Modification of surface states by alkali-metal adsorption and surface reconstruction: An inverse-photoemission study of Na/Ni(110).

Abstract

Unoccupied surface states were investigated on the reconstructed and unreconstructed Na/Ni(110) surface experimentally by inverse photoemission and theoretically by a phase-shift analysis in a nearly-free-electron model. For the (1\ifmmode\times\else\texttimes\fi{}1) surface a downward shift of the surface states is observed as the Na coverage is increased up to monolayer completion. If reconstruction takes place, the direction of the energy shift is reversed and a surface state appears close to the Fermi level. In the theoretical model the alkali-metal-induced downshift is caused by the work-function decrease and by the additional phase shift of the surface-state wave function in the Na adlayer. On the reconstructed surface this effect is counteracted by the removal of Ni atoms from the topmost substrate layer. For near-monolayer coverages the surface states are shown to be closely related to the Na atomic wave functions.