Electrochemical energy conversion devices, such as polymer electrolyte membrane fuel cells (PEMFCs) and PEM electrolyzers are considered as possible candidates for integration in future renewable energy network 1,2 . However, the oxygen reduction reaction (ORR) kinetic at the cathode of a PEMFC is slow and the overpotential at the cathode is generally high (higher than 0.200 V), whereas that of the hydrogen oxidation at the anode is ca. 0.050 V 3 . For this purpose, platinum (Pt) or its alloys are often required as electrocatalyst because of their excellent catalytic activity for the ORR 4 . Electrocatalysis involves surface reactions, therefore, a high surface/inner atoms ratio is desirable to improve the Pt nanoparticles (Pt NPs) performance. NPs with size ranging between 2 to 4 nm are generally preferred 5 .NPs can be obtained through various physical, chemical or physicochemical routes 6,7 . The chemical methods are very versatile in terms of controlling NPs shape and size by varying the reaction conditions. However, NPs chemical synthesis requires additives, which generate by-products difficult to remove and NPs with limited purity. In contrast, physical methods (such as sputtering, thermal evaporation, laser ablation, spark discharge…) on solid substrates avoid the use of additives, allowing the production of pure metallic NPs with the same material composition as that of the starting material. Moreover, these methods can be considered as green approaches using non-toxic reducing agents and avoiding the formation of byproducts 8 . Among physical techniques for preparing electrocatalytic NPs, magnetron sputtering is known to produce efficient Pt NPs deposited on a microporous carbon layer 9 or on a polymer electrolyte membrane 10 to directly fabricate the catalytic layer composite. However, using the sputtering method for the deposition of metal NPs onto such substrates often makes the control of the NPs properties (size, dispersion and morphology) complex. Moreover, this process makes also difficult to create three phase boundaries by the addition of ionomer in comparison with the conventional liquid ink preparation techniques based on classical chemical processes for carbon supported NPs. A solution consists in synthesizing NPs directly in a liquid phase using magnetron sputtering technique and to disseminate the NPs onto a porous substrate. This innovative method

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Molecular dynamics simulations have been performed to study the growth and the final structure of PtxBi1-x clusters under conditions close to those encountered in classical low temperature chemical or physical synthesis methods, such as the water-in-oil route or plasma sputtering route, respectively. According to the simulations, PtxBi1-x nanoparticles should consist in well crystallized Pt core surrounded by Bi structures, with strong interaction between Pt and Bi atoms. The simulation results were compared with physicochemical characterizations of PtxBi1-x/C (x = 1.0, 0.9 and 0.8) materials synthesized at room temperature via the water-in-oil microemulsion method. XRD and XPS measurements led to the conclusion that Pt and Bi were not alloyed in PtxBi1-x nanoparticles and that the nanoparticle surface was bismuth-rich, respectively, in perfect agreement with molecular dynamics simulations. XPS and electrochemical measurements allowed also demonstrating a strong electronic interaction between Pt and Bi, still in agreement with molecular dynamics. The electrocatalytic behaviors of the PtxBi1-x/C catalysts have been studied. PtxBi1-x/C displayed the higher activity towards glycerol electrooxidation in alkaline media, with an onset potential of ca. 0.300 V vs RHE and a unique selectivity towards glyceraldehyde/dihydroxyacetone formation for potentials lower * ISE member than 0.600 V vs RHE. A discussion on the relationship between composition/structure of the PtxBi1-x catalytic materials and activity/selectivity for glycerol electrooxidation allowed proposing a mechanism involving a single-carbon adsorption mode on Pt and an electronic effect for the desorption of low oxidized species from Pt sites driven by the early stage of the Bi 0 to Bi II transition.

ZnS:Cu films were synthetized by co-sputtering. A Cu content higher than 10.6 at% lead to changes as the shrinkage of the ZnS:Cu cell and development of a p-type behavior. These results are explained by the substitution of Zn+2 ions by Cu+ ones.

International audienceA new effective medium theory is introduced to describe the optical properties of a two-dimensional array of metallic nanoislands. This model which takes into account both the nanoisland orientation and their shape distribution is successfully used to interpret the ellipsometric measurements performed on gold nanoislands sputtered on a silicon substrate. By coupling ellipsometry to atomic force microscopy measurements, we show that the growth mechanism involves a Volmer-Weber growth mode. The optical anisotropy of uniaxial films was attributed to in-plane preferential self-orientation of gold nanoislands. Finally, we demonstrate that the optical birefringence and dichroism of nanoisland layers can be tuned during the film growth and are due to the splitting of the plasmon resonance into two modes: the transversal and the longitudinal modes of gold nanoislands

SummaryRecently, the compound semiconductor Cu3BiS3 has been demonstrated to have a band gap of ~1.4 eV, well suited for photovoltaic energy harvesting. The preparation of polycrystalline thin films was successfully realized and now the junction formation to the n-type window needs to be developed. We present an investigation of the Cu3BiS3 absorber layer and the junction formation with CdS, ZnS and In2S3 buffer layers. Kelvin probe force microscopy shows the granular structure of the buffer layers with small grains of 20–100 nm, and a considerably smaller work-function distribution for In2S3 compared to that of CdS and ZnS. For In2S3 and CdS buffer layers the KPFM experiments indicate negatively charged Cu3BiS3 grain boundaries resulting from the deposition of the buffer layer. Macroscopic measurements of the surface photovoltage at variable excitation wavelength indicate the influence of defect states below the band gap on charge separation and a surface-defect passivation by the In2S3 buffer layer. Our findings indicate that Cu3BiS3 may become an interesting absorber material for thin-film solar cells; however, for photovoltaic application the band bending at the charge-selective contact has to be increased.

Nanocomposite films consisting of gold nanoparticles embedded in zinc oxide (ZnO-Au) have been synthesized with different gold loadings by reactive magnetron sputtering at near-room temperature followed by ex situ annealing in air up to 300 °C. Using X-ray diffraction and high resolution transmission microscopy it is shown that during deposition gold substitutes zinc in ZnO as isolated atoms and in nanoparticles still exhibiting the structure of ZnO. Both situations degrade the crystalline quality of the ZnO matrix, but thermal annealing cures it from isolated gold atoms and triggers the formation of gold nanoparticles of size higher than 3 nm, sufficient to observe a strong activation of localized surface plasmon resonance (LSPR). The amplitude of LSPR absorption observed after annealing increases with the gold loading and annealing temperature. Moreover, UV and visible photoluminescence from the ZnO matrix is strongly enhanced upon activation of LSPR showing strong coupling with the gold nanoparticles. Finally, modeling of spectroscopic ellipsometry measurements unambiguously reveals how curing the defects increases the optical bandgap of the ZnO matrix and modifies the optical dielectric functions of the nanocomposite and ZnO matrix.

Molecular dynamics simulations are carried out for describing growth of Pd and PdO nanoclusters using the ReaxFF force field. The resulting nanocluster structures are successfully compared to those of nanoclusters experimentally grown in a gas aggregation source. The PdO structure is quasi-crystalline as revealed by HRTEM analysis for experimental PdO nanoclusters. The role of the nanocluster temperature in the MD simulated growth is highlighted.