Upper surface thermal recovery and formation of subsurface C(sp2) layer in very low-energy nitrogen implanted diamond surfaces studied by synchrotron-based spectroscopic methods

The interaction of 100 eV N 2 + ions at a dose of 1×10 15 ions/cm 2 with polycrystalline diamond (PCD) and surface thermal recovery and CN bonding configuration in post-implantation annealed (500 °C and 1000 °C) PCD films were investigated by variable photon energy X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, providing a depth profile of the different C-C configurations and C-N bonding. It was found that the N-implanted PCD and 500 °C annealed surface displays a dominant C(1s) XP spectral component at 284 eV assigned to a C D-N (stress) hybridized carbon atom exposed to high local stress exerted by the implanted nitrogen atoms on the surrounding diamond lattice. Concurrent with nitrogen partial desorption by 1000 °C annealing, a pronounced decrease of the 284 eV spectral component and an increase of the C(sp 3 ) spectral component at 285 eV occurred. Our analysis shows that the near-surface diamond structure is recovered upon high-temperature annealing through stress relaxation associated with nitrogen diffusion and desorption. However, carbon vacancy diffusion and recombination with the implanted nitrogen result in nitrogen positioning in substitutional sites (N s ), which forms a thermodynamically stable subsurface rich in sp 2 -bonded layer contributing to the 284 eV C(1s) XP spectral component. NEXAFS analysis complements that nitrogen exists in C-N and C=N configurations (from N- K -edge spectra) upon implantation, resulting in C- K pre-edge peaks at 286.5 and 288.5 eV associated with them, respectively.