Unoccupied surface electronic structure of Gd(0001)

The unoccupied surface electronic structure of Gd(0001) was investigated with high-resolution inverse-photoemission spectroscopy. An empty surface state near ${\mathit{E}}_{\mathit{F}}$ is observed at Γ¯. Two other surface-sensitive features are also revealed at 1.2 and 3.1 eV above the Fermi level. Hydrogen adsorption on Gd surfaces was used to distinguish the surface-sensitive features from the bulk features. The unoccupied bulk-band critical points are determined to be ${\mathrm{\Gamma }}_3^{+}$ at 1.9 eV and ${\mathit{A}}_1$ at 0.8 eV.