Electrochemical studies of Ge wafer and the formation of germanene in aqueous media
Ledina, Maria Alekseyevna
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This dissertation discusses studies of germanium electrodeposition, Te deposition onto Ge wafer and electrochemical formation of germanene in aqueous media. Germanene, similar to graphene, is a two-dimensional honeycomb structure. According to theoretical calculations, energetically stable structure of germanene is a low-buckled one, where half of the Ge atoms should be higher than the other half by 0.07 nm. Germanene is predicted to have similar unique properties and applications to those of graphene. The electrodeposition of germanene has been studied by means of voltammetry, coulometry, in situ Scanning Tunneling microscopy (EC-STM), and micro-Raman spectroscopy. EC-STM investigations have demonstrated that initial Ge deposition was kinetically slow and formed deposits were somewhat unstable. It also has been identified that alloy between Ge and Au is observed to form as early as -300 mV vs. Ag/AgCl in pH 4.5 solution if the potential was held long enough. Moreover, presence of the Ge species in Au surface or as adsorbed species has been observed to cause a modification of Au(111) herringbone reconstruction. EC-STM studies of electrodeposition of more than a monolayer of Ge demonstrated a honeycomb-like structure where the atomic distances were found to be about 0.44 ± 0.02 nm, which is only 10% of from what is expected. However, germanene domains identified in the STM images were incoherent. A micro-Raman shift corresponding to germanene signal was observed on one of Ge nanofilms, grown on Cu substrate. The EC-STM data and difficulty to find Raman signal indicates that the deposition of germanene structure has to be improved to more consistently produce the Raman shift. Electrochemical deposition of Te onto Ge(100) wafer has been studied by means of cyclic voltammetry and ultrahigh vacuum surface characterization techniques, such as Auger Electron Spectroscopy (AES) and Low Energy Electron Diffraction (LEED). The investigations have shown that Te bulk was formed between -0.6 V and -0.85 V, whereas the deposition at -0.94 V have resulted in Te atomic layer, and no Te was observed at -1.6 V and lower.