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

Abstract

The effect of 500 eV N2+ irradiation of graphite and diamond surfaces has been investigated by in situ electron spectroscopies (Auger electron spectroscopy and x-ray photoelectron spectroscopy). The chemical state of the implanted nitrogen and carbon have been studied as a function of: (i) implantation temperature in the room temperature (RT) to 800 K range, (ii) annealing of the RT implanted layer up to 800 K, (iii) and ion dose. It is concluded that the implanted nitrogen is present in three different bonding states, denoted as α, β, and γ, for all implantation conditions. The distribution of these states was found to be affected by the substrate nature as well as by the temperature of implantation and annealing process. A chemical interconvertion model is proposed to explain the changes in population of the carbon–nitrogen bonding states as a function of annealing and implantation temperature. It is suggested that the β state includes nitrogen atoms in threefold configurations and may be related to an almost unpolarized carbon–nitrogen chemical bond, which is expected to be present in β-C3N4 phase. A predominant population of this state has been achieved in the case of nitrogen ion implantation into diamond. It has been demonstrated that hot nitrogen implantation results in the formation of the least polarized carbon–nitrogen bonding state [the β state which possess higher N(1s) binding energy] in all studied systems. The structure of the nitrogen implanted layers has been assessed by the analysis of the C(KVV) Auger line shape. Partial conservation of the initial substrate structure has been observed after hot nitrogen implantation of the diamond and graphite surfaces. Our model investigation of carbon nitride formation by low energy ion implantation strongly suggests that it is impossible to populate only one particular carbon–nitrogen bonding state in which carbon is in sp3 and nitrogen in sp2 hybridization state in the frame of the studied experimental conditions. However, this state was found to be formed among a variety of possible other carbon–nitrogen bonding states. The results presented in this work are of importance for understanding the fundamental processes involved in the formation of carbon nitride thin films by ion beam deposition methods.