Characterization of nitrogen species incorporated into graphite using low energy nitrogen ion sputtering

Abstract

The electronic structures of nitrogen species incorporated into highly oriented pyrolytic graphite (HOPG), prepared by low energy (200 eV) nitrogen ion sputtering and subsequent annealing at 1000 K, were investigated by X-ray photoelectron spectroscopy (XPS), angle-dependent X-ray absorption spectroscopy (XAS), and Raman spectroscopy. An additional peak was observed at higher binding energy of 401.9 eV than 400.9 eV for graphitic1 N (graphitic N in the basal plane) in N 1s XPS, where graphitic2 N (graphitic N in the zigzag edge and/or vacancy sites) has been theoretically expected to appear. N 1s XPS showed that graphitic1 N and graphitic2 N were preferably incorporated under low nitrogen content doping conditions (8 × 10(13) ions cm(-2)), while pyridinic N and graphitic1 N were dominantly observed under high nitrogen content doping conditions. In addition, angle-dependent N 1s XAS showed that the graphitic N and pyridinic N atoms were incorporated into the basal plane of HOPG and thus were highly oriented. Furthermore, Raman spectroscopy revealed that low energy sputtering resulted in almost no fraction of the disturbed graphite surface layers under the lowest nitrogen doping condition. The suitable nitrogen doping condition was discovered for realizing the well-controlled nitrogen doped HOPG. The electrochemical properties for the oxygen reduction reaction of these samples in acidic solution were examined and discussed.

Lewis Basicity of Nitrogen-Doped Graphite Observed by CO2 Chemisorption

“…Both center N and valley N are graphitic N connected to three carbon atoms, existing in the graphite basal plane, and at graphite zigzag edges or vacancy sites, respectively [ 18 , 19 ]. The detailed peak assignment of each component was discussed in our previous report [ 12 ]. The estimated amount of each nitrogen component from the fitting results is summarized in Table 1 ; center N is the most prevalent, followed by valley N and pyridinic N.

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“…The spectra are normalized according to the intensity at 430 eV. Three sharp peaks in the π* region can be assigned to pyridinic N (A), cyanide N (B), and graphitic N (center N and valley N) (C) [ 12 , 30 ]. A peak at 407.5 eV corresponds to the σ* state of the nitrogen components.…”

“…A cleaved highly oriented pyrolytic graphite (HOPG, PGCSTM, Panasonic Inc.) plate was annealed at 1000 K for 30 min in an ultra-high vacuum (UHV) (<5 × 10 −7 Pa), sputtered with 8 × 10 13 nitrogen ions cm −2 at 200 eV (equivalent to 2 % nitrogen relative to the surface carbon atoms) at 300 K using an ion gun (OMI-0730, Omegatron Inc.), and annealed again at 1000 K for 1 h for surface cleaning [ 12 ].…”

A rational synthesis of hierarchically porous, N-doped carbon from Mg-based MOFs: understanding the link between nitrogen content and oxygen reduction electrocatalysis

“…The matter is further complicated by the fact that the relative merits of the different functionalities are still not fully understood. [6][7][8][9][10]23,[46][47][48][49] However, clearly nitrogen doping is not enough -the nitrogen atoms also need to be exposed to solution, if their presence is to be felt. Thus, the most important microstructural parameter may be specific surface area -also closely correlated with micropore volume -which determines the solution exposure of active sites.…”

Nitrogen Doped Carbon Nanofibers Derived from Water-Soluble Precursors

“…Graphitic-N can be found either in-plane or along the edge. Kiuchi et al reported on the nitrogen doping of pyrolytic graphite prepared by low energy nitrogen ion sputtering and subsequent annealing at less than 800 °C [40]. As the nitrogen concentration decreased, two graphitic nitrogen components were identified: a graphitic-N in the basal plane (nitrogen bonded to three carbon atoms) at 400.9 eV, and a graphitic-N in the zigzag edge and/or vacancy sites with a binding energies of 401.9 eV.…”