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Now showing items 1 - 16 of 36

  • 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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  • Review of borophene and its potential applications

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

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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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  • 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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  • Interfaces between hexagonal and cubic oxides and their structure alternatives

    Zhou, Hua   Wu, Lijun   Wang, Hui-Qiong   Zheng, Jin-Cheng   Zhang, Lihua   Kisslinger, Kim   Li, Yaping   Wang, Zhiqiang   Cheng, Hao   Ke, Shanming   Li, Yu   Kang, Junyong   Zhu, Yimei  

    Multi-layer structure of functional materials often involves the integration of different crystalline phases. The film growth orientation thus frequently exhibits a transformation, owing to multiple possibilities caused by incompatible in-plane structural symmetry. Nevertheless, the detailed mechanism of the transformation has not yet been fully explored. Here we thoroughly probe the heteroepitaxially grown hexagonal zinc oxide (ZnO) films on cubic (001)-magnesium oxide (MgO) substrates using advanced scanning transition electron microscopy, X-ray diffraction and first principles calculations, revealing two distinct interface models of (001) ZnO/(001) MgO and (100) ZnO/(001) MgO. We have found that the structure alternatives are controlled thermodynamically by the nucleation, while kinetically by the enhanced Zn adsorption and O diffusion upon the phase transformation. This work not only provides a guideline for the interface fabrication with distinct crystalline phases but also shows how polar and non-polar hexagonal ZnO films might be manipulated on the same cubic substrate.
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  • Porous carbon anchored titanium carbonitride for high-performance supercapacitor

    Yan, Hao   Wang, Jianghong   Fang, Yuan   Zhou, Muxuan   Guo, Xiaoya   Wang, Hui-Qiong   Dai, Yang   Li, Wenrong   Zheng, Jin-Cheng  

    Carbon anchored titanium carbonitride for supercapacitor electrode material was prepared by a direct semi-solid-sate carbonitridation method. The prepared sample is highly conductive and mesoporous (250 m(2) g(-1)), enabling fast electron transfer and ion transport. As a result, a high capacitance of 360 F g(-1) at 0.5 A g(-1), and an impressive capacitance retention ratio 100Ag(-1)/1 Ag-1 of 53%, as well as long cyclic capability (>10,000 cycles) can be obtained in 1 MH2SO4. The thick electrode also presents a high area capacitance up to 1.77 F cm(-2). A flexible H2SO4/PVA symmetric supercapacitor was fabricated to demonstrate its practicality. Remarkably, the supercapacitor presents high-rate performance (up to 25 kW kg(-1)) and long cyclic performance (>10,000 cycles), illustrating its potential application in flexible integrated energy storage devices. This work provides a novel insight into designing and preparing carbonitride based materials for high performance supercapacitor. (C) 2019 Elsevier Ltd. All rights reserved.
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  • Porous carbon anchored titanium carbonitride for high-performance supercapacitor

    Yan, Hao   Wang, Jianghong   Fang, Yuan   Zhou, Muxuan   Guo, Xiaoya   Wang, Hui-Qiong   Dai, Yang   Li, Wenrong   Zheng, Jin-Cheng  

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  • Initial surface fluxes in transient heat conduction

    Shih, Tien-Mo   Zheng, Jin-Cheng   Wang, Hui-Qiong  

    In the heat transfer literature, it appears that numerical analyses focusing on surface heat fluxes in the initial phase for transient heat-conduction systems, i.e., q(x) at x = 0 and t = Delta t, have not been sufficiently reported. Due to this scarcity, some results may need to be re-examined for their accuracies or even their validities. The objective of the present study is twofold. First, we have identified two specific cases that may call for the awareness of the heat transfer community. Second, after such identification, we have further developed and proposed a technique, called the surface cubic-spline method, to help improve accuracies of heat-flux solutions. An effort is made to render the implementation of this method easy for interested readers, along with a MATLAB code offered in the appendix for them to directly cut and paste. Finally, some discussions of the second law of thermodynamics are presented, as they are related to transient heat conduction processes, and none of these essential ideas has been adequately reported in the literature. (C) 2013 Elsevier Ltd. All rights reserved.
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  • Knitted graphene-nanoribbon sheet: a mechanically robust structure

    Wei, Ning   Fan, Zheyong   Xu, Lan-Qing   Zheng, Yong-Ping   Wang, Hui-Qiong   Zheng, Jin-Cheng  

    In this paper, a new nanostructure is proposed, namely, the knitted graphene-nanoribbon sheet (KGS), which consists of zigzag and/or armchair graphene nanoribbons. The knitting technology is introduced to graphene nanotechnology to produce large area graphene sheets. Compared with pristine graphene, the chirality of a knitted graphene-nanoribbon sheet is much more flexible and can be designed on demand. The mechanical properties of KGSs are investigated by molecular dynamics simulations, including the effect of vacancies. With hydrogen atoms saturating the ribbon edges, the structure (KGS + H) is found to be of significant mechanical robustness, whose fracture does not rely on the critical bonds. The fracture strain of KGS + H remains nearly unchanged as long as there remains a single defect-free graphene nanoribbon in the tensile direction. This graphene nano knitting technique is experimentally feasible, inspired by a recent demonstration by Fournier et al. [Phys. Rev. B, 2011, 84, 035435] of lifting a single molecular wire using a combined frequency-modulated atomic force and tunnelling microscope.
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  • Graphene-nanotube 3D networks: intriguing thermal and mechanical properties RID H-4690-2011

    Xu, Lanqing   Wei, Ning   Zheng, Yongping   Fan, Zheyong   Wang, Hui-Qiong   Zheng, Jin-Cheng  

    Carbon-based nanomaterials have drawn strong interest for potential applications due to their extraordinary stability and unique mechanical, electrical and thermal properties. For the minimization of microelectronics/micromechanics circuits, bridging the low dimensional microscopic structure and mesoscopic modeling is indispensable. Graphene and carbon nanotubes are suggested as ideal 'building blocks' for the bottom-up strategy, and recently the integration of both materials has stimulated research interests. In this work we investigated the thermal and mechanical performance in the pillared-graphene - constructed by combining graphene sheets and carbon nanotubes to create a three-dimensional nano network. Reverse non-equilibrium molecular dynamics simulations were carried out to analyze the thermal transport behavior. The obtained thermal conductivities are found to be possibly isotropic in two specific directions or highly anisotropic for certain structure configurations. In the mechanical performance analysis, tensile deformations are loaded along graphene plane and along tube axis. The elongation responses and stress-strain relations are observed to be nearly linear, and the calculated strength, fracture strain and Young's moduli are lower than the pristine graphene or carbon nanotubes. The alterations in the thermal and mechanical performances are ascribed to the bond conversion on the junctions.
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  • First principles studies on the thermoelectric properties of (SrO)(m)(SrTiO3)(n) superlattice

    Zhang, Liang   Lo, Tie-Yu   Wang, Hui-Qiong   Zhang, Wen-Xing   Yang, Shuo-Wang   Zheng, Jin-Cheng  

    The electronic structures and thermoelectric properties of (SrO)(m)(SrTiO3)(n) superlattices have been investigated using first-principles calculations and the Boltzmann transport theory. Due to the much reduced dispersion along the c-axis, the thermoelectric properties for n-type superlattices are found to be highly anisotropic with the in-plane electrical conductivity with respect to relaxation time much higher than the out-of-plane one. The reduction of the in-plane Seebeck coefficient compared with SrTiO3 results in a slightly reduced power factor with respect to relaxation time for n-type doped (SrO)(m)(SrTiO3)(n). However, both Seebeck coefficient and electrical conductivity with respect to relaxation time are relatively maintained for p-type doping, leading to a comparable power factor with respect to relaxation time. If the reduced thermal conductivity is taken into account, an improved ZT value can be expected for the (SrO)(m)(SrTiO3)(n) superlattice.
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  • : STM measurements and theoretical calculations

    Wang, Hui-Qiong   Altman, Eric I.   Henrich, Victor E.  

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  • Synchrotron X-ray Absorption Spectroscopy Study of Local Structure in Al-Doped BiFeO3 Powders

    Gholam, Turghunjan   Zheng, Li Rong   Wang, Jia Ou   Qian, Hai Jie   Wu, Rui   Wang, Hui-Qiong  

    The Al-doped BiFeO3, i.e., BFA(x)O powder samples with x =3D 0, 0.025, 0.05, and 0.1, were prepared via the hydrothermal route. The effects of Al substitution on the structural, electrical, and optical properties of BFA(x)O samples were investigated. It is found that the substitution of Al ions at B-site of BiFeO3 did not cause structural change and it still retains the rhombohedral perovskite structure with R3c symmetry, which was confirmed by the X-ray diffraction (XRD) and Raman measurements. X-ray absorption fine structure (XAFS) above the Fe K-edge and Bi L-3-edge in BFA(x)O powders was also measured and analyzed. Fe ions exhibit mixed valence states (Fe2+/Fe3+) while Bi ions keep the +3 valence state in all the samples. Fe K-edge XAFS also indicated that there was a competition between hybridization of Fe 3d and Al 3d with O 2p orbitals and occurrence of the more 4p orbitals with Al doping. The Bi L-3-edge XAFS revealed that transition from 2p(3/2) to 6d state increased, so did the energy of 6d state. Besides, Al ion doping affected both the nearest-neighbor and next-nearest coordination shells of Fe atom and nearest-neighbor shells of Bi atom. Ultraviolet-visible (UV-Vis) spectroscopy results show the BFA(x)O prepared by hydrothermal method could be an appropriate visible-light photocatalytic material.
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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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  • Tuning the Surface Morphologies and Properties of ZnO Films by the Design of Interfacial Layer

    Li, Yaping   Wang, Hui-Qiong   Zhou, Hua   Du, Damin   Geng, Wei   Lin, Dingqu   Chen, Xiaohang   Zhan, Huahan   Zhou, Yinghui   Kang, Junyong  

    Wurtzite ZnO films were grown on MgO(111) substrates by plasma-assisted molecular beam epitaxy (MBE). Different initial growth conditions were designed to monitor the film quality. All the grown ZnO films show highly (0001)-oriented textures without in-plane rotation, as illustrated by in situ reflection high-energy electron diffraction (RHEED) and ex situ X-ray diffraction (XRD). As demonstrated by atomic force microscopy (AFM) images, " ridge-like" and " particle-like" surface morphologies are observed for the ZnO films grown in a molecular O2 atmosphere with and without an initial deposition of Zn adatoms, respectively, before ZnO growth with oxygen plasma. This artificially designed interfacial layer deeply influences the final surface morphology and optical properties of the ZnO film. From room-temperature photoluminescence (PL) measurements, a strong defect-related green luminescence band appears for the ZnO film with a " particle-like" morphology but was hardly observed in the films with flat " ridge-like" surface morphologies. Our work suggests that the ZnO crystallinity can be improved and defect luminescence can be reduced by designing interfacial layers between substrates and epilayers.
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  • (100)

    Wang, Hui-Qiong   Altman, Eric I.   Henrich, Victor E.  

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