Atomic structures of Ag/Ge(1 1 1) √39 × √39 and 6 × 6 surfaces studied by STM: observations of bias dependent reconstruction transformations

The 6×6 and √39×√39 phases on Ag/Ge(1 1 1) have been studied by scanning tunneling microscopy (STM). Four types of 6×6 configurations are found which all consist of a √3×√3 layer with six extra Ag adatoms per 6×6 unit cell. These reconstructions show either mirrored or complementary relations. We observe interesting transitions between the different 6×6 reconstructions. The √39×√39 surface appears to have five extra Ag atoms per unit cell. By using various tip biases, we show that the √39×√39 domain orientation can be changed. Surface structure models of the √39×√39 and 6×6 phases are proposed based on the HCT structure of the underlying √3×√3 surface.