Dissociative electron attachment and dipolar dissociation of H^- electron stimulated desorption from hydrogenated diamond films

In this work we report, a study of the mechanism of H^- electron stimulated desorption (ESD) from hydrogenated diamond films for incident electron energies in the 2-45 eV range. Two types of experiments were carried out in order to assess the nature of the ESD processes leading to desorption as a function of incident electron energy: (i) kinetic energy distribution (KED) of H^- and (ii) H^- anions yield at fixed ion energy (FIE) measurements. The KED measurements show that for incident electrons of up to ∼11 eV the most probable kinetic energy of H^- ions monotonically increases from about 1.7 to 3.3 eV. For higher incident electron energies, the ion energy distribution peaks at about 1.5 eV and is nearly constant. From these measurements it is derived that the H^- ESD cross section has a resonance behavior displaying two well-defined peaks at 9 and 22 eV and a monotonic increase with a threshold at ∼14 eV as a function of incident electron energy. From the KED and FIE spectra the 9- and 22-eV peaks are interpreted as due to dissociative electron attachment via a single Feshbach anion resonance state, albeit accessed directly and indirectly, respectively. A possible intermediate process involving a well-known electronic excitation of the hydrogenated diamond at 13 eV is suggested. For incident electron energies higher than ∼14 eV, H^- ESD proceeds also via dipolar dissociation processes.