Heteroatom Codoped Graphene: The Importance of Nitrogen

Although graphene has exceptional properties, they are not enough to solve the extensive list of pressing world problems. The substitutional doping of graphene using heteroatoms is one of the preferred methods to adjust the physicochemical properties of graphene. Much effort has been made to dope graphene using a single dopant. However, in recent years, substantial efforts have been made to dope graphene using two or more dopants. This review summarizes all the hard work done to synthesize, characterize, and develop new technologies using codoped, tridoped, and quaternary doped graphene. First, I discuss a simple question that has a complicated answer: When can an atom be considered a dopant? Then, I briefly discuss the single atom doped graphene as a starting point for this review's primary objective: codoped or dual-doped graphene. I extend the discussion to include tridoped and quaternary doped graphene. I review most of the systems that have been synthesized or studied theoretically and the areas in which they have been used to develop new technologies. Finally, I discuss the challenges and prospects that will shape the future of this fascinating field. It will be shown that most of the graphene systems that have been reported involve the use of nitrogen, and much effort is needed to develop codoped graphene systems that do not rely on the stabilizing effects of nitrogen. I expect that this review will contribute to introducing more researchers to this fascinating field and enlarge the list of codoped graphene systems that have been synthesized.

Cycloaddition between nitrogen-doped graphene (6π-component) and benzene (4π-component): a theoretical approach using density functional theory with vdW-DF correction

The interaction between nitrogen-doped graphene defects (N3V1 and N4V2 pyridinic, and N3V1 and N3V3 pyrrolic) and benzene have been investigated by applying density functional theory (DFT), together with the vdW-DF correction. We discovered that only the N3V3 pyrrolic defect is a reactive site (6π-component), forming a cycloadduct with benzene (4π-component) that has energy barriers below 154.38 kJ mol-1 (1.60 eV). The conduction and valence bands (HOMO and LUMO) for N3V3 form a degenerate pair of orbitals at the gamma point, with the same ionization potential (IP) and electron affinity (EA). Likewise, inspection of the orbital symmetries for both systems confirms that these must undergo concerted reactions based on the Woodward and Hoffmann principles of orbital symmetry, with the appropriate orbital occupancies. This is the first time that substitutionally doped graphene has been demonstrated to participate as a 6π-component for cycloaddition reactions with benzene.

Structural and magnetic properties of a defective graphene buffer layer grown on SiC(0001): a DFT study

Understanding the role of defects in the magnetic properties of the graphene buffer layer (BL) grown on substrates should be important to provide hints for manufacturing future graphene-based spintronic devices in a controlled fashion. Herein, density functional theory was applied to assess the structure and magnetic properties of defective BL on 6H-SiC(0001). Particularly, we conducted a thorough study of one and two vacancies and Stone-Wales defects in the BL. Our results reveal that the removal of a carbon atom in the BL framework that was originally bonded to a Si atom in the substrate is preferred over that of a sp2-bonded atom. As a result, a hexacoordinated silicon atom is formed with a slightly deviated octahedral geometry. A stable antiferromagnetic (AF) state was verified for the single vacancy system, with a quite different spin-density distribution to the one obtained for the perfect BL. Also, this AF state is nearly degenerate with the non-magnetic and low magnetic states. As for the Stone-Wales defect, the AF sate is almost degenerate with the most stable M = 2 μB magnetic configuration. However, the introduction of two vacancies in the carbon network of BL causes the loss of magnetism of the BL-SiC system. Our theoretical calculations support experimental predictions favoring the BL as the site for single vacancy formation rather than the epitaxial monolayer graphene, by 4.3 eV.