Bombardment-induced desorption of co adsorbed on 304 stainless steel by low energy (75–1000 eV) light active and inert gas ions

Abstract Experiments are described in which the variations of the cross-sections for ion-induced desorption of CO, adsorbed on stainless steel at room temperature, with incident ion energy are determined for ions of hydrogen, deuterium, helium, neon, and argon, at energies between 75 eV and 1 keV. The technique consists of allowing CO from the residual gas in a UHV system at approximately 5 × 10 −9 Torr to adsorb on the target, which is then bombarded by the chosen ion species at the required incident energy. The change in partial pressure of CO when the beam is switched on (or off) is a measure of the desorption cross-section, gas coverage, and beam current density. Knowledge of the gas coverage and mass-spectrometer sensitivity are not necessary, because measurement of the area under the desorption transient obtained by heating the target to a sufficiently high temperature to desorb all the adsorbed CO allows elimination of these quantities from the expression for the gas sputtering cross-section. The cross-section vs. energy curves all show a minimum in the energy region 150–350 eV, and the shapes of the curves are explained in terms of the relative amounts of energy transferred (at different initial ion energies) from the incident ions directly to the adsorbed molecules, following back-scattering from target atoms, and indirectly via the target atoms as a result of collision cascades below the target surface. The magnitudes of the cross-sections obtained vary with ion energy and type in the range 10 −18 to 10 −16 cm 2 .