Photoemission study of the effect of thermal annealing on Cs2O/Si(111) surfaces

The Cs2O overlayers with different thickness were prepared by simultaneous oxygen-cesium adsorption on Si(111) at room temperature. Photoelectron spec troscopy and work-function measurements have been used to study the Cs2O/Si surfaces as a function of annealing temperature. The results show that the interaction of the Cs2O overlayer with the substrate is weak. The Cs2O spe cies is sensitive to x-ray radiation, forming a new species on the top surf ace. The Cs2O/Si surfaces exhibit a negative electron affinity with a work- function value of 0.85 +/- 0.1 eV until the Cs2O species decomposes complet ely. After Cs2O disappears, both Cs-O and Si-O bonds are dominant on the su rfaces with a work function of about 1.2 eV. For further annealing, the oxy gen bonded to cesium gradually transfers to Si due to Cs desorption. The th ickness of the SiO2 overlayer formed after Cs desorption is dependent on th e mount of oxygen in the Cs2O overlayer. (C) 2001 American Institute of Phy sics.