Surface and electronic properties of the Mn : Ge(111) interface at the early stages of growth

The surface structure and the electronic properties of the Mn:Ge(111) interface have been investigated by reflection high-energy electron diffraction (RHEED) and X-ray photoemission (XPS) and absorption spectroscopies (XAS) with the aim to characterize the growth process of an ordered MnxGe1-x alloy upon annealing at temperatures between 130 degrees C and 430 degrees C. The Mn:Ge(111) interface has been produced by e-beam evaporation of Mn ions on a clean, c(2 x 8) reconstructed Ge(111) surface. After an Mn evaporation of 1.3 to 2 ML, annealing at about 300 degrees C yields a (root 3 x root 3)R30 degrees surface reconstruction, while at higher temperatures the onset of C(2 x 8) reconstruction is found superimposed to the (root 3 x root 3)R30 degrees pattern. X-ray photoelectron diffraction (PED) measurements have been carried out to identify the local environment around the Mn atoms, and a preliminary analysis indicates the occurrence of Mn diffusion beneath the surface, even in as-grown thin layers, without the formation of the Mn5Ge3 alloy. These findings indicate that Mn diffusion inside the Ge lattice can be regarded as an important mechanism in the formation of the Mn:Ge(111) interface. In this frame, the electronic properties of the interface are discussed. Once the effects of oxygen contaminations are ruled out, the system does not show a XAS spectrum characteristic of atomic Mn (2+) 2P(5) 3d(6) multiplet, which excludes strong localization effects typical of diluted magnetic semiconductors. However, the lineshape of XAS spectrum indicates that some hybridization between the Mn ion and Ge is present. (c) 2006 Elsevier B.V. All rights reserved.