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Articles you may be interested inClarification of oxygen bonding on diamond surfaces by low energy electron stimulated desorption and high resolution electron energy loss spectroscopy Decay of secondary electron emission and charging of hydrogenated and hydrogen-free diamond film surfaces induced by low energy electronsIn this work we report on a study of the mechanism of O Ϫ electron stimulated desorption ͑ESD͒ from hydrogenated and hydrogen-free polycrystalline diamond films exposed to thermally activated oxygen for incident electron energies in the 4 -22 eV range. Two types of experiments were carried out in order to assess the nature of the ESD processes: ͑i͒ total O Ϫ and H Ϫ yields as a function of incident electron energy and ͑ii͒ kinetic-energy distribution ͑KED͒ of O Ϫ desorbed from the hydrogen-free diamond surface. The discussed ESD mechanism is referred to the information obtained from x-ray photoelectron spectroscopy, near-edge x-ray absorption fine structure, and core level H ϩ photodesorption measurements which reveal formation of CvO and C-O-C bonds on the hydrogen-free diamond surface, and CvO and C-O-H bonds on the hydrogenated one. Based on the maximum kinetic-energy value of O Ϫ and the ESD threshold measured for hydrogen-free surface, all low-energy ͑5-10 eV͒ O Ϫ ions are attributed to desorption by the dissociative electron attachment ͑DEA͒ to C-O-C, while DEA to CvO occurs at the incident electron energy higher than ϳ10 eV. O Ϫ ESD from the hydrogenated diamond surface exposed to thermally activated oxygen is a more complicated process. Its threshold is substantially higher than for hydrogen-free diamond, and the line shape of the ESD yield curve is very similar to that of chemisorbed CO molecules. Several reaction pathways leading to production of O Ϫ by DEA are discussed for this sample. At incident electron energies higher than ϳ15 eV, O Ϫ ESD proceeds also via dipolar dissociation processes for both hydrogenated and hydrogen-free diamond surfaces.

In this work, the decay of secondary-electron emission (SEE) intensity and charging of hydrogenated and hydrogen-free diamond film surfaces subjected to incident electron irradiation at energies between 5 and 20 eV are investigated. Electron emission curves as a function of incident electron energy were measured. For the hydrogenated films, it was found that the SEE intensity decays in intensity under continuous electron irradiation, albeit maintains a nearly constant onset. The decay in time of the SEE intensity was measured for various incident electron energies. From these measurements, the SEE intensity decay rate from the hydrogenated diamond surface was calculated as a function of incident electron energy and found to display a broad peak at ∼9 eV. The decay of the SEE intensity is explained as due to electron trapping in the near-surface region of the hydrogenated diamond films resulting in the formation of a depletion layer and upward surface band bending while overall charge neutrality is maintained. It is suggested that the mechanism of charge trapping is by resonant electron attachment of incident electrons into C–H (ads) bonds present within the near-surface region of the hydrogenated diamond films which displays a similar dependence on incident electron energy. Upward band bending results in a surface potential barrier to secondary electrons created within the solid. For the hydrogen-free diamond surface, decay in intensity and a positive shift in the onset of the SEE were observed for all incident electron energies and currents used. It was found that surface charging increases monotonically with incident electron energy. In this case, charging is associated with electron trapping into localized surface states of π* symmetry. These electronic states are associated with surface reconstruction resulting from hydrogen desorption.