Regensburg 2004 – scientific programme

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O: Oberflächenphysik

O 40: Halbleiteroberflächen und -grenzflächen

O 40.6: Talk

Thursday, March 11, 2004, 17:00–17:15, H45

First-principles calculations for initial adsorption of manganese on Si(001) — •Mahbube Hortaman, Hua Wu, Peter Kratzer, and Matthias Scheffler — Fritz-Haber-Institut der MPG, Faradayweg 4-6, 14195, Berlin

Heterojunctions between a semiconductor and a ferromagnetic metal have attracted attention in the context of spintronics. In this work, we choose the Mn on Si(001) system as a possible candidate for the growth of magnetic thin films, and investigated the adsorption behavior of Mn (coverage θ < 0.5 monolayer) by first-principles total-energy calculations using density functional theory and the FP-APW+lo method. For one Mn atom in the Si(001)(2x2) unit cell, the sub-surface site is 0.9 eV lower in energy than the on-surface position due to the strong Mn-Si covalent bonding. Moreover, we find a pathway to the subsurface region that exhibits a practically zero energy barrier. As seen from the potential-energy surface of Mn in different adsorption geometries, the most stable site on the surface is the hollow site where Mn is placed between two Si dimers in the same row. Diffusion barriers both along and perpendicular to the dimer row are about 0.7 eV, which indicates isotropic diffusion. For on-surface Mn adatoms we find a strong tendency towards the formation of Mn islands on the surface. The resulting structure resembles that of a next Si layer. If the sub-surface site is reached by Mn adatoms before the on-surface islands are formed, a mixed on-surface/sub-surface structure will result. We discuss the above sketched results in a simple physical picture and propose ideas how these different structures may be grown experimentally.