Angle-resolved and angle-integrated synchrotron-radiation photoemission together with scanning tunneling microscopy (STM) were used to study the Sb-stabilized GaSb(100)-(1X3) surface grown by molecular-beam epitaxy. Bulk valence bands were mapped out in the I -6-X direction. The deconvoluted Sb 4d and Ga 3d core-level line shapes were used to construct a structural model for the surface. STM resolved the individual atomic dimers verifying the proposed model and showed partial disorder inherent on this surface.

Scanning-tunneling-microscopy images of annealed Ge(111) show large c(2&8) domains with protrusions that match closely the arrangement of adatom and rest-atom dangling bonds in the simple adatom model. The unit cell, however, appears asymmetric. or "buckled"; namely, the two adatoms or the two rest atoms within the unit cell show significant diA'erences in apparent height. Both the adatom and rest-atom dangling bonds can be simultaneously observed with either bias polarity, indicating that both are partially filled. These results will be discussed in relation to the proposed charge transfer between the adatoms and rest atoms.The Si(111)-(7X7)surface appears to be nearly fully understood, yet there remain unresolved issues for the closely related Ge(111)-c(2X8) surface. The geometrical structure of the Ge(111)-c(2X8) surface is generally considered to be optimally described by a simple adatom model in which the (1 x 1) substrate is decorated with germanium adatoms in alternating (2 x 2) and c (2 x 4) subunits. In this model, each c(2X8) primitive unit cell of eight (1 xi) sites contains two adatoms and two rest atoms, totaling four dangling bonds. Verification of this model has been provided by studies using x-ray diffraction, ' scanning tunneling microscopy (STM), and medium-energy ion scattering.In the STM study of Becker et al. , a pattern of protrusions was observed which matches the arrangement of either the rest atoms or the adatoms, depending of the sample-to-tip bias polarity, but not both simultaneously This o. bservation, combined with information available from a model calculation, ' lead to the following suggestions: (i) The simple adatom model is valid. (ii) There is a complete electron transfer from the adatoms to the rest atoms resulting in a fully occupied rest-atom dangling-bond state and a completely empty adatotn dangling-bond state. A surface electronic band at a binding energy of about 0.8 eV observed by ultraviolet photoemission was ascribed to the occupied restatom dangling-bond state in analogy to the Si(ill)-(7 x 7) case. Two questions remain concerning the above tnodel. The first question arose from a more recent photoemission study revealing the existence of another occupied surface-state band with a dangling-bond character, which could not fit into the model. The second question had to do with the high Coulomb energy needed for a complete charge transfer from the adatoms to the rest atoms. A fully ionic surface appears to be highly unlikely 6 In the work reported here, we examined the Ge(111)-c(2X8) surface with STM under various bias conditions and found features not reported before, which could provide an explanation in connection with the above-mentioned questions. Our results confirm that the simple adatom model is valid except that the c(2X8) unit cell appears "buckled" or asymmetric; namely, the two adatoms or the two rest atoms in a unit cell show significant differences in apparent height depending on the imaging conditions. This observation is somewhat similar to the familiar c...

Scanning tunneling microscopy has been employed to study the adsorption of disilane (Si2H6) and pyrolytic growth on Si(100)-(2X1) at various temperatures. Room-temperature exposures result in a random distribution of dissociation fragments on the surface. Formation of anisotropic monohydride islands and denuded zones as well as island coarsening is observed at higher temperatures. The results are strikingly similar to those reported for growth by molecular-beam epitaxy using pure Si, even though different surface reactions are involved in these two growth processes.

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The adsorption and growth of Ag on Si(lOO) at room temperature have been studied by scanning tunneling microscopy. The initial adsorption of Ag occurs at the twofold bridge site in between adjacent Si dimer rows. Ag atomic chains are formed with preferred lengths. MetalUc Ag islands form at coverages >0.5 monolayer, and develop into (111)-and (110)-oriented crystallites covering the entire surface at higher coverages.