Auxetic Tetrahex Carbon with Ultrahigh Strength and a Direct Band Gap

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 ~ 10 4 cm 2 / (V·s) 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-gap feature maintains intact upon strain application with no direct-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.

Strain engineering of electronic and optical properties of monolayer diboron dinitride

“…Thus direction-dependent tunability of o-B 2 N 2 enables both widening and narrowing of band gap energy over a wide range (0.97-2.92 eV) only through applying tensile strain. Although direction-dependent band gap tunability has already been reported in several 2D materials with intrinsic structural anisotropy such as tetrahex structures (for instance, tetrahex-carbon, tetrahex-SiC, and tetrahex-BN all exhibit this feature with less than 1.0-, 0.5-, and 0.8-eV tunability over 10% tensile strain, respectively [56][57][58]), the ∼2-eV anisotropic tunability found in o-B 2 N 2 makes it outstanding.…”

Dirac Semimetal Protected by Nonsymmorphic Mirror Symmetries in TPH‐Graphene

“…Due to the bonding flexibility of carbon atoms, numerous 2D carbon allotropes have been proposed theoretically. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] These carbon allotropes exhibit some amazing properties, such as ultrahigh ideal strength, [9] high electron mobility at room temperature, [8] superconductivity, [22] good catalytic activity, [23] ferromagnetism, [24] and negative Poisson's ratio. [9,25] It is no doubt that the fascinating properties will encourage further investigations of these 2D carbon materials.…”

New stable two dimensional silicon carbide nanosheets

“…To avoid this effect, the stress in this work adopts the force per unit length in the unit of N/m. It is found that TH-SiC2 and SiC are more ductile in the x (zigzag) direction, similar to the case of tetrahex-C [42].…”

“…Similarly, for the SiC structure in Fig. 1 Table 1 gives a summary of some structural parameters and basic properties of the TH-SiC2 and SiC, along with penta-SiC2 [28], tetrahex-carbon [22,42], penta-graphene [17], graphene and low-buckled silicene [7,27]. Comparing the buckling thickness and two typical bond lengths in TH-SiC2 with those in penta-SiC2, their values are close.…”

“…The formation energy is calculated using graphene and silicene as references (thus *zero for graphene and silicene). Reference: TH-SiC [29], penta-SiC2 [28], tetrahex-C [22,42], penta-graphene [17], silicene [7,27].…”