Buckling and band gap of the Ge(111)2×1 surface studied by low-temperature scanning tunneling microscopy

Low-temperature scanning tunneling microscopy is used to study the 2×1 reconstruction of cleaved Ge(111) surfaces. Buckling of the surface atoms is investigated by observations of the corrugation shift between filled and empty states. In the 〈21¯1¯〉 direction, the shift in corrugation maxima from filled to empty states is found to be negative, consistent with expectations for the “negatively buckled” model for this surface. A surface band gap of 0.54±0.04 eV is measured by tunneling spectroscopy.