Electrodeposition of germanium from supercritical fluids

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