ADSORBATE-INDUCED ENHANCEMENT OF IMAGE-POTENTIAL SURFACE-STATES ON NI(110)

Inverse photoemission data of Ni(110)-c(2 x 2)-S exhibit an adsorbate-induced feature that is interpreted as an image-potential surface state by the following criteria: energetic position and width, dispersion as a function of k, crystal reflectivity, and magnetic exchange splitting. This experiment shows that adsorption of adatoms on a surface not only either quench or shift image-potential surface states but also may enhance their intensity due to an increased crystal reflectivity. In addition, the spin-resolved data reveal an image state on a ferromagnetic surface which is exchange split by about 30 meV.