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Parametric Optimum Design of a Graphene-Based Thermionic Energy Converter

2017-10-24T00:29:18+00:00 October 24th, 2017|Categories: Publications|Tags: , |

A new model of the thermionic energy converter (TEC) configured with the graphene-based cathode is proposed, which includes the thermal radiation between the cathode and the anode electrodes and the heat losses from the anode to the environment. Analytic expressions for the power output density and efficiency of the TEC are derived. The performance characteristics of the TEC are analyzed by numerical calculations. It is found that the maximum efficiency and power density can, respectively, reach 30% and $textsf {0.575},,textsf {Wcm}^{-textsf {2}}$ when the TEC is operated between the two heat reservoirs at temperatures 1500 and 300 K. In addition, the optimum regions of the efficiency, power density, voltage output, electric current, and anode temperature are determined. The maximum efficiency and power density of the graphene-based TEC operated at different temperatures are calculated and compared with those of the metal-based TEC. It shows that the graphene-based TEC operated at 1200–1800 K displays the better performance than the metal-based TEC. The results obtained here may provide guidance for the appropriate selection of electrode materials and optimum design of practical TEC devices.

Published in: "IEEE Transactions on Electron Devices".

Potentiality of Density-Functional Theory in Analyzing the Devices Containing Graphene-Crystalline Solid Interfaces: A Review

2017-10-24T00:29:17+00:00 October 24th, 2017|Categories: Publications|Tags: , |

Graphene-based devices have initiated unprecedented breakthrough in nanoelectronics. Due to its intrinsic ultrathin 2-D nature, the unique structural, mechanical, electronic, optical, and magnetic properties of graphene are found to be extremely dependent on its substrate material. For the synthesis of graphene with pretailored features or fabrication of graphene-based device with tunable functionality, understanding of the graphene interfaces with other materials are of pivotal importance. Density-functional theory (DFT) computations have been proved to be a powerful tool in investigating the interface properties of graphene-crystalline solids and to subsequently correlate the experimental findings with underlying mechanisms, as well as to explore their potential applications. This paper presents a comprehensive review on utility of DFT-based analysis for graphene interfaces/heterostructures with other crystalline solid materials including metals, semiconductors, and insulators. DFT computational efforts to choose the appropriate material for substrate catalyst, probe, and electrode in graphene synthesis/graphene-based nanodevice design have been critically reviewed including the investigation of different combination of complex interfaces as well as unconventional materials. Salient features, advantages, and constraints of the approach have also been summarized.

Published in: "IEEE Transactions on Electron Devices".

Electrostatic-Assisted Liquefaction of Porous Carbons

2017-10-23T20:26:13+00:00 October 23rd, 2017|Categories: Publications|Tags: |

By Peipei Li, Jennifer A. Schott, Jinshui Zhang, Shannon M. Mahurin, Yujie Sheng, Zhen-An Qiao, Xunxiang Hu, Guokai Cui, Dongdong Yao, Suree Brown, Yaping Zheng, Sheng Dai

Abstract Porous liquids are a newly developed porous material that combine unique fluidity with permanent porosity, which exhibit promising functionalities for a variety of applications. However, the apparent incompatibility between fluidity and permanent porosity makes the stabilization of porous nanoparticle with still empty pores in the dense liquid phase a significant challenging. Herein, by exploiting the electrostatic interaction between carbon networks and polymerized ionic liquids, we demonstrate that carbon-based porous nanoarchitectures can be well stabilized in liquids to afford permanent porosity, and thus opens up a new approach to prepare porous carbon liquids. Furthermore, we hope this facile synthesis strategy can be widely applicated to fabricate other types of porous liquids, such as those (e.g., carbon nitride, boron nitride, metal–organic frameworks, covalent organic frameworks etc.) also having the electrostatic interaction with polymerized ionic liquids, evidently advancing the development and understanding of porous liquids. Porous carbon liquids: By exploiting the electrostatic interaction between carbon networks and polymerized ionic liquids, hollow carbon spheres can be stabilized in liquids to afford permanent porosity. Porous carbon liquids (HCS-liquid) are promising for a variety of applications, such as CO2 separation and storage.

Published in: "Angewandte Chemie International Edition".

Spontaneous antiferromagnetic order and strain effect on electronic properties of ${alpha}$-graphyne. (arXiv:1710.07524v1 [physics.comp-ph])

2017-10-23T19:58:58+00:00 October 23rd, 2017|Categories: Publications|Tags: |

By Baojuan Dong, Huaihong Guo, Zhiyong Liu, Teng Yang, Peng Tao, Sufang Tang, Riichiro Saito, Zhidong Zhang

Using hybrid exchange-correlation functional in ab initio density functional theory calculations, we study magnetic properties and strain effect on the electronic properties of $alpha$-graphyne monolayer. We find that a spontaneous antiferromagnetic (AF) ordering occurs with energy band gap ($sim$ 0.5 eV) in the equilibrated $alpha$-graphyne. Bi-axial tensile strain enhances the stability of AF state as well as the staggered spin moment and value of the energy gap. The antiferromagnetic semiconductor phase is quite robust against moderate carrier filling with threshold carrier density up to 1.7$times$10$^{14}$ electrons/cm$^2$ to destabilize the phase. The spontaneous AF ordering and strain effect in $alpha$-graphyne can be well described by the framework of the Hubbard model. Our study shows that it is essential to consider the electronic correlation effect properly in $alpha$-graphyne and may pave an avenue for exploring magnetic ordering in other carbon allotropes with mixed hybridization of s and p orbitals.

Published in: "arXiv Material Science".