Surface structure analysis of Si(111)√3 × √3-Bi by X-ray diffraction — Approach to the solution of the phase problem
X-ray intensity versus energy ( I-E) curves of the integral-order rods have been observed for the Si(111)√3 × √3-Bi structure under nearly normal incidence condition, and the 3-dimensional structure of the surface has been analyzed by utilizing the interference effect between the X-rays diffracted from the surface atoms and the bulk crystal around the Bragg points, which gives information on the positions of the surface atoms, especially of the heavy atoms with respect to the bulk crystal. Bi atoms, forming a trimer with an interatomic distance of 3.08 ±0.08 Å, are bonded to the first-layer Si atoms by means of the dangling bonds, and the displacements of the first- and second-layer Si atoms from their ideal positions are less than 0.15 Å. The spacing between the Bi layer and the ideal first Si layer is 2.68 ±0.02 Å. A Si adatom layer making a honeycomb structure exists 0.80 ±0.20 Å above the Bi layer. The model in which the center of the trimer is on the second-layer Si atoms rather than on the fourth-layer Si atoms is favored.