Desorption of chlorosilanes from and chlorine-induced restructuring of copper/silicon(111) surfaces

This dissertation reports on extensive studies of chlorine chemistry on Cu/Si(111) surfaces. The studies were undertaken with the purpose of gaining an insight into the atomic mechanisms involved in the commercial catalytic “Direct Synthesis” of methylchlorosilanes. Techniques employed included low energy electron diffraction, Auger electron spectroscopy, temperature programmed desorption, and scanning tunneling microscopy.; Both Cl-exposed clean Si(111) and Cu/Si(111) surfaces yield a major TPD peak around 600°C. The presence of Cu on Si(111) leads also to the appearance of two additional low temperature TPD peaks, both consisting of SiCl ₄ and SiCl₂ species, in the 200–300°C temperature range, which is appropriate for the commercial synthesis. The proposed model describes the lower temperature desorption through the formation of an activated SiCl₂ precursor on the copper containing surface.; It was shown that chlorine exposed Cu/Si(111) “5 x 5” monatomic film undergoes a significant restructuring upon heating to ∼450°C. Initially homogeneous Cu/Si(111) “5 x 5” surfaces, after Cl deposition and annealing, separate into coexisting areas of Cu-free Cl/Si(111) 1 x 1 and nearly chlorine-free areas of Cu/Si(111) “5 x 5”. The original copper density is conserved by formation of 3-dimensional Cu ₃Si crystallites on the surface. The restructuring is completely reversible: upon desorption of all chlorine at ∼600°C the surface resumes its original Cu/Si(111) “5 x 5” structure.; The SiCl₂ desorption from Cl-exposed Cu-containing Si(lII) surfaces at 600°C exhibits an unusual autocatalytic behavior, different from that of the clean Si(111). The analysis of desorption kinetics, combined with surface morphology studies, suggests the presence of separate Cu- and Cl-containing regions in dynamic equilibrium with each other at the temperatures of desorption. According to the proposed model, the high-temperature desorption from Cl/Cu/Si(111) surfaces proceeds through Cl transport to the Cu-containing regions, where SiCl₂ formation and desorption occurs.