Photon and electron-stimulated desorption of excited alkali-metal atoms and CN molecules from alkali halide surfaces

Abstract

Abstract Recent advances in photon- and electron-stimulated desorption of excited alkali-metal atoms and CN molecules are discussed. The role of defects created by photon and electron irradiation leading to surface metalization is particularly emphasized in the desorption mechanisms. Two mechanisms are proposed for the creation of excited alkali-metal atoms: (1) appropriate to the low-temperature regime, the first mechanism assumes that surface exoergic reactions between alkali-metal dimers and halogen atoms produce desorbed excited alkali-metal atoms, the surface reactants being formed by radiation-initiated defect processes, and (2) the second mechanism assumes that the gas-phase excitation of ground-state alkali-metal atoms by primary electrons produce the excited alkali-metal atoms. The mechanism responsible for CN desorption may be described in three steps: (1) pre-irradiation produces alkali-metal rich surfaces via defect-mediated processes, (2) when the surface is exposed to CO2 and N2, surface reactions generate CN molecules bound to the alkali-rich surface, and (3) electron or photon bombardment induces the desorption of excited CN molecules from the surface by direct bond-breaking.