CO on Ru (001): Electron stimulated desorption and its correlation with other measurements

Abstract

Electron stimulated desorption (ESD) of CO on Ru (001) leads to emission of CO⁺ and O⁺ ions from the same adsorption states. Following earlier work on this system, a correlated study of its ESD behaviour together with LEED, Δϕ, and TPD measurments has been carried out. The filling of the two states found earlier can be seen in ESD also. The dividing line between the high and low energy states is different in room temperature adsorption on the one hand, and desorption or equilibrium measurements at elevated temperatures on the other, which is explained by incomplete attainment of equilibrium in the layer under the first condition. The behaviour of the ESD ion currents with coverage showstthat part of the molecules occupying high energy sites in the ordered layer of intermediate coverage are shifted to less favourable sites at higher coverage, so that the full layer consists of a mixture of states due to the occupation of different sites in the compressed layer, possibly accompanied by lateral interactions. ESD also suggests that the high energy sites are the on-top sites rather than the threefold sites.