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

► Bi atoms are mobile at low coverage on Rh(111) at RT. ► Bi atoms form incommensurate films on Rh(111) except at 0.5 ML. ► At the coverage of 0.5 ML, Bi atoms form a commensurate structure of c(2 × 4). ► Bi films transform from twofold structure into sixfold structure above 0.5 ML.