ALKALI ADSORPTION ON W(110) STUDIED BY METASTABLE IMPACT ELECTRON-SPECTROSCOPY

The adsorption of alkali atoms (Li, Na, K, Cs) on W(110) at room temperature has been studied by Metastable Impact Electron Spectroscopy (MIES) and UPS as a function of the alkali coverage. In the coverage range up to 0.5 ML (in units of the saturation coverage at room temperature) emission via the Auger de-excitation process involving substrate electrons is observed. Emission which can be associated with the alkali s-levels can be identified only at alkali coverages exceeding 0.4 ML. This conclusion is corroborated by results obtained for the W(110) surface exposed to NaCl and by the oxidation of alkali layers. An explanation is offered for the fact that the interaction of the He(2(1)S) and He(2(3)S) metastables with the surface is different. An attempt is made to analyse and interpret the line shapes of the alkali induced features.