The electronic structures of tungsten carbides, borides, and silicides
The electronic properties of the carbides WC and W$\sb2$C, the borides WB, W$\sb2$B, and W$\sb2$B$\sb5$, and the silicides WSi$\sb2$, MoSi$\sb2$, and W$\sb5$Si$\sb3$ were studied experimentally and theoretically. The occupied and unoccupied states of these compounds were probed using the techniques of soft x-ray emission and absorption spectroscopies, respectively. The emission and absorption spectra were taken with a soft x-ray spectrometer and using monochromatic radiation from a synchrotron storage ring. The absorption data were obtained with the total fluorescence yield (TFY) and total electron yield (TEY) methods The linear muffin-tin orbital (LMTO) method was used to calculate the electronic structures of these compounds, and the band structures and densities of states (DOS) were presented. Since soft x-ray emission (SXE) is site- and angular momentum-selective, site- and angular momentum-projected DOS were compared to the SXE data In some cases, the LMTO results were compared with full-potential calculations. The full-potential linearized augmented Slater orbital (FLASTO) method was used to calculate the electronic structure of W$\sb2$C. The LMTO and FLASTO methods were in good agreement. The results of the LMTO calculation for WC were compared to a published full-potential linear augmented plane wave (FLAPW) calculation which were also in good agreement. It was thus concluded that the LMTO method produces accurate results in calculating the electronic structures of these compounds. In most cases, since the LMTO projected densities of states agreed well with SXE data, additional information regarding bonding mechanisms and hybridization was inferred from the calculations Resonances of the elastic peaks were observed in all of the compounds. In each case, the resonance was identified as the promotion of the excited electron to a localized excitonic state above the Fermi level. In the case of WC, W$\sb2$B, and the silicides, the localized electron acted as a spectator which partially screened the valence electrons from the core hole. The effect of this screening was to shift the spectra to energies that were slightly higher with respect to emission from a state where the hole was not screened