Angle-resolved photoemission study of the surface and bulk electronic structure of Mg(0001) and Mg(112¯0)

Angle-resolved ultraviolet photoemission spectroscopy measurements have been made from the (0001) and (112¯0) surfaces of magnesium in the photon energy range of 15 to 115 eV. Both bulk and surface features are identified. The occupied bands along the [0001] direction are characterized by the measured energy eigenvalues at the Γ point: ${\Gamma }_1^{+}$=6.15±0.1 eV, ${\Gamma }_3^{+}$=1.7±0.1 eV, and ${\Gamma }_4^{\mathrm{-}}$=0.9±0.1 eV. The bandwidth, as measured for both the (0001) and the (112¯0) surfaces, is 10% smaller than that predicted by band-structure calculations, while the ${\Gamma }_3^{+}$-${\Gamma }_4^{\mathrm{-}}$ band gap is twice as big as calculated. The narrower experimental bandwidth is related to the fact that the excitation spectrum of the system is measured, while the origin of the wider experimental gap is not as clear. The final states higher than 28 eV above $E_F$ are well described by a free-electron band of effective mass $m^{\mathrm{*}}$/m=1.04, originating 6.15 eV below the Fermi level, while the low-energy final states deviate greatly from free-electron-like behavior. The peak widths of the bulk features in both the [0001] and the [112¯0] direction are significantly larger than predicted by interacting electron-gas theory. The peak widths along [0001] increase near the middle of the band, due to final-state effects. The binding energy of the Γ¯ surface state on the (0001) surface has been redetermined to be 1.6±0.1 eV. A surface state at M¯ has a binding energy of 1.1±0.1 eV. The Γ¯ surface state shows a sharp intensity resonance near ħω=44 eV giving the location of a state of ${\Gamma }_4^{\mathrm{-}}$ symmetry in the final state. The M¯ surface state shows a similar resonance near ħω=26 eV. The surface-state dispersions have been measured in the Γ¯-M¯ direction.