Flodström Sa

Adsorption of Sn onSi(111)7 × 7: reconstructions in the monolayer regime

Different monolayer phases of Sn on Si(111)7 × 7 have been studied by means of scanning tunneling microscopy (STM), core-level photoelectron spectroscopy (XPS), and Rutherford backscattering spectrometry (RBS). The STM results show that 3 × 3 reconstructions are obtained for room-temperature deposition of 13 ML of Sn followed by sample annealing in a broad temperature range. A T4 Sn adatom 3 ×3 phase is formed for temperatures between 500 and 800°C, with a concentration of defects that is strongly dependent on the temperature and which is as high as 25% for the lowest temperatures. Above 825°C a second 3×3 adatom reconstruction is formed, a mosaic-like phase with a 1:1 mixture of Si and Sn atoms in T4 positions. The results from investigations of the higher coverage 23 × 23 reconstruction by XPS and RBS support the theory that this phase is a two-layer epitaxial Sn structure with all Si(111) dangling bonds saturated. The Sn coverage for this phase was determined to be between 1 and 1.2 ML.

Adsorption of tin on the Ge(111)-c(2 × 8) surface studied with scanning tunneling microscopy and photoelectron spectroscopy

Abstract The growth and epitaxy of Sn on Ge(111) have been investigated using scanning tunneling microscopy (STM), low energy electron diffraction (LEED) and core level photoelectron spectroscopy for coverages ranging from 0.4 monolayers (ML) to above the critical coverage at 1.6 ML. At the lowest coverage a (√3 × √3)R30° reconstruction is formed at an annealing temperature of 250–300°C while an annealing above 500°C creates a dimer-adatom-stacking fault (DAS) (7 × 7) structure. In the (7 × 7) structure we argue that Sn occupies both adatom and dimer sites. A previously suggested difference in the (√3 × √3)R30° reconstruction at different coverages could not be revealed in our STM images and it seems likely that the structure is the same both at 0.4 and 0.7 ML Sn coverage. We also report the observation of a new superstructure, a (4 × √7) reconstruction in the submonolayer regime, which appears as a minority structure in disordered regions adjacent to a (5 × 5) DAS structure. Finally in the post-monolayer region a (3 × 2√3) structure, surrounded by vast areas of an amorphous tin overlayer, has been imaged by STM. As the coverage was increased, the amorphous layer completely covered the ordered (3 × 2√3) phase, which still could be observed in LEED. Additional room temperature deposition of Sn deteriorated the fractional order LEED spots presumably due to indiffusion of Sn from the interface as the critical coverage was surpassed.