Synthesis, Structure, and Properties of Boron‐ and Nitrogen‐Doped Graphene

Abstract

Graphene has emerged as an exciting material because of the novel properties associated with its two-dimensional structure. [1,2] Single-layer graphene is a one-atom thick sheet of carbon atoms densely packed into a two-dimensional honeycomb lattice. It is the mother of all graphitic forms of carbon, including zero-dimensional fullerenes and one-dimensional carbon nanotubes.[1] The remarkable feature of graphene is that it is a Dirac solid, with the electron energy being linearly dependent on the wave vector near the vertices of the hexagonal Brillouin zone. It exhibits a room-temperature fractional quantum Hall effect [3] and an ambipolar electric field effect along with ballistic conduction of charge carriers.[4] It has been reported recently that a top-gated single-layer graphene transistor is able to reach electron-or hole-doping levels of upto 5 Â 10 13 cm À2 . The doping effects are ideally monitored by Raman spectroscopy. [5][6][7][8][9][10] Thus, the G-band in the Raman spectrum stiffens for both electron-and hole-doping, and the ratio of the intensities of the 2D-and G-band varies sensitively with doping. Doping graphene through molecular charge-transfer caused by electron-donor and -acceptor molecules also gives rise to significant changes in the electronic structure of graphenes composed of a few layers, as evidenced by changes in the Raman and photoelectron spectra. [6,7] Charge-transfer by donor and acceptor molecules soften and stiffen the G-band, respectively. The difference between electrochemical doping and doping through molecular charge-transfer is noteworthy. It is of fundamental interest to investigate how these effects compare with the effects of doping graphene by substitution with boron and nitrogen and to understand dopant-induced perturbations of the properties of graphene. Secondly, opening the bandgap in graphene is essential for facilitating its applications in electronics, and graphene bilayers [11] are an attractive option for this. With this motivation, we prepared, for the first time, B-and N-doped graphene (BG and NG) bilayer samples by employing different strategies and investigated their structure and properties. We also carried out first-principles density functional theory (DFT) calculations to understand the effect of substitutional doping on the structure of graphene as well as its electronic and vibrational properties.To prepare BGs and NGs, we exploited our recent result in which it was determined that arc discharge between carbon electrodes in a hydrogen atmosphere yields graphenes (HG) composed of two to three layers.[12] The method makes use of the fact that in the presence of hydrogen, graphene sheets do not readily roll into nanotubes. In the case of BG, we carried out the arc discharge using graphite electrodes in the presence H 2 þ B 2 H 6 (BG1) or using boron-stuffed graphite electrodes (BG2). We prepared NG by carrying out the arc discharge in the presence of H 2 þ pyridine (NG1) or H 2 þ ammonia (NG2). We also performed the transformation of nanodiamond in th...

Electron–Hole Symmetry Breaking in Charge Transport in Nitrogen-Doped Graphene

“…All our samples exhibit a prominent D band ( Figure 1c and Figure S1b), whose intensity is reported to reflect the level of N-dopant concentration in the graphene sheets. 17,34,35 The intensities of the D band exhibit a clear reduction in the films grown at higher temperatures ( Figure S1b). In addition, all the Ndoped graphene films display a strong 2D band, indicating that the as-grown films are of high crystal quality ( Figure 1c and Figure S1b).…”

Structure of graphene and its disorders: a review

“…Doping by substitutional impurities (e.g. nitrogen atoms and boron atoms) is a straightforward way to broaden the van-Hove singularities in the DOS and to shift the Fermi level [264], and these doped graphenes can be characterized by Raman spectroscopy [265]. Chemical bonding of impurities like hydrogen or fluorine on graphene sheet may generate a local distortion of the hexagonal lattice and lead to spin–orbit coupling [266].…”

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

“…11,12 Several approaches have been proposed to open a band gap in graphene, including the restriction of its physical dimensions into ribbons [13][14][15] and the introduction of defects or dopants. 15,16 More specifically the introduction of nitrogen or boron atoms in the graphene lattice is predicted to have a drastic effect on graphene's band structure and to lead to the opening of a band gap, thus resulting in n6 type 17,18 or p6type doping, 19,20 respectively, with carrier concentrations allowing practical transistor applications. 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.…”