[1Ba01-09] Surface Science(SS3) Structure

[1Ba06] Incommensurate phase near (√3×√3)R30° structure on a face-centered cubic (111) surface

*Masamichi Yamada¹, Yudai Sato¹, Masahiro Haze¹, Yukio Hasegawa¹ (1. The Institute for Solid State Physics, The University of Tokyo)

When surface atom density differs slightly from the bulk-truncated value, an incommensurate phase or a commensurate phase with very long periodicity may result. A typical example is the (22×√3) reconstruction on a clean Au(111), where surface Au atoms are compressed in [-110] direction and 23 surface atoms match 22 substrate sites. In this paper, we study structures slightly deviated from close-packed (√3×√3)R30° on an fcc (111) substrate, and compare them with structures deviated from (1×1). Surface atoms occupy only the most stable fcc sites in the (1×1) case. Therefore, a one-period shift is only allowed under uniaxial compression to produce an energetically-equivalent surface atom row. On the other hand, surface atoms occupy four kinds of sites in the √3 case, and then half-period shifts can produce energetically-equivalent rows. The resultant structure is chevron-like, and can be considered as two-dimensional twinning.