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Now showing items 1 - 9 of 9

  • Review of borophene and its potential applications

    Wang, Zhi-Qiang   Lu, Tie-Yu   Wang, Hui-Qiong   Feng, Yuan Ping   Zheng, Jin-Cheng  

    Since two-dimensional boron sheet (borophene) synthesized on Ag substrates in 2015, research on borophene has grown fast in the fields of condensed matter physics, chemistry, material science, and nanotechnology. Due to the unique physical and chemical properties, borophene has various potential applications. In this review, we summarize the progress on borophene with a particular emphasis on the recent advances. First, we introduce the phases of borophene by experimental synthesis and theoretical predictions. Then, the physical and chemical properties, such as mechanical, thermal, electronic, optical and superconducting properties are summarized. We also discuss in detail the utilization of the borophene for wide ranges of potential application among the alkali metal ion batteries, Li-S batteries, hydrogen storage, supercapacitor, sensor and catalytic in hydrogen evolution, oxygen reduction, oxygen evolution, and CO2 electroreduction reaction. Finally, the challenges and outlooks in this promising field are featured on the basis of its current development.
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  • Origin of metallicity in 2D multilayer nickel bis(dithiolene) sheets

    Li, Suchun   Lu, Tie-Yu   Zheng, Jin-Cheng   Yang, Shuo-Wang   Wang, Jian-Sheng   Wu, Gang  

    We systematically studied the electronic structures of two-dimensional (2D) multilayered nickel bis(dithiolene) sheets using first-principles calculations. The monolayer is semiconducting, while all multilayers become good metals. We reveal that the metallicity mainly arises from covalent-like interlayer interaction between the 3pz orbitals of S atoms in adjacent layers. We show that such interlayer orbital hybridization widely exists in many 2D layered materials involving extensively out-of-plane orbitals. This interlayer orbital hybridization greatly enriches the physical properties of this class of 2D layered materials compared to pure van der Waals 2D layered materials. More importantly, we demonstrate that these properties are easily tunable by controlling the interlayer distance or stacking, making them very promising in meeting the desired requirements in practical applications.
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  • A super-stretchable boron nanoribbon network

    Wang, Zhi-Qiang   Cheng, Hao   Lu, Tie-Yu   Wang, Hui-Qiong   Feng, Yuan Ping   Zheng, Jin-Cheng  

    We have studied the mechanical properties of a two-dimensional (2D) boron nanoribbon network (BNRN) subjected to a uniaxial or a biaxial tensile strain using first principles calculations. The results show that the 2D BNRN is super-stretchable. The critical tensile strains of the BNRN in the chi-h1 phase along the a- and b-directions are 0.51 and 0.41, respectively, and that for the biaxial strain reaches an ultrahigh value of 0.84. By analyzing the B-B interatomic distance, coordination number and charge distribution, it is found that with increasing biaxial tensile strain, the chi-h1 BNRN undergoes two structural phase transitions, which are characterized by breaking of the B-B bonds and the partial transformation of the nanoribbon-like structures into chain-like structures. The strain-induced phase transitions significantly reduce the strain energy. We also discuss the elastic constants, Young's modulus, shear modulus, and Poisson's ratios. The super-stretchable and flexible mechanical properties of the BNRNs, together with their superior transport properties, make BNRNs useful in a wide range of applications in nanoscale electronic devices.
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  • Regulate the polarity of phosphorene's mechanical properties by oxidation

    Lu, Tie-Yu   Feng, Hai   Zhang, Yufeng   Lu, Yuerui   Zheng, Jin-Cheng  

    How to effectively manipulate the mechanical properties of atomically thin materials, is critical and can enable many new types of devices for various applications, such as sensing, actuation, energy harvesting, and so on. Here, we propose and demonstrate a new way to regulate the polarity of phosphorene's mechanical properties by controlling the level of oxidation. Phosphorene and its low-level oxides are treated with ab initio methods in order to evaluate the influence of oxidation on the anisotropic mechanical properties of phosphorene. Our results show that the mechanical properties of phosphorene are anisotropic. For the stable configuration, the anisotropy is gradually reduced with the increase of the oxygen coverage. We have fitted the formulas of Young's (shear) modulus and Poisson's ratio of phosphorene oxide. We also investigated the mechanical properties of metastable configurations. The diagonal configuration increases the anisotropy. The horizontal configuration is very unstable and has no shear moduli. Our results demonstrate that the mechanical properties of phosphorene can be regulated by oxidation, which is useful in design of phosphorene-based mechanical and optoelectronic devices. Our general model for calculating the elastic modulus along arbitrary direction can be applied in any 2D materials. (C) 2017 Elsevier B.V. All rights reserved.
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  • Band structure engineering of borophane by first principles calculations

    Wang, Zhi-Qiang   Lu, Tie-Yu   Wang, Hui-Qiong   Feng, Yuan Ping   Zheng, Jin-Cheng  

    We exploited the band structure engineering in W-borophane, the most stable conformer of the fully hydrogenated borophene in the literature, by first principles calculations. Uniaxial strains along the a and b direction, biaxial strains, shear strains, H vacancy and B-H dimer vacancy defects have been considered. Our results show that uniaxial strains along the a, b directions and biaxial strain can not open the band gap for W-borophane. However, band gap opening can be achieved by applying shear strain. The shear strain induced band gap is 53 meV when the applied shear strain is only 0.01. The band gap increases with the increasing shear strain. When the shear strain reaches 0.12, the band gap can reach up to 538 meV. Two different exchange-correlation potentials have been used to confirm the band gap opening. The excellent dynamical stability of W-borophane under shear strain has been proved by the phonon dispersion, indicating that applying shear strain is an effective and feasible approach to open the band gap for W-borophane. In addition, the Dirac cone of W-borophane is maintained well under the uniaxial and biaxial strains. In free-state, the Dirac fermions of W-borophane possess an ultrahigh Fermi velocity (2.13 x 106 m s(-1)) which is higher than that of graphene. It is very interesting that the Fermi velocities of W-borophane can be tuned in a wide range of values by applying uniaxial and biaxial strain.
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  • New crystal structure prediction of fully hydrogenated borophene by first principles calculations

    Wang, Zhiqiang   Lu, Tie-Yu   Wang, Hui-Qiong   Feng, Yuan Ping   Zheng, Jin-Cheng  

    New crystal structures of fully hydrogenated borophene (borophane) have been predicted by first principles calculation. Comparing with the chair-like borophane (C-boropane) that has been reported in literature, we obtained four new borophane conformers with much lower total-energy. The most stable one, washboard-like borophane (W-borophane), has energy about 113.41 meV/atom lower than C-borophane. In order to explain the relative stability of different borophane conformers, the atom configuration, density of states, charge transfer, charge density distribution and defect formation energy of B-H dimer have been calculated. The results show that the charge transfer from B atoms to H atoms is crucial for the stability of borophane. In different borophane conformers, the bonding characteristics between B and H atoms are similar, but the B-B bonds in W-borophane are much stronger than that in C-borophane or other structures. In addition, we examined the dynamical stability of borophane conformers by phonon dispersions and found that the four new conformers are all dynamically stable. Finally the mechanical properties of borophane conformers along an arbitrary direction have been discussed. W-borophane possesses unique electronic structure (Dirac cone), good stability and superior mechanical properties. W-borophane has broad perspective for nano electronic device.
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  • Thermoelectric properties of the 3C,2H,4H,and 6H polytypes of the wide-band-gap semiconductors SiC,GaN,and ZnO

    Huang, Zheng   Lu, Tie-Yu   Wang, Hui-Qiong   Zheng, Jin-Cheng  

    We have investigated the thermoelectric properties of the 3C, 2H, 4H, and 6H polytypes of the wide-band-gap(n-type) semiconductors SiC, GaN, and ZnO based on first-principles calculations and Boltzmann transport theory. Our results show that the thermoelectric performance increases from 3C to 6H, 4H, and 2H structures with an increase of hexagonality for SiC. However, for GaN and ZnO, their power factors show a very weak dependence on the polytype. Detailed analysis of the thermoelectric properties with respect to temperature and carrier concentration of 4H-SiC, 2H-GaN, and 2H-ZnO shows that the figure of merit of these three compounds increases with temperature, indicating the promising potential applications of these thermoelectric materials at high temperature. The significant difference of the polytype-dependent thermoelectric properties among SiC, GaN, and ZnO might be related to the competition between covalency and ionicity in these semiconductors. Our calculations may provide a new way to enhance the thermoelectric properties of wide-band-gap semiconductors through atomic structure design, especially hexagonality design for SiC. (C) 2015 Author(s).
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  • Electronic and thermoelectric properties of the group-III nitrides (BN,AlN and GaN) atomic sheets under biaxial strains

    Huang, Zheng   Lu, Tie-Yu   Wang, Hui-Qiong   Yang, Shuo-Wang   Zheng, Jin-Cheng  

    Based on first-principles methods and Boltzmann transport theory, we investigated the biaxial strain effects on electronic and thermoelectric properties of three group-Ill nitrides (BN, AIN and GaN) 2D honeycomb mono-layered nanosheets. The direct-indirect band gap transitions occurred for BN and GaN nanosheets when the strain was applied. In addition, the band gaps decreased with increase of tensile strain; and we uncovered the mechanism behind by the total and projected density-of-state (PDOS) analyses. At the same time, we presented the contour plots of their electrical transport properties as a function of both temperature and carrier concentration at strain-free states. Power-factors of BN, AIN and GaN nanosheets were also calculated. We found only peak power factors of p-type GaN and n-type BN showed a strong dependence on biaxial strain. Such differences of the strain-dependent thermoelectric performance among BN, MN and GaN may be due to the competition between covalency and ionicity in these 2D structures. Our results provide a new avenue to optimize thermoelectric properties of 2D nanosheets by strain engineering. (C) 2017 Elsevier B.V. All rights reserved.
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  • Tuning the indirect-direct band gap transition of SiC, GeC and SnC monolayer in a graphene-like honeycomb structure by strain engineering: a quasiparticle GW study

    Lu, Tie-Yu   Liao, Xia-Xia   Wang, Hui-Qiong   Zheng, Jin-Cheng  

    We have calculated the electronic properties of graphene and SiC, GeC and SnC monolayers in a two-dimensional graphene-like honeycomb structure under various strained conditions using first principles calculations based on density functional theory and the quasiparticle GW approximation. Our results show that the indirect-direct band gap transition of group-IV carbides can be tuned by strain, which indicates a possible new route for tailoring the electronic properties of ultrathin nanofilms through strain engineering.
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