IN-SITU RHEED AND XPS STUDIES OF EPITAXIAL THIN ALPHA-FE2O3(0001) FILMS ON SAPPHIRE

In situ RHEED and XPS measurements of epitaxial alpha-Fe2O3(0001) film s are reported as a function of the number of deposited monolayers. Th e films were prepared on alpha-Al2O3(0001) substrates by MBE. The RHEE D patterns suggest that layer-by-layer growth of alpha-Fe2O3(0001) occ urs for the first few monolayers. Subsequently, the growth mode change s to three-dimensional growth. The in-plane lattice constant of the fi rst monolayer of alpha-Fe2O3(0001) is expanded relative to that of the bulk, although in the case of lattice matching between alpha-Al2O3 an d alpha-Fe2O3 a contraction would be expected. This can be explained b y assuming a basic hexagonal structure for the first monolayer with a random distribution of ferric ions over the octahedral sites between t he close-packed oxygen layers. Beyond the first monolayer, the ordered corundum structure is formed. The lineshapes of the XPS Fe 2p core le vel spectra are also found to be thickness-dependent. The deviation of the Madelung potential at the surface shifts the positions of the Fe 2p peaks to lower binding energies. For the first few monolayers, the satellite intensity is reduced because the interplanar contraction lea ds to a shorter Fe-O distance.