Refinement of the [formula omitted]-Ag structure by surface X-ray diffraction

Abstract

The structure of the Si(111) 3 × 3 -Ag surface has been determined from the least-squares analysis of nine integral order and nine fractional order rod profiles observed by surface X-ray diffraction. The result is consistent with the HCT (honeycomb chained triangle) model, corresponding to the missing top layer model. Values of the structural and Debye-Waller parameters for the atoms in the top Ag layer and underneath seven Si layers have been obtained. The Ag layer is 3.05 ± 0.02 Å from the top of the intact first Si double layer of substrate. The interatomic distance of nearest-neighbour Ag atoms is 3.43 ± 0.01 Å. The substrate is heavily reconstructed up to the depth of the fourth Si layer,∼ 6.4 Å from the top Ag layer. The Si atoms of the first layer forming the trimer are displayed by − 0.10 ± 0.02 Å in the normal direction and 0.88 ± 0.03 Å in the lateral direction. The third and fourth Si layers are split into two planes in the normal direction by 0.35 ± 0.05 and 0.23 ± 0.04 Å, respectively. The values of the Debye-Waller parameters for the Ag atoms and the Si atoms of the second and one third of the third layers become apparently large compared with the values in crystals.