Electronic Interaction between Nitrogen Atoms in Doped Graphene

Abstract

Many potential applications of graphene require either the possibility of tuning its electronic structure or the addition of reactive sites on its chemically inert basal plane. Among the various strategies proposed to reach these objectives, nitrogen doping, i.e., the incorporation of nitrogen atoms in the carbon lattice, leads in most cases to a globally n-doped material and to the presence of various types of point defects. In this context, the interactions between chemical dopants in graphene have important consequences on the electronic properties of the systems and cannot be neglected when interpreting spectroscopic data or setting up devices. In this report, the structural and electronic properties of complex doping sites in nitrogen-doped graphene have been investigated by means of scanning tunneling microscopy and spectroscopy, supported by density functional theory and tight-binding calculations. In particular, based on combined experimental and simulation works, we have systematically studied the electronic fingerprints of complex doping configurations made of pairs of substitutional nitrogen atoms. Localized bonding states are observed between the Dirac point and the Fermi level in contrast with the unoccupied state associated with single substitutional N atoms. For pyridinic nitrogen sites (i.e., the combination of N atoms with vacancies), a resonant state is observed close to the Dirac energy. This insight into the modifications of electronic structure induced by nitrogen doping in graphene provides us with a fair understanding of complex doping configurations in graphene, as it appears in real samples.

Electronic Structure Modification of Ion Implanted Graphene: The Spectroscopic Signatures of p- and n-Type Doping

“…Nevertheless, here, the experiments were repeated multiple times, on several distinct N atoms, systematically yielding a clearly6discernible π* peak. The repeated fast6scanning approach devised by Ramasse et al 24 to obtain high6signal6to6noise spectra from single atoms was also used and yielded again similar results. It should be noted that the experimental possibility of pyridinic defect N configurations was also considered (including theoretical calculations discussed in more detail in Hardcastle et al, in preparation), such as those discussed by Arenal et al, 38 or defects created by damage or atomic jumps.…”

“…All the predictions on the exact effect of the incorporated dopant atoms in graphene suggest that the resulting band structure depends on the density and periodicity (or not) of the dopant atoms in the graphene lattice, 18,[20][21][22] as well as on the presence of adjacent defects. [23][24][25][26] To add to the complexity of the situation, the synthesis conditions of doped graphene, which most commonly follow the chemical route, yield graphene samples of varying quality, 17 often with several types of dopant atom and defect configurations within the same specimen. [25][26][27] In a bid to produce uniformly6doped single6 layer graphene specimens, the successful implementation of low6energy ion implantation with either N or B was recently demonstrated, [28][29][30] achieving retention levels of the order of ~1% in good agreement with theoretical predictions.…”

Nitrogen doped epitaxial graphene on 4H-SiC(0001) – Experimental and theoretical study

“…To partially overcome these problems the theoretical calculations in the frame of DFT were performed. The influence of the graphitic-N and pyridinic-N configurations on the STM images has been already determined by the DFT calculations [10,12,16,22,48]. Besides these two most common configurations, attempts to calculate STM images of more complex structures were performed [13].…”

“…Besides these two most common configurations, attempts to calculate STM images of more complex structures were performed [13]. Recently it has been shown that the changes in the graphene local electronic properties observed in the STM images can be related to the interaction between nitrogen atoms located at the same or different sublattices [48]. These results can be very useful during identification of nitrogen bond type basing on the STM measurements.…”

Native defects in ultra-high vacuum grown graphene islands on Cu(1 1 1)

“…6,12,13 Most experimental work so far has involved boron and nitrogen substitutions at single C sites. [14][15][16][17][18] These are either incorporated into the lattice during chemical vapor deposition growth 14,17 or afterward by ion irradiation and annealing 15 and provide p-and n-type doping, respectively. A common challenge in functionalizing graphene through defect engineering is in the defects' relatively high formation energy and their tendency to cluster, 7,19 which further motivates study in defect creation and control.…”