Angle-resolved photoemission determination ofΛ-line valence bands in Pt and Au using synchrotron radiation

Abstract

Angle-resolved photoemission spectra are reported for Au (111) and Pt (111) in the photon-energy range $6\le h\nu \le 33$ eV. Experimental dispersion relations along $\Lambda$ were derived for both crystals; comparison with relativistic augmented-plane-wave calculations showed generally good qualitative agreement, but quantitative disagreement of the order of a few tenths of an eV. Band energies are tabulated; values at $\Gamma$ are ${\Gamma }_8=3.55, 5.90$, ${\Gamma }_7=4.45\mathrm{}$ eV for Au; ${\Gamma }_8=1.40, 4.07$, ${\Gamma }_7=2.80\mathrm{}$ eV for Pt. The $s$ band is found to be ca. 1 eV (Pt) and 0.5 eV (Au) less bound than the theoretical prediction. Ligand field parameters at $\Gamma$ are presented for both samples: $\xi \mathrm{}\left(5d\right)=0.71\mathrm{}\pm 0.05$ eV, $10Dq=1.22\pm 0.05$ eV for Au; $\xi \mathrm{}\left(5d\right)=0.66\mathrm{}\pm 0.05$ eV, $10Dq=1.78\pm 0.05$ eV for Pt. The systematics of $10Dq$ in the noble metals is discussed. The polarization dependence of the spectra was used to assign initial-state symmetries empirically: bands 3, 5 show ${\Lambda }_6$ symmetry, bands 2, 4, 6, ${\Lambda }_4+{\Lambda }_5$. Cooling of the Au crystal showed that the "$s-p$ plateau" is due to a thermally insensitive indirect process, and that both thermal diffuse scattering and phonon-assisted inelastic processes contribute to the loss of spectral contrast at room temperature. Resonances in intensity with photon energy were investigated and assigned in terms of the final-state band structure.