XPS study of nitridation of diamond and graphite with a nitrogen ion beam

Diamond (CVD) and graphite (HOPG) samples were nitrided at room temperature by irradiation with 300-700 eV N₂⁺ ion beams. X-ray photoelectron spectra (XPS) were recorded in situ during the nitridation. The XPS spectra of C1s and N1s core levels are divided into three (A, B, C) and four (D, E, F, G) components, respectively. The A component at ∼284.8 eV is assigned to the non-damaged substrate below the ion penetration depth. The B component at ∼286.0 eV originates in the damaged phase and the sub-nitride phase (CN_x: x<1). The C component at ∼287.3 eV is attributed to genuine nitrides such as C₃N₄. The broad N1s XPS peak at ∼400 eV splits clearly into the D (∼398.4 eV) and F (∼401.2 eV) components upon annealing at 600°C in vacuum. The splitting is caused by evaporation of the volatile E component (∼399.7 eV). The intensity of the D component was always comparable to that of the F component in both diamond and graphite cases. The origins of these components are discussed. The G component may be due to nitrogen trapped at defects.