Zhufeng Hou, Xianlong Wang, Takashi Ikeda, Kiyoyuki Terakura, Masaharu Oshima, Masa-aki Kakimoto
Nitrogen doping in graphene has important implications in graphene-based devices and catalysts. We have performed the density functional theory calculations to study the electronic structures of N-doped graphene with vacancies and Stone-Wales defect. Our results show that monovacancies in graphene act as hole dopants and that two substitutional N dopants are needed to compensate for the hole introduced by a monovacancy. On the other hand, divacancy does not produce any free carriers. Interestingly, a single N dopant at divacancy acts as an acceptor rather than a donor. Compared with the case of an isolated N dopant in perfect graphene, the electrons donated by substitutional N dopants would be localized significantly when a N-N pair is formed. The N-N interaction and the interference between native point defect and N dopant strongly modify the role of N doping regarding the free carrier production in the bulk pi bands. Our results are qualitatively consistent with the experimental observation that the concentration of free electrons introduced by N dopants would be lower than that of doped N. We have analyzed N K-edge X-ray adsorption spectroscopy (XAS) spectra of N dopants at vacancies and Stone-Wales (SW) defect. We discuss the relation between the calculated XAS spectra and the experimental ones. We also discuss characteristic scanning tunneling microscope (STM) images originating from the electronic and structural modifications by the N dopant-defect complexes. STM image for small negative bias voltage may provide important information about possible active sites for oxygen reduction reaction.
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http://arxiv.org/abs/1205.6575
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