Abstract
Author(s): Lewandowski, AL; Schlexer, P; Buchner, C; Davis, EM; Burrall, H; Burson, KM; Schneider, WD; Heyde, M; Pacchioni, G; Freund, HJ | Abstract: The growth and microscopic characterization of two-dimensional germania films is presented. Germanium oxide monolayer films were grown on Ru(0001) by physical vapor deposition and subsequent annealing in oxygen. We obtain a comprehensive image of the germania film structure by combining intensity-voltage low-energy electron diffraction (I/V-LEED) and ab initio density functional theory (DFT) analysis with atomic-resolution scanning tunneling microscopy (STM) imaging. For benchmarking purposes, the bare Ru(0001) substrate and the (2×2)3O covered Ru(0001) were analyzed with I/V-LEED with respect to previous reports. STM topographic images of the germania film reveal a hexagonal network where the oxygen and germanium atom positions appear in different imaging contrasts. For quantitative LEED, the best agreement has been achieved with DFT structures where the germanium atoms are located preferentially on the top and fcc hollow sites of the Ru(0001) substrate. Moreover, in these atomically flat germania films, local site geometries, i.e., tetrahedral building blocks, ring structures, and domain boundaries, have been identified, indicating possible pathways towards two-dimensional amorphous networks.
Highlights
Using thin oxide films represents an elegant way to apply electron-based analytical methods to unravel the atomic surface structure of insulating materials [1]
We obtain a comprehensive image of the germania film structure by combining intensity-voltage low-energy electron diffraction (I/V-LEED) and ab initio density functional theory (DFT) analysis with atomic-resolution scanning tunneling microscopy (STM) imaging
The STM images are superimposed with red and blue markers to show the positions of oxygen and germanium atoms, respectively
Summary
Using thin oxide films represents an elegant way to apply electron-based analytical methods to unravel the atomic surface structure of insulating materials [1]. We have investigated silica surfaces and have demonstrated that both crystalline as well as vitreous two-dimensional (2D) films can be prepared and resolved at the atomic level using scanning probe techniques [2]. Given the detailed information derived from thin-film studies for silica, it is likely that one will be able to reveal the network structures for germania and germania-silica mixtures at the atomic level. Intensity-voltage low-energy electron diffraction (I/V-LEED) studies together with ab initio density functional theory (DFT) models provide a consistent view of the germania film structure. First characterization of possible ring structures, ring configurations, and domain boundaries has been made
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