Disordered surface structure of an ultra-thin tin oxide film on Rh(100)

Abstract

The composition and structure of an ultra-thin tin oxide film on Rh(100), prepared by the deposition of a submonolayer of tin followed by annealing in an O2 atmosphere, were examined by a combination of low-energy electron diffraction (LEED), Auger electron spectroscopy, X-ray photoemission spectroscopy (XPS), scanning tunneling microscopy (STM), and ab initio calculations based on density functional theory (DFT). Although the LEED pattern exhibited c(2 × 8) spots clearly, a uniform periodicity of the c(2 × 8) unit cell was not observed in the STM images. The bright dots that were observed periodically in the STM image were similar to those of the ultra-thin Sn2O3 film on Rh(111) and formed a zigzag arrangement with the numerous point and line defects. The XPS study revealed that the Sn 3d5/2 peak of the tin oxide film on Rh(100) showed a metallic state as well as an oxide state that was between the SnO2 and SnO states. The structural models, which were based on the Sn2O3 structure on Rh(111), were determined using DFT total energy calculations. The simulated STM images of the two slightly different honeycomb-chain models well reproduced the zigzag arrangement in the STM image. The STM image and XPS spectrum were interpreted using a combination of the two models.