Unoccupied surface states on W(001) and Mo(001) by inverse photoemission

Abstract

The W(001) and Mo(001) surfaces are investigated by inverse photoemission. At $\overline{\ensuremath{\Gamma}}$ we observe an unoccupied surface state just above the Fermi level. The angular dependence and chemisorption behavior identify it as a ${d}_{{z}^{2}}$ surface state similar to one observed and calculated just below ${E}_{F}$. For W(001) a second state is seen near $\overline{M}$ at 1.4 eV above ${E}_{F}$ and assigned to a ${\overline{\ensuremath{\Sigma}}}_{2}$ backbonding state. The implications of our data on the driving mechanism for the surface reconstruction are discussed using all-electron self-consistent local-density calculations.