Structural transformation of Ge dimmers on Ge(001) surfaces induced by bias voltage

Scanning tunneling microscopy is utilized to investigate the local-bias- voltage-dependent transformation between (2x1) and c(4x2) structures on Ge(001) surfaces, which is reversibly observed at room temperature and a critical bias voltage of -0.80V. Similar transformation is also found on an epitaxial Ge islands but at a slightly different critical bias voltage of -1.00V. It is found that the interaction between the topmost atoms on the STM tip and the atoms of the dimers, and the pinning effect induced by Sb atoms, the vacancies or the epitaxial clusters, can drive the structural transformation at the critical bias voltage.