). In these experiments one needs stable lasers both to cool the atoms and to interrogate them by using stimulated Raman transitions [9]. These Raman transitions require two phase-locked lasers red-detuned by approximately 1 GHz with respect to the cooling wavelength, and with a frequency separation corresponding to the ground state hyperfine splitting of the atom. The performance of the phase-lock is critical since it has a direct impact on the interferometric measurement.

While most atom interferometers use laser systems based on extended-cavity diode lasers (ECDLs) [10], a good alternative is to use frequency-doubled telecom lasers operating around 1.5 µm [11,12]. This technique takes advantage of the maturity of fiber components in the telecom C-band to reduce the amount of free-space optics and to make the setup more compact and less sensitive to mis-alignments. The second Raman frequency is generated by modulating the reference laser with an electro-optic or acousto-optic modulator, thus avoiding phase-locking of two diodes.

We present a new laser source for onboard atom interferometry with two species. It is based on two telecom Distributed Feedback (DFB) lasers at 1560 and 1534 nm that are combined, amplified and frequency-doubled to 780 and 767 nm in order to manipulate Rb and K atoms simultaneously. Both DFBs are frequency-locked on a fiber-based optical frequency comb (FOFC) [13].

We have demonstrated the robustness of this source during parabolic flight campaigns in which we obtained for the first time a double-species magneto-optical trap (MOT) in microgravity aboard the Novespace zero-g aircraft [14]. The system was operated despite temperature fluctuations from 17 to 30 • C, high vibration levels up to 0.5 m.s -2 rms and a vertical acceleration alternating between 0, 10 and 20 m.s -2 . Apart from a free-space module all the components are fibered and fit in standard 19" rack structures. The source meets the usual requirements for atom interferometry (Fig. 1) : separate optical outputs for MOT and Raman lasers with powers of the order of 200 mW, frequency agility over hundreds of MHz, AOM-driven microsecond pulses and high phase stability for the Raman lasers. In the following, we first detail the optical characteristics of the source, then we focus on the phase stability of the lasers and describe the dual-species MOT demonstrated in microgravity.

We stabilize the Rb and K DFB lasers on a common frequency reference by the means of a FOFC. This technique has been preferred over conventional saturated absorption spectroscopy methods because it offers a precise measurement of the absolute optical frequencies, along with common mode frequency noise rejection. The comb has been specifically designed by MenloSystems to be transportable and resistant to vibrations. It is selfreferenced on a 10 MHz ultra-stable quartz oscillator which is the RF frequency reference for the whole atom interferometry experiment [15]. Built-in fibered beat detection units allow the detection of a beat signal between the comb and each of the DFB lasers, and the stabilization of these lasers on the comb. The 1560 nm source is inspired from that described in [15]. A master DFB laser is locked on the FOFC at a fixed frequency by retroacting on the diode current. A slave DFB is then locked on the master laser with an adjustable setpoint, allowing frequency detuning at 1560 nm over 500 MHz in approximately 3 ms. This agility is needed in order to detune the Raman laser for the interferometer sequence. The slave laser is then used for both cooling and interrogating 87 Rb. The 1534 nm source is made of a single DFB locked on the FOFC [16].

The two lasers at 1560 and 1534 nm are combined in the same fiber and amplified to approximately 5W each in a dual-frequency Erbium-Doped Fiber Amplifier manufactured by Keopsys, designed so as to have the same gain at the two wavelengths. By finely adjusting the value of the two input powers we can set the power ratio on the output light to the desired value.

The amplified light is coupled out and frequencydoubled in free-space. We use two double-pass crystals in series to frequency-double the two lasers at 1560 and 1534 nm respectively (see Fig. 1). The light first goes through a 3 cm long PPLN crystal from HCPhotonics phase-matched for the Second Harmonic Generation of 780 nm light starting from 1560 nm. We extract the 780 nm component on a dichroic mirror and send the remaining 1.5 µm light through a second PPLN crystal phasematched for the conversion of 1534 to 767 nm light.The double-pass configuration enables high efficiencies of approximately 4%.W -1 with 5W pump power.

We generate the repumping and second Raman frequencies by modulating the lasers at frequencies close to the hyperfine splittings of 87 Rb and 40 K (6.8 GHz and 462 MHz respectively). On the Rubidium laser we use a fibered phase modulator operating at 1560 nm and driven by a 6.8 GHz signal from our frequency reference. The parasitic sidebands generated by the phase modulator are not critical on the Rubidium setup because they are far away from the atomic transition and have little effect. On Potassium the hyperfine splitting is smaller and phase modulation would lead to spurious sidebands close to resonance, causing enhanced spontaneous emission and parasitic interferometers. We therefore use a free-space acousto-optic modulator (AOM) in a double pass configuration at 767 nm. We superimpose the fundamental order and the one diffracted twice in the AOM so as to get two frequencies separated by 462 MHz.

Each of the two frequency-doubled lasers is sent through an AOM in order to be split in two paths, one for the cooling beam and one for the Raman beam. All 4 paths (2 Rb and 2 K) go through fast mechanical shutters (Uniblitz LS2, 300 µs rise time) and are coupled in polarization-maintaining fibers. The fiber-coupling efficiency is of the order of 70%, and we get around 200 mW optical power at each of the fiber outputs. In addition, a few mW of light of each wavelength is used to generate blowaway beams.

Since the free-space bench is a critical part of the setup we have taken special care to make it as stable as possible. Our experiment is operated in a plane carrying out parabolic flights so the setup has to withstand high levels of vibration, as well as local gravity changes. The optics are screwed on a custom made AW2618 aeronautic grade aluminium breadboard which is more stable than standard AW2017. The breadboard is 43x73 cm 2 and 4 cm thick, with a hollow structure to make it lighter.

We have measured the phase noise due to propagation on the 780 (resp. 767) nm Raman lasers by detecting a beatnote at 6.8 GHz (resp. 462 MHz) on a fast photodiode, and mixing it with the same signal that was used for the sideband generation. On the 780 nm Rb laser the phase noise resulting from the phase modulator and propagation in the system is more than one order of magnitude lower than that of the frequency reference itself, meaning that our solution is a good alternative to phaselocked diode lasers (Fig. 2). The 767 nm source shows similar performance in quiet conditions, but is more sensitive to low frequency-phase noise due to vibrations and air flows because of the physical path separation induced by the double-pass AOM. However, even under strong

Rb laser

Frequency reference Fig. 2. Phase noise due to modulation and propagation for the two lasers compared to that of our 6.8 GHz frequency reference. For the Rb laser, phase noise is dominated by that of the reference. On the K laser excess noise appears at low frequency because of physical separation between the two frequency components. mechanical constraints the RMS phase noise remains below 200 mrad, and below 30 mrad in quiet conditions. Further stabilization can be added by retroacting on the phase of the RF signal driving the AOM.

Finally, the laser source has been validated during parabolic flight campaigns organized by CNES and ESA, by achieving the first dual-species MOT in microgravity. We capture around 10 9 Rb atoms and 5.10 7 K atoms in a static MOT, loaded from a vapor. The FOFC has remained fully locked and stable throughout the flights. The output optical powers were also stable, with no noticeable long-term degradation or influence of vibrations (< 5%). The temperature of Rubidium atoms after sub-Doppler cooling in optical molasses is of the order of 8 µK, allowing high resolution acceleration measurements in the plane [8]. We have measured the temperature of K atoms by a release and recapture method, and estimate it around 200 µK, which is comparable to what has been obtained in [17]. Further cooling to 25 µK in optical molasses has been recently achieved [18,19] and will be implemented soon on our experiment.

Improvements to this laser source could come from the reduction of free-space optics. For instance, the use of pigtailed PPLN waveguides instead of bulk crystals could lead to a smaller setup, along with a reduction of the needed pump power. Studies in this direction are currently under way and promising results have been obtained by Nishikawa and coworkers [20]. Furthermore, fast and polarization maintaining switches with high extinction rations operating at 780 or 767 nm are difficult to find. The maturation of these technologies seems necessary before a fully fibered laser source for atom interferometry can be built.

The laser source we have presented is a compact and versatile setup, designed to test the weak Equivalence Principle in the zero-g plane [21]. A similar design could easily be adapted to other dual-species cold atom experiments, the use of the frequency comb allowing for easy absolute frequency determination and stabilization. The high stability and reliability of this type of fiber-based architecture also make it a good alternative to ECDLbased systems for laboratory experiments.

Fig. 1 .

 1 Fig. 1. Diagram of the complete laser system. DFB : Distributed Feedback laser diode. OI : Optical Isolator. PM : Phase Modulator. FC : Fiber combiner. SHG : Second Harmonic Generation. DM : Dichroic Mirror. PPLN : Periodically Poled Lithium Niobate crystal. AOM : Acousto-Optic Modulator.

We thank L. Mondin and T. Lévèque for their implication in the project. We acknowledge funding supports from CNES, DGA, CNRS, ESA and IFRAF.


Mathieu Sassatelli

Fadoua Bouchikhi

Samir Messaoudi

Fabrice Anizon

Eric Debiton

Chantal Bartomeuf

Michelle Prudhomme

Pascale Moreau

Synthesis and antiproliferative activities of diversely substituted glycosyl-isoindigo derivatives

published or not. The documents may come


Léon Laulusa
email: llaulusa@escpeurope.eu

Confucianism and its implications for industrial relations in China i1

Keywords: Confucianism, industrial relations, danwei, State-owned-enterprise

This study aims to examine the impact of Confucian values on industrial relations in China. The existing literature suggests that these values have a significant influence on industrial relations in China. Authors commonly report that Chinese industrial relations are peculiar and different from those found in some Western counties. Particularly, in China, trade unions and directors of SOEs are not really independent from the State or local governments. In parallel, in private Chinese firms, trade unions are traditionally weakly represented. In this respect, this paper argues that the management-workers relations are still based on Confucian social rules and values rather than on a contract-based system.

Introduction

Since the "open policy" initiated in China in 1978, numerous studies have considered the impact of new Chinese market reform on the industrial relations [START_REF] Fei-Ling | A changing arena of industrial relations in China, What is happening after 1978[END_REF]Zhu & Warner, 2003;[START_REF] Warner | Management-labour relations in the new Chinese economy[END_REF][START_REF] Shen | The Labour dispute arbitration system in China[END_REF][START_REF] Bill | Industrial Relations in China[END_REF][START_REF] Simon | Collective Consultation and Industrial Relations in China[END_REF][START_REF] Wrathall | The impact of economic reform and associated changes in regulatory and institutional arrangements on the role of trade unions in the People"s Republic of China[END_REF][START_REF] Ying | Major changes under Way in China"s Industrial Relations[END_REF]. For instance, [START_REF] Warner | An emerging model of employment relations in China : A divergent path from the Japanese ?[END_REF] mostly define industrial relations as labour relations (laodong guanxi) in China instead of labour-capital relations (laozi guanxi) like in most East Asian countries. These authors argue that most of Chinese firms are not "capitalist" such as State-owned enterprises (SOE) and collectively owned enterprises (COE) and therefore commonly accepted definitions of industrial relations should not be extended to the Chinese peculiar environment. However, it is noteworthy that laozi guanxi could however refer to private sectors in China. The study of Jie [START_REF] Shen | The Labour dispute arbitration system in China[END_REF] analyses the characteristics, development and implementation of the Chinese labour arbitration systems. Whereas [START_REF] Fei-Ling | A changing arena of industrial relations in China, What is happening after 1978[END_REF] discusses the main evolution of the industrial relations since its economic reform, he points out that the industrial relations have shifted away from a rigid state-controlled system to a more flexible actor-pro-negotiation arena, where tripartism (state-firms-unions)2 emerges but cannot fully disclose the reality of Chinese labour. As a matter of fact, labour representation stems from official trade unions like ACFTU3 and unofficial unions such as self-organisation of workers supported by international Non Government Organizations (NGO).

While analyzing this evolution, some studies also outline the potential impact of Chinese Culture, in particular Confucian values on industrial relations although very few document its influence. The purpose of this paper is thus to examine the impact of one of the most dominant Chinese cultural values, namely Confucian values, on industrial relations in China. According to the existing literature, these values could significantly influence industrial relations in Chinese firms (Warner & Zhu, 2000; Wrathall, 2003; J. Scoville & J. Lawler & Xiang Yi, 2005 4 ). Subsequently, we also formulate this hypothesis and use it as a research design base. More precisely, we attempt to tackle the following questions:  Are the industrial relations encountered in China peculiar and different from some Western countries?  If yes, can this specificity be explained by the influence of Confucian Values?  What are the implications of these values for industrial relations in China?

In order to ease the investigation process of these issues, our paper is split up into three parts. Firstly, we briefly examine the key features of industrial relations in China. Secondly, we introduce the basics of Chinese social rules according to the Confucianism inheritance. Thirdly, we discuss the potential influence of Confucian values on industrial relations in Chinese firms. We conclude finally by providing some answers to the previously discussed research questions and underlining their shortcomings and drawbacks that will help us propose some future research avenues.

Main features of industrial relations in China since 1949

Brief historical view

During the "planned economy" period in China, the reconciliation of the interests of workers, managers and the state was achieved within an administrative framework guaranteed by the government and the Communist Party (Clark et al., 2004). The industrial relations followed the three irons policy and "cradle to the grave" welfare is provided to workers, "iron rice bowl" (tie fan wan) which refers to lifetime employment, "iron wages" which refers to stable and fixed reward system and "iron chair" which refers to inflexible positions of managers. There were also the practice of job inheritance (dingti) passing from parents to children and family [START_REF] Warner | An emerging model of employment relations in China : A divergent path from the Japanese ?[END_REF]. Danwei (work unit) which is embodied to "iron rice bowl" and hukou (urban residency permit) provided a sense of belonging and identity for the worker. The enterprise was responsible to provide housing and all welfare, medical and retirement benefits as well as for social and entertainment needs [START_REF] Sarosh | Change and transformation in Asia[END_REF]. Wages and welfare were determined generally by government policies [START_REF] Bill | Industrial Relations in China[END_REF]. Workers and management were not separate parties.

At that time and before the Cultural Revolution in 1966, the unions were clearly subordinate to the Party playing as "transmission-belt" [START_REF] Gordon | Chinese Trade Unions in the Transition from Socialism: Towards Corporatism or Civil Society?[END_REF]. Their main responsibility was to transmit the Party"s current ideological line and policies to the urban working class and try to secure their support and compliance. On the other side, "they were also supposed to protect the interest of the workers and staff members" (White, 1996, p.437) But after 1980, the arrangement of "iron rice bowl" has been phased out as China entered into a new environment with market economy, the entrance and flow with Foreign Investment and accession WTO [START_REF] Ding | The end of the "Iron Rice-Bowl": whither Chinese human resource management?[END_REF]Warner, 2003). In this system, management can recruit, dismiss workers and increase their wages. Performance driven reward system has been more applied in SOEs. Social security has also been diluted and is now dependent on individual workers" contribution added to by the employers. SOEs are no more employment centers but responsibility centers or profit centers [START_REF] Léon | L"influence des valeurs confucéennes durant le processus de contrôle organisationnel au sein des entreprises chinoises en Asie : Etudes de cas en Chine, à Singapour et à Taiwan[END_REF]. At the same time, International MNC implemented their HRM policy and system in their Chinese Ventures and offered high wages for locals.

The three irons metaphor is replaced by the three metals bowls to differentiate the employment"s market, "golden bowls" which refer high wages and positions, "silver bowls" which refers to good ones and "iron bowls" which refers to normal ones. The government issued new labour law in 1994 in order to create a new industrial relations system in China [START_REF] Bill | Industrial Relations in China[END_REF] clarifying the relationship between employers and the workers in enterprises. According to [START_REF] Fei-Ling | A changing arena of industrial relations in China, What is happening after 1978[END_REF], despite the Chinese Law to legalise strike, collective or class labour dispute (jiti laodong zhengyi) jumped six-fold in 2006 since the enactment of Law Contract Law. These disputes were often resolved through unofficial channels.

Chinese divergences from Western

However, in this context of change since three decades, we notice some aspects of industrial relations in China which can be distinguished from those of Western countries: Firstly, trades unions are relatively dependent on the State or local governments. From a historical point of view, trades unions were re-established through the All China Federations of Trades Unions (ACFTU) in 1978. The ACFTU plays a dual role [START_REF] Simon | Collective Consultation and Industrial Relations in China[END_REF]). On the one hand, it has to defend the workers" right and interests. On the other hand, it has to promote social stability and reform assigned by the State, by encouraging workers to increase productivity and by enforcing labour discipline and by conducting extensive propaganda on behalf of management. But its first role, "transmission-belt of the State" seems to be more important. [START_REF] Bill | Industrial Relations in China[END_REF] note that it is still common that trade union cadres are content to take orders from the superior leaders and the Party. It is also showed in White research (1996), the workers perceived that trades unions in enterprises are instruments for securing obedience and work effort. [START_REF] Bill | Industrial Relations in China[END_REF] observe that there is an increase in autonomy for local trade unions (subordinated to province government) but at national level, the ACFTU often upholds the stand of the government. The first role is to maintain social stability and harmony. Even in dispute resolution, enterprise trade unions do not seem to intervene. Workers rely more on direct appeals to management or government than on trade unions [START_REF] Bill | Industrial Relations in China[END_REF].

Secondly, danwei is a kind of family organization. In Chinese common language danwei refers to organization, shop, enterprise, work unit, administrative unit and the entity where we belong. This term actually encompasses numerous features. During the planned economy, danwei were not only an economic work unit but were also political, social units which bounds individuals live to the administrative system. Lü and Perry (1997, p.8) state that the political and social functions "may be characterized as "paternalistic" and "maternalistic" respectively. As in a traditional family, the danwei acts as a patriarch who disciplines and sanctions his children, while at the same time serving as a maternal provider of care and daily necessities". Thought the significance of danwei has diminished due to the broken "iron rice bowl", danwei still refers ideologically for the Chinese to a kind of family organization within which we can count on. In the same danwei, individuals developed not only working relationships but also social networks. These ties become in long term friendship or even family. Danwei also cultivate a strong group identity which favours group orientation.

Thirdly, collective contract system is more a formal device than an effective tool because it is not based on the negotiated regulation of labour relations between the two sides independently representing the interests of employer and employees [START_REF] Simon | Collective Consultation and Industrial Relations in China[END_REF]. The enterprise director and the trades unions fail to represent the interests of employer and employees as both continue to be subject of the direction of the Party. The system is thus based on the continuing assumption of harmonious "unity interest between the enterprise, traditionally owned the whole people, and the workers, traditionally the master of the enterprise, expressed in a common commitment to the observance of legal norms" (Clarke et al, 2004, p.237). The formal roles of the three forces within the enterprise are theoretically equal: "the Party is supposed to be the "nucleus" (hexin), the management the "centre" (zhongxin) and the workers the "masters" (zhurenweng) (White, p.445). In reality, the power is unbalanced and more on the Party, central or local governments" hands in the SOEs than on workers and management.

Fourthly, conflict is seen natural and social improvement in Western context whereas in China, conflict avoidance, when it is possible, is the motto for keeping harmonious relationship. Under communist period, the managers and workers were considered "masters" of the enterprises and the state, the employer. Taylor et al (2003, p.136) state that "the interests of senior managers were similar to those of workers, because in the planned economy, managers took little personal risk or responsibility, and their only economic objective was the need to fulfil the planned quota assigned by the senior administrative agencies". Since market economy, conflicts of interest between management and workers increase. For example, Wang (2008) emphasizes the rural migrant workers who loosed their rights and material benefits because of not having local hukou (household registration) or zanzhizhng (temporary resident permission certificate) are active in conducting activities resistant like wildcat strikes and streets protests. These disputes remain however localised and the government adopt a conciliatory way to handle its in order to maintain social stability and pursuit reform [START_REF] Bill | Industrial Relations in China[END_REF]. Workers in general are inclined to be obedient and limit challenging the superior or being in conflict and direct confrontation between superiors and subordinates [START_REF] Léon | L"influence des valeurs confucéennes durant le processus de contrôle organisationnel au sein des entreprises chinoises en Asie : Etudes de cas en Chine, à Singapour et à Taiwan[END_REF]. Trade unions also which are supposed to defend the interest of workers are reluctant to challenge management [START_REF] Wrathall | The impact of economic reform and associated changes in regulatory and institutional arrangements on the role of trade unions in the People"s Republic of China[END_REF][START_REF] Simon | Collective Consultation and Industrial Relations in China[END_REF]. Li (2000 5 , cited by Clarke et al, 2004, p.240) found in his research that Party-state continues to regulate labour relations along with collective contract "with management remaining reluctant to make any specific commitments and trades unions reluctant to press employees" demands, in the interest of maintaining harmonious labour relations".

Before analysing the possible impact of Confucianism on industrial relations, its values are first examined.

Confucian inheritance

Confucian values

Chinese culture can be characterized by five main movements: Taoïsm (daojia), Confucianism (rujia), Buddhism, Mohism (mojia) and legalism (fajia). However, according to most Western and Chinese scholars, Confucianism, which is sometimes being considered as a religion (not at the Western meaning) is probably the dominant one as it has been the state cult for thousand-year-old. Confucianism comes from Confucius" seminal work reported by his disciples like Mencius. Confucius (Latinised name of Kong Fu Zi, literally Master Kong) lived around 551 to 479 BCE. But as Confucius said he was not the founder of this thought, he just theorized and made operational the philosophy, the "code of conduct" from ancient legendary kings like Yao and Shun: "I invent nothing, I just transmit it" (VII, 1). Confucianism is a rationalist doctrine, meaning that it did not believe in magic and it had systematically unified the relation between God and the world and therewith its own ethical relationship to the world.

The central thought of Confucianism is morale that advocates loyalty (zhong), filial piety (xiao), benevolence and justice (Yang Jian 6 , 1996; Achille Weinberg 7 , 2001). Regarding morals, Confucius seeks to establish a hierarchical, fair and harmonious social order. According to him, the harmony can be found in social and collective peace [START_REF] Léon | L"influence des valeurs confucéennes durant le processus de contrôle organisationnel au sein des entreprises chinoises en Asie : Etudes de cas en Chine, à Singapour et à Taiwan[END_REF]. Fairness is echoed in the concept of ren (humanity). For Confucius, the best way to govern is to rule by virtue or ren which means through human quality, with benevolence. If the superior embodies ren, effective management in state will impose naturally, without using any force [START_REF] Léon | L"influence des valeurs confucéennes durant le processus de contrôle organisationnel au sein des entreprises chinoises en Asie : Etudes de cas en Chine, à Singapour et à Taiwan[END_REF]. As Mencius, a famous disciple of Confucius, said: "the virtue of the prince is like wind and that of people is like grass. When the wind blows on grass, it bows necessarily" (Couvreur, 1981, Mencius, Livre III, Chap, I, § 2). This means that if the prince fulfils his sovereign function, that is to be benevolent, people will then follow. In the contrary, people will come to rebel and the prince will lose his heaven mandate [START_REF] Léon | L"influence des valeurs confucéennes durant le processus de contrôle organisationnel au sein des entreprises chinoises en Asie : Etudes de cas en Chine, à Singapour et à Taiwan[END_REF].

Ren represents the highest degree of Confucian virtue and is made up of two characters, « man » and « two »; which express a relationship between one individual with another. In other words, an individual can only exist through the relationship that links him to another. This relationship has to be based on fairness. As a brief summary, it could be argued that the Confucianism inheritance in term of social relationship is threefold: 2000) " A study of labour relations in State-owned enterprises in China: the continued dominance of the State and the failure of the collective contract system", PhD Thesis, City University of Hong Kong 6 . Thinking on the fundamentals and the particularity of the culture face the development of the modern science and technology, Culture: Diversité et coexistence dans le dialogue Chine-Occident, Actes du colloque international de Nanjing, 1996. 7 . Achille Weinberg, 2001, Questions sur la « pensée orientale », in Sciences Humaines : La pensée orientale, une invention de l'Occident ?, n°118, juillet, pp.22-30.

5 Li Q. (
(1) The individual exists through, and is defined by, his relationship with others: The social interaction between individuals is mainly described by the five basic Confucian relationships (wu lun): " [...] five general laws are those which govern the relationship between prince and subject, between father and son, between husband and wife, between elder brother and younger brother, between friends " (Couvreur, 1981, L"Invariable milieu, Tchoung Ioung, 20 or see Entretiens de Confucius, Chap.18, 7). Furthermore, Confucius contents that in order to preserve this relationship, one should respect the following five principles:

 Righteousness between prince/subject : protection, security (from prince) / respect, loyalty (from subject),  Sincerity between father and son : education (from father) / respect, filial piety, cult of ancestors (from son),  Separation between husband and wife,  Order between brothers : benevolence (from elder) / respect, obedience (from younger),  Trust between friends: sincerity and solidarity.

Three of these relations are family relations. Confucius thought that who came from a family knowing the tao (the way to behave properly) would have a good influence on others. Family education is then essential for individual and for the basis of the development of all relation in the society. Besides, these human relations are also based five virtues8 (de) to cultivate:  Sense of human (ren)/ benevolence/ kindheartedness,  righteousness (yi),  propriety or etiquette (li),  wisdom (zhi),  trustworthiness (xin).

(2) These relationships are based on a hierarchical framework structure or social order: the Confucian concept of relationships emphasizes the importance of social hierarchical order and the social group-based classification of a person. Accordingly, Confucius" famous saying underlines the importance of such a social order asserting that: « Let the prince be prince, the subject be subject, the father be father and the son be son ».

(3) The social order will be secured when each party honours the requests. The success of these requests depends on socialization rules.

Socialization rules derived from Confucianism

Confucianism thus advocates harmony as a standard precept for interpersonal relationships. This harmony cannot be obtained without respecting basic social behaviour rules, the main ones being which derive from Confucian tradition are: guanxi (interpersonal relationship), renqing (humanized obligations), reciprocity (pao) and face (mianzi).

Guanxi:

Literally "the gate of human relations", this notion refers to the status and to the intensity of a relationship between two parties. The Confucian system has shown that the Chinese exist only through their relationships. Consequently, they naturally put much care into improving their guanxi. However, some individuals can limit their desire to increase their guanxi because of the resulting obligations. As a matter of fact, the more an individual benefits from advantages of the guanxi network, the more demanding are the obligations of renqing.

Renqing: This word literally means a human feeling towards others. For Mencius, it is « the reaction to the unbearable that is the root of humanity"s feeling, [...] which, itself, summarizes the morality » (F. Jullien, 1995). This feeling of humanity also includes the idea of obligation. Min [START_REF] Chen | Asian management systems[END_REF] defines renqing as an « obligation to humanity ». According to K.K. [START_REF] Kwang-Kuo | Face and favor: the Chinese power game[END_REF], renqing encompasses three different meanings:  Renqing indicates « emotional responses of an individual confronting the various situations of daily life. Li-Chi (Book of Ritual) says: «What is so-called renqing? It consists of happiness, anger, sadness, fear, love, hate, and desire; all of them are acquired at birth ».  Renqing means resources that an individual can present to another person as gifts during a social exchange.  Renqing denotes a set of social norms that an individual has to respect in order to get along well with others in Chinese society.

Reciprocity (pao):

The principle of reciprocity is universal [START_REF] Yang | The concept of pao as a basis for social relations in China[END_REF]. However, this concept which implies the idea of exchange is particularly important for the Chinese. In Chinese culture, the norm of reciprocity includes renqing. The main differences between these two norms come from their applications in different domains of interpersonal links, from their different ways of being carried out, from the length of time involved in allocating benefits and from the repayment of resources [START_REF] Kwang-Kuo | Face and favor: the Chinese power game[END_REF].

Face: According to [START_REF] Redding | The role of face in the organizational perceptions of Chinese managers[END_REF], face contains two dimensions in Chinese culture:  Lien which evokes moral character, "the idea of being a "decent human being"" [START_REF] Redding | The role of face in the organizational perceptions of Chinese managers[END_REF].  Mianzi which means the « physical » face and carries the idea of reputation based on one"s own efforts. The way in which these two dimensions affect behavior differs. Thus, having no lien means having no integrity, whereas having no mianzi expresses the idea that we have failed in achieving success. So, we have seen that guanxi implies reciprocity, in particular, renqing. The latter can depend on face. These social rules are, what [START_REF] Kwang-Kuo | Face and favor: the Chinese power game[END_REF] calls, "the Chinese power game".

Some implications on labour relations

The Confucian ethical system considers Chinese organization within family metaphor and its socialization rules derived from the five cardinal relationships (wu lun). Both have practical implications on the management-workers relations. We are going to explore some of them, which seem to be particularly important.

Chinese social organization: a family metaphor

According to some Chinese sociologists (like Wong, 1985), work organization needs to be consider with the concept of "familism". Fan Xing (1995, p.17) agrees and called "family-ism" in Chinese social organizations in so far as "employees are provided with housing, free medical care, and education for their children by the organization they work for. Their activities and personal lives are closely connected to the organizations whose management, in many ways, functions as the parents of extended families, responsible both for business and solving employees" personal problems. Hiring, selecting, compensation and other management decisions may all involve family-ism". The obligations and duties between management-workers are not only based on contracts but above all on ties or kin obligations and duties as if there are members of the same family [START_REF] Léon | L"influence des valeurs confucéennes durant le processus de contrôle organisationnel au sein des entreprises chinoises en Asie : Etudes de cas en Chine, à Singapour et à Taiwan[END_REF]. Fatherchild relations are replaced to employees-employer relations in Chinese organizations (Scoville et al, 2005). According to Chao (19949 , p. 30), work organization with "root in an agrarian past cherished values as loyalty, paternalistic authority, family cohesion and altruism, rules of seniority and respect for the wisdom of elders". Familism implies respect to hierarchy, paternalism and group orientation.

Respect to hierarchy is part of Confucian tradition. Hierarchy is seen in terms of respect to rank that is to say authority or power, older age and seniority. One person has to give respect towards superiors, seniority and a person with older age. This seems to be innate. Scoville et al (2005, p.100) observes that "one first must determine his or her relationship to the other person involved in an interaction, particularly who is the superior and who is the inferior" in order to see whom has to give respect and reverence to the other. As a direct result, control by hierarchy by the superior is expected and natural. Therefore, this could explain that a control by values like loyalty and seniority is widely spread in Chinese companies [START_REF] Max | The nature of managerial work in the Chinese Enterprise Reforms. A study of Six Directors[END_REF][START_REF] Léon | L"influence des valeurs confucéennes durant le processus de contrôle organisationnel au sein des entreprises chinoises en Asie : Etudes de cas en Chine, à Singapour et à Taiwan[END_REF]. Respecting traditional values seem to be of much importance for Chinese employees since these social standards are largely taken into account in their career plan design. For instance, loyalty to the Party in general and to superiors in particular is considered as an important criterion for job promotion [START_REF] Chen | Asian management systems[END_REF].

Paternalism is derived from the five cardinal relationships (wu lun) that rule personal interpersonal relationship. According to Scoville et al (2005), Chinese tradition has a long history regarding government as a parent and the term "parent officials" are still used to local government functionaries. These authors carry on (p.101), "organizations and leaders should treat their employees like children -with ren (benevolence) -and employees in return should exhibit zhong (loyalty) and yi (righteousness or appropriate behaviour) to the organizations and leaders. [START_REF] John | Management in China during the age of reform[END_REF] documents that some SOEs use paternalism. During the period of reform, Child reports that the director has to display continuously a Confucian benevolence towards employees and is expected to get involved intimately into workers" personal and professional problems (e.g. education, housing, health).

In China like in others Asian countries, group orientation is favoured whereas in many Western societies the value system places a greater emphasis on individual rights [START_REF] Silva (de) S | Elements in the shaping of Asian Industrial Relations, International Labour Organization (ILO)[END_REF]. Group orientation is also part of Confucian tradition which emphasizes ties of kinship or close personal relations. As we mentioned earlier, individual exists through his relations with others. One individual can develop his career and personal affair through community. Xing (1995, p.17) notices that "the individuals exist for the benefit of the group, group pressure is applied to ensure conformity through eliciting shame (losing face), and conflict is generally handled through intragroup mediation rather than an external legal system". For [START_REF] Xing | The Chinese Cultural System : Implications for Cross-Cultural Management[END_REF], the group orientation is expressed by danwei, where the focus is not only on work-related activities but also on exercises and control in non-work areas. "As a result, the social needs of the people in a workplace tend to be ranked higher than autonomy and self-actualization needs" (Xing, 1995, p.17).

Management-workers relations through the practice of socialization rules

In familism or group orientation, relations have to be kept harmonious. To reach this purpose, socializations rules as said before are to be practised and respected by each other. Mianzi (face), pao (reciprocity), renqing (humanized obligations), guanxi are part of these rules. When one individual does not fulfil one of the values, he breaks the rules and risks to be ignored by the group and so, not to benefit from its support. It is said in Cantonese common language that he does not know how to behave like human (bu hui zuo ren).

Giving face (mianzi) to one superior by his subordinate allows maintaining group harmony. If one worker criticizes his superior, it means that he does not respect his authority by making his superior lose face and he interrupts their mutual obligations, that of worker to respect and giving face and that of the superior to protect and help his workers. The worker runs the risk that his superior will not take care of him or he will give him bad evaluation. Challenging one superior especially in public or to be in conflict with him is not an appropriate and expected behaviour. As an example, subordinates commonly avoid to ask questions during a meeting if his direct superior also attends it in order to preserve and protect his face [START_REF] Léon | L"influence des valeurs confucéennes durant le processus de contrôle organisationnel au sein des entreprises chinoises en Asie : Etudes de cas en Chine, à Singapour et à Taiwan[END_REF]. In such an environment, asking a question can be interpreted as a sign of incompetence by his superior. Moreover, hierarchical difference has to be respected. In the interest of harmony, one individual will publicly obey but will defy privately [START_REF] Hwang | The Deep Structure of Confucianism: A Social Psychological Approach[END_REF]. One subordinate pursues his personal goals privately when possible. Scoville et al (2005, p.102) observe that "employees who feel work requirements are too demanding may never raise objection directly, but they reduce effort when unobserved by superiors".

Management-workers relations have also to be based on mutual obligations, pao (reciprocity). Management has to show ren (benevolence) and protection towards workers whereas workers have to be loyal and righteous. According to Scoville et al (2005), the SOEs operate post-1949 respect this reciprocity. Employees enjoyed lifelong benefits and employment. In return, workers showed reverence and loyalty to superiors. If one dishonours pao, group harmony is broken. Walder (1989 10 quoted by [START_REF] Bill | Industrial Relations in China[END_REF] analysed the management-labour relationship in Chinese SOEs in the 1980s and noticed an implicit agreement between management and workers. Management distributed to workers bonuses and others benefits not linked to their performance in order to garner their cooperation. Conflict is also avoided by not making working quotas too tight to the workers. The management seems to observe renqing (humanized feeling) to the workers. Another 10 Walder A. (1989), "Factory and Manager in an Era of Reform",The China Quarterly,No. 118 , example of giving renqing to his subordinate is when the superior does not sanction his bad performance [START_REF] Léon | L"influence des valeurs confucéennes durant le processus de contrôle organisationnel au sein des entreprises chinoises en Asie : Etudes de cas en Chine, à Singapour et à Taiwan[END_REF]. In some Chinese companies, employees are evaluated in term of how they will fulfil their « human obligations » (renqing) toward group or Society [START_REF] Léon | L"influence des valeurs confucéennes durant le processus de contrôle organisationnel au sein des entreprises chinoises en Asie : Etudes de cas en Chine, à Singapour et à Taiwan[END_REF].

Last but not least, guanxi (interpersonal relations, social networks) can play an important role in the relationship between management-workers. Recruitment, promotion and wages are often influenced by guanxi which shows in some circumstance favouritism or nepotism. The appointment of the Party members in SOEs or relatives and family members instead of competent out-group members is common practice in privates firms [START_REF] Léon | L"influence des valeurs confucéennes durant le processus de contrôle organisationnel au sein des entreprises chinoises en Asie : Etudes de cas en Chine, à Singapour et à Taiwan[END_REF][START_REF] Chen | Asian management systems[END_REF]. Giving guanxi depends on the closeness of the relations of the two parties. The relation is like a concentric circle where the nucleus is family, the next circle is made of close friends and the most distant circle is stranger. [START_REF] Hwang | The Deep Structure of Confucianism: A Social Psychological Approach[END_REF] reminds us that in Confucian ethical system, there are two fundamental rules: honour the superior and favour the intimate. Employee referral is also widely used to recruit lower levels jobs as hiring one employee is a social or ethical control. By selecting people from guanxi and from other employees" recommendations, some Chinese companies chiefly seek to control their attitude and behaviour. Wang (1997) also notes that many private employers hired people based on family connections or referrals.

Conclusions

Industrial relations in China have changed importantly since 1949 to nowadays. The main change concerns the transition from "iron rice bowl" system to a more tripartism system. However, Chinese industrial relations are peculiar and different from those found in some Western countries. In China, trade unions and directors of SOEs are not really independent from the State or local governments. In private Chinese firms, trade unions seem to be low. The management-workers" relations are still from time to time based on Confucian socialization rules than on a contract-based system. For example, in some SOEs, within a formal organizational chart where authority is bound to hierarchical function, there has in parallel an informal chart which structures interpersonal relationships and is based on Confucian values [START_REF] Léon | L"influence des valeurs confucéennes durant le processus de contrôle organisationnel au sein des entreprises chinoises en Asie : Etudes de cas en Chine, à Singapour et à Taiwan[END_REF]. Feelings prevail sometimes rules. The goal to be reached of both parties is to maintain social harmony. The conflict of interest between management and workers are reduced or even low if each party honours their mutual obligations. Our study has explained the main features of Chinese industrial relations, particularly management-workers relations, through socio-cultural lens with Confucian values. These latter seem to influence the way on how the industrial relations have progressed in China or why the industrial relations taken place in China diverge with those encountered in Western countries. But, we have at the same time to be cautious when saying that Chinese culture, in particular Confucianism, can explain solely and shape a specifically "Chinese" industrial relations system. Industrialization processes, economic, politic social systems, globalization and others Chinese thoughts (Taoïsm, Legalism and Buddhism) also influence the industrial relations. According to de Silva (1998, p.2), "one fundamental reason for the divergence between Western and Eastern (and developing country) industrial relations systems is to be found in the different industrialization processes followed and the consequences for social systems such as industrial relations".

Besides, Confucian values seem to soften conflict of interests but do not erase it. As the market economy becomes a daily reality, labour disputes and problems exist and even increase since the promulgation of labour law. The value for money which is also important in China [START_REF] Léon | L"influence des valeurs confucéennes durant le processus de contrôle organisationnel au sein des entreprises chinoises en Asie : Etudes de cas en Chine, à Singapour et à Taiwan[END_REF] and a raise in self-interest [START_REF] Wrathall | The impact of economic reform and associated changes in regulatory and institutional arrangements on the role of trade unions in the People"s Republic of China[END_REF] could explain the increase in labour turnover and recruitment problems in China. The financial incentives may be important for Chinese instead of the motivation by values and respect of Confucian values. In this case, traditional values may not have strong effect as in the past. To verify this, further research could look at Chinese private companies in China. A comparison with large overseas Chinese companies which seem to be more westernized in their management, at least in appearance may also be relevant to analyse management and workers relations. Any way, Chinese are pragmatic and any model or values that lead to stability and maintain harmony in labour relations will be reinforced or implemented in China. For now, Confucian values seem to play this role as the government seems to demand its coming back progressively as a State doctrine.

Published in Journal of ManagementSpirituality and Religion, Vol. 5, Issue 4, December

At the national level, Labour Ministry represents the State, the Chinese Enterprise Directors" Association (CEDA) represents employers and the All China Federations of Trade Unions represents the workers officially[START_REF] Warner | An emerging model of employment relations in China : A divergent path from the Japanese ?[END_REF]

All China Federation of Trade Unions (ACFTU) which was created in 1925 to act as a part of labour administration to coordinate with the State in supervising the workforce.

In Budd, Scoville (Ed), The Ethics of HumanResources and Industrial Relations, 2005

« virtue » does not mean an opposition to vice but rather like in the latin virtus, the natural influence or charism that someone has and that imposes without any particular force to other, and above all without resort to any external coercitive »(Cheng, 1997, p.74)

Culture and Work Organization : The Chinese Case in Kao H., Sinha D., Ng S.H. (1994), Effective Organizations and Social Values, Sages Publications, 352 pages