Formation, electronic structure, and stability of film nanophases of transition metals on silicon

Abstract

This paper is devoted to the study of the morphology, growth, electronic structure, and stability of ultrathin (0.03–3 nm) Co and Fe films on the Si(111) and Si(100) surfaces using Auger-electron spectroscopy, electron-energy loss spectrometry, low-energy electron diffraction, and atomic-force microscopy. It is shown that layer-by-layer growth of the metal with the formation of the film nanophase and the segregation of a submonolayer amount of Si on the film’s nanophase surface occurs during the process of layer-by layer growth of Co and Fe on Si(111)-7 × 7 and Si(100)-2 × 1 at room temperature after the growth of two-dimensional metal phases (the surface phase, the monolayer, and two metal monolayers). After these stages, the formation and growth of the bulk’s metal phase with the dissolution of silicon segregated before occur. It is shown that the upper layers of Si adjoining the surface phase, the monolayer, and two Co and Fe monolayers have respectively three different densities of the electron plasma that are higher than the density of the electron plasma in the volume of the silicon substrate. The nonmonotonous character of the morphological and chemical stability of Fe films with quantum-size thicknesses on Si(100) is discovered. After annealing, the film is first smooth, then it is nonuniform across its thickness; afterwards it is again smooth and then nonuniform across its thickness. In this case, the metal phase, different Fe silicides, and the bulk’s metal phase form successively in Fe films on Si(100) after annealing.