In situ STM observations of ordering behaviors on Ge(110) surfaces and atomic geometry of the Ge{17151} facet

Ordering behaviors on Ge(1 10) surfaces upon cooling were investigated by in situ STM observations and clarified that the assemblage of fluctuating steps to the 117 15 I} facet, the appearance of the 16x 2 structure and rearrangement of five-membered clusters of Ge adatoms to the c(8 x 10) structure take place in turn. The stability of the five-membered clusters on Ge(1 10) surfaces was discussed and attributed to energy gain by new bonding. It is conjectured from the discussion and the behaviors of the c(8 x 10) ordering that disordered surface above 430 C consists of the five-membered clusters densely and randomly arranged. Structural models of the 117 15 1} facet were constructed and optimized by means of ab initio total energy calculations. STM images computed from an optimized model could well reproduce features seen in experimental STM images, which suggests the existence of zigzag chains composed of not five-membered clusters but four-membered ones of Ge adatoms in the 117 15 1) facet, differing from in the 16x 2 structure. (C) 2004 Elsevier B.V. All rights reserved.