Rearrangement of up-and-down terrace in Si(1 1 0) “16 × 2” induced by Sn adsorption

We have studied Sn/Si(1 1 0) surface structures with scanning tunneling microscopy (STM). The unique dense-step structure in a clean Si(1 1 0) “16 × 2” phase is successfully modified as a function of Sn coverage up to 0.4 monolayer (ML). The width of about 2.5 nm of the up-and-down terrace (“16 × 2”) is broadened stepwise by Sn adsorption passing through the “28 × 2” phase (0.2 ML), the mixture of “14 × 2” and “7 × 2” (0.3 ML) and the “7 × 2” (0.4 ML) phases. In particular, the “28 × 2” phase is formed by the ordered up-and-down terrace structures of about 4 nm width. High-resolution STM images clearly reveal that in the series of structural changes, the Si pentagons, which are the elemental structures of the “16 × 2” phase [T. An, M. Yoshimura, I. Ono, K. Ueda, Phys. Rev. B 61 (2000) 3006], rearrange in accordance with Sn trimers. The relaxation process of the surface stress plays a key role in determining the surface morphology.