The co-adsorption of cesium and oxygen was studied by performing measurements of elemental surface concentrations, work functions and electron reflectivities. The elemental surface concentrations were determined by Auger electron spectroscopy and the work functions and reflectivities by the field emission retarding potential technique. Simultaneous deposition of cesium and oxygen on substrates produced a thick oxide layer. This oxide layer had a work function of 1.0±0.05eV and an electron reflectivity at threshold of 0.45±0.10eV. Brief stepwise heatings of this layer indicated stability up to 390K. The threshold reflectivity for some higher work function surfaces depended strongly upon whether the final deposition was cesium or oxygen. Coadsorption of Cesium and Oxygen on Iridium and Lanthanum Hexaboride. Danielson, L.R.: Journal of Applied Physics, 1981, 52[1], 300-4