INVESTIGATION OF ELECTRONIC AND MAGNETICPROPERTIES OF MN-DOPED GE(111) AND Ε-GASE(0001) SURFACES

In this thesis an investigation of the electronic and magnetic properties of Mn:Ge(111) and Mn:GaSe (0001) interfaces is presented. These materials are relevant for potential applications in the field of spintronics. After an introduction to the physics of these systems (Chapter 1), in Chapter 2, the experimental and computational details on X-ray spectroscopy of interest are presented. The physical principles and the experimental setups underlying the X-ray photoemission (XPS), X-ray absorption (XAS) and the resonant photoemission (ResPES) spectroscopies are described; a brief introduction to parameterized, configuration integration (CI), models is provided, as this approach has been adopted to calculate the Mn spectral weight in core-level and valence band photoemission. In Chapter 3, the electronic and magnetic properties of the Mn-doped Ge(111) surface/interface are described. The preparation of Mn:Ge surface- /interface, which is an MnxGe1−x diluted magnetic semiconductor (DMS) system, as evidenced by Mn 2p line shape from the XPS, is described. A parameterized CI model is used to calculate the experimental spectrum. The information on the electronic interaction between the localized Mn ions and the ligand orbitals in the system is also analysed. The magnetic behavior of these systems has been explored by SQUID magnetometry measurements. In Chapter 4, the growth of an ordered metallic Mn5Ge3 ultra-thin interface is described. The electronic properties of the sample have been studied by XPS, XAS, and ResPES techniques. In particular, the ResPES technique has been a very useful tool to investigate the dynamics of valence electrons triggered by the Mn 2p-3d transition. In Chapter 5, the Mn-doped ϵ-GaSe(0001) surface has been explored starting from growth and characterization measurements. Evaporation of Mn for 9 consecutive steps on an ultra high vacuum cleaved ϵ-GaSe(0001) surface has been carried out. The XPS results show that Mn substitutes Ga site at the surface, for low Mn concentrations. This experiments allowed to investigate the cation substitution mechanism, and to identify the limits of Mn dilution before the onset of Mn segregation processes at the surface. Once the segregation limits have been established, new samples have been prepared, with a Mn content below this limit in order to study the electronic, and magnetic, properties the Ga1−xMnxSe surface alloy obtained by thermally-driven diffusion of Mn ions evaporated on the surface of a freshly cleaved ϵ-GaSe(0001) single crystal. The surface electronic properties of this system have been explored by core and valence band photoelectron spectroscopy, XAS, and ResPES. Parameterized CI models have been used to calculate the Mn spectral weight in core and valence band photoemission.