C. Kendrick et al., BIAS-DEPENDENT IMAGING OF THE IN-TERMINATED INAS(001) (4X2) C(8X2) SURFACE BY STM - RECONSTRUCTION AND TRANSITIONAL DEFECT/, Physical review. B, Condensed matter, 54(24), 1996, pp. 17877-17883
We use low-energy electron diffraction (LEED) and scanning tunnelling
microscopy (STM) to study the In-terminated InAs(001) surface prepared
by argon sputtering and annealing. Characterization by LEED shows the
formation of a highly ordered surface with a mixture of (4X2) and c(8
x2) phases. We systematically vary the sample bias in STM to obtain bi
as-dependent images over the same surface regions, allowing discrimina
tion between topographic and electronic features. Atomic resolution TM
images confirm the existence of both (4x2) and c(8X2) phases and iden
tify an electronic signature at the transition between the two reconst
ructions. Images of (4x2) regions are consistent with a previously pro
posed model for this surface in which the unit cell contains one In di
mer in the first layer and two In dimers in the third la)er. The c(8X2
) reconstruction, though similar to the (4x2), is found to arise from
a shift in the third- and/or first-layer In dimers by one lattice spac
ing. Filled-state imaging at the (4X2)-to-c(8X2) boundary shows two br
ight spots positioned midway between the first-layer In dimer rows. In
empty states, these spots are entirely absent, underlining their elec
tronic origin. These electronic features are explained in terms of a l
ocalization of charge due either to a structural defect or to the pres
ence of a sulfur doping atom at the transition from (4X2) to c(8X2) re
constructions.