Appearance of the minoritydz2surface state and disappearance of the image-potential state: Criteria for clean Fe(001)

Abstract

The unoccupied surface electronic structure of clean and oxidized Fe(001) was studied with spin-resolved inverse photoemission and target current spectroscopy. For the clean surface, we detected a ${d}_{{z}^{2}}$ surface state with minority spin character just above the Fermi level, while the image-potential surface state disappears. The opposite is observed for the ordered $p$($1\ifmmode\times\else\texttimes\fi{}1$)O/Fe(001) surface: the ${d}_{{z}^{2}}$-type surface state is quenched, while the image-potential state shows up as a pronounced feature. This behavior indicates enhanced surface reflectivity at the oxidized surface. The appearance and disappearance of specific unoccupied surface states prove to be decisive criteria for a clean Fe(001) surface. In addition, enhanced spin asymmetry in the unoccupied states is observed for the oxidized surface. Our results have implications for the use of clean and oxidized Fe(001) films as spin-polarization detectors.