Low-energy electron diffraction and scanning tunnelling microscopy were used to study an In-terminated InAs(001) surface prepared by argon sputtering and annealing. Characterization by low-energy electron diffraction revealed the formation of a highly ordered surface with a mixture of (4 x 2) and c(8 x 2) phases. The sample bias in the scanning tunnelling microscope was systematically varied so as to obtain bias-dependent images over the same surface regions; thus permitting a discrimination between topographic and electronic features. Atomic resolution scanning tunnelling microscopic images confirmed the existence of both (4 x 2) and c(8 x 2) phases and an electronic signature was identified at the transition between the two 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), was found to arise from a shift in the third- and/or first-layer In dimers by one lattice spacing. Filled-state imaging at the (4 x 2)-to-c(8 x 2) boundary revealed two bright spots positioned mid-way between the first-layer In dimer rows. In empty states, these spots were entirely absent; thus underlining their electronic origin. These electronic features were explained in terms of a localization of charge due either to a structural defect or to the presence of a sulfur doping atom at the transition from (4 x 2) to c(8 x 2) reconstruction.

Bias-Dependent Imaging of the In-Terminated InAs(001) (4 x 2)/c(8 x 2) Surface by STM: Reconstruction and Transitional Defect. C.Kendrick, G.LeLay, A.Kahn: Physical Review B, 1996, 54, 17877-83