Low-energy electron diffraction and scanning tunnelling microscopy were used to study In-terminated (001) surfaces which had been prepared by Ar sputtering and annealing. The low-energy electron diffraction data revealed the formation of a highly-ordered surface with a mixture of 4 x 2 and c(8 x 2) phases. Atomic-resolution scanning tunnelling microscopic images confirmed the existence of both 4 x 2 and c(8 x 2) phases, and identified an electronic signature at the transition between the 2 reconstructions. The images of 4 x 2 regions were consistent with a previously proposed model, for this surface, in which the unit cell contained one In dimer in the first layer and two In dimers in the third layer. The c(8 x 2) reconstruction, although similar to the (4 x 2) reconstruction, was found to arise from a shift - in the third-layer and/or first-layer In dimers - by one lattice spacing. Filled-state imaging of the (4 x 2)/c(8 x 2) boundary revealed 2 bright spots that were positioned mid-way between the first-layer In dimer rows. In the case of empty states, these spots were entirely absent; thus underlining their electronic origin. The electronic features were explained in terms of a charge localization that was due either to a structural defect or to the presence of a S dopant atom at the reconstruction transition from (4 x 2) to c(8 x 2).

C.Kendrick, G.LeLay, A.Kahn: Physical Review B, 1996, 54[24], 17877-83