Dimer structures of Ge/Si(001) and Sb/Si(001) studied by medium-energy ion scattering

Abstract

We have determined the structure and positions of Ge and Sb dimer atoms on a Si(001)-2×1 surface using medium-energy ion scattering (MEIS), and demonstrated that the surface structure can be determined with a much higher accuracy by modifying the layer structure of the substrate. When a heavy atom layer (in this case Ge layer) is embedded with atomic scale layer precision, the blocking processes of scattered ions from the embedded layer are restricted and dips in the blocking profiles can be uniquely assigned to the scattering-blocking pairs. In addition, the effect of thermal vibration becomes small because a suitable distance between scattering and blocking atoms can be selected. Therefore, we can observe sharp blocking dips in the profile of embedded Ge signals, and they can be assigned to the dimer structures on the reconstructed surface. Based on the proposed method, the bond length and the tilt angle of asymmetric Ge–Ge dimers are determined to be 2.4±0.1 Å and 13.5±2.0°. The bond length of symmetric Sb–Sb dimers is determined to be 2.84±0.1 Å.