Auxetic tetrahex-carbon with ultrahigh strength and direct band gap

TL;DR

This study predicts that tetrahex-carbon, a buckled 2D carbon allotrope, exhibits ultrahigh strength, negative Poisson's ratio, and maintains a direct band gap under strain, making it promising for nanomechanics and nanoelectronics.

Contribution

First-principles calculations reveal the mechanical robustness, negative Poisson's ratio, and stable direct band gap of tetrahex-carbon under strain, highlighting its potential for advanced applications.

Findings

Ultrahigh ideal strength surpassing graphene and penta-graphene.

Intrinsic negative Poisson's ratio at specific strain thresholds.

Stable direct band gap of 2.64 eV under applied strain.

Abstract

Tetrahex-carbon is a recently predicted two dimensional (2D) carbon allotrope which is composed of tetragonal and hexagonal rings. Unlike flat graphene, this new 2D carbon structure is buckled, possesses a direct band gap ~ 2.6 eV and high carrier mobility with anisotropic feature. In this work, we employ first-principles density-functional theory calculations to explore mechanical properties of tetrahex-C under uniaxial tensile strain. We find that tetrahex-C demonstrates ultrahigh ideal strength, outperforming both graphene and penta-graphene. It shows superior ductility and sustains uniaxial tensile strain up to 20% (16%) till phonon instability occurs, and the corresponding maximal strength is 38.3 N/m (37.8 N/m) in the zigzag (armchair) direction. It shows intrinsic negative Poisson's ratio. This exotic in-plane Poisson's ratio takes place when axial strain reaches a threshold value of 7% (5%) in the zigzag (armchair) direction. We also find that tetrahex-C holds a direct band gap of 2.64 eV at the center of Brillouin zone. This direct-band-gap feature maintains intact upon strain application with no direction-indirect gap transition. The ultrahigh ideal strength, negative Poisson's ratio and integrity of direct-gap under strain in tetrahex-C suggest it may have potential applications in nanomechanics and nanoelectronics.