Physical Review B

Photoemission study of WC(0001)

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We report results of photoemission experiments and a new bulk band-structure calculation for monotungsten carbide (WC). Three types of photoemission experiment were performed on a WC(0001) surface, with the use of synchrotron radiation. Normal-emission angle-resolved spectra in the range 10h30 eV cannot be interpreted assuming dominance of direct transitions, rather a one-dimensional density-of-states (1D DOS) sampling of initial states is required. By exploiting the natural polarization of the synchrotron-radiation source, initial-state symmetries of three features are unambiguously assigned, 1 at -9.4 and -1.0 eV and 3 at -3.0 eV, and these same features are associated with appropriate-symmetry high-DOS regions along (-A) in the bulk band structure. Two features displaying no clear-cut polarization dependence cannot be associated with high-DOS regions along and are attributed to emission scattered from elsewhere in the Brillouin zone. The strong amplitude dependence with emission angle of a sharp peak near EF is attributed to symmetry selection rules related to a mirror-plane collection geometry excited by polarized radiation. Data from a second experiment using a cylindrical mirror analyzer (CMA), 10h30 eV, are also interpreted with the use of the bulk band structure, but with more limited success. Here, however, clear evidence of direct transitions is seen. A total DOS is probed in the third experiment, which again uses a CMA, with 65h200 eV. The main valence band extends 8 eV below EF while C 2s electrons form a separate band, 3-eV FWHM centered at -12.5 eV. Utilizing the W 5d Cooper minimum at 160 eV=h, we assign the upper half of the main valence band to predominately W 5d derived states, while in the lower half, C 2p derived states dominate. © 1984 The American Physical Society.