Development of structural phases of iron silicide films on Si(111) studied by LEED, AES and STM

The structural properties of the system Fe/Si(111) developing upon the deposition of(sub)monolayer quantities of iron by solid-phase epitaxy and the early stages of silicide formation were investigated with low-energy electron diffraction (LEED), Auger electron spectroscopy (AES) and scanning tunneling microscopy (STM). AES data indicate that the iron-silicon (silicide) reaction starts well. below room temperature. Independent of the amount of iron deposited, i.e. up to 7 monolayers (ML), two distinct him structures, namely a (1 x 1) and a (2 x 2) phase form at different annealing temperatures. Substantial differences between the two phases in stoichiometry and structure are indicated by AES amplitudes as well as LEED intensities (IV spectra). Three types of islands or film patches are observed by STM for the (2 x 2) phase, exhibiting different growth modes. Nevertheless, we find the same adatom termination in (2 x 2) arrangement on all types of islands. Combination of the LEED, AES and STM results suggests that film growth is incomplete, with different amounts of clean surface areas exposed depending on the initial coverage (Theta). For Theta less than or equal to 5 ML the crystalline structures of the film patches are probably similar for each phase at different coverages, but different between the (1 x 1) and the (2 x 2) phases.