Local coordination of Mn atoms at the Mn:Ge(111) interface from photoelectron diffraction experiments

Abstract

X-ray photoelectron diffraction (PED) experiment on the metallic Mn:Ge(111) surface alloy has been carried out in the initial stage of mixed phase growth. Our findings show that the ${\mathrm{Mn}}_{5}{\mathrm{Ge}}_{3}$ phase is not yet formed for a 1.3 ML (monolayer) coverage, as well as for a 2 ML coverage, followed by an annealing at temperature $(\ensuremath{\sim}300\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C})$. Rather, we observed the formation of an ordered surface alloy by Mn occupation of the hollow ${\mathrm{H}}_{3}$ sites in the topmost layer, while about 10% of Mn atoms are found in subsurface layers, partially confirming the theoretical expectations by Zhu et al. [Phys. Rev. Lett. 93, 126102 (2004)]. However, the contribution to PED patterns from subsurface Mn atoms is found compatible with the occupation of interstitial sites only for the 1.3 ML coverage and with the occupation of both interstitial and unexpected substitutional sites for the 2 ML coverage. These findings thus open questions about the determination of the kinetic path to Mn subsurface migration in diluted alloys.