Electrodeposition of germanium from supercritical fluids

Abstract

Several Ge(II) and Ge(IV) compounds were investigated as possible reagents for the electrodeposition of Ge from liquid CH₃CN and CH₂F₂ and supercritical CO₂ containing as a co-solvent CH₃CN (scCO₂) and supercritical CH₂F₂ (scCH₂F₂). For Ge(II) reagents the most promising results were obtained using [NBuⁿ₄][GeCl₃]. However the reproducibility was poor and the reduction currents were significantly less than the estimated mass transport limited values. Deposition of Ge containing films was possible at high cathodic potential from [NBuⁿ₄][GeCl₃] in liquid CH₃CN and supercritical CO₂ containing CH₃CN but in all cases they were heavily contaminated by C, O, F and Cl. Much more promising results were obtained using GeCl₄ in liquid CH₂F₂ and supercritical CH₂F₂. In this case the reduction currents were consistent with mass transport limited reduction and bulk electrodeposition produced amorphous films of Ge. Characterisation by XPS showed the presence of low levels of O, F and C, XPS confirmed the presence of Ge together with germanium oxides, and Raman spectroscopy showed that the as deposited amorphous Ge could be crystallised by the laser used in obtaining the Raman measurements.