Synchrotron radiation study of surface versus sub-surface deuterium in diamond films produced by exposure to deuterium activated by hot filament-high vacuum and ex situ microwave plasma

摘要

In the present study, the chemical state of adsorbed deuterium and its thermal stability in diamond films surface and subsurface regions are investigated by photon stimulated ion desorption (PSID0, near-edge X-ray absorption fine structure (NEXAFS), and secondary electron emission (SEE) measurements. To this effect, undoped polycrystalline diamond films were exposed to deuterium activated by ex situ microwave (MW) plasma or in situ by hot filament (HF0 in ultrahigh vacuum conditions. D~+ PSID measurements of polycrystalline diamond films were performed after annealing to temperatures in the range of 25-1000 deg C. Even after moderate annealing to 350 deg C of the MW-deuterated diamond film, PSID spectra showed a substantial decrease in total deuterium desorption yield, as well as change of the dynamics of desorption in favor of direct processes induced by corehole relaxation. D~+ PSID of diamond films in situ exposed to deuterium activated by the HF showed different behavior. The desorption yield of deuterium ions and the relation between direct and indirect desortion processes were nearly unchanged when heated up to approx 800 deg C. The effect of annealing on D~+ desorption yield and on the dynamics of the desorption process was associated with structural changes in the near-surface region as identified by NEXAFS spectroscopy, and changes in the electron emission properties, as measured by SEE. On the basis of these results it is suggested that in contrast to ex situ MW plasma deuteration, in situ exposure of the films to HF-produced activated deuterium does not lead to bulk diffusion of deuterium atoms.