Structures of quasi-freestanding ultra-thin silicon films deposited on chemically inert surfaces

• Published in: Chemical physics 2014-11, Vol.444, p.1-6
• Main Authors: Baba, Y., Shimoyama, I., Hirao, N., Sekiguchi, T.
• Format: Article
• Language: English
• Subjects: HOPG; Polarization dependence; Sapphire; Silicon thin film; Synchrotron radiation; XAFS
• ISSN: 0301-0104
• DOI: 10.1016/j.chemphys.2014.09.011

[Display omitted] •Structures of ultra-thin silicon films on sapphire and HOPG have been investigated.•Si K-edge XAFS spectra show resonance peaks of Si 1s→π∗ and Si 1s→σ∗.•Polarization dependences of XAFS show that a part of π∗ orbitals points to perpendicular to the surface.•The results support the existence of quasi-freestanding single-layered Si with sp2 configuration. Silicon thin films were deposited on a sapphire and a highly oriented pyrolytic graphite (HOPG), which have atomically flat and chemically inert surfaces. The electronic and geometrical structures of the films were analyzed by X-ray photoelectron spectroscopy (XPS) and polarization-dependent X-ray absorption fine structure (XAFS). It was found that the silicon K-edge XAFS spectra for ultra-thin silicon films thinner than 0.2 monolayer exhibited two distinct resonance peaks which were not observed for bulk silicon. The peaks were assigned to the resonance excitations from the Si 1s into the valence unoccupied orbitals with π∗ and σ∗ characters. The average tilted angle of the π∗ orbitals was determined by the polarization dependencies of the peak intensities. It was demonstrated that direction of a part of the π∗ orbitals in silicon film is perpendicular to the surface. These results support the existence of quasi-freestanding single-layered silicon films with sp2 configuration.