ADSORPTION OF CS ON WSE2 VANDERWAALS SURFACES - TEMPERATURE AND SPUTTER EFFECTS ON GROWTH-PROPERTIES

The adsorption of Cs on cleaved and Ar+ sputtered WSe2(0001) surfaces at low temperature (LT) and room temperature (RT) has been studied by LEED and photoemission spectroscopy using synchrotron radiation (SXPS). Cesium is adsorbed in an ionic state, Cs+, at low coverages, whereas at high coverages, it forms metallic clusters. The clustering is stronger at RT than at LT. At low coverages (< 0.1 ML) strong band bending (0.4 eV) is observed which is reduced again at higher coverages. Ar+ sputtering removes preferentially most of Se from the outmost layer of WSe2, thus exposing large areas (islands) of metallic W to the surface. Cesium is mainly chemisorbed on these islands, the work function is reduced to 1.7 eV and the adsorption behavior of Cs resembles that on metallic substrates.