The chemical composition of (100) n-GaAs electrode surfaces has been studied for the first time during cathodic hydrogen evolution in acidic aqueous solutions by in situ spectroscopic techniques. Cathodic decomposition of GaAs is observed in the entire potential range where hydrogen evolution occurs, decomposition products being Ga) or Ga) and As or A5H3(,), depending on the potential. In situ UV-visible ellipsometry shows unambiguously that the surface is partially covered by metallic gallium at sufficiently negative potentials. In situ infrared spectroscopy in the differential mode reveals that when hydrogen evolution occurs, hydrogen always binds to arsenic atoms, not to gallium atoms. The submonolayer hydrogen coverage is approximately linear with the applied potential and shows hysteresis upon cycling of the applied potential. A correlation between hydrogen surface coverage, current density, and applied potential gives direct new evidence that an increase in the hydrogen surface coverage of GaAs electrodes causes a negative shift of the flatband potential. Measurements of the time response of hydrogen surface coverage to changes of the applied potential provide the first direct evidence that hydrogen evolution follows a Volmer-Heyrovsk route. InfroductionDue to its commercial applications, GaAs is, after Si, the semiconductor for which wet (electro)chemical processing has been the most widely investigated by electrochemical methods.' Nevertheless, the influence of changes in the chemical composition of the surface on the electrochemical behavior of GaAs has remained relatively obscure. For instance, one of the fundamental questions is whether the negative shifts of the flatband potential resulting from hydrogen evolution on n-GaAs are related to changes of the Ga-to-As surface atom ratio4 or to the displacement of surface hydroxyl groups by hydride groups.5

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Miniaturized rechargeable batteries with high specific power are required for substitution of the large sized primary batteries currently prevalent in integrated systems since important implications in dimensions and power are expected in future miniaturized applications. Commercially available secondary microbatteries are based on lithium metal which suffers from several well-known safety and manufacturing issues and low specific power when compared to (super) capacitors. A high specific power and novel dual-metal-ion microbattery based on LiMnO, zinc, and an aqueous electrolyte is presented in this work. Specific power densities similar to the ones exhibited by typical electrochemical supercapacitors (3400 W kg) while maintaining specific energies in the range of typical Li-ion batteries are measured (∼100 Wh kg). Excellent stability with very limited degradation (99.94% capacity retention per cycle) after 300 cycles is also presented. All of these features, together with the intrinsically safe nature of the technology, allow anticipation of this alternative micro power source to have high impact, particularly in the high demand field of newly miniaturized applications.

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Anodic decomposition of a vinylmagnesium halide or an ethynylmagnesium halide at a surface-hydrogenated silicon electrode leads to the formation of polymeric layers covalently anchored to the silicon surface. These layers have been characterized using spectroellipsometry and photoluminescence, infrared, and X-ray photoelectron spectroscopy. In the case of vinyl precursors, it appears that the multiple bonds are largely broken in the process. In the case of ethynyl, the layer formation rate is much higher for the chloride than for the bromide. The obtained polymer appears as a saturated skeleton bearing halide and unsaturated ethynyl groups. Furthermore, it appears that the solvent may be attacked by the ethynyl radicals leading to contamination of the polymer by solvent fragments, an effect that can largely be avoided by using appropriate solvents. The reaction pathways are discussed.