IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Semiconductors Thursday Sessions
       Session SC+SS-ThA

Paper SC+SS-ThA6
First-Principles Study of Thermal Fluctuation of Si(111)@sr@3 X @sr@3 - Ag Surface Appeared in Non contact AFM Images

Thursday, November 1, 2001, 3:40 pm, Room 111

Session: Semiconductor Surface Structure
Presenter: M. Tsukada, University of Tokyo, Japan
Authors: M. Tsukada, University of Tokyo, Japan
N. Sasaki, University of Tokyo, Japan
S. Watanabe, University of Tokyo, Japan
Correspondent: Click to Email
Until recently ''Honeycomb-Chained-Triangle (HCT)" model for the atomic structure of Si(111) @sr@3 X @sr@3 -Ag surface (referred to @sr@3 -Ag surface hereafter) seemed to be accepted. However, a new structural model called ''InEquivalent-Triangle (IET)" model was proposed by Aizawa et al.@footnote 1@ based on the first-principles calculation as well as the low temperature STM. The IET model is energetically more favorable than the HCT model by about 0.1 eV per @sr@3 X @sr@3 unit cell. In IET model, a mirror plane symmetry is broken and the inequivalent Ag triangles are located in the unit cell. In the present work, we calculated NC-AFM images of IET structure based on a density functional theory. In simulating two-dimensional NC-AFM images, we used a "Fourier expansion method". In this method, the two-dimensional symmetry of the tip-surface system is considered. The thermal averaged images of the fluctuating two different phases of IET structures are calculated in the following way. Namely, at each scanning position of the tip over the surface, the frequency shift is calculated from the force-curve which is obtained from the canonical weighted average of the both phases of IET. The simulated theoretical images reproduces fairly well the experimental observation at room temperature. Therefore our result confirms that the room temperature apparent HCT structure is the thermal fluctuated structures of the two phases of IET. The effect of the tip apex structure on AFM images is also discussed together with the thermal fluctuation. @FootnoteText@ @footnote 1@ H.Aizawa, M.Tsukada, N.Sato and S.Hasegawa, Surf. Sci. 429, L509 (1999).