A number of surface reconstructions formed on InSb(100) have been observed with atomic resolution using scanning tunneling microscopy (STM). Cycles of low-energy ion bombardment and annealing result in the formation of an In-rich surface with a c(8 X2) diffraction pattern. Filled-states images of this indicate a (4X1) periodicity arising from imaging occupied lone-pair orbitals on exposed second-layer Sb atoms. The controlled deposition of Sb4 from a Knudsen effusion source onto the c(8 X2) surface at elevated temperatures led to the formation of a (1X1), c(4X4), and an asymmetric (1X3)structure, in order of decreasing Sb/In ratio. Filledand empty-states STM images of all these Sb-rich reconstructions were generated and the coexistence of the different structures was also observed. Both the (1X1) and asymmetric (1 X 3) surfaces showed a high degree of disorder while the c(4 X 4) surface was highly ordered. The c (4 X4) structure, which involves the chemisorption of Sb onto an already Sb-terminated surface, is characterized by blocks of three pairs of well-resolved Sb dimers. Structural models are proposed for the ordered structures observed.

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The growth of thin films of Au on InSb( 1(0) has been studied by low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). Adsorption of increasing amounts of gold (up to 6.5 ML) results in gradual disappearance of the LEED pattern. At 0.5 ML coverage, STM images show an even distribution of gold clusters on the wen ordered InSb (100) -c (8 X 2) surface. At higher coverages; the gold layer forms parallel ridges. Upon annealing to 625 K, the LEED pattern changes to a (2J2x2J2)R45° structure. Previous Auger spectroscopy measurements suggest that this is a result of the migration of the Au into the near-surface region of the InSb sample leaving an excess of Sb on the surface. A relatively large sized (> 500 A X 500 A) ordered region of this surface is also observed by STM. The local translational symmetry, however, differs from that corresponding to the LEED measurements reflecting the different spatial sensitivities of the two structural probes.

Scanning tunnelling microscopy (STM) has been used to produce images of lnSb(100) prepared by in situ treatment of several cycles of low-energy argon ion bombardment and annealing. Electron diffraction studies, following annealing to 625 K, show the c(8 x 2) pattern associated with the In-rich reconstruction also observed during MBE growth. These STM images demonstrate the improved surface ordering with successive cycles resulting in atomically flat terraces over areas of the sample in excess of 1000 A x 1000 A. The observed reduction of macroscopic morphological defects. s u c h as In droolets. is discussed as a function of surface treatment.