Quadrene: A Novel Quasi-2D Carbon Allotrope with High Carrier Mobility

TL;DR

The paper introduces Quadrene, a novel quasi-2D carbon allotrope with a rectangular, open framework that yields strong anisotropy in mechanics, optics, and charge transport. Using first-principles DFT (CASTEP) with PBE and HSE06, complemented by phonon analysis and ab initio molecular dynamics at 1000 K, the authors establish dynamic and thermal stability and predict an indirect bandgap of $E_g^{PBE}=0.80$ eV and $E_g^{HSE06}=1.58$ eV. They report highly anisotropic carrier mobilities up to $6.40 imes10^{6}$ cm$^{2}$/V·s for electrons along one direction and $5.83 imes10^{6}$ cm$^{2}$/V·s for holes along another, alongside in-plane stiffness up to several hundred GPa and a Poisson ratio up to 0.80. The results indicate Quadrene could enable directionally selective nanoelectronics and polarization-sensitive optoelectronics, offering a route to semiconducting carbon-based devices beyond graphene.

Abstract

We present a comprehensive first-principles investigation of a novel carbon allotrope characterized by quasi-tetragonal atomic motifs and quasi-two-dimensional structural behavior. Structural analysis reveals an open framework composed of alternating diamond-like and square units, while thermodynamic assessments indicate a negative formation energy, suggesting high intrinsic stability. Phonon spectra confirm dynamical robustness, and \textit{ab initio} molecular dynamics simulations at 1000~K validate its thermal resilience. Furthermore, the system exhibits an indirect bandgap of 1.58 eV at the HSE06 level, anisotropic mechanical behavior, and a broadband optical response, reinforcing its potential for nanoelectronic and optoelectronic applications. The highly anisotropic mechanical behavior is characterized by an in-plane Young's modulus ranging from 80 to 550 GPa, depending on crystallographic direction. Additionally, the electronic transport properties exhibit pronounced anisotropy, with hole mobilities reaching up to 5.83 x 10^6 cm^2/V . s and electron mobilities up to 6.40 x 10^6 cm^2/V . s along different crystallographic directions, highlighting the material's potential for directionally selective nanoelectronic device applications.

Figures (7)

• Figure 1: Atomic structure of the proposed quasi-2D carbon material. (a) Top view showing the rectangular unit cell defined by vectors $\vec{a}$ and $\vec{b}$. (b) and (c) Side views along the $x$- and $y$-directions, respectively, revealing a finite thickness of 3.60 Å due to the buckled configuration.
• Figure 2: (Phonon dispersion curves of Quadrene calculated along high-symmetry directions in the Brillouin zone.
• Figure 3: Total energy per atom as a function of time during AIMD simulations at 1000 K, with representative atomic snapshots illustrating structural preservation throughout the simulation.
• Figure 4: Mechanical response of Quadrene. (a) Polar plot of the directional Poisson's ratio, showing a four-lobed anisotropic pattern. (b) Directional dependence of the in-plane Young’s modulus, revealing marked anisotropy between the $x$ and $y$ directions.
• Figure 5: Electronic structure of Quadrene. (a) Electronic band structure computed using PBE and HSE06 functionals along high-symmetry directions, indicating an indirect bandgap with the valence band maximum (VBM) at the $\Gamma$ point and the conduction band minimum (CBM) at the X point. (b) Projected density of states (PDOS) showing that $p$-orbitals are the dominant contributors near the Fermi level.