Decay of secondary electron emission and charging of hydrogenated and hydrogen-free diamond film surfaces induced by low energy electrons

Abstract

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.

An Insight into Grain Refinement Mechanism of Ultrananocrystalline Diamond Films Obtained by Direct Current Plasma-Assisted Chemical Vapor Deposition

“…Moreover, the present study was conducted at substrate temperatures higher than those in their reports. It would bear some effects on the ESD process in the present study relative to those previous reports employing the electron beam, which should be studied further in the future.…”

“…On the other hand, it is worth to note here that the diamond growth environment in the present study differs somewhat from the experimental conditions in the previously reported hydrogen ESD studies: their ESD studies were conducted in a vacuum, in contrast to the reaction gas environment at a relatively high chamber pressure employed in the present study. Their experiments employed the electron beam with well‐defined energy, while the energy of the electrons directed to the anode in the present study was generated in the reaction gas plasma, and were consequently subjected to a Maxwellian distribution.…”

“…The hydrogen desorption was reported to be driven chemically by the atomic hydrogen, via the hydrogen abstraction reactions . By contrast, a physical pathway of such hydrogen desorption from the hydrogenated diamond surface, enabled by the electron bombardment, and known as the electron‐stimulated desorption (ESD), has been extensively studied . The ESD of hydrogen from the hydrogen‐terminated diamond surface was studied as a function of the bombarding electron energy to reveal that “the cross‐section of the ESD has a resonance behavior displaying two well‐defined peaks at 9 and 22 eV;” the resonance behavior was attributed to a resonant scattering phenomenon known as the “Feshbach resonance.” The effect of substrate temperature on the phenomenon was also reported: the resonant energy of the bombarding electron weakly decreased as the temperature was increased up to 450 K …”

Effect of surface modification on the radiation stability of diamond ohmic contacts

“…For instance, H-diamond shows a negative electron affinity (NEA) and surface conductivity, but under continuous low-energy electron irradiation, the secondary electron emission intensity of H-diamonds films is decayed. [11] O-diamond can be used as an excellent surface isolation and passivation layer. In addition, radiation stability is also important for device application.…”

Secondary Emission Enhanced Photoinjector

“…• Ability of diamond to be doped to desired boron concentration and hence desired electrical resistivity, low trap density and high carrier mobility • Hydrogenated, boron doped as well as undoped diamond has shown to have negative electron affinity [2,3] increasing the secondary electron yield. Indeed, Boron doped, hydrogenated polycrystalline diamond has been shown [4] to be an effective secondary emitter with an enhancement factor of > 80.…”