Electron spectroscopic study of C-N bond formation by low-energy nitrogen ion implantation of graphite and diamond surfaces

The effect of 500 eV N-2(+): irradiation of graphite and diamond surfaces h as been investigated by in situ electron spectroscopies (Auger electron spe ctroscopy and x-ray photoelectron spectroscopy). The chemical state of the implanted nitrogen and carbon have been studied as a function of: (i) impla ntation temperature in the room temperature (RT) to 800 K range, (ii) annea ling of the RT implanted layer up to 800 K, (iii) and ion dose. It is concl uded that the implanted nitrogen is present in three different bonding stat es, denoted as alpha, beta, and gamma, for all implantation conditions. The distribution of these states was found to be affected by the substrate nat ure as well as by the temperature of implantation and annealing process. A chemical interconvertion model is proposed to explain the changes in popula tion of the carbon-nitrogen bonding states as a function of annealing and i mplantation temperature. It is suggested that the beta state includes nitro gen atoms in threefold configurations and may be related to an almost unpol arized carbon-nitrogen chemical bond, which is expected to be present in be ta-C3N4 phase. A predominant population of this state has been achieved in the case of nitrogen ion implantation into diamond. It has been demonstrate d that hot nitrogen implantation results in the formation of the least pola rized carbon-nitrogen bonding state [the beta state which possess higher N( 1s) binding energy] in all studied systems. The structure of the nitrogen i mplanted layers has been assessed by the analysis of the C(KVV) Auger line shape. Partial conservation of the initial substrate structure has been obs erved after hot nitrogen implantation of the diamond and graphite surfaces. Our model investigation of carbon nitride formation by low energy ion impl antation strongly suggests that it is impossible to populate only one parti cular carbon-nitrogen bonding state in which carbon is in sp(3) and nitroge n in sp(2) hybridization state in the frame of the studied experimental con ditions. However, this state was found to be formed among a variety of poss ible other carbon-nitrogen bonding states. The results presented in this wo rk are of importance for understanding the fundamental processes involved i n the formation of carbon nitride thin films by ion beam deposition methods . (C) 1999 American Vacuum Society. [S0734-2101(99)02902-4].