Analysis of monolayer films during molecular beam epitaxy by reflection electron energy loss spectroscopy

Abstract

Reflection electron energy loss spectroscopy at high electron energies is an analytic technique well-suited to compositional analysis at the monolayer level during molecular beam epitaxial growth. For submonolayer-thickness Ge films grown on (2 × 1)-reconstructed Si (001) substrates, the variations in core loss intensities with film thickness and scattering angle are well described by a simple geometrical model for scattering, in the absence of surface resonance effects. Surface resonant scattering leads to an enhancement in the core loss intensity detected for thin epitaxial films, as the azumithal incidence direction is varied around the [110] azimuth, at a fixed incidence angle relative to the substrate plane. Increased surface roughness leads to a decreased inelastic scattering contribution relative to smooth surfaces, with low loss spectra that are more characteristic of transmission scattering. Detection limits for C have been established for reflection electron energy loss spectroscopy, enabling in situ analysis of surface cleaning prior to silicon molecular beam epitaxy. Short range structural information has been obtained using extended edge energy loss fine structure (EXELFS) for a newly-observed Sn reconstruction on a Si(001) surface, a (3 × 1) Sn overlayer on clean, hydrogen-terminated (1 × 1) Si (001).