STM study of low pressure adsorption of silane on Si(111)7 × 7

We report a study of silane adsorption on the Si(111)7 × 7 surface. We have been interested in the first stages of chemisorption at room temperature. Reactive sites of the unit cell have been clearly identified on Scanning Tunneling Microscopy (STM) images: the reaction involves the rest atom and the adjacent adatom of the DAS structure with preferential adsorption on the center adatom. We propose an original chemisorption mechanism which leads to the formation of two SiH₂ species by chemisorption and involves the breaking of Si---Si backbonds of the adatom.     

The adsorption of C6H5Cl on Si(111)7 × 7 studied by STM

The adsorption of chlorobenzene on Si(111)7 × 7 at room temperature was studied by scanning tunneling microscopy (STM). Selective chemisorption was observed at different adatom sites. It was found that the center adatoms were more reactive than the corner adatoms, and the faulted half of the unit cell was more reactive than the unfaulted. The mechanism is discussed in terms of the electronic and atomic structures in Si(111)7 × 7. Both preferences indicate that chlorobenzene was present initially in a mobile precursor state.     

STM investigation of the adsorption and temperature dependent reactions of ethylene on Pt(111)

The adsorption and reactions of ethylene adsorbed in UHV on Pt(111) have been studied as a function of temperature by STM. The STM images taken at 160K show an ordered structure of adsorbed ethylene. Annealing to 300 K produces ethylidyne (C-CH₃) irreversibly, as has been demonstrated by a wide variety of surface science techniques. The ethylidyne on Pt(111) is not visible to the STM at room temperature. Cooling the sample allows direct observation of the ethylidyne ordered structure by STM. Annealing above 430 K results in further dehydrogenation, eventually leaving only carbon on the surface. The decomposition products appear as small clusters which are localized and uniformly distributed over the surface. Further annealing to temperatures >800 K results in the growth of graphite islands on the Pt(111) surface. The annealed graphite islands exhibit several supersturctures with lattice parameters of up to 22 Å, which are thought to result from the higher order commensurability with the Pt(111) substrate at different relative rotations.     

Xe and Kr adsorption on the Si(111) 7 × 7 surface

A study of adsorption of Xe and Kr on the Si(111) 7 × 7 surface is presented. Low energy electron diffraction indicates the substrate structure is not appreciably modified by the adsorption. The data consist primarily of isobars, i.e. the amount adsorbed as a function of temperature at fixed pressure. The stepwise adsorption of each of the first several adatoms per surface unit mesh is resolved. This indicates a sequence of distinguishable adsorption sites in the mesh each of which can be occupied by a single atom. There are appreciable differences in the measured binding energies between the various sites. Pairwise sums of 6–12 potentials have been used to estimate binding energies expected for sites presented by proposed structural models of the surface. The observed sequence of sites seems to exclude buckled models and those models which involve only arrays of identical entities. No presently published model is consistent with these data in detail. The triangular island models with some modifications might present sufficiently large binding energies and rich sequences of sites. Whatever the actual structure, it must be more complex than those which have usually been considered.