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In acidic liquid ammonia, the anodic behaviour of the p-GaAs semiconductor is strongly different than in aqueous media. The anodic process in liquid ammonia involves the formation and adsorption of a thin film onto the p-GaAs surface. This thin film leads to the oxidation of the solvent. The initial state of the semiconductor electrode was recovered by photoreduction of the thin film.

Investigation of oxide chemistry and reactivity of III–V semiconductors has been undergone with an electrochemical approach coupled with surface analysis. Growth and stability of anodic oxides obtained on n-GaAs and n-InP was investigated with potensiostatic mode under illumination at pH 9. For the two compounds, the transient photocurrent, the recovery of the photocurrent and XPS analysis were performed in the same conditions. InP and GaAs present very different behaviours, which are linked to the stability of the oxidised interface. InP evidences a thin, stable and electrically blocking oxide film, while GaAs exhibits a thicker, unstable and porous oxide layer. This work point out that XPS analysis has to be coupled with in situ techniques as transient photocurrent, to understand accurately the oxide growth mechanism.

Surface films are obtained on Hg 0.79 Cd 0.21 Te and CdTe by treatment in a solution of 0.1 M Fe(CN) 6 3 (ferricyanide) in 0.5 M KOH. Composition profiles are obtained by X-ray photoelectron spectroscopy (XPS), and they reveal the presence of cadmium oxide (CdO) and elemental tellurium (Te 0 ). The film on Hg 0.79 Cd 0.2 21 Te is porous and thick (e.g. 800 A), whereas the film on CdTe is nonporous and thin (

As conventional 2D scaling of microelectronic devices shows limitations, 3D chip stacking is clearly identified as a solution for performance gain at lower cost in applications such as image sensors, stacked memories, high performance processor-memory assemblies and advanced system in package (SiP) leading to heterogeneous integration. In that respect, Through Silicon Via (TSV) technology is one on the key process step to enable new interconnection schemes. Metallization of TSV structures is currently attracting a lot of attention due to the multiple technical challenges associated with this new technology [K. Kondo, T. Yonezawa, D. Mikami, T. Okubo, Y. Taguchi, K. Takahashi, D.P. Barkey, J. Electrochem. Soc. 152 (2005) H173; O. Luhn, C. Van Hoof, W. Ruythooren, J.-P. Celis, Electrochim. Acta 2007, doi:10.1016/j.electacta.2008.04.002]. Copper electrodeposition has soon been identified as a technique of choice for such connections based on the widely acceptance of copper as wiring material for submicronic interconnections [T.P. Moffat, D. Wheeler, M. Edelstein, D. Josell, IBM J. Res. Dev. 49 (2005) 19; J. Reid, Jpn. J. Appl. Phys. - Part 1 40 (2001) 2650]. However, the specificity of TSV structures, combining both high aspect-ratios and via depth ranging from tenth to several hundred microns, implies the development of new deposition methodologies and chemistries. In particular, the mode of action of organic additives (accelerator, suppressor and leveller) promoting the so-called ''bottom-up filling'' can be greatly affected by mass transportation and convection effects associated with large volumes TSV vias compared to Damascene structures. Here we present a study aiming at optimizing the accelerator concentration in the plating bath in order to maximise the copper deposition rate while preserving a reduced overburden at the via mouth. Cyclic voltammetry data correlated with filling experiments conducted on [email protected] vias with an aspect-ratio of 2, will be presented in order to better understand the relationship between chemical composition and process efficiency in such TSV structures.

The electrical response of Pt microelectrodes, with a radius of 10 μm, was studied in liquid ammonia (−50°C). The question of a suitable time scale for steady state measurements in liquid ammonia is important. The proton reduction currents were measured for different scan rates. A suitable experimental time scale of 20 mV s −1 was determined to reach a stationary state. The diffusion coefficient of protons in liquid ammonia was deduced from these electrochemical results: D (NH 4 + ) NH 3 =(3.8±0.4)×10 −9 m 2 s −1 .

The photoanodic dissolution of n-GaAs was investigated in a buffered solution at an intermediate pH (pH 9). At this pH, the GaAs dissolution rate was limited by the growth of an anodic oxide film. A laser illumination leads to a local oxide growth only in the illuminated part on to GaAs. Transient photocurrent and capacitance measurements clearly show dissolution kinetics in two steps: the first step is about a few tens of seconds and is correlated with gallium oxide dissolution, and the second step is greater than a few minutes, indicating the origin of at least two surface films onto GaAs. A parallel approach using in-situ electrochemistry and ex-situ surface analysis (XPS) was performed to characterise the growth of an anodic film on to GaAs. A gallium enrichment was detected on this oxide film. The arsenic deficiency in this oxide results from a higher arsenic oxide solubility. The limitation of the GaAs dissolution is due to the dissolution of gallium oxide at pH 9.

Photoluminescence (PL) was used as an in situ method for studying the electrodeposition of copper on p-GaAs. During electrodeposition, PL of GaAs decayed due to growth of the metallic layer, and the PL signal was sensitive to a fraction of a monolayer of copper. Recovery of the initial PL intensity was observed after anodic stripping of the copper deposit. A quantitative empirical relationship was established between the PL decrease and the amount of deposited copper. Variation in PL intensity is mainly due to modification of the optical properties of the interface rather than to a change in semiconductor band bending. PL can be a convenient method for monitoring metal electrodeposition on other semiconductors too.

The use of buffered neutral liquid ammonia medium for the first time provided evidence for a current doubling effect on p-InP during oxygen photoreduction. Unlike results in aqueous medium, a common mechanism of O2 reduction was observed at p-InP and p-GaAs electrodes. When protons were added to the solution, two different oxygen reduction mechanisms occurred at these electrodes. This study emphasizes the important results of the hydrogenated p-InP surface and revealed that liquid ammonia (at 223 K) was perfectly appropriate to understand the mechanism of O2 reduction at InP electrodes.

Photoluminescence was used as an in-situ method for following the electrodeposition of copper on p-type GaAs electrodes from a 0.5 M H2SO4 solution containing Cu(II) sulphate. The method appeared to be very sensitive to copper coating and to be able to detect a copper amount of the monolayer range. Moreover, during anodic polarisation of the metallised electrode, photoluminescence measurements showed the complete dissolution of the copper layer. In-situ photoluminescence measurements were confirmed by ex-situ analyses at different stages of the electrochemical treatment of the GaAs electrode.

Copper electrodeposition was performed on an n-type InP electrode at two different potentials: −0.55 and −0.90 V (MSE). For each deposition potential value, the compactness of the deposit is discussed, on the basis of SEM observations and line profile analysis of the surface of the coated electrode. A clear difference in the morphology of the layer appeared and a more homogeneous film was observed, when the deposition was performed in the higher overpotential conditions (at −0.9 V). Copper deposits obtained in an acidic solution were then reoxidized in an alkaline medium (10 −2 M KOH), and two different voltammograms could be observed for a given copper amount depending on the initial deposition potential. This difference poses the problem of the nature of the path of the interfacial charge transfer on a semiconducting InP sample with homogeneous or heterogeneous copper coverage.

The electrochemical behaviour of a copper coated p-type InP electrode has been investigated. The copper coating was obtained by electrodeposition from a Cu 2+ containing sulfuric acid solution under illumination. This reduction reaction can compete with H + reduction and with its side reaction, the cathodic decomposition of InP, depending on the illumination level, on the Cu 2+ concentration in the electrolyte, and on the rotation speed of the electrode. It appears that when the amount of Cu 2+ at the InP|electrolyte interface is sufficient to convert the whole flux of the photocarriers, the Cu 2+ reduction becomes the main photoprocess, hindering the hydrogen evolution and the cathodic decomposition. A metal deposit up to about 100 equivalent monolayers can form on the electrode surface without any decrease of the photocurrent, as a result of a non-uniform coverage rate of the metal.

In liquid acidic ammonia, the mechanism of oxygen reduction begins as in acidic aqueous solutions, by the successive contribution of the conduction band and then of the valence band (doubling effect). However, unlike in the acidic aqueous solutions, soon after the oxygen photoreduction, an activation process of the p-GaAs surface is initiated, tied to the presence of protons in the solution. This activation of the surface allows the passage from a reduction mechanism via a conduction band to a reduction mechanism via a valence band (oxygen reduction in the dark).

Zn(S, O, OH) represents the most studied Cd-free material for replacing chemical bath deposited (CBD)-CdS buffer layers in Cu(In, Ga)Se2-based solar cells. However, the record performances remain lower than the CdS. The aim of this work is to study new bath compositions for CBD-Zn(S, O, OH), by introducing new complexing and non-complexing reactants for higher efficiencies, and to analyze their effects on growth mechanisms. Promising bath compositions based on the combined used of H2O2 and tri-sodium citrate have been developed, and could be a new avenue to outperform the CdS-based solar cells.

International audience; Topography and chemical evolutions of the iridium surface in the successive steps of bias-enhanced nucleation and growth were investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), and nano-Auger analyses. This sequential approach, which was performed in localized areas at the nanoscale, provides three new experimental and complementary concepts that can enhance the knowledge of nucleation pathways on iridium. First, SEM imaging at low-acceleration voltage enables the detection of diamond nuclei or stable precursors after the BEN step. Second, domains consist of iridium furrows that are covered by an amorphous carbon overlayer, with a thickness of 6.8 nm, according to AFM and X-ray photoemission spectroscopy data. Third, SEM observations also suggest a close relationship between furrows created under ion bombardment and domains in our study conditions. These results prompted us to propose a scheme that describes the topography and surface chemistry of domains.

The surface chemistry of CdTe was studied by XPS and X-AES. Interface modifications resulted from immersion in solutions containing either Ce 4+ or Fe(CN) 6 3- ions. Reproducible surfaces are obtained that allow the study of Cd X-AES spectra for different surface chemical compositions.

Photoluminescence techniques are used as a probe of energetic surface band edge configuration for n-type CdTe in the presence of Ce 4+ ions. The band shift observed for a part of the potential range is perfectly detected by photoluminescence. The results agree with those obtained from capacitance measurements. The photoluminescence response has been modelled according to the dead layer model, using as fitting parameters the donor density N D and the flat band potential V FB . The best agreement between our experimental results and those predicted by the model is obtained with the donor density derived from the capacitance measurements.

International audience; Our recent paper has reported the determination of diffusion area, A(Diff)O(2), related to oxygen reduction reaction (ORR) in porous electrodes structures based on Platinum Organically Grafted Electrocatalyst (Pt-OGE) nanoparticles and carbon nanotubes. It was clearly shown that diminishing the electrocatalyst coverage density at the carbon nanotube surface resulted in a strong increase of A(Diff)O(2), though some of the trends observed as a function of platinum loading were not clearly understood. Previous work considered the ORR selectivity, i.e. n, the average electron number exchanged per 02 molecule as being 4 whatever the Pt loading and the electrode feature. The present paper addresses this point using a recently reported new method for the determination of selectivity that can be implemented directly on porous electrodes, without using rotating disc or ring disc electrodes. Then, the paper considers the determination of specific A(Diff)O(2) (S-A(Diff)O(2)) as a function of electrocatalyst loading on both, porous electrode based on Pt-OGE's grafted with Low Molecular Weight Organic (Pt-LMWO) and with High Molecular Weight Organics (Pt-HMWO). For five kinds of porous electrode structures combining carbon nanotubes and involving both kinds of Pt-OGE's, the n corrected trends for S-A(Diff)O(2) expressed in m(2) gPt(-1), are discussed. It is highlighted that for a given porous Pt-OGE/carbon nanotubes electrode structure two feature parameters can be found: a S-A(Diff)O(2) value independent of Pt loading for which the value of n is found to be approximate to 4, and a critical electrocatalyst loading below which n < 4 and S-A(Diff)O(2) deviates from its feature value. These trends are explained in the frame of small sized electrodes arrays at which spherical diffusion regime occurs. As a conclusion, it is finally proposed that S-A(Diff)O(2) could be considered as a feature parameter of interest to characterize the ORR electrocatalysts in porous electrode structures.

International audience; In previous work we reported oxygen reduction reaction (ORR) studies on porous electrodes based on capped platinum (Pt) electrocatalyst and carbon nanotubes. These structures exhibited a significant activity but a very low platinum electrochemically active surface area (Pt-EASA) due to the grafted molecules on the platinum core nanoparticle surface. The present paper reports on thermal pre-treatment of such electrodes at moderate temperature aiming at degrading the organic capping without changing the nanoparticle Pt core feature. Using X-ray diffraction, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) it is shown that a treatment at 100 C under air fit these requirements. This results in a strong increase of the Pt-EASA. However, it is evidenced by TEM and XRD that, as soon as the organic capping is modified by partial oxidation of sulfur atoms involved in initial strong Pt-S bond, the electrochemical measurement triggers dramatic changes on the Pt dispersion and Pt core feature. Much bigger size Pt regions are formed, complete oxidation of the sulfur atoms is observed and organic capping molecules are significantly eliminated in the electrolyte. Finally, although it was not possible to prove systematically that we get rid of organic contamination after the involved treatments, the dramatic changes of Pt catalyst nanoparticles compared to the initial organically capped ones are clearly established. These original results demonstrate the essential stabilizing role of the grafted thiol molecules in the initial system and allow proposing a scenario for the ageing of these capped electrocatalyst when submitted to prolonged ORR.

Many modern technologies are based on materials that are deposited on special underlying materials. Optical coatings can prevent tarnishing, give anti-reflection benefits, and in some cases filter out harmful UV rays. In consumer devices, many modern optoelectronic devices that make up a vast majority of electronic products such as active displays, touch screens etc. are based thin film transistors and transparent materials, as are parts of solar cells, smart windows, antireflection coatings for a range of devices and applications, anti-fingerprint and antifogging glass, among many other modern uses of see-through materials and coatings with well-defined characteristics in visible light. While the science and technology of controlling materials into a whole host of electronics and photonic or optical devices has advanced considerably in the last decade, industry still requires all this to be done without using critical raw materials, expensive coating methods that are often very slow, and to do so at much lower temperatures for coating on to curved or flexible displays or materials – all without sacrificing quality that current methods provide. Here, we report a facile solution processed technique for the formation of a transparent thin film through an inter-diffusion process involving substrate dopant species at a range of low annealing temperatures compatible with processing conditions required by many state-of-the-art devices. The inter-diffusion process facilitates the movement of Si, Na and O species from the substrate into the as-deposited vanadium oxide thin film forming a composite fully transparent V0.0352O0.547Si0.4078Na0.01. Thin film X-ray diffraction and Raman scattering spectroscopy show the crystalline component of the structure to be α-NaVO3 within a glassy matrix. This optical coating exhibits high broadband transparency, exceeding 90-97% absolute transmission across the UV-to-NIR spectral range, while having low roughness and free of surface defects and pinholes. The production of transparent films for advanced optoelectronic devices, optical coatings, and low- or high-k oxides is important for planar or complex shaped optics or surfaces. It provides opportunities for doping metal oxides to new ternary, quaternary or other mixed metal oxides on glass, encapsulants or other substrates that facilitate diffusional movement of dopant species. References (1) C. Glynn, D. Creedon, H. Geaney, T. Collins, E. Armstrong, M. A. Morris and C. O'Dwyer, Sci. Rep., 5, 11574 (2015). (2) C. Glynn, D. Aureau, G. Collins, S. O'Hanlon, A. Etcheberry and C. O'Dwyer, Nanoscale, 7, 20227 (2015). (3) S. O'Hanlon, C. Glynn and C. O'Dwyer, ECS J. Solid State Sci. Technol., 5, R3100 (2016). (4) K. K. Banger, Y. Yamashita, K. Mori, R. L. Peterson, T. Leedham, J. Rickard and H. Sirringhaus, Nat. Mater., 2011, 10, 45-50. (5) K. Ellmer, Nat. Photon, 2012, 6, 809-817. (6) C. G. Granqvist, Thin Solid Films, 2014, 564, 1-38. (7) H. Dotan, O. Kfir, E. Sharlin, O. Blank, M. Gross, I. Dumchin, G. Ankonina and A. Rothschild, Nat. Mater., 2013, 12, 158-164. Figure 1

We report an attempt to provide evidence for the doping-dedoping of lithium cations into an F−-doped SnO2 transparent conductive substrate. The investigation was performed in anhydrous acetonitrile charged with alkaline salts containing Li+ ions: 0.1 M LiBF4 and 0.1 M LiSO3CF3. After polarization in a potential range sufficiently positive to ensure that Li deposition does not occur, the material was analyzed by scanning electron microscopy and energy-dispersive X-ray analysis, and the chemical composition of the surface layers was determined by X-ray photoelectron spectroscopy.

Silicon nitride is a common material in the microelectronic industry, thanks to its dielectric, chemical and mechanical properties. However, when exposed to atmosphere, the silicon nitride layer tends to oxidize. This work presents several efficient ways to remove this native oxide layer while controlling the resulting surface chemistry. Achieving such a control may provide a reliable starting point for further surface functionalization by organic molecules. The silicon nitride thin films are deposited by magnetron sputtering. The silicon nitride stoichiometry can be tuned by varying the gas fluxes (Ar, N2) during deposition. Three wet treatments are studied and optimized: hydrofluoric acid (HF), ammonium fluoride (NH4F) and potassium hydroxide (KOH). The treatment efficiency is controlled by X-ray Photoelectron Spectroscopy measurements (XPS). The surface chemistry is investigated by combining Attenuated Total Reflection InfraRed (ATR-IR) and XPS measurements. All of the three chemical treatments yield the removal of the native oxide, albeit at different rates. HF solution is an efficient and fast etching treatment of silicon nitride. On the resulting surface, fluorine is detected by XPS, suggesting the presence of Si-F bonds. No Si-H bonds are detected on the etched surface by ATR-IR, in agreement with the literature results. NH4F solution is as efficient as HF in etching the silicon nitride surface, although much slower. This also leads to Si-F bonds, but in a lesser amount than after a HF treatment. KOH can also etch the native oxide of the silicon nitride layer. In this case, the resulting surface contains more oxygen than with the two previous solutions, a likely fingerprint of the presence of surface Si-OH species. Interestingly, the etching rate of the bulk silicon nitride appears much reduced upon etching with KOH as compared to HF. The formation of Si-H bonds can be forced thanks to a H2plasma treatment performed after the wet native oxide stripping. As shown in the figure, a broad SiH stretching vibration builds up in the infrared spectra upon submitting the silicon nitride film to such a plasma treatment at room temperature. The detailed analysis of XPS signals of samples submitted to various treatment durations shows that the initial surface Si-F bonds are not broken by the plasma, but that the silicon nitride film is progressively etched during the treatment. The film roughens during its dry etching, accounting for the large increase of the SiH signal. An important parameter we also investigated is the silicon-nitrogen ratio. The chemistry of the etched surface is highly dependent on this ratio. As shown in the figure, with a silicon-rich silicon nitride layer, a HF treatment leads to the formation of some Si-H bonds on surface. Figure 1

The electrochemical behaviour of n - and p -GaSb samples was explored with or without Ce 4+ salts diluted in 2 M H 2 SO 4 solutions. In the presence of Ce 4+ we observed a typical reduction current that is attributed to a pure hole injection during the Ce 4+ reduction in Ce 3+ . As for the other III–V compounds, the holes collected at the surface give rise to the anodic dissolution of the material. No electron injection was observed in the conduction band from corrosion intermediates. All the processes take place on a Sb-enriched oxidized surface characterized by XPS measurements. The two-step process of the GaSb dissolution in the presence of Ce 4+ species is not perturbed by this Sb-enriched oxidized surface.

In the present work, gallium arsenide is submitted to hydrogen radiofrequency plasma, and cadmium telluride either to hydrogen radiofrequency plasma, to hydrogen implantation by a Kaufman source or to annealing under molecular hydrogen gas. The different hydrogen treatments induce a modification of the surface stoichiometry, resulting in cation (Ga or Cd) enrichment compared to the initial chemically etched surface, and a deoxidation of the semiconductor surface. This new surface chemical state is more or less stable with respect to further oxidation in air ambient. This stability in air is correlated to the difference from stoichiometry (gallium or cadmium enrichment) and the simultaneous accumulation of hydrogen in the superficial layers of the compound.

Journal: Advanced Functional Materials 22, 4900 (2012); International audience; We use hexagonal mesophases made of oil-swollen surfactant-stabilized tubes arranged on a triangular lattice in water and doped with metallic salts as templates for the radiolytic synthesis of nanostructures. The nanostructures formed in this type of soft matrix are bimetallic palladium-platinum porous nanoballs composed of 3D-connected nanowires, of typical thickness 2.5 nm, forming hexagonal cells. We demonstrate using electron microscopy and small-angle X-ray scattering that the pore size of the nanoballs is directly determined by the diameter of the oil tube of the doped mesophases, which we have varied in a controlled fashion from 10 to 55 nm. Bimetallic nanostructures comprising various proportions of palladium and platinum can be synthesized. Their alloy structure was evidenced by X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, and high-angular dark field scanning transmission electron microscopy experiments. Our templating approach allows therefore the synthesis of bimetallic nanoballs of tunable porosity and composition.

This study addresses the potential of different approaches to improve the generated current density in ultrathin Cu(In,Ga)Se 2 (CIGSe) based solar cells down to 0.1 µm. Advanced photon management, involving both absorption enhancement and reflection reduction in the absorber, is studied. In this contribution, the three main approaches used are: - The reduction of the CIGSe thickness by chemical etching which combines thickness reduc tion and smoothing effect on the absorber. - Optical management by front contact engineering and by the replacement of the back cont act by the "lift-off" of CIGSe layer from the Mo layer and the depositio n of a new reflective back contact. - Application of plasmonic structures to CIGSe solar cells enabling light conf inement at the subwavelength scale. Keywords: Solar cells, ultrathin CIGSe, light management, plasmonic 1. INTRODUCTION Reducing the thickness of the absorber is a strategic issue in the Cu(In,Ga)Se 2 (CIGSe) technology associated to the minimization of indium utilization [1]. During the last decade, an increasing attention has been brought to the preparation of thinner absorber layers in Cu(In,Ga)Se

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International audience; In order to develop novel electroactive hosts for biosensor design, the possibility to use nanostructured vanadate phases as alternatives to well-known V2O5 gels was studied. For this purpose, the formation of M[V3O8] and M-x[V6O16] (x = 1 and 2) oxides by the sol-gel process has been studied over a wide range of cations (M+ = Li+, Na+, K+, Cs+, and NH4+; M2+ = Ca2+, Mg2+ and Ba2+). By a combination of XRD, V-51 NMR and SEM studies, it was possible to evidence the influence of the nature and hydration state of cations on the size and morphology of the resulting particles as well as on the kinetics of their formation. On this basis, K-2[V6O16] was evaluated for glucose oxidase encapsulation, either via impregnation or co-precipitation methods. When compared to V2O5, these novel bioelectrodes exhibit higher stability under pH conditions of optimum enzymatic activity, as well as better sensitivity, and reproducibility for glucose detection via amperometric titration.

The effects of chemical sulphuration on GaSb mesa photodiodes performance were investigated by electrical characterization. (NH 4 ) 2 S treatment was found to be very effective in reducing the reverse dark currents by one module value, leading them down to I = 0.2 μ A (V = 1 V) for a φ = 60μ m diameter diode. The capacitance variation versus frequency, investigated from 10 kHz to 1 MHz, becomes flat over the whole range of frequency, attesting of a volume conduction mechanism. These performances exhibited a remarkable stability during 1 year, without encapsulation. The X-ray photoelectron spectrum of the Sb 3d level shows that after (NH 4 ) 2 S treatment the surface is free of native Sb oxides, Sb-.sbnd;S bonds being created by the adsorption of sulphur atoms on the surface These surface modifications are responsible for the observed improvement in characteristics and their stability.

Compounds (III)—(VI) and (VIII) are characterized by FTIR and UV/VIS spectroscopy, and magnetic susceptibility and electrochemical measurements.

Within the UltraCIS project we have started to explore the possibility of reducing down the thickness of the Cu(In, Ga)Se 2 (CIGSe) layer to the sub-micron level (0.1μm) while maintaining a high efficiency level of solar cells. The three main approaches we used are: — Reducing the CIGSe thickness by chemical etching combining the thickness reduction and smoothing effect of the absorber. Efficiency higher than 10 % on small area cells with an absorber thickness of 0.5 μm are obtained. Losses were attributed exclusively to the reduced photocurrent and the loss on texturation of the absorber — Optical management by front contact texturation or by replacement of the back contact by the “lift-off” of CIGSe layer from the Mo layer and deposition of a new reflective back contact. — Application of plasmonic structures to CIGSe solar cells enabling light confinement at the subwavelength scale

International audience; In this paper we report the determination of the diffusion area for oxygen reduction in porous electrode structure having a controlled platinum loading and based on capped platinum electrocatalysts and carbon nanotubes. Such a parameter is expected to be higher than the macroscopic geometrical area of the active porous layer. The oxygen diffusion area is determined by cyclic voltammetry after impregnation of the electrode structure by the electrolyte, and using the equations available for peak potential and peak current as a function of scan speed for irreversible redox couple. First it is found first that the oxygen diffusion area is dependent on the total amount of platinum in the electrode. Second, for a given platinum loading, the diffusion area is higher when the mass ratio of platinum to carbon nanotube decreases. This point indicates that the accessibility of platinum capped electrocatalyst is better in such cases. It is thus concluded that the oxygen diffusion area determination in porous electrode structures may be used to characterize the accessibility of the capped electrocatalysts for oxygen reduction. Even if this area is different in nature from the one calculated by Hydrogen Underpotential Deposition, we believe that its determination might be of interest for the characterization of porous electrodes structures in which the electrocatalyst is combined with a finely divided carbon support

The interface structure of the semiconductor/electrolyte junctions in nonaqueous solvents is an open question, and as in water, the study of the influence of pH on the flat band potential can lead to an important part of its knowledge and to applications such as pH measurements. In water, the flat band potential shifts of many semiconducting materials can be connected with pH shifts. In this paper we show it is the case for nInP electrodes in acetonitrile and methanol (96% in weight in water) at room temperature, and in liquid ammonia at low temperature, −55°C. Therefore this material can be used as a probe of pH. Using this property we were able to find again, for example, the values of the self-ionization constants of the studied solvents and the acidity constants of water in liquid ammonia and of acetic acid in methanol.

Using XPS and SIMS analyses combined with effusion experiments it is shown that hydrogen-plasma treatment of GaAs surface induces both a modification of the superficial stoichiometry and a loss of reactivity toward oxygen. This phenomenon is explained by the accumulation of hydrogen in the near-surface region. When this hydrogen is outgassed by thermal annealing, the GaAs recovers partially its reactivity toward oxygen.

In order to qualify the reactivity of various aluminium and silicon oxide substrates for elastomer adhesion applications, X-ray photoelectron spectroscopy (XPS) and rest-electrochemical potential measurements have been performed on those surfaces. The interpretation of XPS binding energy shift measurements in terms of Fermi level variation from one surface to another, as proposed by Mullins and Averbach in 1988, is discussed in view of results on an aluminosilicate compound surface. The correlation with electrochemical restpotential measurements on an anodized aluminium surface and a silane coupling agent is described and discussed. The possibility of surface reactivity assessment through correlated XPS and electrochemical measurements for metal oxides is demonstrated.

Epitaxial CdSe films have been electrodeposited on the (100) face of InP and GaAs single crystals. The quality of the epitaxy and chemical composition of CdSe films have been investigated by reflection high-energy electron diffraction, X-ray diffraction and XPS measurements. A good stability of the InP and GaAs surfaces, in presence of the deposition electrolytes, was found. The choice of the deposition parameters is crucial for the growth of epitaxial and stoichiometric layers.

The linear dependency of the n-InP photocurrent on the level of illumination is indepedent of the solution composition, the type of illumination, the exposed crystalline face, or the level of doping. The photodissolution mechanism (for photocurrents between 1.1 and 65 mA cm−2) utilizes six charges to dissolve one molecule. In the absence of an insoluble oxide layer, the ratio between photogenerated holes and injected electrons is independent of the exposed crystalline face, the photon flux, the solution composition and the level of doping. Solutions containing oxygen bearing mineral anions (such as ClO−4, H2PO−2, or SO−24) are predisposed to the formation of an insoluble oxide layer on the surface of the InP under strong illumination.

The use of buffered neutral liquid ammonia medium for the first time provided evidence for a current doubling effect on p-InP during oxygen photoreduction. Unlike results in aqueous medium, a common mechanism of O2 reduction was observed at p-InP and p-GaAs electrodes. When protons were added to the solution, two different oxygen reduction mechanisms occurred at these electrodes. This study emphasizes the important results of the hydrogenated p-InP surface and revealed that liquid ammonia (at 223 K) was perfectly appropriate to understand the mechanism of O2 reduction at InP electrodes.

International audience; Recently we reported the preparation and electrochemical behaviour of porous electrodes based on the controlled combination of carbon nanotubes and capped platinum nanoparticles towards oxygen reduction. Due to the organic crown of the nanoparticles, the electrodes exhibited low hydrogen underpotential deposition (H upd) electroactive surface areas but significant activity towards oxygen reduction was recorded down to very low platinum loadings of few mu g/cm(2). While the presence of organic stabilizing material, at the surface of the electrocatalyst synthesized by wet chemistry, may be considered as a potential drawback in fuel cell community, we present in this paper results showing that our capped electrocatalyst associated with carbon nanotubes can be used without any pre-treatment and exhibit high performances in fuel cell devices, in spite of low platinum loadings. Beyond the practical interest of such capped nanoparticles in fuel cell technology demonstrated here, fundamental question related to the high performances of the capped electrocatalyst are still opened and are currently under investigation.

No comment; International audience; Polyurethane (PU) catheters made of Pellethane 2363-80AE® were treated in two different ways: a new treatment with low temperature plasma that could be used to decontaminate reusable polymer devices in hospitals, and an e-beam (EB) irradiation. Polymer structure and bulk properties were studied by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), infrared spectroscopy (FTIR) and size exclusion chromatography (SEC). Although PU was strongly modified by the e-beam irradiation leading to branching of polymer chains, it had no or little impact on the thermo-mechanical properties of the catheters and on the hard/soft segment organization of PU. For plasma-treated samples, no modification in the polymer bulk was observed, confirming that plasma treatment might be considered as an alternative to e-beam irradiation. The analysis of surface modifications showed an evolution of superficial topology and chemical composition (grafting of oxygen and nitrogen species) of the catheters after treatment, with a more polar and hydrophilic surface. © 2009 Elsevier Ltd. All rights reserved.

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Institut Lavoisier de Versailles, CNRS-UMR 8180, PRES UniverSud, Universite de Versailles Saint-Quentin-en-Yvelines, 45 Avenue des Etats-Unis, 78035 Versailles Cedex, France FIELD Email Address: English; Gold nanorods synthesized by radiolysis were selectively end-functionalized by a fully conjugated thiol bearing a pendant terpyridine group; addition of ferrous ions led to the end-to-end 1D self-assembly of the nanorods. Similar results have been obtained when the preformed [(HStpy)Fe(tpySH)](2+) dithiol complex was directly added to the gold nanorods.[on SciFinder (R)] FIELD Check Tags

Quantitative XPS analysed are carried out to study the III-V semiconductor/solution interface. In the presence of ceric ions (Ce 4+ ) solvated acid (H 2 SO 4 , 0.5-2 M), III-V compounds undergo a dissolution which is completely goverged by an electrochemical process. Competition between a superficial oxide growth and its quasi-simultaneous dissolution determines the behaviour of the interface as a function of time. On Inp some typical surface evolutions are observed, such as a decrease in the hole injection current during the reduction of cerium oxidized species

The linear dependency of the n-InP photocurrent on the level of illumination is indepedent of the solution composition, the type of illumination, the exposed crystalline face, or the level of doping. The photodissolution mechanism (for photocurrents between 1.1 and 65 mA cm−2) utilizes six charges to dissolve one molecule. In the absence of an insoluble oxide layer, the ratio between photogenerated holes and injected electrons is independent of the exposed crystalline face, the photon flux, the solution composition and the level of doping. Solutions containing oxygen bearing mineral anions (such as ClO−4, H2PO−2, or SO−24) are predisposed to the formation of an insoluble oxide layer on the surface of the InP under strong illumination.

Ultrathin palladium hexagonal nanosheets were synthesized in emulsions constituted of droplets of toluene containing Pd complexes in water and stabilized by CTAB as surfactant and in quaternary mesophases formed by water, toluene containing Pd complexes, CTAB, and a cosurfactant. We have identified slow reduction and nucleation provided by CO and adsorption at the CTAB interface as key factors for the formation of Pd nanosheets. These nanosheets exhibit a broad absorption band from the visible to the near-infrared region.

In the frame of an investigation on adhesion phenomena between elastomers and oxide substrates, X-ray photoelectron spectroscopy (XPS) and rest electrochemical potential measurements have been used in order to attempt a characterization of the reactivity of various oxides. The first step of the study is a definition of donor/acceptor properties for a solid surface in an interactive model such as the Lewis one. In this case, the Fermi level is an appropriate parameter. An experimental approach is developed to estimate this parameter through photoelectronical data obtained by XPS. As proposed by Mullins and Averbach in 1988 in the case of Al and Si oxides, XPS allows an estimation of the Fermi energy EF, defined as the energy difference between the Fermi level and the upper occupied valence band. A classification of EF values is obtained for different samples of aluminum and silicon oxides; the donor (acceptor) behavior increases for decreasing (increasing) EF. The second step is the validation of the EF classification obtained by XPS. A potentiometric method is used to estimate the rest potential Eo in aqueous solution. The relationship between the Eo and the solution pH is a Nernst law for a large range of pH values, which means that the system is governed by acid-base interactions in Bronsted definition in the interfacial area. When the nature of the oxide substrate is modified, the translation of the Eo versus pH line can be correlated with the EF classification obtained previously. This confirms the relationship already reported between point of zero charge and EF. It can also be considered as a validation of the idea that XPS allows the classification of EF values for those oxides.