Surface Science 185 (1987) L453-L458 L453 North-Holland, Amsterdam SURFACE SCIENCE LETTERS WORK FUNCTION OF CESIUM-COVERED POLYCRYSTALLINE BERYLLIUM G.S. TOMPA *, M. SEIDL *, W.C. ERMLER * * and W.E. CARR * Stevens Institute of Technology, Hoboken, NJ 07030, USA Received 18 February 1987; accepted for publication 16 March 1987 The dependence of the work function on Cs coverage of clean polycrystalline Be has been measured. The maximum shift obtainable is 2.3 eV. Photoemission and thick Cs overlayer measurements indicate that the minimum work function surface is at 1.6 eV. This new measure- ment is one of many showing that cesium covered metals and semiconductors are observed to have a minimum work function close to 1.6 eV. In general the minimum work function value is observed to be weakly dependent on the substrate. The work function is determined by the polarization of the Cs overlayer with the increase of electronic charge in the Cs-substrate interface. The work function reduction of many metal and semiconductor surfaces by coating with Cs is well known [1]. The change in work function of Be with Cs coverage has not been reported. This paper presents a summary of such an investigation. The work function as a function of dose shows the characteristic quadratic behavior, passing through a minimum before leveling off at high coverage.' The minimum work function surface produced is 1.6 eV. This value is in agreement with the minimum value produced on other materials. The final work function value of 1.94 eV reported by Wilson for Cs on Be did not pass through a minimum before reaching this value [2]. The minimum work function produced is due to the outward-positive dipole layer formed by the polarization of Cs with the increase of electronic charge in the Cs-substrate interface. We have used Auger electron spectroscopy (AES) to verify surface purity. Our experimental procedure and apparatus have been previously described and will only briefly be reviewed here [3]. The vacuum vessel has a base pressure < 5 • 10-n Torr. The experiment is performed at room temperature and at an operational pressure of (2-8) • 10 -l~ Torr. Two analytic stations are employed: the retarding field electron diode work function shift measure- * Department of Physics and Engineering Physics. * * Department of Chemistry and Chemical Engineering. 0039-6028/87/$03.50 9 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)