Thermal stability of cesium on oxygenated W(110)

Abstract

Cesium adsorption on an oxygen-covered W(110) surface was studied by low energy electron diffraction (LEED), Auger electron spectroscopy (AES), thermal desorption spectroscopy (TDS) and work function measurements. Room temprature work functions were measured by Kelvin probe and high temperature work functions were deduced from thermionic emission measurements. It was found that: (1) annealing of the WO 2-on-W(110) surface at 1250 K produced a two-dimensional oxide layer, in agreement with the earlier results of Bauer and Engel; (2) the 2D-oxide layer was stable for prolonged annealing up to 1250 K; (3) adsorptiondesorption cycles of Cs on 2D-oxide (up to 1250 K) did not affect the 2D-oxide layer and always led to the same work function minimum φ min = 1.11 ± 0.05 eV; (4) simultaneous heating of the 2D-oxide surface at 700 K and exposure to a Cs flux resulted in the same room temperature φ min; (5) the thermionic work function minimum in the presence of a Cs flux increased exponentially from 1.1 to 1.38 eV in the 300 to 700 K temperature range; (6) exposure to air of the WO 2/W(110) surface did not affect the subsequent production of the 2Doxide in UHV, and deposition of Cs on this surface led again to φ min = 1.1 eV.