Atomic structure of the Ag / Ge ( 111 ) - ( 3 × 3 ) surface: From scanning tunneling microscopy observation to theoretical study

The atomic structure of the Ag / Ge ( 111 ) - ( 3 × 3 ) R 30 ° surface is studied by scanning tunneling microscopy (STM) and the density functional theory (DFT) calculations. Our STM images have shown a structure which is different from the widely accepted honeycomb-chained-triangle (HCT) model before. The structure is similar to the inequivalent triangle (IET) model found for the Ag / Si ( 111 ) - ( 3 × 3 ) R 30 ° surface. This model proposed two types of silver triangles with different sizes in the unit cell, corresponding to the bright spots and the dark spots in the STM image. A distinguishable hexagonal pattern of the IET structure was well disclosed in the temperature range from 100 to 473 K in our STM studies for Ag / Ge ( 111 ) - ( 3 × 3 ) R 30 ° . Furthermore, the result of the DFT calculations showed that the IET structure is 0.20 eV energetically more stable than the HCT model. Besides, the Ge triangles, which were not disclosed in earlier STM research, are found in this study.