SURFACE CHARACTER IN THE EXPERIMENTAL FERMI-SURFACE OF EPITAXIAL ERSI1.7(0001) BY PHOTOEMISSION SPECTROSCOPY

The electronic structure of erbium silicide, ErSi1.7(0001), 100-Angstr om-thick films epitaxially grown on Si(lll), has been measured by angu lar-resolved ultraviolet photoemission (ARUPS) using synchrotron radia tion. Valence-band spectra for different collection angles along the G amma M Gamma and Gamma KM directions of the substrate Si(111)-(1x1) su rface Brillouin zone (SBZ) and different Fermi-surface maps have been measured by the photoemission technique using photon energies of 21.2, 33, and 55 eV. The Fermi surface is characterized by hole-and electro n pockets at particular high-symmetry points in the SBZ. In opposition to what was expected considering both the crystallographic structure and calculated band structure, the shape of the Fermi-surface maps obt ained for different photon energies are very similar. Moreover, the ph otoemission spectra using different photon energies show a very weak d ispersion as a function of the k wave vector perpendicular to the surf ace (k(perpendicular to)). All these findings suggest that the electro nic states which contribute to the experiment ally determined Fermi su rface have st strong bidimensional character. No noticeable effect of the light polarization on the valence-band curves is observed indicati ng a hybrid nature of the involved orbitals.