Diffusion, coalescence, and reconstruction of vacancy defects in graphene layers are investigated by tight-binding molecular dynamics (TBMD) simulations and by first principles total energy calculations. It is observed in the TBMD simulations that two single vacancies coalesce into a 5-8-5 double vacancy at the temperature of 3000 K, and it is further reconstructed into a new defect structure, the 555-777 defect, by the Stone-Wales type transformation at higher temperatures. First principles calculations confirm that the 555-777 defect is energetically much more stable than two separated single vacancies, and the energy of the 555-777 defect is also slightly lower than that of the 5-8-5 double vacancy. In TBMD simulation, it is also found that the four single vacancies reconstruct into two collective 555-777 defects which is the unit for the hexagonal haeckelite structure proposed by Terrones et al. [Phys. Rev. Lett. 84, 1716 (2000)].

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Diffusion, Coalescence, and Reconstruction of Vacancy Defects in Graphene Layers

Hui Zheng,1 Xian-Bin Li,1,* Nian-Ke Chen,1 Sheng-Yi Xie,1 Wei Quan Tian,1,2 Yuanping Chen,3 Hong Xia,1 S. B. Zhang,1,4,† and Hong-Bo Sun1,‡ 1State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130012, China 2Institute of Theoretical Chemistry, Jilin University, Changchun 130012, China 3Laboratory for Quantum Engineering and Micro-Nano Energy Technology, Xiangtan University, Xiangtan 411105, China 4Department of Physics, Applied Physics, & Astronomy, Rensselaer Polytechnic Institute, Troy, New York 12180, USA (Received 11 January 2015; revised manuscript received 14 May 2015; published 21 September 2015)

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Monolayer II-VI semiconductors: A first-principles prediction

Single-layer materials such as graphene and boron nitride promise alternative routes to electronic devices. Hybrid density functional calculations for single-layer boron pnictides boron nitride (BN), boron phosphide (BP), boron arsenide (BAs), and boron antimonide (BSb) show that these materials exhibit a direct bandgap of 6.1, 1.4, 1.2, and 0.6 eV, respectively, that originates from the energy difference of the pz orbitals of the species and is tunable by strain. The bandgap linearly decreases with strain for BN, while it increases non-linearly for BP, BAs, and BSb. The calculated natural band offsets between the various boron pnictides are all of type I.

http://absimage.aps.org/image/MAR13/MWS_MAR13-2012-001027.pdf

Electronic Structures of Single-Layer Boron Pnictides

We have calculated the thermal conductivities (κ) of cubic III-V boron compounds using a predictive first principles approach. Boron arsenide is found to have a remarkable room temperature κ over 2000 W m(-1) K(-1); this is comparable to those in diamond and graphite, which are the highest bulk values known. We trace this behavior in boron arsenide to an interplay of certain basic vibrational properties that lie outside of the conventional guidelines in searching for high κ materials, and to relatively weak phonon-isotope scattering. We also find that cubic boron nitride and boron antimonide will have high κ with isotopic purification. This work provides new insight into the nature of thermal transport at a quantitative level and predicts a new ultrahigh κ material of potential interest for passive cooling applications.

/pdf/first-principles-determination-of-ultra-high-thermal-3y8osb2tib.pdf

First principles determination of ultra-high thermal conductivity fo Boron Arsenide: A competitor for diamond?

Herein, we systematically investigated the effect of Al, Ga, and In doping and other defects on the structural and electronic properties of 2D-BSb with the first principle density-functional theory (FP-DFT). The 2D-BSb is a planar structure having a direct bandgap value of 0.332 eV. Similarly, the direct bandgap values of B, Sb, and double vacancies are 0.472, 0.374, and 0.341 eV, correspondingly, which are larger than the pristine 2D-BSb structure. Moreover, B/Sb antisite and exchange defects significantly decrease the bandgap of pristine 2D-BSb from the value of 0.332 to 0.137, 0.134, and 0.289 eV, respectively, while the structure preserves a direct bandgap behavior. Alternatively, Al, Ga, and In doping increase the direct bandgap of 2D-BSb structure from 0.332 to 0.425, 0.391, and 0.378 eV, correspondingly. This study might be helpful in providing effective strategies on tuning the electronic bandgap and would be useful for novel optoelectronics and nanoelectronics devices.

Rasidul Islam

Papers

Tuning the structural and electronic properties of two dimensional boron antimonide with defects and group-III dopants