It was noted that ultra-thin films of manganese silicides on Si were of relevance as a possible system for building spintronics devices using Si technology. In order to achieve insight into the epitaxial growth of such films on Si(001), total-energy calculations were presented using density-functional theory and the full-potential augmented plane wave plus local orbital method. For adsorption of a single Mn atom on Si(001), it was found that binding at the sub-surface sites below the Si surface dimers was some 0.9eV stronger than on-surface adsorption. There was an energy barrier of only 0.3eV for adsorbed Mn to go sub-surface, and an energy barrier of 1.2eV for the reverse process. From the calculated potential-energy surface for the Mn adatom, it was concluded that the most stable site on the surface corresponded to the hollow site where Mn was placed between two Si surface dimers. For on-surface diffusion, along or perpendicular to the Si dimer rows, the Mn atoms had to overcome energy barriers of 0.65eV. For the deposition of 0.5 of a monolayer or more, the Si dimers of the Si(001) surface were broken up, and a mixed MnSi layer became the energetically most favourable structure. For coverages above 1ML, the lowest-energy structure changed to a full Mn sub-surface layer, capped with a layer of Si adatoms. This transition was identified with the onset of Mn-silicide formation in an epitaxially stabilized CsCl-like crystal structure. Such MnSi films were found to have sizable magnetic moments at the Mn atoms near the surface and interface, and ferromagnetic coupling of the Mn magnetic moments within the layers. Layer-resolved electronic densities of state were presented that showed a high degree of spin polarization at the Fermi level; up to 45% and 27% for films with two or three Si-Mn layers, respectively.

Epitaxy of Mn on Si(001) - Adsorption, Surface Diffusion and Magnetic Properties Studied by Density-Functional Theory. M.Hortamani, H.Wu, P.Kratzer, M.Scheffler: Physical Review B, 2006, 74[20], 205305 (10pp)