Interpolation of Atomically Thin Hexagonal Boron Nitride and Graphene: Electronic Structure and Thermodynamic Stability in Terms of All-Carbon Conjugated Paths and Aromatic Hexagons

Abstract

Two-dimensional hexagonal composite materials (BN) n (C 2 ) m (n, m = 1, 2, ...), which all are isoelectronic with graphene and hexagonal boron nitride (h-BN), have been studied by density functional theory (DFT) with a focus on the relative energies of different material isomers and their band gaps. The well-established chemical concepts of conjugation and aromaticity were exploited to deduce a rationale for identifying the thermodynamically most stable isomer of the specific composites studied. We find that (BN) n (C 2 ) m materials will not adopt structures in which the B, C, and N atoms are finely dispersed in the 2D sheet. Instead, the C atoms and CÀC bonds, which provide for improved conjugation when compared to BÀN bonds, gather and form all-carbon hexagons and paths; that is, the (BN) n (C 2 ) m materials prefer nanostructured distributions. Importantly, there are several isomers of similarly low relative energy for each (BN) n (C 2 ) m composite type, but the band gaps for these nearly isoenergetic isomers differ by up to 1.0 eV. This feature in the band gap variation of the most stable few isomers is found for each of the four composites studied and at two different DFT levels. Consequently, the formation of a distinct (BN) n (C 2 ) m material isomer with a precise (small) band gap will likely be nontrivial. Therefore, one likely has to invoke nonstandard preparation techniques that exploit nanopatterned h-BN or graphene with voids that can be filled with the complementary all-carbon or boron nitride segments.

Tuning the band gaps and work functions via topology and carbon concentration: a first-principles investigation of Cx(BN)y compounds

“…17 Similarly, in the BN-doped graphene superlattice, the band gap increases with the increasing size of BN nanodots, but regardless of their shapes. 18 In terms of the conjugation and aromaticity concepts, a recent density functional theory (DFT) calculation confirmed that for a certain stoichiometric (BN) n (C 2 ) m monolayer, several isomers with similarly low relative energies have different band gaps by up to 1.0 eV, 19 and this feature is common for the compounds with different n : m ratios and carbon content. 19 These theoretical results have revealed some interesting features different from the ''mean-field'' pictures, in which the electronic properties of BCN layers would be changed asymptotically with the decreasing of carbon content.…”

Electronic properties of mixed-phase graphene/h-BN sheets using real-space pseudopotentials

“…9 Computational studies support the phase separation of such films into carbon and BN domains, with conjugation and aromaticity as driving forces. 10 In such a film graphene domains and h-BN domains are distributed inhomogeneously to form a disordered superlattice. Although the interface between h-BN and graphene domains contains unfavorable B-C and N-C bonds, such mixed films can nevertheless be realized by exploiting growth kinetics.…”

How Much N-Doping Can Graphene Sustain?

“…1, along with other two-dimensional BCN alloys considered theoretically. 3,[13][14][15][16][17][18][19][20] Here, we use the densityfunctional theory and cluster expansion to establish the theoretical limits of N doping in g-NG, and investigate its stability and electronic properties. We demonstrate that the nitrogen concentration in g-NG can in principle be as high as 33.3%-37.5%, and that most of these structures are metallic.…”

“…Smaller circles show other two-dimensional BCN systems considered previously. 3,[12][13][14][15][16][17][18][19][20] Mixing energies of the 2D carbon-nitrogen alloy were obtained using the cluster expansion (CE) method. 51 …”