Interaction of cesium and barium on partially oxygen covered Nb(110)

Abstract

We present results of investigations of the adsorption and desorption of Cs and Ba on clean and oxygenated Nb(110) surfaces. The experiments were conducted under ultrahigh vacuum conditions using the techniques of line-of-sight thermal desorption mass spectrometry, Auger electron spectroscopy, and retarding potential work function measurement. The room temperature work function was found to increase from 4.62 eV for clean Nb(110) to 5.63 eV for Nb(110) with a saturated chemisorbed layer of oxygen. For a 4.8 L (1 L=1 Langmuir=1×10−6 Torr s) oxygen exposure, corresponding to about 70% of saturated oxygen coverage, minimum work functions of 2.21 and 1.42 eV were found with the adsorption of Ba and Cs, respectively. The minimum work function tends to increase with further adsorption of oxygen. The adsorption of Cs on the Ba/Nb(110) surface yielded a minimum work function of 1.47 eV. The results of the thermal desorption studies showed an initial (low coverages) binding energy of 3.72 eV for Ba on Nb(110) and 2.42 eV for Cs on Nb(110). We also present desorption energy data for Cs on the Ba/Nb(110) surface.