PCF-Graphene: A 2D sp²-Hybridized Carbon Allotrope with a Direct Band Gap

Abstract

Motivated by the recent progress in synthesizing graphene by using aromatic benzene molecules as precursors, herein, we propose a new two-dimensional (2D) carbon allotrope by using nonaromatic molecule cyclooctatetraene as the precursor from a bottom-up approach. In this structure, all the carbon atoms are threefold coordinated, similar to the sp2-hybridized atoms in graphene; thus, we name the poly-cyclooctatetraene framework as PCF-graphene. First-principles calculations reveal that although PCF-graphene is metastable compared with graphene, it is thermally, mechanically, and dynamically stable. Different from graphene with a single-atomic thickness and zero band gap, PCF-graphene has a finite thickness of 2.45 Å and is a semiconductor with a direct band gap of 0.77 eV. It exhibits anisotropies in mechanical properties, carrier mobility, and optical adsorption because of its anisotropic lattice. This study not only sheds insights into the design of 2D carbon materials from some simple organic molecules but also expands the 2D purely three-coordinated carbon family from a single-atomic layer to a finite thickness. PCF-graphene can be used as a rung in the ladder to stabilize three-dimensional three-coordinated carbon system that remains elusive currently.

PBCF‐Graphene: A 2D Sp2 Hybridized Honeycomb Carbon Allotrope with a Direct Band Gap

“…Inspires by the work of Shen et al ., PBCF‐graphene can self‐assembly by the addition reactions of unsaturated hydrocarbon molecules between COT with BD, as shown in Figure . COT (with the formula C8H8) is a cyclic polyolefin with a nonplanar bathtub‐like structure and no aromatic properties.…”

“…It is noted that C 20 is the smallest nanostructured fullerene as determined experimentally and cyclo[18]carbon is the first cyclocarbon molecules with 18 carbon atoms, as determined experimentally. In addition, PBCF‐graphene has the same total energy as PCF‐graphene . To examine the thermal stability of PBCF‐graphene, we further perform ab initio molecular dynamics (AIMD) simulations with a canonical ( NVT ) ensemble at 300 and 1000 K using a larger 3×3×1 rhombohedral supercell (containing 216 carbon atoms).…”

“…With improvements in theoretical developments and the progression of technology, first‐principles calculations based on density functional theory have been widely used to predict and analyze the properties of new materials . For example, penta‐graphene, C‐57 carbon, Stone‐Wales grapheme, S‐graphene, D‐graphene, E‐graphene, twin grapheme, α ‐graphyne, β ‐graphyne, γ ‐graphyne, ψ‐graphene, PCF‐graphene and THD‐graphene have been either proposed or synthesized. Among the proposed or synthesized 2D carbon allotropes, the semi‐metallic allotropes with Dirac cones, such as α ‐graphyne, α ‐2 graphyne, circumcoro‐graphyne, ph‐graphene and S‐graphene have attracted particular attention.…”

“…In recent years, an increasing number of 2D carbon allotropes have been predicted. Inspired by the non‐aromatic nature of cyclooctatetraene and the cycloaddition reactions of unsaturated hydrocarbon molecules, Shen et al . proposed a 2D sp 2 hybridized PCF‐graphene, which has a direct band gap of 0.77 eV and a finite thickness of 2.45 Å.…”

Azugraphene: a new graphene-like hexagonal carbon allotrope with Dirac cones

“…In addition, there are many predicted 2D carbon allotropes with exotic geometric structures, such as the penta-graphene composed of only carbon pentagons 5 and the PCF-graphene with a nite thickness. 6 Among all these 2D allotropes, the Dirac cone materials attract more attentions because of its extraordinary electrical properties. From 2012, a series of 2D carbon allotropes with Dirac cones were predicted using the rst principle methods, such as a-graphdiyne, 7 a-, b-, and 6,6,12-graphyne, 8 14,14,14graphyne and 14,14,18-graphyne, 9 S-, D-, and E-graphene, 10 phagraphene, 11 and a-2 graphyne.…”