Influence of 1 keV N2 + Implantation on Nitrogen Bonding, Defect Formation, and Thermal Stability of the Polycrystalline Diamond Near-Surface Region Studied by XPS, TPD, and HREELS

In this study, the near-surface physicochemical properties of low-energy nitrogen-implanted polycrystalline diamond (PCD) and their evolution with the annealing temperature were investigated. The nitrogen concentration, its chemical state, and defects created in the PCD near-surface upon 1 keV N-2(+) implantation at different doses of 6 x 10(13) (D1), 3 x 10(14) (D2), 3 x 10(15) (D3), and 1 x 10(16) (D4) N-2(+)/cm(2) at room temperature were investigated up to annealing temperatures of 1000 degrees C. These studies were carried out using X-ray photoelectron spectroscopy (XPS), high-resolution electron energy loss spectroscopy, and thermal-programmed desorption (TPD). The highest nitrogen retention ratio was measured for D1, followed by the D2 case. It was found that the implanted nitrogen near-surface concentration obtained similar values for the D3 and D4 cases. From the C(1s) and N(1s) XP line shape analysis, it is determined that upon D1 implantation, nitrogen is bonded into interstitial sites in mostly a single-bonding configuration, C-N\C & boxH;N, and very low levels of point defects are produced by the implantation process. As the dose increases to D2, nitrogen bonding also occurs to point defects, creating a low concentration of C equivalent to N (nitrile-like) bonds. For D3 and D4 cases, the near-surface region is fully amorphized/graphitized, and the implanted nitrogen is bonded in a multitude of bonding configurations characteristic of nitrogen bonded to a disordered graphitic structure. The TPD measurements show that N-2 and HCN are the main desorption species and their desorption rate depends on implantation dose and surface temperature. Hydrogen was found to be chemically bonded with surface carbon atoms as well as to some of the implanted nitrogen. From the C(1s) XP line shape analysis, it is determined that for D1, only point defects were created upon implantation, which cannot be annealed within the temperature range used in the present study. For the higher doses, the density of defects increases, and a graphitic layer is found to evolve with annealing temperature. It was found that upon annealing, the relative concentration of different nitrogen states formed varies alongside the relaxation of the disordered carbon layer, suggesting the possibility of complex chemical processes involving diffusion, desorption, and interconversion between the implanted species.