Abstract
Understanding the modification of the graphene’s electronic structure upon doping is crucial for enlarging its potential applications. We present a study of nitrogen-doped graphene samples on SiC(000) combining angle-resolved photoelectron spectroscopy, scanning tunneling microscopy and spectroscopy and X-ray photoelectron spectroscopy (XPS). The comparison between tunneling and angle-resolved photoelectron spectra reveals the spatial inhomogeneity of the Dirac energy shift and that a phonon correction has to be applied to the tunneling measurements. XPS data demonstrate the dependence of the N 1s binding energy of graphitic nitrogen on the nitrogen concentration. The measure of the Dirac energy for different nitrogen concentrations reveals that the ratio usually computed between the excess charge brought by the dopants and the dopants’ concentration depends on the latter. This is supported by a tight-binding model considering different values for the potentials on the nitrogen site and on its first neighbors.
Highlights
We have investigated the effect of nitrogen-doping on the band dispersion of graphene by Angle-Resolved Photoelectron Spectroscopy (ARPES) experiments
A careful inspection of the spectra and their Energy Distribution Curves (EDCs) shows no evidence for a gap opening in these doped graphene samples[17,18,19] as expected for the concentrations and the type of doping reported in this study[20,21]
In order to link these shifts with the nitrogen concentration, we have counted the number of protrusions [cf. reference 6] in the Scanning Tunneling Microscopy (STM) images and we have found c = 0, 0.08, 0.20, 0.27 and 1.1% for T = 0, 7.5, 15, 30 and 90 min respectively, with a relative uncertainty of ~20%
Summary
The link between the nitrogen concentration and the Dirac energy is found to deviate from a rigid band model where one electron would be given by each nitrogen atom. It turns out that in many cases various experiments have been interpreted in terms of doping rates ne/nN (references[2,3,5,16]) In this context, we explain here how a simple model taking into account the resonant behavior of the nitrogen can interpret the experimental and ab initio results. We explain here how a simple model taking into account the resonant behavior of the nitrogen can interpret the experimental and ab initio results This deviation is explained by the formation of a localized state that captures a part of the additional electron of nitrogen
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