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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 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.

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).

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.

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.