4 years ago

Electrochemical Scanning Tunneling Microscopic Study of the Potential Dependence of Germanene Growth on Au(111) at pH 9.0

Electrochemical Scanning Tunneling Microscopic Study of the Potential Dependence of Germanene Growth on Au(111) at pH 9.0
Theodore J. Reber, Maria Ledina, Nhi N. Bui, Jin Jung, John L. Stickney
Germanene is a 2D material whose structure and properties are of great interest for integration with Si technology. Preparation of germanene experimentally remains a challenge because, unlike graphene, bulk germanene does not exist. Thus, germanene cannot be directly exfoliated and is mostly grown in ultrahigh vacuum. The present report uses electrodeposition in an aqueous HGeO3 solution at pH 9. Germanene deposition has been limited to 2–3 monolayers, thus greatly restricting many applicable characterization methods. The in situ technique of electrochemical scanning tunneling microscopy was used to follow Ge deposition on Au(111) as a function of potential. Previous work by this group at pH 4.5 suggested germanene growth, but no buffer was used, resulting in change in surface pH. The addition of borate buffer to create pH 9.0 solution has reduced hydrogen formation and stabilized the surface pH, allowing systematic characterization of germanene growth versus potential. Initial germanene nucleated at defects in the Au(111) herringbone (HB) reconstruction. Subsequent growth proceeded down the face-centered cubic troughs, slowly relaxing the HB. The resulting honeycomb (HC) structure displayed an average lattice constant of 0.41 ± 0.06 nm. Continued growth resulted in the addition of a second layer on top, formed initially by nucleating around small islands and subsequent lateral 2D growth. Near atomic resolution of the germanene layers displayed small coherent domains, 2–3 nm, of the HC structure composed of six-membered rings. Domain walls were based on defective, five- and seven-membered rings, which resulted in small rotations between adjacent HC domains.

Publisher URL: http://dx.doi.org/10.1021/acsnano.7b05236

DOI: 10.1021/acsnano.7b05236

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