Thin manganese films on Si(111)-(7x7): electronic structure and strain in silicide formation

The electronic and structural properties of thin epitaxial Mn films on Si(111)-(7 x 7) and their silicide reaction are studied by means of low-energy electron diffraction, scanning tunnelling microscopy (STM) and photoemission spectroscopy (PES). The deposition of Mn at room temperature initially results in the growth of islands. The metal-silicon reaction already occurs at this temperature, which is further enhanced by annealing up to 400degreesC, leading to the formation of manganese silicide and turning islands into nearly closed films at higher coverage. A pseudo-(1 x 1) phase develops for Mn films of up to I monolayer (ML) thickness. For films of higher thicknesses of up to 5 ML, a (root3 x root3)R30degrees phase is observed. STM images show that then the silicide film is almost closed and exhibits a strain relief network reflecting an incommensurate interface structure. PIES reveals that the (1 x 1) phase is semiconducting while the (root3 x root3)R30degrees phase is metallic. For both phases, Si 2p core level photoemission data indicate that the surface is probably terminated by Si atoms.