Our Publications

  • XUE Minmin, QIU Hu, GUO Wanlin. Exceptionally fast water desalination at complete salt rejection by pristine graphyne monolayers. Nanotechnology 2013, 24, 505720.

    Exceptionally fast water desalination at complete salt rejection by pristine graphyne monolayers

    Minmin Xue, Hu Qiu and Wanlin Guo

    Key Laboratory for Intelligent Nano Materials and Devices of the Ministry of Education, State Key Laboratory of Mechanics and Control of Mechanical Structures, and Institute of Nanoscience, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, People's Republic of China
    M Xue and H Qiu contributed equally.

    Issue 50 (20 December 2013)
    Received 5 September 2013, in final form 10 October 2013
    Published 27 November 2013

    Abstract

    Desalination that produces clean freshwater from seawater holds the promise of solving the global water shortage for drinking, agriculture and industry. However, conventional desalination technologies such as reverse osmosis and thermal distillation involve large amounts of energy consumption, and the semipermeable membranes widely used in reverse osmosis face the challenge to provide a high throughput at high salt rejection. Here we find by comprehensive molecular dynamics simulations and first principles modeling that pristine graphyne, one of the graphene-like one-atom-thick carbon allotropes, can achieve 100% rejection of nearly all ions in seawater including Na+, Cl−, Mg2+, K+ and Ca2+, at an exceptionally high water permeability about two orders of magnitude higher than those for commercial state-of-the-art reverse osmosis membranes at a salt rejection of ~98.5%. This complete ion rejection by graphyne, independent of the salt concentration and the operating pressure, is revealed to be originated from the significantly higher energy barriers for ions than for water. This intrinsic specialty of graphyne should provide a new possibility for the efforts to alleviate the global shortage of freshwater and other environmental problems.

    link to this article

  • ZHANG Ziyue, MIAO Chunyang, GUO Wanlin. Nano-solenoid: helicoid carbon-boron nitride hetero-nanotube. Nanoscale. 2013, 5(23):11902-9.

    Nano-solenoid: helicoid carbon-boron nitride hetero-nanotube

    Zhang ZY, Miao C, Guo W.
    Author information
    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. wlguo@nuaa.edu.cn.

    Abstract
    As a fundamental element of a nanoscale passive circuit, a nano-inductor is proposed based on a hetero-nanotube consisting of a spiral carbon strip and a spiral boron nitride strip. It is shown by density functional theory associated with nonequilibrium Green function calculations that the nanotube exhibits attractive transport properties tunable by tube chirality, diameter, component proportion and connection manner between the two strips, with excellent 'OFF' state performance and high current on the order of 10-100 μA. All the hetero-nanotubes show negative differential resistance. The transmission peaks of current are absolutely derived from the helicoid carbon strips or C-BN boundaries, giving rise to a spiral current analogous with an energized nano-solenoid. According to Ampere's Law, the energized nano-solenoid can generate a uniform and tremendous magnetic field of more than 1 tesla, closing to that generated by the main magnet of medical nuclear magnetic resonance. Moreover, the magnitude of magnetic field can be easily modulated by bias voltage, providing great promise for a nano-inductor to realize electromagnetic conversion at the nanoscale.

    Link to article

  • FU Xuewen, GUO Wanlin, YU Dapeng, et al. Modifying optical properties of ZnO nanowires via strain-gradient. Frontiers of Physics 2013, 8(5): 509-515.

    Modifying optical properties of ZnO nanowires via strain-gradient

    Xue-Wen Fu, Qiang Fu, Liang-Zhi Kou, Xin-Li Zhu, Rui Zhu, Jun Xu, Zhi-Min Liao, Qing Zhao, Wan-Lin Guo, Da-Peng Yu

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

    Journal
    Frontiers of Physics
    Volume 8, Issue 5 , pp 509-515

    Cover Date
    2013-10-01
    DOI
    10.1007/s11467-013-0386-9

    Abstract
    We conduct systematical cathodoluminescence study on red-shift of near-band-edge emission energy in elastic bent ZnO nanowires with diameters within the exciton diffusion length (∼ 200 nm) in liquid nitrogen temperature (81 K). By charactering the emission spectra of the nanowires with different local curvatures, we find a linear relationship between strain-gradient and the red-shift of near-band-edge emission photon energy, an elastic strain-gradient effect in semiconductor similar to the famous flexoelectric effect in liquid crystals. Our results provide a new route to understand the inhomogeneous strain effect on the energy bands and optical properties of semiconductors and should be useful for designing advanced nano-optoelectronic devices.

    Keywords
    strain-gradient
    ZnO nanowire
    cathodoluminescene
    exciton energy
    energy bands

    Link to article

  • GUO Yufeng, GUO Wanlin. Effects of graphene coating and charge injection on water adsorption of solid surfaces. Nanoscale, 2013,5, 10414-10419.

    Effects of graphene coating and charge injection on water adsorption of solid surfaces
    Yufeng Guo*a and Wanlin Guo*a

    a.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, China
    E-mail: yfguo@nuaa.edu.cn, wlguo@nuaa.edu.cn;
    Fax: +86 25 84895827 ;
    Tel: +86 25 84890513

    Nanoscale, 2013,5, 10414-10419
    DOI: 10.1039/C3NR02867D
    Received 03 Jun 2013, Accepted 17 Aug 2013
    First published online 27 Aug 2013

    Abstract

    The adhesion and cohesion of water molecules on graphene-coated and bare copper and mica substrates under charge injection have been extensively studied by first-principles calculations. Water adsorption on graphene-coated copper surface is weakened by injecting negative charges into the substrate, while enhanced by positive charges. Both negatively and positively charge injecting on graphene-coated mica strengthen the adsorption between water and the surface. While the adhesive and cohesive energies of water adsorption on charged bare copper and mica exhibit similar trends and much stronger response to charge injection. The charge sensitivity of water adsorbing on positively charged surfaces is significantly weakened by the graphene coating layer, mainly due to lower interfacial charge exchange. Our results suggest a viable way to modify water adsorption on a graphene-coated surface and unveil the role of graphene as a passivation layer for the wetting of a charged substrate.

    Link to article

  • FEI Wenwen, YIN Jun, LIU Xiaofei, GUO Wanlin. Dendritic graphene domains: Growth, morphology and oxidation promotion. Materials Letters 2013, 110, 225-228.

    Dendritic graphene domains: Growth, morphology and oxidation promotion

    Wenwen Fei, Jun Yin, Xiaofei Liu, Wanlin Guo

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

    Highlights
    •Monolayer and well-crystallized dendritic graphene domains were synthesized under controlled CVD conditions.
    •The different morphologies of graphene domains on two copper surfaces were investigated.
    •Square-shaped graphene domains were obtained when the pre-annealing time was reduced.
    •The oxidization of copper surface was promoted by the covered dendritic graphene domains.

    Abstract

    The morphology of graphene domains is very sensitive to growth conditions in the chemical vapor deposition process. Here, we demonstrate the growth of well-crystallized monolayer dendritic graphene domains with size up to 100-micron under controlled conditions. The dendritic graphene domains appear only on the copper surface closer to the quartz tube, while graphene on the opposite copper surface is of traditional fractal shape. By reducing the pre-annealing time of copper, we obtained square-shaped graphene domains. And it is unexpected that some dendritic graphene domains promoted the oxidation of the underlying copper after being kept at atmospheric conditions for a long term, which is in sharp contrast to the anti-oxidation property of graphene during the short annealing process as previously reported.

    Keywords
    Graphene; Chemical vapor deposition; Oxidation promotion

    Link to article

  • WU Wenzhi, GUO Wanlin, ZENG Xiao Cheng. Intrinsic electronic and transport properties of graphyne sheets and nanoribbons. Nanoscale 2013, 5, 9264–9276.

    Intrinsic electronic and transport properties of graphyne sheets and nanoribbons

    Wenzhi Wu,ab Wanlin Guo*a and Xiao Cheng Zeng*b

    a State Key Laboratory of Mechanics and Control of Mechanical Structures and Key Laboratory for Intelligent Nano Materials and Devices of MOE, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China. E-mail: wlguo@nuaa.edu.cn
    b Department of Chemistry and Center for Materials & Nanoscience, University of Nebraska-Lincoln, Lincoln, Nebraska, 68588, USA. E-mail: xzeng1@unl.edu

    Received 20th June 2013
    Accepted 16th July 2013

    Graphyne, a two-dimensional carbon allotrope like graphene but containing doubly and triply bonded carbon atoms, has been proven to possess amazing electronic properties as graphene. Although the electronic, optical, and mechanical properties of graphyne and graphyne nanoribbons (NRs) have been previously studied, their electron transport behaviors have not been understood. Here we report a comprehensive study of the intrinsic electronic and transport properties of four distinct polymorphs of graphyne (a, b, g, and 6,6,12-graphynes) and their nanoribbons (GyNRs) using density functional theory coupled with the non-equilibrium Green's function (NEGF) method. Among the four graphyne sheets, 6,6,12-graphyne displays notable directional anisotropy in the transport properties. Among the GyNRs, those with armchair edges are nonmagnetic semiconductors whereas those with zigzag edges can be either antiferromagnetic or nonmagnetic semiconductors. Among the armchair GyNRs, the a-GyNRs and 6,6,12-GyNRs exhibit distinctive negative differential resistance (NDR) behavior. On the other hand, the zigzag a-GyNRs and zigzag 6,6,12-GyNRs exhibit symmetry-dependent transport properties, that is, asymmetric zigzag GyNRs behave as conductors with nearly linear current–voltage dependence, whereas symmetric GyNRs produce very weak currents due to the presence of a conductance gap around the Fermi level under finite bias voltages. Such symmetry-dependent behavior stems from different coupling between p* and p subbands. Unlike a- and 6,6,12-GyNRs, both zigzag b-GyNRs and zigzag g-GyNRs exhibit NDR behavior regardless of the symmetry.

  • Yeung Yu Hui and LIU Xiaofei et al, Wanlin Guo and Shu Ping Lau. Exceptional Tunability of Band Energy in a Compressively Strained Trilayer MoS2 Sheet. ACS Nano 2013, 7, 7126–7131.

    Exceptional Tunability of Band Energy in a Compressively Strained Trilayer MoS2 Sheet

    Yeung Yu Hui,†,^ Xiaofei Liu,‡,^ Wenjing Jie,† Ngai Yui Chan,† Jianhua Hao,† Yu-Te Hsu,§ Lain-Jong Li,§
    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, China,
    ‡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,
    §Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan.

    ^Y. Y. Hui and X. Liu contributed equally to this work.

    ABSTRACT
    Tuning band energies of semiconductors through strain engineering can significantly enhance their electronic, photonic, and spintronic performances. Although low-dimensional nanostructures are relatively flexible, the reported tunability of the band gap is within 100 meV per 1% strain. It is also challenging to control strains in atomically thin semiconductors precisely and monitor the optical and phonon properties simultaneously. Here, we developed an electromechanical device that can apply biaxial compressive strain to trilayer MoS2 supported by a piezoelectric substrate and covered by a transparent graphene electrode. Photoluminescence and Raman characterizations show that the direct band gap can be blue-shifted for∼300 meV per 1% strain. First-principles investigations confirm the blue-shift of the direct band gap and reveal a higher tunability of the indirect band gap than the direct one. The exceptionally high strain tunability of the electronic structure in MoS2 promising a wide range of applications in functional nanodevices and the developed methodology should be generally applicable for two-dimensional semiconductors.

    KEYWORDS: MoS2 . strain engineering . piezoelectric substrate . Raman spectroscopy . photoluminescence

  • YIN Jun, LI Xuemei, ZHOU Jianxin, GUO Wanlin. Ultralight Three-Dimensional Boron Nitride Foam with Ultralow Permittivity and Superelasticity. Nano Lett. 2013, 13, 3232−3236.

    Ultralight Three-Dimensional Boron Nitride Foam with Ultralow Permittivity and Superelasticity

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

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

    Received: April 12, 2013
    Revised: June 24, 2013
    Published: June 25, 2013

    ABSTRACT
    Dielectrics with ultralow permittivity within 2 times that of air, excellent mechanical performance, and high thermal stability are highly attractive to many applications. However, since the finding of silica aerogels in the 1930s, no alternative ultralight porous dielectric with density below 10 mg/cm3 has been developed. Here we present three-dimensional hierarchical boron nitride foam with permittivity of 1.03 times that of air, density of 1.6 mg/cm3, and thermal stability up to 1200 °C obtained by chemical vapor deposition on a nickel foam template. This BN foam exhibits complete recovery after cyclic compression exceeding 70% with permittivity within 1.12 times that of air. Gathering all these exceptional characters, the BN foam should create a breakthrough development of flexible ultralow-permittivity dielectrics and ultralight materials.

    KEYWORDS: Ultralight, ultralow permittivity, superelasticity, three-dimensional, boron nitride, aerogels

  • XIANG Mujing, GUO Wanlin. Formulation of the stress fields in power law solids ahead of three-dimensional tensile cracks. Int. J. Solids. Struct. 2013, 50, 3067–3088.

    Formulation of the stress fields in power law solids ahead of three-dimensional tensile cracks

    Mujing Xiang a,b, Wanlin Guo a,

    a State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and Astronautics, 29 Yu-Dao Street, Nanjing 210016, China
    b R&D Institute of Pump Division of Sany, Sany Industrial Park, Xingsha Enterprise Zone, Changsha 410100, China

    Received 13 April 2012
    Received in revised form 6 May 2013
    Available online 1 June 2013

    a b s t r a c t
    To accurately predict damage behavior in engineering applications, it is important to investigate the three-dimensional (3D) stress state near a real crack border. Introducing the out-of-plane stress constraint factor Tz, Guo and his colleagues derived out the 3D asymptotic fields near the tensile crack border in power law plastic (Guo, 1993a, 1993b, 1995) and creeping solids (Xiang et al., 2011). However, these theoretical solutions are presented in curves and too complicated for application. Here we formulize the 3D theoretical solutions into a set of empirical explicit formulae in the whole range of out-of-plane stress constraint from Tz = 0 at plane stress state to Tz = 0.5 at plane strain state. At the two limits of Tz = 0 and 0.5, the empirical formulae degrade into the two dimensional (2D) HRR (Hutchinson, 1968; Rice and Rosengren, 1968) or RR (Riedel and Rice, 1980) solutions with high accuracy. Detailed finite element analyses are performed for cracked plates with finite thickness under power law plastic and creeping conditions to verify the formulation of the asymptotic crack border stress fields. It is shown that the in-plane stress components and stress triaxiality on the ligament ahead of the crack border can be efficiently predicted by the explicit formulae. We also investigate the dominance of the formulation of stress components in the whole forward sector to give a more convenient description for wide applications. Based on the formulation, we discuss the influence of both in-plane and out-of-plane constraints. Three- arameter descriptions, such as the J–Tz–QT description for plastic solids proposed by Guo (2000) and the C(t)–Tz–Q⁄ description for creeping solids proposed by Xiang et al. (2011) are evaluated based on comparison of the empirical formulae and 3D finite element results. The three-parameter descriptions are shown to be necessary and efficient under large scale yielding or extensive creeping conditions in the whole forward sector of cracked plates with finite thickness.

    Keywords:
    Three-dimensional crack
    Power law plastic and creeping solids
    Out-of-plane stress constraint factor Tz
    Explicit formulae
    Three-parameter descriptions

  • YU Jin, GUO Wanlin. Two-Dimensional Hexagonal Beryllium Sulfide Crystal. J. Phys. Chem. Lett. 2013, 4, 1856−1860.

    Two-Dimensional Hexagonal Beryllium Sulfide Crystal

    Jin Yu and Wanlin Guo

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

    Received: April 1, 2013
    Accepted: May 17, 2013
    Published: May 17, 2013

    ABSTRACT: We report a new two-dimensional hexagonal beryllium sulfide (h-BeS) sheet with exceptional properties by extensive first-principles calculations. The h-BeS sheet presents an indirect energy gap of 4.26 eV and an outstanding thermodynamic stability up to 1000 K. Armchair-edged nanoribbons of h-BeS are wide-energy-gap semiconductors with a giant Stark effect, while the zigzag-edged ones are metals with spin glass state. Especially, the ferromagnetic zigzag nanoribbons exhibit a net magnetic moment of nearly 1.15 μB. These interesting electronic and magnetic properties suggest the promise of the h-BeS crystal for potential applications and should inspire experimental enthusiasm.

  • ZHANG Zhuhua, GUO Wanlin, YAKOBSON Boris I. Self-modulated band gap in boron nitride nanoribbons and hydrogenated sheets. Nanoscale, 2013,5, 6381-6387.

    Self-modulated band gap in boron nitride nanoribbons and hydrogenated sheets
    Zhuhua Zhang,*ab Wanlin Guoa and Boris I. Yakobsonb

    a.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
    E-mail: zz19@rice.edu, wlguo@nuaa.edu.cn, biy@rice.edu
    b.Department of Mechanical Engineering and Materials Science, Rice University, Houston, USA

    Nanoscale, 2013,5, 6381-6387
    DOI: 10.1039/C3NR01180A
    Received 08 Mar 2013, Accepted 29 Apr 2013
    First published online 07 May 2013

    Abstract

    Using hybrid density functional theory calculations with van der Waals correction, we show that polar boron nitride (BN) nanoribbons can be favorably aligned via substantial hydrogen bonding at the interfaces, which induces significant interface polarizations and sharply reduces the band gap of insulating ribbons well below the silicon range. The interface polarization can strongly couple with carrier doping or applied electric fields, yielding not only enhanced stability but also widely tunable band gap for the aligned ribbons. Furthermore, similar layer-by-layer alignment also effectively reduces the band gap of a 2D hydrogenated BN sheet and even turns it into metal. This novel strategy for band gap control appears to be general in semiconducting composite nanostructures with polar nonbonding interfaces and thus offers unique opportunities for developing nanoscale electronic and optical devices.

    Link to article

  • QIU Hu, GUO Wanlin. Electromelting of Confined Monolayer Ice. Phys. Rev. Lett. 2013, 110, 195701.

    Phys. Rev. Lett. 110, 195701 (2013) [5 pages]

    Electromelting of Confined Monolayer Ice

    Hu Qiu and Wanlin Guo
    State Key Laboratory of Mechanics and Control of Mechanical Structures and the Key Laboratory for Intelligent Nano Materials and Devices of MOE, Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

    Received 13 August 2012; revised 18 December 2012; published 6 May 2013

    Abstract
    In sharp contrast to the prevailing view that electric fields promote water freezing, here we show by molecular dynamics simulations that monolayer ice confined between two parallel plates can melt into liquid water under a perpendicularly applied electric field. The melting temperature of the monolayer ice decreases with the increasing strength of the external field due to the field-induced disruption of the water-wall interaction induced well-ordered network of the hydrogen bond. This electromelting process should add an important new ingredient to the physics of water.

    © 2013 American Physical Society
    URL: http://link.aps.org/doi/10.1103/PhysRevLett.110.195701
    DOI: 10.1103/PhysRevLett.110.195701
    PACS: 64.70.dj, 61.20.Ja, 68.18.Fg

  • LIU Xiaofei, XU Tao, WU Xing, SUN Li-Tao, GUO Wanlin et al. Top–down fabrication of sub-nanometre semiconducting nanoribbons derived from molybdenum disulfide sheets. Nat. Commun. 2013, 4, 1776.

    NATURE COMMUNICATIONS | ARTICLE OPEN

    Top–down fabrication of sub-nanometre semiconducting nanoribbons derived from molybdenum disulfide sheets

    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
    Xiaofei Liu, Zhuhua Zhang, Jin Yu & Wanlin Guo

    SEU-FEI Nano-Pico Center, Key Laboratory of MEMS of Ministry of Education, School of Electronic Science and Engineering, Southeast University, Nanjing 210096, China
    Tao Xu, Xing Wu & Li-Tao Sun

    National Laboratory of Microstructures, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China
    Hao Qiu & Xin-Ran Wang

    Center for Electron Microscopy, State Key Laboratory of Silicon Materials, Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China
    Jin-Hua Hong, Chuan-Hong Jin & Ji-Xue Li

    Corresponding authors
    Correspondence to: Wanlin Guo or Li-Tao Sun

    Nature Communications 4, Article number: 1776 doi:10.1038/ncomms2803
    Received 22 January 2013 Accepted 27 March 2013 Published 30 April 2013

    Abstract
    Developments in semiconductor technology are propelling the dimensions of devices down to 10 nm, but facing great challenges in manufacture at the sub-10 nm scale. Nanotechnology can fabricate nanoribbons from two-dimensional atomic crystals, such as graphene, with widths below the 10 nm threshold, but their geometries and properties have been hard to control at this scale. Here we find that robust ultrafine molybdenum-sulfide ribbons with a uniform width of 0.35 nm can be widely formed between holes created in a MoS2 sheet under electron irradiation. In situ high-resolution transmission electron microscope characterization, combined with first-principles calculations, identifies the sub-1 nm ribbon as a Mo5S4 crystal derived from MoS2, through a spontaneous phase transition. Further first-principles investigations show that the Mo5S4 ribbon has a band gap of 0.77 eV, a Young’s modulus of 300GPa and can demonstrate 9% tensile strain before fracture. The results show a novel top–down route for controllable fabrication of functional building blocks for sub-nanometre electronics.

  • YU Jin, ZHANG Zhuhua and GUO Wanlin. Electronic properties of graphene nanoribbons stacked on boron nitride nanoribbons. J. Appl. Phys. 2013, 113, 133701.

    Electronic properties of graphene nanoribbons stacked on boron nitride nanoribbons

    Jin Yu, Zhuhua Zhang, and Wanlin Guo

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

    (Received 30 January 2013; accepted 15 March 2013; published online 1 April 2013)

    Abstract

    Hexagonal boron nitride sheet has been shown to be the best insulating substrate for graphene electronics. Using first-principles calculations, we here show that BN nanoribbons (BNNRs) can not only serve as a desirable substrate but also bring new properties into the supported graphene nanoribbons (GNRs). In particular, zigzag GNRs on zigzag BNNRs become a spin-relevant semiconductor that can be easily tuned into a half-metal, thanks to polar character of the BNNRs. In contrast, armchair GNRs can basically have all their electronic properties survived from the interaction of armchair BNNRs. Our findings provide helpful guide for developing hybrid BN-graphene nanodevices.

  • HUANG Fengling, GUO Wanlin. Structural and mechanical properties of the spines from Echinocactus grusonii cactus. J Mater Sci 2013, 48, 5420–5428.

    Structural and mechanical properties of the spines from Echinocactus grusonii cactus

    Fengling Huang, Wanlin Guo

    Received: 24 September 2012 / Accepted: 19 March 2013 / Published online: 29 March 2013

    Abstract
    It is intuitional that most cactus spines are hard and sharp, but their structures and properties have never been systematically studied. Here, we report a comprehensive study on the microstructures and mechanical properties of spines from Echinocactus grusonii cactus for the first time by combining optic and scanning electron microscope investigations, x-ray microanalysis, as well as nanoindentation and tensile tests. It is found that the cactus spine consists of fibres with diameter of 5–15 lm and length of hundreds of micrometres and sclerified epidermis, but contains no mineralisation component as some hard substance does. The spine fibres have high crystallinity and in high alignment. Nanoindentation experiments show that the spine has much higher longitude hardness than that of bamboo reported in the literatures, although their transverse hardness is nearly identical to that of woods, crops, and bamboo. The indentation modulus of the spine cell wall is also within the same order of magnitude as woods, crops and bamboo, with detailed value similar to that of bamboo and slightly lower than that of woods and crops. The tensile strength of the dry spine is measured to be 140 MPa within the range of tensile strength of bamboo reported in the literatures. It is also found that the fresh spine has certain toughness, but the dry spine becomes brittle. The high crystallinity and high alignment of fibres in the cactus spines as well as the very small multifibrillar angle within each fibre can explain the special mechanical properties of the spines.

  • LIU Xiaofei, ZHANG Zhuhua, GUO Wanlin. Universal Rule on Chirality-Dependent Bandgaps in Graphene Antidot Lattices. Small 2013, 9(8), 1405–1410.

    Full Paper
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    Universal Rule on Chirality-Dependent Bandgaps in Graphene Antidot Lattices

    Xiaofei Liu, Zhuhua Zhang, Wanlin Guo*

    Key Laboratory for Intelligent Nano Materials and Devices of MOE, State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and Astronautics, Nanjing, P. R. China
    Email: Wanlin Guo (wlguo@nuaa.edu.cn)

    Article first published online: 26 MAR 2013

    DOI: 10.1002/smll.201202988

    Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

    Issue
    Small
    Special Issue: Low-Dimensional Carbon Materials
    Volume 9, Issue 8, pages 1405–1410, April 22, 2013

    Keywords:
    graphene;chirality-dependence;bandgaps;antidots;first-principles calculations

    Abstract
    Graphene with periodically patterned antidots has attracted intense research attention as it represents a facile route to open a bandgap for graphene electronics. However, not all graphene antidot lattices (GALs) can open a bandgap and a guiding rule is missing. Here, through systematic first-principles calculations, it is found that bandgaps in triangular GALs are surprisingly well defined by a chirality vector R = n a1 + ma2 connecting two neighboring antidots, where a1 and a2 are the basis vectors of graphene. The bandgap opens in the GALs with (n-m)mod3 = 0 but remains closed in those with (n-m)mod3 = ±1, reminiscent of the gap-chirality rule in carbon nanotubes. Remarkably, the gap value in GALs allows ample modulation by adjusting the length of chirality vectors, shape and size of the antidots. The gap–chirality relation in GALs stems from the chirality-dependent atomic structures of GALs as revealed by a super-atom model as well as Clar sextet analyses. This chirality-dependent bandgap is further shown to be a generic behavior in any parallelogram GAL and thus serves as an essential stepping stone for experimenters to realize graphene devices by antidot engineering.

  • YU Jin, GUO Wanlin. A New Paradigm to Half-Metallicity in Graphene Nanoribbons. J. Phys. Chem. Lett., 2013, 4(6), 951–955.

    A New Paradigm to Half-Metallicity in Graphene Nanoribbons

    Jin Yu and Wanlin Guo
    Key Laboratory for Intelligent Nano Materials and Devices of MOE and State Key Laboratory of Mechanics and Control of Mechanical Structures, Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

    J. Phys. Chem. Lett., 2013, 4 (6), pp 951–955
    DOI: 10.1021/jz4001328

    Publication Date (Web): March 5, 2013
    Copyright © 2013 American Chemical Society

    Abstract
    In contrast to the well-recognized transverse-electric-field-induced half-metallicity in zigzag graphene nanoribbons, here, we demonstrate by first-principles calculations that zigzag graphene nanoribbons sandwiched between hexagonal boron nitride nanoribbons or sheets can be tuned into half-metal simply by a bias voltage or a moderate compressive strain. The half-metallicity is attributed to an enhanced coupling effect of spontaneous polarization and asymmetrical exchange correlation along the ribbon width. The findings should open a viable route for efficient spin-resolved band engineering in graphene-based devices that are compatible with the current technology of the semiconductor industry.

    Keywords: graphene nanoribbons; boron nitride; heterostructure; half-metallicity

  • ZHAO Junhua et al. A comparative study of two molecular mechanics models based on harmonic potentials. J. Appl. Phys. 2013, 113, 063509.

    A comparative study of two molecular mechanics models based on harmonic potentials

    Junhua Zhao,1,2,a) Lifeng Wang,3 Jin-Wu Jiang,2 Zhengzhong Wang,4 Wanlin Guo,3,b)
    and Timon Rabczuk2,c)

    1. School of Mechanical Engineering, Jiangnan University, 214122 Wuxi, People’s Republic of China
    2. Institute of Structural Mechanics, Bauhaus-University Weimar, 99423 Weimar, Germany
    3. State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and Astronautics, 210016 Nanjing, People’s Republic of China
    4. Department of Materials and Structural Engineering, Northwest A&F University, 712100 Yangling, Shaanxi, People’s Republic of China

    (Received 7 November 2012; accepted 28 January 2013; published online 12 February 2013)

    We show that the two molecular mechanics models, the stick-spiral and the beam models, predict considerably different mechanical properties of materials based on energy equivalence. The difference between the two models is independent of the materials since all parameters of the beam model are obtained from the harmonic potentials. We demonstrate this difference for finite width graphene nanoribbons and a single polyethylene chain comparing results of the molecular dynamics (MD) simulations with harmonic potentials and the finite element method with the beam model. We also find that the difference strongly depends on the loading modes, chirality and width of the graphene nanoribbons, and it increases with decreasing width of the nanoribbons under pure bending condition. The maximum difference of the predicted mechanical properties using the two models can exceed 300% in different loading modes. Comparing the two models with the MD results of AIREBO potential, we find that the stick-spiral model overestimates and the beam model underestimates the mechanical properties in narrow armchair graphene nanoribbons under pure bending condition.

  • YU Peishi, GUO Wanlin. An equivalent thickness conception for evaluation of corner and surface fatigue crack closure. Eng. Fract. Mech. 2013, 99, 202–213.

    An equivalent thickness conception for evaluation of corner and surface fatigue crack closure

    Peishi Yu a,b, Wanlin Guo a,

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

    Received 28 March 2011
    Received in revised form 26 August 2012
    Accepted 20 December 2012
    Available online 16 January 2013

    abstract
    The out-of-plane constraint-based equivalent thickness conception developed previously
    for corner cracks is extended here to surface-cracked plates based on systematical finite
    element simulations for the purpose to evaluate the plasticity-induced fatigue closure of
    corner and surface cracks. A semi-analytical solution for equivalent thickness of semi-elliptic
    surface cracks is obtained by numerical analyses of three-dimensional stress fields near
    the crack borders and comparing with that of ideally straight-through cracks in plates of
    finite thickness. The fatigue opening stresses of corner and surface cracks are evaluated
    based the recognized equations of straight-through cracks using the equivalent thickness
    conception. Comparison against available finite element and experimental results shows
    that the developed method can provide satisfied prediction of fatigue closure for both corner
    and surface cracks.

    Keywords:
    Crack opening stress
    Equivalent thickness
    Out-of-plane constraint
    Corner and surface crack
    Three-dimensional finite element analysis

  • ZHAO Junhua et al, GUO Wanlin, Timon Rabczuk. A theoretical analysis of cohesive energy between carbon nanotubes, graphene and substrates. Carbon 2013, 57, 108-119.

    A theoretical analysis of cohesive energy between carbon nanotubes, graphene and substrates

    Junhua Zhao a,b,*, Jin-Wu Jiang b, Yue Jia b, Wanlin Guo c, Timon Rabczuk b

    a School of Mechanical Engineering, Jiangnan University, 214122 Wuxi, PR China
    b Institute of Structural Mechanics, Bauhaus-University Weimar, 99423 Weimar, Germany
    c State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and Astronautics, 210016 Nanjing, PR China

    Received 28 October 2012
    Accepted 17 January 2013
    Available online 25 January 2013

    A B S T R A C T
    Explicit solutions for the cohesive energy between carbon nanotubes, graphene and substrates are obtained through continuum modeling of the van der Waals interaction between them. The dependence of the cohesive energy on their size, spacing and crossing angles is analyzed. Checking against full atom molecular dynamics calculations and available experimental results shows that the continuum solution has high accuracy. The equilibrium distances between the nanotubes, graphene and substrates with minimum cohesive energy are also provided explicitly. The obtained analytical solution should be of great help for understanding the interaction between the nanostructures and substrates, and designing composites and nanoelectromechanical systems.

  • GUO Yufeng and GUO Wanlin. Soliton-like thermophoresis of graphene wrinkles. Nanoscale, 2013, 5, 318.

    Soliton-like thermophoresis of graphene wrinkles

    Yufeng Guo and Wanlin Guo

    Affiliation Information
    1. 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, China

    Nanoscale, 2013,5, 318-323
    DOI: 10.1039/C2NR32580B
    Received 04 Sep 2012, Accepted 01 Nov 2012
    First published on the web 02 Nov 2012

    Abstract

    We studied the thermophoretic motion of wrinkles formed in substrate-supported graphene sheets by nonequilibrium molecular dynamics simulations. We found that a single wrinkle moves along applied temperature gradient with a constant acceleration that is linearly proportional to temperature deviation between the heating and cooling sides of the graphene sheet. Like a solitary wave, the atoms of the single wrinkle drift upwards and downwards, which prompts the wrinkle to move forwards. The driving force for such thermophoretic movement can be mainly attributed to a lower free energy of the wrinkle back root when it is transformed from the front root. We establish a motion equation to describe the soliton-like thermophoresis of a single graphene wrinkle based on the Korteweg–de Vries equation. Similar motions are also observed for wrinkles formed in a Cu-supported graphene sheet. These findings provide an energy conversion mechanism by using graphene wrinkle thermophoresis.

  • FU Xue-Wen, GUO Wanlin and YU Da-Peng et al. Improvement of ultraviolet photoresponse of bent ZnO microwires by coupling piezoelectric and surface oxygen adsorption/desorption effects. Nanoscale, 2013, 5, 916.

    Communication
    Improvement of ultraviolet photoresponse of bent ZnO microwires by coupling piezoelectric and surface oxygen adsorption/desorption effects

    Xue-Wen Fu , Zhi-Min Liao , Jun Xu , Xiao-Song Wu , Wanlin Guo and Da-Peng Yu

    Affiliation Information
    1. State Key Laboratory for Mesoscopic Physics,Department of Physics,Peking University, Beijing 100871, P.R. China

    Nanoscale, 2013,5, 916-920
    DOI: 10.1039/C2NR33281G
    Received 22 Oct 2012, Accepted 10 Dec 2012
    First published on the web 13 Dec 2012

    Abstract

    Localized ultraviolet photoresponse properties of bent ZnO microwires bridging two perfect Ohmic contacts in both atmospheric and high vacuum (8 × 10−6 torr) environments have been investigated for the first time to explore the bending strain effect on the photoelectrical properties of ZnO. It is found that the ZnO microwire has higher photoconductivity and faster rising speed when photo-excitation is localized at the bending region in an atmospheric environment, while the rising speeds are almost the same when photo-excitations are localized at the bending and straight regions under vacuum. The bending strain induced improvement of the UV photoresponse in air was well explained by considering the coupling of piezoelectric effects and the surface oxygen adsorption/desorption procedure on the bent ZnO microwire. Our results are valuable for designing and fabricating strain modulated photoelectrical micro/nano-devices.

  • GUO Yufeng and GUO Wanlin. Electronic and Field Emission Properties of Wrinkled Graphene. J. Phys. Chem. C, 2013, 117, 692–696.

    Electronic and Field Emission Properties of Wrinkled Graphene

    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

    J. Phys. Chem. C, 2013, 117 (1), pp 692–696
    DOI: 10.1021/jp3103063
    Publication Date (Web): December 17, 2012

    Abstract

    Wrinkles can be seen as a kind of protrusion formed on the surface of graphene sheets. The response of the electronic properties of graphene wrinkles to charge injecting and external electric field, which is closely related to field emission properties, has been extensively studied by our first-principles calculations. We find that increasing the wrinkle size and its top curvature not only improves the field enhancement factor of the wrinkled graphene but also decreases the electron affinities and ionization potentials. When injecting charges, both the charge accumulation and depletion mostly distribute at the top parts of the wrinkles and become more concentrated in the wrinkle with a higher curvature. The change of the highest occupied molecular orbital and the lowest unoccupied molecular orbital caused by electric field mainly locates at the wrinkled parts, especially at its top. These results demonstrate that wrinkled graphene could be a good candidate for field emitter.