Stabilities and novel electronic structures of three carbon nitride bilayers

Abstract

We predict three novel phases of the carbon nitride (CN) bilayer, denoted α-C2N2, β-C2N2 and γ-C4N4, respectively. All of them consist of two CN sheets connected by C-C covalent bonds. The phonon dispersions reveal that all these phases are dynamically stable, because no imaginary frequency is present. The transition pathway between α-C2N2 and β-C2N2 is investigated, which involves bond-breaking and bond-reforming between C and N. This conversion is difficult, since the activation energy barrier is 1.90 eV per unit cell, high enough to prevent the transformation at room temperature. Electronic structure calculations show that all three phases are semiconductors with indirect band gaps of 3.76/5.22 eV, 4.23/5.75 eV and 2.06/3.53 eV, respectively, by PBE/HSE calculation. The β-C2N2 has the widest band gap among the three phases. All three bilayers can become metallic under tensile strain, and the indirect gap of γ-C4N4 can turn into a direct one. γ-C4N4 can become an anisotropic Dirac semimetal under uniaxial tensile strain. Anisotropic Dirac cones with high Fermi velocity of the order of 105 m/s appear under 12% strain. Our results suggest that the three two-dimensional materials have potential applications in electronics, semiconductors, optics and spintronics.

2D Octagon-Structure Carbon and Its Polarization Resolved Raman Spectra

“…In recent years, people found many 2D materials from allotropes of carbon and from group V elements. Some of them have potential application in optoelectronic, nano electronic devices and hydrogen storage, because of their unique electronic and mechanical properties [4][5][6][7][8][9][10]. In 2018, Cao et al found the twisted bilayer graphene is able to be an insulator or superconductor [11,12].…”

Density Functional Theory Investigation of Thermal Conductivity in α-CN and α-CP Monolayers: Implications for Thermal Management of Electronic Devices

“…The optimized lattice parameters of α-CX (X = N and P) are 2.368 and 2.881 Å, respectively, which are in excellent agreement with the previously reported data (see Table ). ,, As the computation of all ground-state properties of a system crucially depends on the crystal structure, symmetry, and optimized lattice parameters, the assurance of well-converged parameters is of major importance. Apart from this, to confirm the energetic stability of the systems, we have calculated the energy of formation.…”

Ga4C-family crystals, a new generation of star thermoelectric materials, achieved by band degeneracies, valley anisotropy, and strong phonon scattering among others

“…Carbon is one of the earliest light elements used by human beings, and has abundant allotropic phases with exceedingly rich physical features. 23,24 In particular, as the tetrahedral carbon atom in a diamond crystal is replaced by a C 4 tetrahedron, a new allotropic phase of carbon crystal, i.e. , supertetrahedral carbon (T-carbon), can be constructed.…”