Electrodeposition of a thin germanium film on gold from a room temperature ionic liquid

The electrodeposition of germanium on flame annealed Au(111) films was investigated by cyclic voltammetry (CV) and in situ scanning tunneling microscopy (STM) in the room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate containing GeI4 as germanium source. The CV shows two quasireversible redox processes at 485 +/-5 mV and -30 +/-5 mV, one peak couple at -430 +/- 20 mV and two irreversible diffusion controlled reduction peaks at -910 +/- 10 mV and -1510 +/- 10 mV vs. Pt quasi reference. At potentials positive from the open circuit potential (ocp), gold oxidation starts at the steps with detectable rates up to 1 nm s(-1). At -2000 mV vs. Pt quasi reference, germanium overpotential deposition is observed. The surface shows a remarkable reordering: an almost disordered surface structure transforms to a layered structure on the time scale of about 1 h with an averaged terrace height of 330 +/- 30 pm indicative of a (111) oriented germanium bilayer. At -1500 mV the reoxidation starts both at the interior and at the edges of the deposited layers, leading to random wormlike nanostructures which heal on the time scale of about 2 h. The healing is a complex process comprising (electro)dissolution/electrodeposition and surface diffusion phenomena. A chemical attack of GeI4 on the deposits is clearly observed.