Steps on As-Terminated Ge(001) Revisited: Theory versus Experiment

We examine the double-layer B-type steps on As-terminated vicinal Ge(001) surfaces. The currently accepted structure is a chemically inert bulklike structure without any gap state, and with all the chemical bonds of the Ge and As atoms being satisfied. However, we show that the need for optimizing the p³ pyramidal angles of the threefold coordinated As atoms drives unusual atomic rearrangement. This leads to a more stable reconstruction involving odd-membered (5-7-5) rings at the step edge. Comparison between theoretical and experimental scanning tunneling microscopy images yields excellent agreement.