Influence of RF(N2) plasma conditions on the chemical interaction and stability of activated nitrogen with polycrystalline diamond surfaces: A XPS, TPD and HREELS study

Abstract

In this study, the chemical interaction of nitrogen with polycrystalline diamond surfaces is investigated. The interaction of nitrogen with the diamond surface was activated using a non-line of sight interaction RF(N2) plasma source equipped with a neutralizer placed at the exit of the plasma source to decrease the density of the high energetic nitrogen species arriving at the surface. Nitridation process has been carried out for different N2 plasma exposure time (20 and 30 min) and pressure (3 × 10−2 and 7 × 10−2 Torr) at plasma power of 36 W. The chemical and structural properties of nitrided (as-processed, annealed to different temperatures and hydrogenated) diamond surfaces were evaluated using X-ray photoelectron spectroscopy, high-resolution electron energy loss spectroscopy (HREELS) and temperature programmed desorption (TPD). The HREELS analysis of nitrided diamond surfaces suggests that the plasma processing pressure and the exposure time play a crucial role in controlling surface structural quality. The presence of the optical phonon (∼300 meV), which is a signature feature of well-defined and defects-free diamond surface; confirms the crystalline quality of nitride surfaces and nitrogen present in different bonding configurations: CNH2 and CN. Further, the HREELS analysis shows that NH surface bonds stability is below 700 °C. TPD spectra show N2 and HCN peaks at ∼600 °C that are associated with nitrogen surface bonded species. Hydrogenation of annealed surfaces revealed that the surface structural recovery is possible with the low level of structural damage.