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Abstract
This dissertation discusses the electrochemical deposition of Ge and germanene on Au. Simply applying an anodic potential on Au electrode in an aqueous Ge solution results in reductive Ge deposition that is limited at a thickness of about 3.5 monolayers (ML), “Bait and Switch” (B&S) method can be used to form a thicker Ge film from aqueous media. Even though Ge film deposited using the B&S method consistently exhibited amorphous Ge Raman signal, electrochemical analysis using cyclic voltammetry (CV) revealed different species of Ge on the Au surface when thin Ge film was deposited on Au surface. One of the species present on the surface is believed to be germanene. Germanene is a crystalline allotrope of Ge and an elemental two-dimensional (2D) material. Similar to graphene, germanene features properties such as ballistic conduction and high optical opacity. Unlike graphene, the energetically favorable structure of germanene has a low-buckling, half of Ge atoms are raised by 0.07 nm.
Electrochemical deposition of Ge and germanene was studied using CV, in situ Raman spectroscopy, and electrochemical scanning tunneling microscopy (EC-STM). EC-STM was used to obtain an atomic resolution image of germanene structures on the Au substrate. Atomic resolution images of one ML of Ge film on Au surface exhibited small domains of germanene surrounded by defective germanene structures, presumably due to nucleation and growth process on polycrystalline Au substrate. The small domains are believed to have limited germanene Raman signal from a Ge deposit.
In situ Raman spectroscopy was used to obtain spectroscopic evidence of electrochemical deposition of germanene. When one ML thick Ge deposit on a SERS active Au substrate was irradiated by 780 nm Raman excitation laser, a sharp germanene Raman peak centered around 296 cm-1 was observed. Irradiation using 532 nm Raman excitation laser did not result in the formation of the 296 cm-1 peak. Irradiating a SERS active Au substrate with 780 nm laser may have created Au surface plasmon that recrystallized Ge deposit to form larger domains of germanene.
Electrochemical deposition of Ge and germanene was studied using CV, in situ Raman spectroscopy, and electrochemical scanning tunneling microscopy (EC-STM). EC-STM was used to obtain an atomic resolution image of germanene structures on the Au substrate. Atomic resolution images of one ML of Ge film on Au surface exhibited small domains of germanene surrounded by defective germanene structures, presumably due to nucleation and growth process on polycrystalline Au substrate. The small domains are believed to have limited germanene Raman signal from a Ge deposit.
In situ Raman spectroscopy was used to obtain spectroscopic evidence of electrochemical deposition of germanene. When one ML thick Ge deposit on a SERS active Au substrate was irradiated by 780 nm Raman excitation laser, a sharp germanene Raman peak centered around 296 cm-1 was observed. Irradiation using 532 nm Raman excitation laser did not result in the formation of the 296 cm-1 peak. Irradiating a SERS active Au substrate with 780 nm laser may have created Au surface plasmon that recrystallized Ge deposit to form larger domains of germanene.