A new two-dimensional all-sp3 carbon allotrope with an indirect band gap and superior carrier mobility.

The success of fascinating graphene has motivated much interest in exploiting new two-dimensional (2D) carbon allotropes with excellent electronic and mechanical properties such as graphdiyne and penta-graphene. However, there are only very few reported structures for stable 2D all-sp3 carbon allotropes. Here, we proposed a new 2D all-sp3 carbon allotrope, named as TTH-carbon. Using first-principles calculations, we investigated its structure, stability, elastic constants, band structure, carrier mobility and optical properties. The results show that it exhibits good stability. Meanwhile, it possesses a total monolayer thickness of 1.35 Šand an indirect band gap of 3.23 eV, comparable to those of well-known penta-graphene (1.20 Šand 3.25 eV). The calculated mechanical and optical properties of TTH-carbon strongly depend on the crystal orientation. The mobilities of electrons and holes along the y direction are ∼3000 cm2 V-1 s-1, which are ten times of its carrier mobilities along the x direction and three times of that of black phosphorus (∼1000 cm2 V-1 s-1). The proposed structure richens the 2D all-sp3 carbon allotropes and its properties make it a promising material for nanoelectronic and photoelectronic devices.

A new two-dimensional semiconducting carbon allotrope with direct band gap: a first-principles prediction.

Two-dimensional (2D) carbon materials with an appropriate band gap play important roles in the various electronics fields. Here, based on first-principles calculations, we predict a new 2D carbon allotrope containing 32 atoms, consists of pentagonal, hexagonal, octagonal and decagonal rings. This new allotrope is named as Po-C32, which possesses P4/MMM symmetry with a tetragonal lattice and has a vertical distance of 2.22 Å between the uppermost and undermost atoms. The cohesive energy, phonon band structure,ab initiomolecular dynamics simulations and elastic constants fitting confirm Po-C32 has high stabilities. The fitted in-plane Young's modulus and Poisson's ratio alongaandbdirections areYa=Yb= 244 N m-1andva=vb= 0.14, respectively, exhibiting the same mechanical properties alongaandbdirections. Interestingly, Po-C32 is a semiconductor with a direct band gap of 2.05 eV, comparable to that of phosphorene, exhibiting great potential in nanoelectronics. Moreover, two stable derivative allotropes are also predicted based on Po-C32. Po-C24-3D is an indirect narrow band gap (1.02 eV) semiconductor, while Po-C32-3D possesses a wider indirect band gap of 3.90 eV, which can be also applied in optoelectronic device.