Mechanisms and dynamics of electron-stimulated desorption ofD−from deuterated diamond surfaces: Surface versus subsurface stimulated desorption

Abstract

In this work we report on a study of low-energy electron-stimulated desorption (ESD) of ${\mathrm{D}}^{\mathrm{\ensuremath{-}}}$ from in situ hot-filament-deuterated surfaces of diamond films. This deuteration procedure ensures that deuterium is predominantly adsorbed on the diamond surface and that no significant diffusion underneath the surface takes place. For incident electron energies in the 5--35-eV range, dissociative electron attachment (DEA) and dipolar dissociation (DD) processes occur. The cross section for ${\mathrm{D}}^{\mathrm{\ensuremath{-}}}$ ESD obtains a maximum value at \ensuremath{\sim}8 eV, whereas the DD process displays a threshold at \ensuremath{\sim}14 eV. Ion kinetic-energy distribution (KED) measurements show that in the DEA regime desorption results in a narrow peak whose energy position increases with the incident electron energy to a value that corresponds, minus a multiphonon excitation factor, to the thermodynamic limit, in agreement with gas-phase considerations. In the DD regime the ion KED displays a peak at \ensuremath{\sim}2 eV which does not depend on the incident electron kinetic energy. To study the effect of inelastic interactions between the desorbing ${\mathrm{D}}^{\mathrm{\ensuremath{-}}}$ ions and the surface, in the DEA regime, KED measurements were performed as a function of desorbing angle with respect to the surface normal. It was found that with an increasing angle from the surface normal the ${\mathrm{D}}^{\mathrm{\ensuremath{-}}}$ KED broadens, and its lower-energy component increases in intensity. These results clearly show that inelastic interaction between the outgoing ${\mathrm{D}}^{\mathrm{\ensuremath{-}}}$ and the solid surface takes place, and determines the KED of desorbing ions. The ESD results obtained for the in situ deuterated surface are compared with those previously obtained for deuterated diamond films that contain some subsurface deuterium for which broad KED's were measured. A difference in the ${\mathrm{D}}^{\mathrm{\ensuremath{-}}}$ KED in the DD regime is also measured. The indirect DEA process observed in the case of hydrogenated (deuterated) diamond films is strongly reduced in the present case of an on-top deuterated diamond surface. Our results show that ESD may be used to determine the presence of surface versus subsurface hydrogen (deuterium) adsorbed on diamond.