Nitrogen bonding, work function and thermal stability of nitrided graphite surface: An in situ XPS, UPS and HREELS study

Abstract In this study, we investigate the chemical and electronic properties of nitrogen incorporated highly oriented pyrolytic graphite (N–HOPG) surface. The N–HOPG surfaces were prepared by three methods: radio frequency N2 (RF(N2)) plasma, microwave N2 (MW(N2)) plasma and N2+ ion implantation. The surface chemical states of carbon–nitrogen bonds on the N–HOPG surfaces, evolution of defects and thermal stability were investigated by X-ray photoelectron spectroscopy, high-resolution electron energy loss spectroscopy (HREELS) and ultraviolet photoelectron spectroscopy. Nitrogen exists in graphitic–N bonding state predominantly on the low damage N–HOPG surfaces (RF(N2) plasma at 9.3 Pa and 200 eV N2+ ion implantation) and in pyridine–N bonding state on high damage N–HOPG surfaces (RF(N2) plasma at 4.0 Pa and 500 eV N2+ ion implantation). Partial structural recovery is possible for low damage N–HOPG surfaces upon annealing. HREELS analysis revealed preferential bonding of hydrogen to defect sites and retention of graphite lattice structure for N–HOPG surfaces with low-level of surface damage. Furthermore, low damage N–HOPG surfaces exhibited low work function due to incorporation of nitrogen at graphitic sites. HCN temperature programmed desorption spectra showed a broad peak positioned at 550 °C which is associated with desorption of pyrrolic–N content.