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

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Abstract
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 s. 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 s. 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.

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