Detailed studies of the density of states of amorphous NbSi obtained by synchrotron radiation photoemission

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Abstract
Ultraviolet photoemission experiments using radiation from a synchrotron source have been used to study details of the valence bands of amorhous NbxSi1-x on either side of the metal-insulator transition. The alloys were prepared in situ by RF magnetron sputtering with surface and bulk characterization obtained by Auger electron spectroscopy and EXAFS respectively. The variation of the intensities of several features in the UV spectra with photon energy are due to the presence of resonant photoemission and Cooper minima in photoionization, and these effects can be used to identify the atomic origins of the partial densities of states in different parts of the valence bands. In the metallic phase such measurements show 'pure' Nb 4d states close to the Fermi edge, whereas for the insulating material there is no Fermi edge and little evidence for the Nb resonance.