Our Publications

  • ZUO Guangchao, SHEN Rong, GUO Wanlin. Self-Adjusted Sustaining Oscillation of Confined Water Chain in Carbon Nanotubes. Nano Letters, 2011, 11, 5297–5300.

    Self-Adjusted Sustaining Oscillation of Confined Water Chain in Carbon Nanotubes

    Guangchao Zuo, 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

    Nano Lett., 2011, 11 (12), pp 5297–5300
    DOI: 10.1021/nl2027537
    Publication Date (Web): November 4, 2011

    Abstract

    We show by molecular dynamics and first principle calculations that a water chain confined in carbon nanotubes can self-adjust into regular oscillation with remarkably lower entropy from random thermal motion with higher entropy at room temperature. The turning between the two phases is triggered by the water orientation fluttering into or from the energy optimum configuration of the chain. The findings are expected to be helpful in creation of self-sustaining nanoelectromechanical systems driven by ambient energy.

    Keywords: Self-adjusted; self-sustained; water molecules; carbon nanotube; dipole autocorrelation; molecular dynamics simulation

    Link to ACS

  • ZHAO Junhua, GUO Wanlin, ZHANG Zhiliang, Rabczuk T. Size-dependent elastic properties of crystalline polymers via a molecular mechanics model. Appl. Phys. Lett. 2011, 99, 241902.

    Size-dependent elastic properties of crystalline polymers via a molecular mechanics model

    Junhua Zhao1,2, Wanlin Guo3, Zhiliang Zhang2, and Timon Rabczuk1

    1Institute of Structural Mechanics, Bauhaus-University Weimar, 99423 Weimar, Germany
    2NTNU Nanomechancial Lab, Department of Structural Engineering, Norwegian University of Science and Technology, 7491 Trondheim, Norway
    3Institute of Nanoscience, Nanjing University of Aeronautics and Astronautics, 210016 Nanjing, People’s Republic of China

    Appl. Phys. Lett. 99, 241902 (2011); http://dx.doi.org/10.1063/1.3668110 (4 pages)
    Received 31 August 2011; accepted 18 November 2011; published online 12 December 2011

    An analytical molecular mechanics model is developed to obtain the size-dependent elastic properties of crystalline polyethylene. An effective “stick-spiral” model is adopted in the polymer chain. Explicit equations are derived from the Lennard-Jones potential function for the van der Waals force between any two polymer chains. By using the derived formulas, the nine size-dependent elastic constants are investigated systematically. The present analytical results are in reasonable agreement with those from present united-atom molecular dynamics simulations. The established analytical model provides an efficient route for mechanical characterization of crystalline polymers and related materials toward nanoelectromechanical applications.

    Keywords
    elastic constants, Lennard-Jones potential, molecular dynamics method, polymer structure, polymers, van der Waals forces

  • FU Xuewen, LIAO Zhimin, ZHOU Jianxin, ZHOU Yangbo, WU Hanchun et al. Strain dependent resistance in chemical vapor deposition grown graphene. Appl. Phys. Lett. 2011, 99, 213107.

    Strain dependent resistance in chemical vapor deposition grown graphene

    Xue-Wen Fu1, Zhi-Min Liao1, Jian-Xin Zhou2, Yang-Bo Zhou1, Han-Chun Wu3, Rui Zhang1, Guangyin Jing4, Jun Xu1, Xiaosong Wu1, Wanlin Guo2, and Dapeng Yu1

    1. State Key Laboratory for Mesoscopic Physics, Department of Physics, Peking University, Beijing 100871, People’s Republic of China
    2. Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, People’s Republic of China
    3. School of Physics and CRANN, Trinity College, Dublin 2, Ireland
    4. Physics Department, Northwest University, Xi’an 710069, China

    Appl. Phys. Lett. 99, 213107 (2011); http://dx.doi.org/10.1063/1.3663969 (3 pages)
    Received 20 September 2011; accepted 3 November 2011; published online 22 November 2011

    The strain dependence of conductance of monolayer graphene has been studied experimentally here. The results illustrate the notable transitions: the slight increase, the dramatic decrease, and the sudden dropping of the conductance by gradually increasing the uniaxial strain. The graphene conductance behaves reversibly by tuning of the elastic tensile strain up to 4.5%, while it fails to recover after the plastic deformation at 5%. The change in conductance due to strain is surprisingly high, which indicates the potential applications in electromechanical devices.

    Keywords
    chemical vapour deposition, electric admittance, graphene, plastic deformation

  • KOU Liangzhi, TANG Chun, CHEN Changfeng, GUO Wanlin. Hybrid W-shaped graphene nanoribbons: Distinct electronic and transport properties. J. Appl. Phys. 2011, 110, 124312.

    Hybrid W-shaped graphene nanoribbons: Distinct electronic and transport properties

    Liangzhi Kou1,2, Chun Tang2, Changfeng Chen2, and Wanlin Guo1

    1State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
    2Department of Physics and High Pressure Science and Engineering Center, University of Nevada, Las Vegas, Nevada 89154, USA

    J. Appl. Phys. 110, 124312 (2011); http://dx.doi.org/10.1063/1.3669496 (4 pages)
    Received 26 August 2011; accepted 11 November 2011; published online 21 December 2011

    We present a first-principles study of electronic and transport properties of a novel W-shaped graphene nanoribbon (W-GNR) structure that comprises hybrid GNR segments with alternating armchair and zigzag edges. Such hybrid W-GNRs exhibit semiconducting characteristics with distinct properties that stem from a unique combination of the features of the armchair and zigzag constituents. When the ribbon is narrow, the interplay of the two GNR components leads to much reduced variation in band gap. The spin-polarized edge states of the zigzag GNR engender an electric-field-driven half-metallicity. Moreover, spin-dependent density of states at the band edge produces asymmetric spin transmission coefficients, yielding unequal spin currents under a large bias voltage. These findings suggest that these new W-GNRs hold great promise for applications in nanoscale spintronic devices.

    Keywords
    ab initio calculations, electronic density of states, energy gap, graphene, nanostructured materials, semiconductor materials, spin polarised transport

  • WU Wenzhi, LU Peng, ZHANG Zhuhua, GUO Wanlin. Electronic and Magnetic Properties and Structural Stability of BeO Sheet and Nanoribbons. ACS Appl. Mater. Interfaces, 2011, 3 (12), 4787–4795.

    Electronic and Magnetic Properties and Structural Stability of BeO Sheet and Nanoribbons

    Wenzhi Wu, Peng Lu, Zhuhua Zhang*, and Wanlin Guo*

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

    ACS Appl. Mater. Interfaces, 2011, 3 (12), pp 4787–4795
    DOI: 10.1021/am201271j
    Publication Date (Web): October 31, 2011

    The novel electronic and magnetic properties of BeO nanoribbons (BeO NRs) as well as their stability are investigated through extensive density functional theory calculations. Different from semiconducting graphene nanoribbons and insulating BN ribbons, all zigzag edged BeO NRs are revealed to display ferromagnetic and metallic natures independent of the ribbon width and edge passivation. The polarized electron spins in H-passivated zigzag BeO NRs are from the unpaired electrons around the weakly formed Be–H bonds, while those of bare zigzag BeO NRs are due to the 2p states of edge O atoms. In sharp contrast, all armchair BeO NRs are nonmagnetic insulators regardless of the edge passivation. In particular, all bare armchair BeO NRs have a nearly constant band gap due to a peculiar edge localization effect. Interestingly, the band gaps of all armchair BeO NRs can be markedly reduced by an applied transverse electric field and even completely closed at a critical field. The critical electric field required for gap closing decreases with increasing ribbon width, thus the results have practical importance. Further stability analysis shows that bare BeO NRs are more stable than H-passivated BeO NRs of similar ribbon widths and bare armchair BeO NRs are energetically the most favorable among all the nanoribbons.

    Keywords: BeO; sheet; nanoribbons; electronic structure; magnetism; stability

  • ZHANG Zhuhua, ZENG Xiaocheng, GUO Wanlin. Fluorinating Hexagonal Boron Nitride/Graphene Multilayers into Hybrid Diamondlike Nanofilms with Tunable Energy Gap. J. Phys. Chem. C, 2011, 115 (44), 21678–21684.

    Fluorinating Hexagonal Boron Nitride/Graphene Multilayers into Hybrid Diamondlike Nanofilms with Tunable Energy Gap

    Zhuhua Zhang*†‡, Xiao Cheng Zeng*‡, and Wanlin Guo*†

    Key Laboratory of Intelligent Nano Materials and Devices (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

    J. Phys. Chem. C, 2011, 115 (44), pp 21678–21684
    DOI: 10.1021/jp207175u
    Publication Date (Web): October 3, 2011

    Using ab initio calculations and quantum molecular dynamics simulations, we demonstrate that a few layers of graphene sandwiched between hexagonal boron nitride (h-BN) layers can undergo spontaneous transformation into hybrid cubic BN-diamond (c-BN/Dmd) nanofilms upon fluorination. This spontaneous transformation stems from the remarkably higher stability of thin c-BN/Dmd nanofilm with sp3 hybridization over the precursor multilayer with sp2 hybridization and is promoted by strong selectivity of fluorination with the boron atoms of the coating BN layers. Upon increasing the total number of multilayers, however, the transformation is no longer spontaneous due to emergence of the energy barrier. Nevertheless, adding more h-BN layers to the hybrid nanofilm can assist the transformation into c-BN/Dmd nanofilms upon fluorination. The electronic properties of the c-BN/Dmd nanofilms can be tuned by controlling the ratio of the BN component and film thickness, which can yield narrow-gap semiconductors for novel electronic applications. In addition, the energy gap in the nanofilms can be modulated linearly by applying external electric fields.

  • GUO Yufeng, GUO Wanlin. Favorable Zigzag Configuration at Etched Graphene Edges. J. Phys. Chem. C, 2011, 115 (42), 20546–20549.

    Favorable Zigzag Configuration at Etched Graphene Edges

    Yufeng Guo* and Wanlin Guo

    Institute of Nanoscience and Key Laboratory for Intelligent Nano Materials and Devices of Ministry of Education, Nanjing University of Aeronautics and Astronautics, Nanjing, 210016, P. R. China

    J. Phys. Chem. C, 2011, 115 (42), pp 20546–20549
    DOI: 10.1021/jp205671r
    Publication Date (Web): September 20, 2011

    To control and improve edge quality during etching process is a desired goal for fabricating graphene nanostructure. The preferred edge atomic configurations and shapes when etching pure armchair and zigzag graphene edges have been extensively studied by first-principles calculations. In the beginning stage of etching, it is energetically favorable to remove a specific four-atom carbon segment from flat armchair edge and a three-atom segment from zigzag edge. The subsequent etching on armchair edge shows strong tendency to start from the etched site because of higher chemical reactivity, and a triangle pit with an angle of 120° and zigzag boundary configuration is expected to form on armchair edge. In contrast, the initial etched site on zigzag edge exhibits similar chemical reactivity to other unetched edge atoms. Nevertheless, all created configurations at the etched boundaries are zigzag-edged despite the fact that armchair or zigzag edge could be etched into several shapes. Our results promise that the zigzag chirality be dominating on the edges of graphene nanostructure after patterned under proper etching condition.

  • ZHANG Zhuhua, GUO Wanlin. Controlling the Functionalizations of Hexagonal Boron Nitride Structures by Carrier Doping. J. Phys. Chem. Lett., 2011, 2 (17), 2168–2173.

    J. Phys. Chem. Lett., 2011, 2 (17), pp 2168–2173
    DOI: 10.1021/jz2009506
    Publication Date (Web): August 15, 2011

    Controlling the Functionalizations of Hexagonal Boron Nitride Structures by Carrier Doping

    Zhuhua Zhang and Wanlin Guo

    Key Laboratory of Intelligent Nano Materials and Devices of Ministry of Education and Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

    Using density functional theory calcualtions, we reveal a novel control on the functionalizations of hexagonal boron nitride (h-BN) structures by carrier doping. When the system is electron-doped, adatoms (e.g., H or F atoms) will exclusively bond with B atoms, resulting in possible magnetization of the system, whereas hole doping favors the adatoms to form insulating orthodimer structures on the BN structures. This behavior is caused by a peculiar chemical bond formed between the N and adatoms, whose strength significantly depends on the carrier type and level. Moreover, the adatoms’ diffusion on these BN structures can be steered along a designable path by the carrier doping, still attributted to the carrier-dependent bond stability. This carrier control of functionalizations is robust via adatom concentration and the physical conditions of BN structures, thus offering an easy route to controllably anchor the properties of functionalized BN systems for desired applications.

    Link to Article
    http://pubs.acs.org/doi/abs/10.1021/jz2009506

  • YIN Jun, ZHOU Jianxin, LI Xuemei, CHEN Yaqing, TAI Guo'an, GUO Wanlin. Enhanced gas-flow-induced voltage in graphene. Appl. Phys. Lett., 2011, 99, 073103.

    Appl. Phys. Lett. 99, 073103 (2011)

    doi:10.1063/1.3624590 (3 pages)

    Enhanced gas-flow-induced voltage in graphene

    Jun Yin, Jianxin Zhou, Xuemei Li, Yaqing Chen, Guoan Tai, and 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

    Received 4 July 2011; accepted 22 July 2011; published online 15 August 2011

    Abstract
    We find experimentally that gas-flow-induced voltage in monolayer graphene is more than twenty times of that in bulk graphite. Examination over samples with sheet resistances ranging from 307 to 1600 Ω/sq shows that the induced voltage increases with the electric resistance and can be further improved by controlling the quality and doping level of graphene. The induced voltage is nearly independent of the substrate materials and can be well explained by the interplay of Bernoulli’s principle and the carrier density dependent Seebeck coefficient. The results demonstrate that graphene has great potential for flow sensors and energy conversion devices.

    Link to Article
    http://link.aip.org/link/doi/10.1063/1.3624590

  • ZHANG Zhuhua, ZENG Xiaocheng, GUO Wanlin. Fluorinating Hexagonal Boron Nitride into Diamond-Like Nanofilms with Tunable Band Gap and Ferromagnetism. J. Am. Chem. Soc., Article ASAP. DOI: 10.1021/ja206703x

    J. Am. Chem. Soc., Article ASAP
    DOI: 10.1021/ja206703x
    Publication Date (Web): August 11, 2011

    Fluorinating Hexagonal Boron Nitride into Diamond-Like Nanofilms with Tunable Band Gap and Ferromagnetism

    Zhuhua Zhang,1, Xiao Cheng Zeng,2, and Wanlin Guo,1
    1. 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
    2. Department of Chemistry and Center for Materials & Nanoscience, University of Nebraska—Lincoln, Lincoln, Nebraska 68588, United States

    Abstract
    Cubic boron nitride (c-BN) possesses a number of extreme properties rivaling or surpassing those of diamond. Especially, owing to the high chemical stability, c-BN is desired for fabricating electronic devices that can stand up to harsh environments. However, realization of c-BN-based functional devices is still a challenging task due largely to the subtlety in the preparation of high-quality c-BN films with uniform thickness and controllable properties. Here, we present a simple synthetic strategy by surface fluorination of few-layered hexagonal boron nitride (h-BN) sheets to produce thermodynamically favorable F-terminated c-BN nanofilms with an embedded N–N bond layer and strong inbuilt electric polarization. Due to these specific features, the fluorinated c-BN nanofilms have controllable band gap by thickness or inbuilt and applied electric fields. Especially, the produced nanofilms can be tuned into substantial ferromagnetism through electron doping within a reasonable level. The electron-doping-induced deformation ratio of the c-BN nanofilms is found to be 1 order of magnitude higher than those of carbon nanotubes and graphene. At sufficient high doping levels, the nanofilm can be cleaved peculiarly along the N–N bond layer into diamond-like BN films. As the proposed synthesis strategy of the fluorinated c-BN nanofilms is well within the reach of current technologies, our results represent an extremely cost-effective approach for producing high-quality c-BN nanofilms with tunable electronic, magnetic, and electromechanical properties for versatile applications.

    Link to Article
    http://pubs.acs.org/doi/abs/10.1021/ja206703x

  • ZHANG Shaoqin, GUO Wanlin, LI He, DENG Ying. Experimental investigation of three-dimensional mixed-mode fracture of a titanium alloy at room and elevated temperatures. Sci China Tech Sci, 2011, 54: 2760-2767.

    Experimental investigation of three-dimensional mixed-mode fracture of a titanium alloy at room and elevated temperatures

    ZHANG ShaoQin1,2*, GUO WanLin1*, LI He2, DENG Ying2

    1. State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China;
    2. School of Civil Engineering and Architecture, Nanchang HangKong University, Nanchang 330063, China

    SCIENCE CHINA Technological Sciences 2011, 54: 2760-2767
    Received 2011-01-21 Revised 2011-05-03 Online: 2011-07-14
    DOI: 10.1007/s11431-011-4498-6

    Abstract:
    Damage tolerance of titanium alloy structures is very important for the safety of modern aircraft under complex loading and environmental conditions. However, there is no available systematic knowledge about the effect of alloy thickness under mixed-mode loading at elevated temperatures. In the present study, a newly developed fracture experimental technique based on high-temperature moiré interferometry was employed to investigate experimentally I-II mixed-mode fracture in titanium alloy TC11 of various thicknesses at room and elevated temperatures. Compact shear specimens with thickness ranging from 1.8 to 7.1 mm were tested. The effects of temperature, thickness, and loading angle on the load capacity and crack initiation angle were investigated systematically. The TC11 alloy was shown to possess varied fracture performance at elevated temperature, and an opposite thickness effect at room temperature. Increasing temperature would enhance the fracture load capacity of thick specimens but reduce the fracture load capacity of thin specimens. Crack initiation angles under I-II mixed-mode loading showed the thickness-temperature coupling effects. These complex effects call for new development in three-dimensional mixed-mode fracture theory and technologies for damage tolerance assessment.

    Keywords: mixed-mode fracture titanium alloy fracture toughness crack initiation angle thickness effect high-temperature moiré interferometry

  • XIANG Mujing, YU Zhenbo, GUO Wanlin. Characterization of three-dimensional crack border fields in creeping solids. International Journal of Solids and Structures, Article in Press.

    Characterization of three-dimensional crack border fields in creeping solids

    Mujing Xiang,1, Zhenbo Yu,1, and Wanlin Guo,1

    1. State Key Laboratory of Strength and Vibration for Mechanical Structures, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

    Received 29 December 2010; revised 15 May 2011. Available online 25 May 2011.

    Abstract
    Creep fracture of solids at high temperature is vital to applications of many advanced materials, but most of the previous works are performed within the frame of two-dimensional theory. By using the out-of-plane stress constraint factor Tz, here we derive out three-dimensional asymptotic fields near the border of mode-I through-thickness cracks in power law creeping solids. It is found that the asymptotic fields near the crack border are dominated by both Tz and C(t) integral. Detailed finite element analyses are carefully performed for single-edge cracked specimens and centre-cracked tension specimens to investigate the dominance of the asymptotic solution for the crack border fields. It is shown that the C(t)-Tz description based on the obtained three-dimensional asymptotic solution can provide efficient prediction for the tensile stress ahead of the crack front under small scale creep condition. Under extensive creep conditions, a third parameter Q* should be introduced to take into account of the loss in the in-plane constraint caused by in-plane geometries and loading configuration at extensive creeping, and a three-parameter C(t)-Tz-Q* description is proposed and proven to be efficient to predict the tensile stress on the ligament ahead of the crack for both specimens. Therefore, the two-parameter C(t)-Tz and three-parameter C(t)-Tz-Q* descriptions can provide advanced theoretical basis for small and extensive creeping fracture assessments, respectively.
    Keywords: Three-dimensional constraints; Creeping crack border fields; Two-parameter description C(t)-Tz; Three-parameter description C(t)-Tz-Q*.

    doi:10.1016/j.ijsolstr.2011.05.013

  • ZHU Chunzhang, GUO Wanlin. C-directional compression of nano-graphite: a comparison between effects of uniform and non-uniform pressure. Physica B: Condensed Matter, 2011, 406(14), 2763-2766.

    Physica B: Condensed Matter
    Volume 406, Issue 14, 15 July 2011, Pages 2763-2766

    doi:10.1016/j.physb.2011.04.023

    C-directional compression of nano-graphite: a comparison between effects of uniform and non-uniform pressure

    Chunzhang Zhu,1, Wanlin Guo,2

    1. School of Materials Science and Engineering, Nanjing Institute of Technology, Nanjing 211167, People's Republic of China
    2. Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, People's Republic of China

    Received 29 November 2010; revised 28 February 2011; Accepted 11 April 2011. Available online 15 April 2011.

    Abstract
    The mechanism of phase transition and evolution in graphite under uniform compression and spherical nanoindentation along the c-direction is investigated through systematical molecular dynamics simulations. Under both the loading conditions, the soft graphite phase can sustain pressure up to 16–20 GPa, beyond which it transforms into a new phase characterized by a much higher stiffness. More and more interlayer bonds will be created in the new hard phase with the increase of the pressure until an unstable state is reached. The critical pressure to produce the quenchable hard phase with a permanent sp3 bonding remaining after unloading is shown to be as high as ∼880 GPa under uniform compression, as opposed to only ∼75 GPa under nanoindentation. Therefore, application of non-uniform pressure is significantly more helpful for creating diamond-like sp3 structures in graphite by cold-compressive technique.

    Keywords: Graphite; Molecular dynamics; Phase transition; Hard phase

  • TAI Guo'an, MIAO Chunyang, WANG Yubo, BAI Yunrui, ZHANG Haiqian, GUO Wanlin. Solvothermal synthesis and thermoelectric properties of indium telluride nanostring-cluster hierarchical structures. Nanoscale Research Letters 2011, 6:329.

    Solvothermal synthesis and thermoelectric properties of indium telluride nanostring-cluster hierarchical structures

    Guo'an Tai,1, Chunyang Miao,1, Yubo Wang,1, Yunrui Bai,1, Haiqian Zhang,2 and Wanlin Guo,1

    1 Institute of Nanoscience, Nanjing University of Aeronautics and Astronautics, 29 Yudao Street, Nanjing 210016, People's Republic of China
    2 College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, 29 Yudao Street, Nanjing 210016, People's Republic of China

    Nanoscale Research Letters 2011, 6:329 doi:10.1186/1556-276X-6-329
    Received: 7 October 2010
    Accepted: 13 April 2011
    Published: 13 April 2011

    Abstract
    A simple solvothermal approach has been developed to successfully synthesize n-type α-In2Te3 thermoelectric nanomaterials. The nanostring-cluster hierarchical structures were prepared using In(NO3)3 and Na2TeO3 as the reactants in a mixed solvent of ethylenediamine and ethylene glycol at 200°C for 24 h. A diffusion-limited reaction mechanism was proposed to explain the formation of the hierarchical structures. The Seebeck coefficient of the bulk pellet pressed by the obtained samples exhibits 43% enhancement over that of the corresponding thin film at room temperature. The electrical conductivity of the bulk pellet is one to four orders of magnitude higher than that of the corresponding thin film or p-type bulk sample. The synthetic route can be applied to obtain other low-dimensional semiconducting telluride nanostructures.

  • JIANG Yan, SHE Chongmin, YU Peishi, GUO Wanlin. Three-dimensional stress concentrations at circular pin holes in clearance-fit lugs. Fatigue & Fracture of Engineering Materials & Structures 2011, 34(8), 573–580.

    Three-dimensional stress concentrations at circular pin holes in clearance-fit lugs

    Y. JIANG, C. SHE, P. YU, W. GUO

    Fatigue & Fracture of Engineering Materials & Structures
    Volume 34, Issue 8, pages 573–580, August 2011
    DOI: 10.1111/j.1460-2695.2011.01548.x
    Article first published online: 1 APR 2011

    Keywords:
    bonding clearance;circular hole;stress concentration;three-dimensional finite element method

    ABSTRACT
    The influences of thickness and bonding clearance on stress concentration factors (SCFs) at circular holes in pin-loaded straight lugs are systematically investigated using the finite element method. The three-dimensional effect on stress concentration at pin hole is strong when the thickness B of lug is higher than the radius R of pin hole. The maximum tensional SCF Kmax normalized by its corresponding plane stress solution Kp–σ increases with increasing B/R when B/R is higher than 2 for all of r/R (the radius of pin to that of lug), and also increases with decreasing r/R for a given B/R. It is also found that the plane stress SCF Kp–σ nearly remains a constant when r/R < 0.98, but is strongly sensitive to r/R and increases by 30% with r/R changing from 0.98 to 1. On the other hand, the friction coefficient, Young's modulus and the load level have also influences on stress concentrations, which should not be neglected in design of structures. An empirical formula of the maximum SCF is obtained for convenience of engineering applications.

  • JIANG Lai, GUO Wanlin. A molecular mechanics study on size-dependent elastic properties of single-walled boron nitride nanotubes. J. Mech. Phys. Solids, 2011, 59(6), 1204-1213.

    A molecular mechanics study on size-dependent elastic properties of single-walled boron nitride nanotubes

    Lai Jiang,1, and Wanlin Guo,1

    1. Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, PR China

    Received 16 January 2010; revised 28 February 2011; accepted 13 March 2011. Available online 17 March 2011.

    Abstract
    We present an analytical study for the elastic properties of single-walled boron nitride nanotubes via a molecular mechanics model. Closed-form expressions for Young's modulus, Poisson's ratio and surface shear modulus are derived as functions of the nanotube diameter. The results are helix angle sensitive and comparable to those from ab initio calculations. This work is a first effort to establish analytical model of molecular mechanics for composite nanotubes and reveals the dissimilarities between size-dependent elastic properties of carbon and boron nitride nanotubes.

    Keywords: Boron nitride nanotubes; Composite nanotubes; Elastic properties; Molecular mechanics; Multiscale

    doi:10.1016/j.jmps.2011.03.008

  • LU Peng, ZHANG Zhuhua, GUO Wanlin.Electronic Structures of BC2N Nanoribbons. J. Phys. Chem. C, 2011, 115(9), 3572–3577.

    Electronic Structures of BC2N Nanoribbons

    J. Phys. Chem. C, 2011, 115 (9), pp 3572–3577
    DOI: 10.1021/jp110217t

    Publication Date (Web): February 10, 2011

    Peng Lu, Zhuhua Zhang, and Wanlin Guo

    Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, People’s Republic of China

    We reveal a rich variety of electronic and magnetic properties of H-terminated BC2N nanoribbons (BC2NNRs) by using extensive first-principles calculations. Zigzag edged BC2NNRs (z-BC2NNRs) can be semiconducting or metallic depending on the alignment of edge atoms. In particular, magnetic and even half-metallic behaviors can appear in some edged z-BC2NNRs when the ribbon width is over a critical value. Armchair-edged BC2NNRs also can be semiconducting or metallic but determined by the proportion of carbon, nitrogen, and boron atoms in the ribbons. The band gaps of all semiconducting BC2NNRs can be explained by a universal mechanism that is due to the charge polarization between the opposite edges, which is impaired with increasing ribbon width.

    Link to Article

  • TANG Chun, GUO Wanlin, CHEN Changfeng. Structural and mechanical properties of partially unzipped carbon nanotubes. Phys. Rev. B, 2011, 83, 075410.

    Structural and mechanical properties of partially unzipped carbon nanotubes

    Phys. Rev. B 83, 075410 (2011) [6 pages]

    Received 4 July 2010; revised 20 November 2010; published 8 February 2011

    Chun Tang,1,2, Wanlin Guo,2, and Changfeng Chen,1
    1. Department of Physics and High Pressure Science and Engineering Center, University of Nevada, Las Vegas, Nevada 89154, USA
    2. Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

    We report molecular dynamics simulations of structural and mechanical properties of partially unzipped carbon nanotubes. Our results show that in the absence of edge passivation, partially unzipped carbon nanotubes are unstable with rising temperature depending on the geometry of cutting. When the length-to-width ratio of the graphene segment is not sufficiently large, the dangling bonds at the cutting front tend to reconnect to each other and form back to carbon nanotube structure; otherwise the structures roll up at the graphene end due to the competition of bending stiffness between longitudinal direction and transverse direction. When the graphene edges are hydrogen saturated, the self-healing behavior is suppressed. Tensile tests show that partially unzipped carbon nanotubes exhibit brittle fracture behavior, with a Young’s modulus around 700 GPa, which is comparable to that of carbon nanotubes and graphene.

    URL: http://link.aps.org/doi/10.1103/PhysRevB.83.075410
    DOI: 10.1103/PhysRevB.83.075410

  • LIU Xinsheng, LV Bo, GUO Wanlin. The size distribution of protein families within different types of folds. Biochem. Biophys. Res. Commun., 2011, 406, 218-222.

    The size distribution of protein families within different types of folds

    Biochemical and Biophysical Research Communications
    Volume 406, Issue 2, 11 March 2011, Pages 218-222

    Xinsheng Liu,1, Bo Lv,2, and Wanlin Guo,1

    1. Institute of Nanoscience, and Key Laboratory for Intelligent Nano Materials and Devices of Ministry of Education, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
    2. College of Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

    Received 13 January 2011. Available online 6 February 2011

    It is well known that the structure is currently available only for a small fraction of known protein sequences. It is urgent to discover the important features of known protein sequences based on present protein structures. Here, we report a study on the size distribution of protein families within different types of folds. The fold of a protein means the global arrangement of its main secondary structures, both in terms of their relative orientations and their topological connections, which specify a certain biochemical and biophysical aspect. We first search protein families in the structural database SCOP against the sequence-based database Pfam, and acquire a pool of corresponding Pfam families whose structures can be deemed as known. This pool of Pfam families is called the sample space for short. Then the size distributions of protein families involving the sample space, the Pfam database and the SCOP database are obtained. The results indicate that the size distributions of protein families under different kinds of folds abide by similar power-law. Specially, the largest families scatter evenly in different kinds of folds. This may help better understand the relationship of protein sequence, structure and function. We also show that the total of proteins with known structures can be considered a random sample from the whole space of protein sequences, which is an essential but unsettled assumption for related predictions, such as, estimating the number of protein folds in nature. Finally we conclude that about 2957 folds are needed to cover the total Pfam families by a simple method.

    Keywords: Size distribution; Protein families; Folds; Power-law

  • FU Qiang, et al. Linear strain-gradient effect on the energy bandgap in bent CdS nanowires. Nano Research, 2011, 4, 308-314.

    Linear strain-gradient effect on the energy bandgap in bent CdS nanowires

    Nano Research (23 December 2010), pp. 1-7.
    doi:10.1007/s12274-010-0085-6

    Qiang Fu, Zi Zhang, Liangzhi Kou, Peicai Wu, Xiaobing Han, Xinli Zhu, Jingyun Gao, Jun Xu, Qing Zhao, Wanlin Guo, Dapeng Yu

    Although possible non-homogeneous strain effects in semiconductors have been investigated for over a half century and the strain-gradient can be over 1% per micrometer in flexible nanostructures, we still lack an understanding of their influence on energy bands. Here we conduct a systematic cathodoluminescence spectroscopy study of the strain-gradient induced exciton energy shift in elastically curved CdS nanowires at low temperature, and find that the red-shift of the exciton energy in the curved nanowires is proportional to the strain-gradient, an index of lattice distortion. Density functional calculations show the same trend of band gap reduction in curved nanostructures and reveal the underlying mechanism. The significant linear strain-gradient effect on the band gap of semiconductors should shed new light on ways to tune optical-electronic properties in nanoelectronics.

    Keywords Strain-gradient effect – CdS nanowire – bending deformation – cathodoluminescence

  • QIU Hu, SHEN Rong, GUO Wanlin. Vibrating Carbon Nanotubes as Water Pumps. Nano Research, 2011, 4(3), 284-289.

    Vibrating carbon nanotubes as water pumps

    NANO RESEARCH
    Volume 4, Number 3, 284-289, DOI: 10.1007/s12274-010-0080-y

    Hu Qiu, Rong Shen and Wanlin Guo

    Nanopumps conducting fluids directionally through nanopores and nanochannels have attracted considerable interest for their potential applications in nanofiltration, water purification, and hydroelectric power generation. Here, we demonstrate by molecular dynamics simulations that an excited vibrating carbon nanotube (CNT) cantilever can act as an efficient and simple nanopump. Water molecules inside the vibrating cantilever are driven by centrifugal forces and can undergo a continuous flow from the fixed to free ends of the CNT. Further extensive simulations show that the pumping function holds good not only for a single-file water chain in a narrow (6,6) CNT, but also for bulk-like water columns inside wider CNTs, and that the water flux increases monotonically with increasing diameter of the nanotube.

    Keywords Nanopump – carbon nanotube – nanofluidics – centrifugal forces – water dynamics

  • JIANG Yan, GUO Wanlin. Convex-concave nanostructure transition on highly oriented pyrolitic graphite surface induced by atomic force microscope tip under bias voltage. Journal of Experimental Nanoscience, 2011, 6, 96.

    Convex-concave nanostructure transition on highly oriented pyrolitic graphite surface induced by atomic force microscope tip under bias voltage

    Journal of Experimental Nanoscience
    Volume 6, Issue 2, 2011, Pages 96 - 101

    Yan Jiang,1, Wanlin Guo,2

    1. School of Material Science and Engineering, Jiangsu University, Zhenjiang, Jiangsu 212013, P.R. China
    2. Institute of Nanoscience, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, P.R. China

    Convex and concave nanoscale dots were formed on a highly oriented pyrolitic graphite surface in air by an atomic force microscope tip under positively applied bias voltage. It was found that the increasing amplitude or duration of the bias voltage over threshold values can change the convex profiles into concave ones. The threshold voltage duration for the profile transition increases sharply with decreasing amplitude of the voltage and a nonlinear relationship between them was obtained. For enough long duration, there exists a threshold voltage amplitude, about 4.1-5 V in this study, for the profile transition as well.

    Keywords: nanostructures; highly oriented pyrolitic graphite; atomic force microscope; bias voltage

    Link to Article

  • KOU Liangzhi, ZHANG Yi, LI Chun, GUO Wanlin, CHEN Changfeng. Local-Strain-Induced Charge Carrier Separation and Electronic Structure Modulation in Zigzag ZnO Nanotubes: Role of Built-In Polarization Electric Field. J. Phys. Chem. C, 2011, 115, 2381.

    Local-Strain-Induced Charge Carrier Separation and Electronic Structure Modulation in Zigzag ZnO Nanotubes: Role of Built-In Polarization Electric Field

    J. Phys. Chem. C, 2011, 115 (5), pp 2381–2385
    DOI: 10.1021/jp108591b

    Publication Date (Web): January 19, 2011

    Liangzhi Kou*†‡, Yi Zhang*†, Chun Li§, Wanlin Guo‡, and Changfeng Chen†
    † Department of Physics and Astronomy and High Pressure, Science and Engineering Center, University of Nevada, Las Vegas, Nevada 89154, United States
    ‡ Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
    § School of Mechanics, Civil Engineering and Architecture, Northwestern Polytechnical University, Xi’an 710072, China

    By use of first-principles calculations, we examine the effects of uniaxial strain and radial deformation on electronic properties of zigzag ZnO nanotubes. Our results show that local strain or deformation can cause significant reduction of the band gap owing to quantum-confined Stark effect induced by the built-in electric polarization. Driven by this polarization field, the charge carriers are separated with hole and electron states localized on the opposite ends of the tube. In sharp contrast, uniform tensile strain tends to widen the band gap while compressive strain and radial deformation have negligible effects on the band gap, although they can produce considerable shifts in edge-state energies. The present results reveal the key role of local strain as an effective tool in tuning the properties of zigzag ZnO nanotubes. Such local-strain-induced electronic structure modulation suggests an effective approach to design and implementation of ZnO nanotubes in nanoscale devices.

    Link to Article

  • KOU Liangzhi, TANG Chun, GUO Wanlin, CHEN Changfeng. Tunable Magnetism in Strained Graphene with Topological Line Defect. ACS Nano, 2011, 5(2), 1012–1017.

    Tunable Magnetism in Strained Graphene with Topological Line Defect

    ACS Nano, 2011, 5 (2), pp 1012–1017
    DOI: 10.1021/nn1024175

    Publication Date (Web): January 13, 2011

    Liangzhi Kou†‡§, Chun Tang†§, Wanlin Guo‡*, and Changfeng Chen†*
    † Department of Physics and High Pressure Science and Engineering Center, University of Nevada, Las Vegas, Nevada 89154, United States
    ‡ Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

    We examine the magnetic properties of two-dimensional graphene with topological line defect using first-principles calculations and predict a weak ferromagnetic ground state with spin-polarized electrons localized along the extended line defect. Our results show that tensile strain along the zigzag direction can greatly enhance local magnetic moments and ferromagnetic stability of the system. In sharp contrast, tensile strain applied along the armchair direction quickly diminishes these magnetic moments. A detailed analysis reveals that this intriguing magnetism modulation by strain stems from the redistribution of spin-polarized electrons induced by local lattice distortion. It suggests a sensitive and effective way to control magnetic properties of graphene which is critical for its applications in nanoscale devices.

    Keywords: graphene; topological line defect; magnetism modulation; strain control

    Link to Article