Our Publications

  • ZHANG Ziyue, GUO Wanlin. Intrinsic and extrinsic strain induced structural change of zigzag graphene nanoribbon. Physics Letters A 2012, 377, 118–123.

    Intrinsic and extrinsic strain induced structural change of zigzag graphene nanoribbon

    Zi-Yue Zhang, Wanlin Guo

    Key Laboratory for Intelligent Nano Materials and Devices (MOE) and State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

    http://dx.doi.org/10.1016/j.physleta.2012.10.057

    Abstract
    When a graphene nanoribbon with zigzag edges is doped by a foreign element X, an intrinsic strain will be inevitable introduced into the doped system, which can induce structural change of the system. We find by first-principles calculations that doped nanoribbons could fold at the doping site for n-type dopants and the XC bonds elongated substantially when X are p-type dopants. The height of apophysis and the length of XC bonds can be modulated by doping charge states and the extrinsic strains in different directions. We have proposed a model of volume change unexpected contrary with the common expectation to explain this unusual behavior in ribbon structures.

    Highlights
    ► We study a zigzag graphene nanoribbon doped by Be, O, Al, Si and P atoms. ► The structures are greatly different for various doping charge states. ► We propose a volume model to explain this structural difference. ► The doped ribbons under extrinsic strain exx and eyy are studied.

  • ZHANG Zhuhua, GUO Wanlin and YAKOBSON Boris I. Electromechanical coupling effect on electronic properties of double-walled boron nitride nanotubes. Acta Mechanica Sinica 2012, 28, 1532–1538.

    Title
    Electromechanical coupling effect on electronic properties of double-walled boron nitride nanotubes

    Authors
    Zhu-Hua Zhang (1) (2)
    Wan-Lin Guo (2)
    Boris I. Yakobson (1)

    Author Affiliations
    1. Department of Mechanical Engineering and Materials Science, Rice University, Houston, Texas, 77005, USA
    2. Key Laboratory for Intelligent Nano Materials and Devices of Ministry of Education and Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, 210016, Nanjing, China

    Journal
    Acta Mechanica Sinica
    Volume 28, Issue 6 , pp 1532-1538

    Cover Date
    2012-12-01

    DOI
    10.1007/s10409-012-0163-y

    Abstract
    We report on a first-principles study of a novel band modulation in zigzag double-walled boron nitride nanotubes (DBNNTs) by applying radial strain and coupled external electric field. We show that the band alignment between the inner and outer walls of the DBNNTs can be tuned from type I to type II with increasing radial strain, accompanied with a direct to indirect band gap transition and a substantial gap reduction. The band gap can be further significantly reduced by applying a transverse electric field. The coupling of electric field with the radial strain makes the field-induced gap reduction being anisotropic and more remarkable than that in undeformed DBNNTs. In particular, the gap variation induced by electric field perpendicular to the radial strain is the most remarkable among all the modulations. These tunable properties by electromechanical coupling in DBNNTs will greatly enrich their versatile applications in future nanoelectronics.

  • GUO Wanlin. AMS theme collection on “Mechanics of Nanomaterials”. Acta Mechanica Sinica 2012, 28(6), 1511–1512.

    Title
    AMS theme collection on “Mechanics of Nanomaterials”

    Authors
    Wan-Lin Guo

    Author Affiliations
    1. College of Aerospace Engineering, Nanjing University of Aeronautics and Astronautics, 210016, Nanjing, China

    Journal
    Acta Mechanica Sinica
    Volume 28, Issue 6 , pp 1511-1512

    Cover Date
    2012-12-01

    DOI
    10.1007/s10409-012-0168-6

  • ZHANG Zhuhua, LIU Xiaofei, YAKOBSON Boris I., GUO Wanlin. Two-Dimensional Tetragonal TiC Monolayer Sheet and Nanoribbons. Journal of the American Chemical Society 2012, 134, 19326-19329.

    Two-Dimensional Tetragonal TiC Monolayer Sheet and Nanoribbons

    Zhuhua Zhang *†‡, Xiaofei Liu †, Boris I. Yakobson ‡, and Wanlin Guo *†

    † State Key Laboratory of Mechanics and Control of Mechanical Structures, Key Laboratory of Intelligent Nano Materials and Devices of MoE and Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
    ‡ Department of Mechanical Engineering and Materials Science, Rice University, Houston, Texas 77005, United States

    J. Am. Chem. Soc., 2012, 134 (47), pp 19326–19329
    DOI: 10.1021/ja308576g
    Publication Date (Web): November 8, 2012

    Abstract

    We report a two-dimensional tetragonal Titanium Carbide (TiC) monolayer sheet with distinguished structure and properties based on comprehensive first-principles calculations. The TiC sheet exhibits a novel zigzag-shaped buckling structure with all atoms being quasiplanar tetracoordinate, as favored by strong in-plane C2p–Ti3d bonding and synergetic out-of-plane electronic delocalization. This unique structure endows the sheet with high kinetic stability and anisotropic mechanical properties. Moreover, the TiC sheet displays orientation-dependent electronic properties derived from its special rectangular symmetry, with indirect band gap of 0.2 eV and substantial ferromagnetism along its edges, thus promising for wide applications in nanoelectronics.

  • LU Peng, XIAO Xiaojun, GUO Wanlin and ZENG Xiaocheng. Strain-dependent electronic and magnetic properties of MoS2 monolayer, bilayer, nanoribbons and nanotubes. Physical Chemistry Chemical Physics 2012, 14, 13035-13040.

    Strain-dependent electronic and magnetic properties of MoS2 monolayer, bilayer, nanoribbons and nanotubes

    Lu P, Wu X, Guo W, Zeng XC.

    State Key Laboratory of Mechanics and Control of Mechanical Structures, and Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China.

    Abstract
    We investigate the strain-dependent electronic and magnetic properties of two-dimensional (2D) monolayer and bilayer MoS(2), as well as 1D MoS(2) nanoribbons and nanotubes using first-principles calculations. For 2D monolayer MoS(2) subjected to isotropic or uniaxial tensile strain, the direct band gap of MoS(2) changes to an indirect gap that decreases monotonically with increasing strain; while under the compressive strain, the original direct band gap is enlarged first, followed by gap reduction when the strain is beyond -2%. The effect of isotropic strain is even stronger than that of uniaxial strain. For bilayer MoS(2) subjected to isotropic tensile strain, its indirect gap reduces monotonically to zero at strain about 6%; while under the isotropic compressive strain, its indirect gap increases first and then reduces and turns into direct gap when the strain is beyond -4%. For strained 1D metallic zigzag MoS(2) nanoribbons, the net magnetic moment increases slightly with axial strain from about -5% to 5%, but drops to zero when the compressive strain is beyond -5% or increases with a power law beyond 5%. For 1D armchair MoS(2) nanotubes, tensile or compressive axial strain reduces or enlarges the band gap linearly, and the gap can be fully closed for nanotubes with relatively small diameter or under large tensile strain. For zigzag MoS(2) nanotubes, the strain effect becomes nonlinear and the tensile strain can reduce the band gap, whereas compressive strain can initially enlarge the band gap and then decrease it. The strain induced change in projected orbitals energy of Mo and the coupling between the Mo atom d orbital and the S atom p orbital are analyzed to explain the strong strain effect on the band gap and magnetic properties.

  • LIU Xinsheng, LIU Hui, GUO Wanlin, and YU Keming. Codon substitution models based on residue similarity and their applications. Gene 2012, 509, 136-141.

    Codon substitution models based on residue similarity and their applications

    Liu X, Liu H, Guo W, Yu K.

    Institute of Nano Science, State Key Laboratory of Mechanics and Control of Mechanical Structures, and College of Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China. xsliu@nuaa.edu.cn

    Abstract
    Codon models are now widely used to draw evolutionary inferences from alignments of homologous sequence data. Incorporating physicochemical properties of amino acids into codon models, two novel codon substitution models describing the evolution of protein-coding DNA sequences are presented based on the similarity scores of amino acids. To describe substitutions between codons a continue-time Markov process is used. Transition/transversion rate bias and nonsynonymous codon usage bias are allowed in the models. In our implementation, the parameters are estimated by maximum-likelihood (ML) method as in previous studies. Furthermore, instantaneous mutations involving more than one nucleotide position of a codon are considered in the second model. Then the two suggested models are applied to five real data sets. The analytic results indicate that the new codon models considering physicochemical properties of amino acids can provide a better fit to the data comparing with existing codon models, and then produce more reliable estimates of certain biologically important measures than existing methods.

  • YU Peishi and GUO Wanlin. An equivalent thickness conception for prediction of surface fatigue crack growth life and shape evolution. Engineering Fracture Mechanics 2012, 93, 65-74.

    An equivalent thickness conception for prediction of surface fatigue crack growth life and shape evolution

    Peishi Yu,a,b, Wanlin Guo,a,
    a State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
    b College of Mechanics and Materials, Hohai University, Nanjing 210098, China

    Abstract
    Based on the newly developed equivalent-thickness-based fatigue crack closure evaluation, a surface fatigue crack model is proposed for evaluating the growth rate at each point on the crack border from material base curves obtained by standard straight-through cracked specimens. Using this model, surface fatigue crack propagations in specimens with different initial shapes are predicted through detailed finite element simulations. Good coincidence between the predictions and available experimental results shows that the equivalent thickness conception can serve as a realistic bridge from fatigue crack growth base curves from standard specimens to fatigue crack growth life prediction for three-dimensional engineering structures.

  • SHEN Rong and GUO Wanlin. Mechanism for Variable Selectivity and Conductance in Mutated NaK Channels. Journal of Physical Chemistry Letters 2012, 3, 2887-2891.

    Mechanism for Variable Selectivity and Conductance in Mutated NaK Channels

    Rong Shen and Wanlin Guo
    Institute of Nano Science, State Key Laboratory of Mechanics and Control for Mechanical Structures, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

    J. Phys. Chem. Lett., 2012, 3 (19), pp 2887–2891
    DOI: 10.1021/jz301225d
    Publication Date (Web): September 20, 2012

    Abstract

    Na+ conduction has been demonstrated in a few K+ channels and has been widely used to characterize the physiological selectivity and C-type inactivation in K+ channels. By using molecular dynamics simulations and free-energy calculations, we found that K+ and Na+ have distinct preferable binding configurations in the conductive filter of two highly K+ selective channels, which are mutated from the nonselective NaK channel and can conduct Na+ upon removal of K+. Disruption of a conserved hydrogen bond interaction between residues in the filter and the pore helices can significantly decrease the free-energy differences and barriers between the K+ binding configurations, whereas it has little effect on the free-energy landscape for Na+. We propose that the enhancement of the fluctuation of the filter structure decreases the affinity and conducting barrier of K+ and therefore the ability of K+ to block Na+ currents, predominantly responsible for the reduced K+ selectivity.

    Keywords: NaK channel; mutation; ion selectivity; ion conductance; hydrogen bond; molecular dynamics simulation

  • ZHAO Junhua and GUO Wanlin. Three-parameter K-T-T-z characterization of the crack-tip fields in compact-tension-shear specimens. Engineering Fracture Mechanics 2012, 92, 72-88.

    Three-parameter K-T-T-z characterization of the crack-tip fields in compact-tension-shear specimens

    Junhua Zhao, , Wanlin Guo,
    State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and Astronautics, 210016 Nanjing, China

    Abstract
    A complete three-parameter K–T–Tz description of the mixed-mode I/II three-dimensional (3D) crack-tip stress fields has been proposed, in which the stress intensity factor K, T-stress and out-of-plane constraint factor Tz around mix-mode I/II crack front in compact-tension-shear specimens are all the functions of the Poisson ratio v, thickness ratio zB and load angle φ. By fitting the numerical results with the least squares method, empirical formulae have been obtained to accurately describe the 3D distributions of the three parameters for the convenience of engineering applications, which can be used to characterize the 3D crack-tip stress fields completely and establish the three-parameter dominated stress fields.

  • HAN Xiaobin, et al. Strain-Gradient Effect on Energy Bands in Bent ZnO Microwires. Advanced Materials 2012, 24, 4707-4711.

    Strain-Gradient Effect on Energy Bands in Bent ZnO Microwires

    Xiaobing Han1, Liangzhi Kou2, Zhuhua Zhang2, Ziyue Zhang2, Xinli Zhu1, Jun Xu1, Zhimin Liao1, Wanlin Guo2,*, Dapeng Yu1,*

    1. State Key Laboratory for Mesoscopic Physics and Electron Microscopy Laboratory, Department of Physics, Peking University, Beijing 100871, China
    2. State Key Laboratory of Mechanics and Control of Mechanical Structures and Key Laboratory for Intelligent Nano Materials and Devices of MoE, Institute of Nanoscience, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

    Article first published online: 26 MAR 2012

    DOI: 10.1002/adma.201104372

  • ZHAO Junhua, GUO Wanlin, Timon Rabczuk. An analytical molecular mechanics model for the elastic properties of crystalline polyethylene. Journal of Applied Physics 2012, 112, 033516.

    An analytical molecular mechanics model for the elastic properties of crystalline polyethylene

    Junhua Zhao1,2, Wanlin Guo3, and Timon Rabczuk2

    1. Department of Materials and Structural Engineering, Northwest A&F University, 712100 Yangling, Shaanxi, People’s Republic of China
    2. Institute of Structural Mechanics, Bauhaus-University Weimar, 99423 Weimar, Germany
    3. Institute of Nanoscience, Nanjing University of Aeronautics and Astronautics, 210016 Nanjing, People’s Republic of China

    Received 18 May 2012; accepted 11 July 2012; published online 8 August 2012

    Abstract

    We present an analytical model to relate the elastic properties of crystalline polyethylene based on a molecular mechanics approach. Along the polymer chains direction, the united-atom (UA) CH2-CH2 bond stretching, angle bending potentials are replaced with equivalent Euler-Bernoulli beams. Between any two polymer chains, the explicit formulae are derived for the van der Waals interaction represented by the linear springs of different stiffness. Then, the nine independent elastic constants are evaluated systematically using the formulae. The analytical model is finally validated by present united-atom molecular dynamics (MD) simulations and against available all-atom molecular dynamics results in the literature. The established analytical model provides an efficient route for mechanical characterization of crystalline polymers and related materials

  • LU Peng, ZHOU Rulong, GUO Wanlin and ZENG Xiaocheng. Amide Functionalization of Graphene and Carbon Nanotubes: Coverage- and Pattern-Dependent Electronic and Magnetic Properties. Journal of Physical Chemistry C 2012, 116, 13722-13730.

    Amide Functionalization of Graphene and Carbon Nanotubes: Coverage- and Pattern-Dependent Electronic and Magnetic Properties

    Peng Lu †‡, Rulong Zhou ‡§, Wanlin Guo *†, and Xiao Cheng Zeng *‡
    † Key Laboratory for Intelligent Nano Materials and Devices of Ministry of Education and Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
    ‡ Department of Chemistry and Center for Materials & Nanoscience, University of Nebraska-Lincoln, Lincoln, Nebraska, 68588, United States
    § School of Science and Engineering of Materials, Hefei University of Technology, Hefei, Anhui 230009, China

    J. Phys. Chem. C, 2012, 116 (25), pp 13722–13730
    DOI: 10.1021/jp3009578
    Publication Date (Web): June 14, 2012

    Abstract

    Motivated by successful synthesis of dimethylamide-functionalized graphene (Collins, et al. Angew. Chem. 2011, 123, 9010), we investigate electronic, magnetic, and electron transport properties of covalently functionalized graphene and carbon nanotubes (CNTs) by the amide groups [CON(CH3)2] using density functional theory calculations. We find that when both sublattices of the graphene are evenly functionalized with the amide groups, the band gap of the modified (semiconducting) graphene can be substantially enlarged by increasing the coverage of amide groups. If the modified graphene is metallic, however, its electronic properties are little affected by increasing the coverage. When the two sublattices of the graphene are functionalized unevenly, the decorated graphene exhibits magnetism. As the coverage of amide groups is increased, the electronic properties of the functionalized graphene can be transformed from semiconducting to half metallic and to metallic. Moreover, the electronic structures of functionalized graphene can be regulated by increasing the number of zigzag chains along the supercell edge. For zigzag CNTs (ZCNTs), when the two sublattices are unevenly functionalized by the amide groups, the functionalized CNTs can be either metallic or semiconducting, depending on the pattern of decoration. ZCNTs with large diameters may exhibit magnetism as well. When the two sublattices are unevenly functionalized, the functionalized ZCNTs are always semiconducting with their band gap increasing with the distance between two neighboring amide groups in the radial direction. For armchair CNTs, however, all functionalized systems are metallic without showing magnetism, regardless of the coverage or pattern of amide groups. We also find that the conductivity of the amide functionalized graphene and CNT is lower than that of the pristine counterparts.

  • GUO Wanlin,GUO Yufeng,ZHANG Zhuhua,WANG Lifeng. Strength, plasticity, interlayer interactions and phase transition of low-dimensional nanomaterials under multiple fields. Acta Mechanica Solida Sinica 2012, 25, 221-243.

    Strength, plasticity, interlayer interactions and phase transition of low-dimensional nanomaterials under multiple fields

    Wanlin Guo, , Yufeng Guo, , Zhuhua Zhang, Lifeng Wang

    State Key Laboratory of Mechanics and Control of Mechanical Structures and Key Laboratory for Intelligent Nano Materials and Devices of MOE, Institute of Nanoscience, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

    Abstract
    Atoms are hold together to form different materials and devices through short range interactions such as chemical bonds and long range interactions such as the van der Waals force and electromagnetic interactions. Quantum mechanics is powerful to describe the short range interactions of materials at the nanometer scale, while molecular mechanics and dynamics based on empirical potentials are able to simulate material behaviors at much large scales, but weak in handling of processes including charge transfer and redistributions, such as mechanical-electric coupling of functional nanomaterials, plastic deformation, fracture and phase transition of nanomaterials. These issues are also challenging to quantum mechanics which needs to be extended to van der Waals distance and larger spatial as well as temporal scales. Here, we make brief review and discussions on such kind of mechanical behaviors of some important functional nanomaterials and nanostructures, to probe the frontier of nanomechanics and the trend to multiscale physical mechanics.

    Key Words
    low-dimensional nanomaterials; nano device; physical mechanics; multiple field coupling; multiscale

  • MIAO Chunyang, LI Haijun, GUO Wanlin. Radial breathing modes of multi-walled carbon nanotubes by an atomic beam-spring model. Sci China-Phys Mech Astron, 2012, 55(6): 940–946.

    Radial breathing modes of multi-walled carbon nanotubes by an atomic beam-spring model

    ChunYang Miao, HaiJun Li, WanLin Guo

    Science China Physics, Mechanics and Astronomy
    June 2012, Volume 55, Issue 6, pp 940-946

    Abstract
    Based on molecular force fields, a new finite element model is constructed for multi-walled carbon nanotubes where the interlayer interactions and C—C bonds are simulated by the elements of piece-wise linear spring and rectangular cross section beam, respectively. For high computation efficiency and atomic reification, the radial breathing modes of multi-walled carbon nanotubes are studied systemically using this model. The results show the correspondence between carbon nanotube structures and vibrational modes, which provide unequivocal data for the experimental characterization of carbon nanotubes. An empirical relationship of radial breathing modes frequencies with the nanotube radius are also obtained for two-layer carbon nanotubes.

  • LIAO Zhimin, et al. Strain induced exciton fine-structure splitting and shift in bent ZnO microwires. Scientific Reports 2012, 2, 452.

    Strain induced exciton fine-structure splitting and shift in bent ZnO microwires

    Zhi-Min Liao,1,5 Han-Chun Wu,a,2,5 Qiang Fu,1,5 Xuewen Fu,1 Xinli Zhu,1 Jun Xu,1 Igor V. Shvets,2 Zhuhua Zhang,3 Wanlin Guo,3 Yamin Leprince-Wang,4 Qing Zhao,1 Xiaosong Wu,1 and Da-Peng Yub,1

    1. State Key Laboratory for Mesoscopic Physics, Department of Physics, Peking University, Beijing 100871, P.R. China
    2. CRANN and School of Physics, Trinity College Dublin, Dublin 2, Ireland
    3. Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, P. R. China
    4. Laboratoire de Physique des Materiaux Divises et Interfaces, CNRS- FRE3300, Universite Paris-Est, Marne la Vallee 77454, France
    5. These authors contributed equally to this work.

    a. Email: wuhc@tcd.ie
    b. Email: yudp@pku.edu.cn

    Abstract

    Lattice strain is a useful and economic way to tune the device performance and is commonly present in nanostructures. Here, we investigated for the first time the exciton spectra evolution in bent ZnO microwires along the radial direction via high spatial/energy resolution cathodeluminescence spectroscopy at 5.5 K. Our experiments show that the exciton peak splits into multi fine peaks towards the compressive part while retains one peak in the tensile part and the emission peak displays a continuous blue-shift from tensile to compressive edges. In combination with first-principles calculations, we show that the observed NBE emission splitting is due to the valence band splitting and the absence of peak splitting in the tensile part maybe due to the highly localized holes in the A band and the carrier density distribution across the microwire. Our studies may pave the way to design nanophotonic and electronic devices using bent ZnO nanowires.

  • QIU Hu, SHEN Rong, GUO Wanlin. Ion solvation and structural stability in a sodium channel investigated by molecular dynamics calculations. Biochim Biophys Acta 2012, doi:10.1016/j.bbamem.2012.06.003

    Ion solvation and structural stability in a sodium channel investigated by molecular dynamics calculations

    Hu Qiu, Rong Shen, Wanlin Guo

    State Key Laboratory of Mechanics and Control of Mechanical Structures, Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

    Received 18 November 2011. Revised 23 May 2012. Accepted 4 June 2012. Available online 11 June 2012.
    http://dx.doi.org/10.1016/j.bbamem.2012.06.003

    Abstract
    The stability and ion binding properties of the homo-tetrameric pore domain of a prokaryotic, voltage-gated sodium channel are studied by extensive all-atom molecular dynamics simulations, with the channel protein being embedded in a fully hydrated lipid bilayer. It is found that Na+ ion presents in a mostly hydrated state inside the wide pore of the selectivity filter of the sodium channel, in sharp contrast to the nearly fully dehydrated state for K+ ions in potassium channels. Our results also indicate that Na+ ions make contact with only one or two out of the four polypeptide chains forming the selectivity filter, and surprisingly, the selectivity filter exhibits robust stability for various initial ion configurations even in the absence of ions. These findings are quite different from those in potassium channels. Furthermore, an electric field above 0.5 V/nm is suggested to be able to induce Na+ permeation through the selectivity filter.

    Highlights
    ► We study the stability and ion binding properties of a sodium ion channel (NavAb). ► Sodium ions in the selectivity filter are highly hydrated. ► Sodium ions bind with the channel protein in an asymmetric manner. ► Robust stability of the NavAb channel ► Ion permeation through NavAb can be induced by an electric field above 0.5 V/nm.

    Keywords
    Sodium channels; Molecular dynamics; Structural stability; Ion hydration

  • ZHANG Zhuhua, GUO Wanlin. Intrinsic Metallic and Semiconducting Cubic Boron Nitride Nanofilms. Nano Lett., Article ASAP.

    Intrinsic Metallic and Semiconducting Cubic Boron Nitride Nanofilms

    Zhuhua Zhang*†‡ and Wanlin Guo*†

    † State Key Laboratory of Mechanics and Control of Mechanical Structures, Key Laboratory for Intelligent Nano Materials and Devices of Ministry of Education and Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
    ‡ Department of Mechanical Engineering and Materials Science, Rice University, Houston, Texas 77005, United States

    Nano Lett., Article ASAP
    DOI: 10.1021/nl301406f
    Publication Date (Web): June 5, 2012

    We show by density functional theory calculations with both hybrid and semilocal functionals that cubic boron nitride (111) nanofilms are intrinsically metallic and even turn into semiconductors once the thickness is less than 0.69 nm, which is in sharp contrast to the known insulating nature of boron nitride materials. The exceptional metallic or semiconducting band gap is due to a combined effect of thickness-dependent inbuilt electric polarization and labile near-gap states unique in the polar nanofilms. The band gap and dipole moment of the nanofilms can be further significantly tuned by applying an in-plane strain. These distinguished features of the boron nitride nanofilms are robust to surface passivation and can be enhanced by hybridizing with diamond films, thereby opening an exciting prospect of using the versatile cubic nanofilms in future electronic and piezoelectric devices.

    Keywords: Boron nitride; metal; semiconductor; nanofilm; strain; density functional theory calculations

  • LI Xuemei, YIN Jun, ZHOU Jianxin, WANG Qin, GUO Wanlin. Exceptional high Seebeck coefficient and gas-flow-induced voltage in multilayer graphene. Appl. Phys. Lett. 2012, 100, 183108.

    Exceptional high Seebeck coefficient and gas-flow-induced voltage in multilayer graphene

    Xuemei Li, Jun Yin, Jianxin Zhou, Qin Wang, and Wanlin Guo

    State Key Laboratory of Mechanics and Control of Mechanical Structures and the Key Laboratory for Intelligent Nano Materials and Devices of the Ministry of Education, Institute of Nanoscience, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

    Appl. Phys. Lett. 100, 183108 (2012); http://dx.doi.org/10.1063/1.4707417 (4 pages)
    Received 15 February 2012; accepted 11 April 2012; published online 3 May 2012

    Seebeck coefficient of graphene is an important parameter for defining its thermoelectric performance and thus practical applications, such as gas-flow-induced voltage. Here, we find a unique layer-dependence of the graphene Seebeck coefficient that exceptionally increases with increasing thickness to reach a peak value at six layers that is ∼77% higher than monolayer and ∼296% higher than graphite, unlike the monotonic decrease in electric resistance. However, the gas flow-induced voltage is significantly higher in 2, 4, 5, 6, and 7 layered graphene samples than in 1, 3, and 8 layered ones, against the prevailing wisdom that it should be proportional to Seebeck coefficient.

  • GUO Yufeng, GUO Wanlin. Mechanically tunable magnetism on graphene nanoribbon adsorbed SiO2 surface. J. Appl. Phys. 2012, 111, 074317.

    Mechanically tunable magnetism on graphene nanoribbon adsorbed SiO2 surface

    Yufeng Guo and Wanlin Guo

    State Key Laboratory of Mechanics and Control of Mechanical Structures and MOE Key Laboratory for Intelligent Nano Materials and Devices, Institute of Nanoscience, Nanjing University of Aeronautics and Astronautics, Nanjing, 210016, China

    Received 26 September 2011; accepted 9 March 2012; published online 11 April 2012

    Our first-principle calculations reveal that the O-terminated surface of zigzag graphene nanoribbon adsorbed (100) α-quartz SiO2 exhibits antiferromagnetic ground state. This is due to unpaired electrons of dangling O atoms forming on the SiO2 surface, which are caused by the edge C atoms of the adsorbed nanoribbon. The resulting magnetism and spin-resolved states on the SiO2 surface can be effectively tuned by mechanical strain applied on the substrate, with the antiferromagnetic state transforming into ferromagnetic state as well as the total magnetic moment varying from negative to positive when the strain turns from tensile to compressive. We elucidate the mechanism for the modification of the surface magnetism by orbital hybridization between C and O atoms and part of dangling O atoms bonding with the nanoribbon under strain.

  • YIN Jun, ZHANG Zhuhua, LI Xuemei, ZHOU Jianxin, GUO Wanlin. Harvesting Energy from Water Flow over Graphene? Nano Lett., 2012, 12 (3), 1736–1741.

    Harvesting Energy from Water Flow over Graphene?

    Jun Yin, Zhuhua Zhang, Xuemei Li, Jianxin Zhou, and Wanlin Guo*

    State Key Laboratory of Mechanics and Control of Mechanical Structures, Key Laboratory for Intelligent Nano Materials and Devices of the Ministry of Education, and Institute of Nanoscience, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

    Nano Lett., 2012, 12 (3), pp 1736–1741
    DOI: 10.1021/nl300636g
    Publication Date (Web): March 1, 2012

    It is reported excitingly in a previous letter (Nano Lett.2011, 11, 3123) that a small piece of graphene sheet about 30 × 16 μm2 immersed in flowing water with 0.6 M hydrochloric acid can produce voltage 20 mV. Here we find that no measurable voltage can be induced by the flow over mono-, bi- and trilayered graphene samples of 1 × 1.5 cm2 in size in the same solution once the electrodes on graphene are isolated from interacting with the solution, mainly because the H3O+ cations in the water adsorb onto graphene by strong covalent bonds as revealed by our first-principles calculations. When both the graphene and its metal electrodes are exposed to the solution as in the previous work, water flow over the graphene-electrode system can induce voltages from a few to over a hundred millivolts. In this situation, the graphene mainly behaves as a load connecting between the electrodes. Therefore, the harvested energy is not from the immersed carbon nanomaterials themselves in ionic water flow but dominated by the exposed electrodes.

    Keywords: Graphene; electrode; energy harvesting; water flow; ion adsorption

  • QIU Hu, GUO Wanlin. Detecting ssDNA at single-nucleotide resolution by sub-2-nanometer pore in monoatomic graphene: A molecular dynamics study. Appl. Phys. Lett. 2012, 100, 083106.

    Detecting ssDNA at single-nucleotide resolution by sub-2-nanometer pore in monoatomic graphene: A molecular dynamics study

    Hu Qiu and Wanlin Guo

    Institute of Nano Science, State Key Laboratory of Mechanics and Control for Mechanical Structures, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

    Appl. Phys. Lett. 100, 083106 (2012); http://dx.doi.org/10.1063/1.3686921 (4 pages)
    Received 21 October 2011; accepted 21 January 2012; published online 22 February 2012

    Obtaining a sequence-based signal at a resolution of single nucleotide during the passage of a DNA strand through nanopores remains a challenging problem. Here, we demonstrate by molecular dynamics simulations that the single-base resolution detection can be realized by pulling a single-stranded DNA through graphene nanopores with diameters down to ∼1 nm. By simply monitoring and analyzing the peak values of the pulling force profile, each nucleotide in the DNA strand can be identified and characterized, except for cytosine and thymine which remain indistinguishable. This intriguing character through narrow nanopores should help realize the low-cost and time-efficient DNA sequencing.

  • PEI Yong, et al. Interlocked Catenane-Like Structure Predicted in Au-24(SR)(20): Implication to Structural Evolution of Thiolated Gold Clusters from Homoleptic Gold(I) Thiolates to Core-Stacked Nanoparticles. J. Am. Chem. Soc.2012, 134, 3015-3024.

    Interlocked Catenane-Like Structure Predicted in Au-24(SR)(20): Implication to Structural Evolution of Thiolated Gold Clusters from Homoleptic Gold(I) Thiolates to Core-Stacked Nanoparticles

    Pei Y, Pal R, Liu C, Gao Y, Zhang Z, Zeng XC.

    Department of Chemistry, Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education, Xiangtan University, Hunan Province 411105, China. ypnku78@gmail.com

    Abstract
    Atomic structure of a recently synthesized ligand-covered cluster Au(24)(SR)(20) [J. Phys. Chem. Lett., 2010, 1, 1003] is resolved based on the developed classical force-field based divide-and-protect approach. The computed UV-vis absorption spectrum and powder X-ray diffraction (XRD) curve for the lowest-energy isomer are in good agreement with experimental measurements. Unique catenane-like staple motifs are predicted for the first time in core-stacked thiolate-group (RS-) covered gold nanoparticles (RS-AuNPs), suggesting the onset of structural transformation in RS-AuNPs at relatively low Au/SR ratio. Since the lowest-energy structure of Au(24)(SR)(20) entails interlocked Au(5)(SR)(4) and Au(7)(SR)(6) oligomers, it supports a recently proposed growth model of RS-AuNPs [J. Phys. Chem. Lett., 2011, 2, 990], that is, Au(n)(SR)(n-1) oligomers are formed during the initial growth of RS-AuNPs. By comparing the Au-core structure of Au(24)(SR)(20) with other structurally resolved RS-AuNPs, we conclude that the tetrahedral Au(4) motif is a prevalent structural unit for small-sized RS-AuNPs with relatively low Au/SR ratio. The structural prediction of Au(24)(SR)(20) offers additional insights into the structural evolution of thiolated gold clusters from homoleptic gold(I) thiolate to core-stacked RS-AuNPs. Specifically, with the increase of interfacial bond length of Au(core)-S in RS-AuNPs, increasingly larger "metallic" Au-core is formed, which results in smaller HOMO-LUMO (or optical) gap. Calculations of electronic structures and UV-vis absorption spectra of Au(24)(SR)(20) and larger RS-AuNPs (up to ~2 nm in size) show that the ligand layer can strongly affect optical absorption behavior of RS-AuNPs.

  • TANG Chun, KOU Liangzhi, and CHEN Changfeng.Tunable band gap and magnetism in C-2x-(BN)(y) sheets and ribbons. Chemical Physics Letters 2012, 523, 98-103.

    Tunable band gap and magnetism in C-2x-(BN)(y) sheets and ribbons

    Chun Tang,a, Liangzhi Kou,a,b, Changfeng Chen,a
    a Department of Physics and High Pressure Science and Engineering Center, University of Nevada, Las Vegas, NV 89154, USA
    b Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

    Abstract
    We predict using first-principles calculations that recently synthesized C-BN nanostructures exhibit rich magnetic and electronic properties that are sensitive to system dimensionality and chirality. Due to different C-B(N) pz-orbital hybridization at the interface, two-dimensional zigzag C-BN sheets and one-dimensional zigzag nanoribbons show weak and strong magnetism respectively. Moreover, the band gap of the zigzag ribbons shows strong sensitivity to the edge magnetism and the BN concentration. For armchair systems, the band gap of the C-BN sheets and ribbons exhibits distinct variation trends with the changing BN concentration, correlating with the width of the adjacent graphene nanoribbon.

    Highlights
    ► 2-D zigzag C-BN show distinct magnetism from 1-D ribbons due to orbit hybridization. ► They also show different band-gap variation due to the distinct magnetic properties. ► The band gaps of armchair C-BN sheets and ribbons show distinct scaling rules.

  • TAI Guo'an, et al. Nonlithographic Fabrication of Crystalline Silicon Nanodots on Graphene. J. Phys. Chem. C, 2012, 116 (1), 532–537.

    Nonlithographic Fabrication of Crystalline Silicon Nanodots on Graphene

    Guo’an Tai†‡, Kai Wang†, Zhenhua Sun†, Jun Yin‡, Sheung Mei Ng†, Jianxin Zhou‡, Feng Yan†, Chi Wah Leung†, Kin Hung Wong†, Wanlin Guo*‡, and Shu Ping Lau*†

    † Department of Applied Physics and Materials Research Centre, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR, People's Republic of China
    ‡ Key Laboratory for Intelligent Nano Materials and Devices of the Ministry of Education and the State Key Laboratory of Mechanics and Control of Mechanical Structures, Institute of Nanoscience, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, People's Republic of China

    J. Phys. Chem. C, 2012, 116 (1), pp 532–537
    DOI: 10.1021/jp210713q
    Publication Date (Web): December 7, 2011

    We report a nonlithographic fabrication method to grow uniform and large-scale crystalline silicon (Si) nanodot (c-SiNDs) arrays on single-layer graphene by an ultrathin anodic porous alumina template and Ni-induced Si crystallization technique. The lateral height of the template can be as thin as 160 nm and the crystallization of Si can be achieved at a low temperature of 400 °C. The effects of c-SiNDs on graphene were studied by Raman spectroscopy. Furthermore, the c-SiNDs/graphene based field effect transistors were demonstrated.

  • ZHANG Ziyue, GUO Wanlin. Strain-Modulated Half-Metallic Properties of Carbon-Doped Silicon Nanowires with Single Surface Dangling Bonds. J. Phys. Chem. C, 2012, 116 (1), pp 893–900.

    Strain-Modulated Half-Metallic Properties of Carbon-Doped Silicon Nanowires with Single Surface Dangling Bonds

    Z.-Y. Zhang and W. Guo*

    Institute of Nano Science, State Key Laboratory of Mechanics and Control for Mechanical Structures, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

    J. Phys. Chem. C, 2012, 116 (1), pp 893–900
    DOI: 10.1021/jp209110z
    Publication Date (Web): December 12, 2011

    Abstract
    The electronic and magnetic properties of hydrogen-passivated silicon nanowires (SiNWs) doped with an interstitial carbon atom are investigated by spin polarized first-principles calculations. It is found that the doped nanowire can have a novel ferromagnetic ground state when a surface dangling bond is created by removing a terminated H atom. In particular, when interstitial carbon is inserted at the core hollow sites, the nanowires with a dangling bond can become half-metallic with 100% spin polarization, independent of wire size and the doped concentration of C atoms. It is interesting that the half-metallicity and ferromagnetic states can be enhanced when the nanowires are axially tensioned but can be quenched when compressed. This magnetic modulation is derived from the interplay between the localization of the defect states and pairwise π–π interaction among the unsaturated surface Si dangling bond states, carbon atom, and its neighboring Si atoms. Our results highlight a new physical coupling between the doped states and surface dangling bonds in silicon nanowires and open a new opportunity for the development of nanoscale spintronics.

  • LU Peng, ZHANG Zhuhua, C.H. Woo, GUO Wanlin. Nonlinear Linear Transition of Magnetoelectric Effect in Magnetic Graphene Nanoflakes on Substrates. J. Phys. Chem. C 2012, 116, 626–631.

    NonlinearLinear Transition of Magnetoelectric Effect in Magnetic Graphene Nanoflakes on Substrates

    Peng Lu,† Zhuhua Zhang,*,† C. H. Woo,‡ and Wanlin Guo*,†

    †Institute of Nano Science and Key Laboratory of Intelligent Nano Materials and Devices of Ministry of Education, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
    ‡Department of Electronic and Information Engineering, The Hong Kong Polytechnic University, Hong Kong SAR, China

    J. Phys. Chem. C, 2012, 116 (1), pp 626–631
    DOI: 10.1021/jp205841z
    Publication Date (Web): November 14, 2011

    Abstract
    Linear magnetoelectric (ME) effect provides an ideal way to control magnetism by an external electric field and has long been pursued in spintronics. However, the essential conditions for linear ME effects are still not well understood, especially for the newly emerged metal-free ME systems. Here, using density functional theory calculations, we reveal a novel nonlinear–linear transition of the ME effect in graphene nanoflakes (GNFs) placed on substrates with different chemical activities. We show that the ME effect is nonlinear in a magnetic GNF on graphene substrate. Interestingly, the ME effect in the same GNF becomes highly linear with markedly increased ME coefficient when an h-BN sheet is inserted between the GNF and graphene layer. We reveal that the weak electronic hybridization between the GNFs and substrate is the essential mechanism for the linear ME behavior in the graphene-based magnets. The tunable nonlinear–linear transition in ME coupling opens up new opportunities to fabricate and manipulate high-quality ME devices.