Symmetrical transition of an atomic arrangement for 2D Bi films on Rh(111)

The atomic arrangement of submonolayer Bi films on Rh(111) surface was examined using low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). With low coverage, the LEED patterns showed incommensurate (IC) spots. The unit cell of IC was close to c(2 × 4) and had twofold symmetry. As the coverage increased, the unit cell shrank continuously along the [ 1 ¯ 10 ] direction, and the commensurate c(2 × 4) was formed at a coverage of 0.5 ML. At the coverage above 0.5 ML, two different structures of c(2 × 4) and (4 × 4) were observed by STM. When the surface is fully saturated by monolayer Bi atoms, Bi atoms formed the uniform (4 × 4) structure with sixfold symmetry. This is due to a strong Bi–Rh attractive interaction resulting in the two-dimensional localization of Bi adsorbates on the surface. As a result, a symmetrical transition of Bi films from twofold to sixfold symmetry occurred on Rh(111).