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

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Abstract
The Cs2O overlayers with different thickness were prepared by simultaneous oxygen–cesium adsorption on Si(111) at room temperature. Photoelectron spectroscopy 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 species is sensitive to x-ray radiation, forming a new species on the top surface. 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 completely. After Cs2O disappears, both Cs–O and Si–O bonds are dominant on the surfaces with a work function of about 1.2 eV. For further annealing, the oxygen bonded to cesium gradually transfers to Si due to Cs desorption. The thickness of the SiO2 overlayer formed after Cs desorption is dependent on the mount of oxygen in the Cs2O overlayer.

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