X-ray photoemission study of MgB_2 films synthesized from in-situ annealed MgB_2/Mg multilayers

摘要

Superconducting MgB_2 films were obtained by in-situ annealing of precursor multilayers deposited at low substrate temperature by sputtering from a MgB_2 stoichiometric target and by thermal evaporation of pure Mg. After an in-situ annealing at 500-600℃, the films showed a zero resistance critical temperature up to 31 K. The as-obtained MgB_2 films were investigated by X-ray photoelectron spectroscopy (XPS) and X-ray auger electron spectroscopy (XAES). The electronic structure was studied by monitoring the B 1s, Mg 2p, O 1s core-levels and the Mg KL_2L_3 Auger line. For comparison, the electronic structure of an MgB_2 commercial superconducting sputtering target, of a not-annealed precursor film and of a sample obtained by direct sputtering from the MgB_2 target have also been investigated. Electron spectroscopy showed that in the superconducting systems the Mg KL_2L_3 Auger line kinetic energy position is always higher by about 0.9 eV with respect to the energy position of the same Auger line measured in the non-superconducting samples.