Stabilities and novel electronic structures of three carbon nitride bilayers

TL;DR

This paper predicts three new stable carbon nitride bilayer phases with unique electronic properties, including high stability and wide band gaps, suggesting their potential in electronics and optoelectronic applications.

Contribution

The study introduces three novel, dynamically stable CN bilayer phases with detailed stability, transition pathways, and electronic properties, expanding the family of 2D materials.

Findings

All three phases are dynamically stable with no imaginary phonon frequencies.

Transition between N and eta-CN involves a high energy barrier of 1.90 eV.

The phases are semiconductors with wide indirect band gaps, especially eta-CNN.

Abstract

Three new novel phases of carbon nitride (CN) bilayer, which are named as \alpha-C$_{2}$N$_{2}$, \beta-C$_{2}$N$_{2}$ and \gamma-C$_{4}$N$_{4}$, respectively, have been predicted in this paper. All of them are consisted of two CN sheets connected by C-C covalent bonds. The phonon dispersions reveal that all these phases are dynamically stable, since no imaginary frequency is found for them. Transition path way between \alpha-C$_{2}$N$_{2}$ and \beta-C$_{2}$N$_{2}$ is investigated, which involves bond-breaking and bond-reforming between C and N. This conversion is difficult, since the activation energy barrier is found to be 1.90 eV per unit cell, high enough to prevent the transformation at room temperature. Electronic structures calculations show that they are all semiconductors with indirect band gap of 3.76 / 5.22 eV, 4.23 / 5.75 eV and 2.06 / 3.53 eV by PBE / HSE calculation, respectively. The \beta-C$_{2}$N$_{2}$ has the widest band gap among the three phases. From our results, the three new two-dimensional materials have potential applications in the electronics, semiconductors, optics and spintronics.