Cesium Adsorption on W: Ellipsometry, Auger Spectroscopy, and Surface Potential Difference Studies

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Abstract
A study has been made of cesium adsorption of W and Ti using the combined measurements of ellipsometry, Auger spectroscopy, and surface potential difference measurements. The single and polycrystals of W have been cleaned in ultrahigh vacuum (∼2×10−10 Torr) and the cesium deposited as an ion beam at low voltages (5–30 V). The deposition of Cs+ did not occur unless some oxygen was detected on the sample by Auger spectroscopy. The sticking coefficient for Cs/W proved to be directly proportional to the concentration of oxygen on the W in the range 0–0.1 fraction of a monolayer oxygen coverage. The optical constants of bulk Cs can be used to interpret ellipsometric results for the adsorption of Cs on W and Ti in the region above, at and below monolayer coverage. The coverage obtained for the work-function minimum is consistent with earlier work by Taylor and Langmuir.