Our Publications

  • Xiaofei Liu and Wanlin Guo. Intrinsic Rashba-like splitting in asymmetric Bi2Te3/Sb2Te3 heterogeneous topological insulator films. Appl. Phys. Lett 105, 082401 (2014)

    Applied Physics Letters
    Xiaofei Liu and Wanlin Guo Appl.Phys. Lett 105, 082401 (2014) doi: 10.1063/1.4893987
    Intrinsic Rashba-like splitting in asymmetric Bi2Te3/Sb2Te3 heterogeneous topological insulator films
    Xiaofei Liu and Wanlin Guo

    wlguo@nuaa.edu.cn
    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, People's Republic of China

    Dates
    Received 16 June 2014
    accepted 13 August 2014
    published online 25 August 2014

    Abstract

    We show by density functional theory calculations that asymmetric hetero-stacking of Bi2Te3/Sb2Te3 films can modulate the topological surface states. Due to the structure inversion asymmetry,an intrinsic Rashba-like splitting of the conical surface bands is aroused. While such splitting in homogeneous Bi2Te3-class topological insulators can be realized in films with more than three quintuple layers under external electric fields, the hetero-stacking breaks the limit of thickness for preserving the topological nature into the thinnest two quintuple layers. These results indicate that
    the hetero-stacking can serve as an efficient strategy for spin-resolved band engineering of topolog-ical insulators. VC 2014 AIP Publishing LLC.

    ARTICLE LINK

  • Ying Xu, Xiaofei Liu and Wanlin Guo.Tensile strain induced switching of magnetic states in NbSe2 and NbS2 single layers. Nanoscale, 2014, 6(21), 12929-12933

    Nanoscale
    Ying Xu et al 2014 Nanosacale 6(21),12929 doi: 10.1039/c4nr01486c

    Tensile strain induced switching of magnetic states in NbSe2 and NbS2 single layers
    Ying Xu, Xiaofei Liu and Wanlin Guo

    wlguo@nuaa.edu.cn
    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, People's Republic of China

    Dates
    Issue 6(21) 2014
    Received 1 8th March 2014,
    Accepted 21st August 2014,
    Published on 22 August 2014

    Abstract

    Two dimensional crystals, be fi tting nanoscale electronics and spintronics, can bene fit strain-tunable applications due to their ultrathin andflexible nature. We show by first-principles calculations that tensile strain can enhance the exchange splitting of spins in NbSe2 and NbS2 single layers. Particularly, a switch from antiferro- to ferro-magnetism is realized by strain engineering. Under strains lower than 4%, an anti-ferromagnetic state with opposite spins aligned on the next-nearest-neighbor rows of Nb atoms is favored in energy due to a superexchange interaction; with higher strains the ground state turns to be ferromagnetic with a double exchange origin. In contrast, the VSe2 and VS2 single layers, though with the same trigonal prismatic coordination, remain ferromagnetic even under compressive strains.

    ARTICLE LINK

  • Zhao Junhua, Jiang Jin-Wu, Wang Lifeng, Guo Wanlin and Timon Rabczuk. Coarse-grained potenti als of sin gle-walled carbo n nanotubes. J. Mech. Phys. Solids, 2014, 71, 197-218.

    Journal of the Mechanics and Physics of Solids
    Junhua Zhao et al 2014 J. Mech. Phys. Solids 71 197 doi:10.1016/j.jmps.2014.06.011

    Coarse-grained potenti als of single-walled carbon nanotubes
    Zhao Junhua, Jiang Jin-Wu, Wang Lifeng, Guo Wanlin and Timon Rabczuk

    wlguo@nuaa.edu.cn
    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, People's Republic of China

    Dates
    Issue 71 (11 June 2014)
    Received 27 May 2013 Received in revised form 7 June 2014 Accepted 11 June 2014 Available online 16 July 2014

    Abstract

    We develop the coarse-grained (CG) potentials of single-walled carbon nanotubes (SWCNTs) in CNT bundles and buckypaper for the study of the static and dynamic behaviors. The explicit expressions of the CG stretching, bending and torsion potentials for the nanotubes are obtained by the stick-spiral and the beam models, respectively. The non-bonded CG potentials between two different CG beads are derived from analytical results based on the cohesive energy between two parallel and crossing SWCNTs from the van der Waals interactions. We show that the CG model is applicable to large deformations of complex CNT systems by combining the bonded potentials with non-bonded potentials. Checking against full atom molecular dynamics calculations and our analytical results shows that the present CG potentials have high accuracy. The established CG potentials are used to study the mechanical properties of the CNT bundles and buckypaper efficiently at minor computational cost, which shows great potential for the design of micro- and nanomechanical devices and systems.

    ARTICLE LINK

  • GUO Wanlin, LIU Xiaofei. 2D materials: Metallic when narrow. Nature Nanotechnology 2014, 9, 413–414.

    NATURE NANOTECHNOLOGY | NEWS AND VIEWS

    2D materials: Metallic when narrow

    Wanlin Guo & Xiaofei Liu

    Affiliations
    Wanlin Guo and Xiaofei Liu are at the Key Laboratory of Intelligent Nano Materials and Devices of Ministry of Education, State Key Laboratory of Mechanics and Control of Mechanical Structures, Institute of Nano Science of Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

    Corresponding author
    Correspondence to: Wanlin Guo

    Nature Nanotechnology 9, 413–414 (2014) doi:10.1038/nnano.2014.106
    Published online 04 June 2014

    ARTICLE LINK

  • LIU Xiaofei, PAN Douxing, HONG Yuanzhou, GUO Wanlin. Bending Poisson Effect in Two-Dimensional Crystals. Phys. Rev. Lett. 2014, 112, 205502.

    Bending Poisson Effect in Two-Dimensional Crystals

    Phys. Rev. Lett. 112, 205502 – Published 21 May 2014

    Xiaofei Liu1, Douxing Pan2, Yuanzhou Hong2, and Wanlin Guo1,*

    1State Key Laboratory of Mechanics and Control for Mechanical Structures and Key Laboratory for Intelligent Nano Materials and Devices (MOE), Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
    2Institute of Mechanics, Chinese Academy of Science, Beijing 100190, China
    *wlguo@nuaa.edu.cn

    ABSTRACT
    As the Poisson effect formulates, lateral strains in a material can be caused by a uniaxial stress in the perpendicular direction, but no net lateral strain should be induced in a thin homogeneous elastic plate subjected to a pure bending load. Here, we demonstrated by ab initio simulations that significant exotic lateral strains can be induced by pure bending in two-dimensional crystals, in which the lateral components of chemical bonds can respond to bending curvature directly. The bending Poisson ratio, defined as the ratio of lateral strain to the curvature, is a function of curvature depending on chemical constitution, bonding structure, and atomic interaction of the crystal, and is anisotropic.

    DOI: http://dx.doi.org/10.1103/PhysRevLett.112.205502

  • YIN Jun, ZHANG Zhuhua, LI Xuemei, YU Jin, ZHOU Jianxin, CHEN Yaqing, GUO Wanlin. Waving potential in graphene. Nature Communications 2014, 5, 3582.

    NATURE COMMUNICATIONS | ARTICLE

    Waving potential in graphene

    Jun Yin, Zhuhua Zhang, Xuemei Li, Jin Yu, Jianxin Zhou, Yaqing Chen & Wanlin Guo

    These authors contributed equally to this work
    Jun Yin & Zhuhua Zhang

    Affiliations
    State Key Laboratory of Mechanics and Control of Mechanical Structures, The Key Laboratory of Intelligent Nano Materials and Devices of DoE, Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
    Jun Yin, Zhuhua Zhang, Xuemei Li, Jin Yu, Jianxin Zhou, Yaqing Chen & Wanlin Guo

    Contributions
    W.G. and J.Yin conceived the experiments; J.Yin and X.L. performed the experiments; Z.Z. and J.Yu performed the calculations; W.G., Z.Z. and J.Yin analysed the data; and W.G. and Z.Z. wrote the paper. All authors discussed the results and commented on the manuscript.

    Competing financial interests
    The authors declare no competing financial interests.

    Corresponding author
    Correspondence to: Wanlin Guo

    Nature Communications 5, Article number: 3582 doi:10.1038/ncomms4582
    Received 01 October 2012 Accepted 07 March 2014 Published 06 May 2014

    Abstract
    Nanoscale materials offer much promise in the pursuit of high-efficient energy conversion technology owing to their exceptional sensitivity to external stimulus. In particular, experiments have demonstrated that flowing water over carbon nanotubes can generate electric voltages. However, the reported flow-induced voltages are in wide discrepancy and the proposed mechanisms remain conflictive. Here we find that moving a liquid–gas boundary along a piece of graphene can induce a waving potential of up to 0.1 V. The potential is proportional to the moving velocity and the graphene length inserted into ionic solutions, but sharply decreases with increasing graphene layers and vanishes in other materials. This waving potential arises from charge transfer in graphene driven by a moving boundary of an electric double layer between graphene and ionic solutions. The results reveal a unique electrokinetic phenomenon and open prospects for functional sensors, such as tsunami monitors.

    ARTICLE LINK

  • FU Xuewen, GUO Wanlin, FENG Ji, LI Ju and YU Dapeng, et al. Tailoring Exciton Dynamics by Elastic Strain-Gradient in Semiconductors. Adv. Mater. 2014, 26, 2572–2579.

    Tailoring Exciton Dynamics by Elastic Strain-Gradient in Semiconductors

    Xuewen Fu1,†, Cong Su2,4,†, Qiang Fu1, Xinli Zhu1, Rui Zhu1, Chuanpu Liu1, Zhimin Liao1, Jun Xu1, Wanlin Guo3,*, Ji Feng2,*, Ju Li4,* andDapeng Yu1,*

    Article first published online: 27 JAN 2014

    DOI: 10.1002/adma.201305058

    Author Information
    1State Key Laboratory for Mesoscopic Physics and Electron Microscopy Laboratory, School of Physics, Peking University, and Collaborative Innovation Center of Quantum Matter, Beijing, China
    2International Center for Quantum Materials, School of Physics, Peking University and Collaborative Innovation Center of Quantum Matter, Beijing, China
    3Key Laboratory of Intelligent Nano Materials and Devices of MOE, Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing, China
    4Department of Nuclear Science and Engineering and Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA

    These authors contributed equally to this work.

    *E-mail: yudp@pku.edu.cn, jfeng11@pku.edu.cn, liju@mit.edu, wlguo@nuaa.edu.cn

    Publication History
    Issue published online: 16 APR 2014
    Article first published online: 27 JAN 2014
    Manuscript Revised: 8 NOV 2013
    Manuscript Received: 10 OCT 2013

    Keywords:
    strain-gradient;exciton dynamics;ZnO microwire;pure bending;cathodoluminescence

    Abstract
    In purely bent ZnO microwires, the excitons can be effectively driven and concentrated by the elastic strain-gradient towards the tensile outer side of the purely bent wire. Experimental and theoretical approaches are combined to investigate the dynamics of excitons in an inhomogeneous strain field with a uniform elastic strain-gradient. Cathodoluminescence spectroscopy analysis on purely bent ZnO microwires verifies that excitons can be effectively driven and concentrated along the elastic strain-gradient.

    Article link

  • YIN Jun,LI Xuemei,YU Jin,ZHANG Zhuhua, ZHOU Jianxin, GUO Wanlin. Generating electricity by moving a droplet of ionic liquid along grapheme. Nature Nanotechnology 2014, 9, 378–383.

    NATURE NANOTECHNOLOGY | ARTICLE

    Generating electricity by moving a droplet of ionic liquid along grapheme

    Jun Yin, Xuemei Li, Jin Yu, Zhuhua Zhang, Jianxin Zhou & Wanlin Guo

    Affiliations
    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, 29 Yudao Street, Nanjing 210016, China

    Contributions
    W.G. conceived the project and designed the experiments with J.Yin. J.Yin, X.L. and J.Z. performed the experiments. J.Yu and Z.Z. performed the calculations. W.G., J.Yin and J.Yu analysed the data. W.G., J.Yin and Z.Z. wrote the paper. All authors discussed the results and commented on the manuscript.

    Abstract
    Since the early nineteenth century, it has been known that an electric potential can be generated by driving an ionic liquid through fine channels or holes under a pressure gradient. More recently, it has been reported that carbon nanotubes can generate a voltage when immersed in flowing liquids, but the exact origin of these observations is unclear, and generating electricity without a pressure gradient remains a challenge. Here, we show that a voltage of a few millivolts can be produced by moving a droplet of sea water or ionic solution over a strip of monolayer graphene under ambient conditions. Through experiments and density functional theory calculations, we find that a pseudocapacitor is formed at the droplet/graphene interface, which is driven forward by the moving droplet, charging and discharging at the front and rear of the droplet. This gives rise to an electric potential that is proportional to the velocity and number of droplets. The potential is also found to be dependent on the concentration and ionic species of the droplet, and decreases sharply with an increasing number of graphene layers. We illustrate the potential of this electrokinetic phenomenon by using it to create a handwriting sensor and an energy-harvesting device.

    ARTICLE LINK

  • HUANG FengLing, QIU Hu, GUO WanLin. Microstructures and mechanical properties of fiber cells from Echinocactus grusonii cactus spine. Sci China Tech Sci, 2014, 57, 706-712.

    Title
    Microstructures and mechanical properties of fiber cells from Echinocactus grusonii cactus spine

    Journal
    Science China Technological Sciences
    Volume 57, Issue 4 , pp 706-712

    Cover Date
    2014-04-01

    DOI
    10.1007/s11431-014-5504-6

    Authors
    FengLing Huang (1) (2)
    Hu Qiu (1)
    WanLin Guo wlguo@nuaa.edu.cn (1)

    Author Affiliations
    1. State Key Laboratory for 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
    2. Department of Biomedical Engineering, College of Automation Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing, 210016, China

    Keywords
    spine
    fibers
    microstructure
    indentation modulus

    Abstract
    Spine is the sharpest and hardest part of many plants, which contains highly aligned fiber cells. Here, we report the microstructures and mechanical properties as well as their correlation of single spine fiber cells (SFCs) from the cactus Echinocactus grusonii. It is found that the SFCs are 0.32–0.57 mm in length and 4.6–6.0 μm in width, yielding an aspect ratio of 53–124. X-ray diffraction and Fourier transform infrared spectrophotometry show that the spine fiber is mainly made up of cellulose I with a crystallinity index up to ∼76%. Nanoindentation tests show that a natural spine presents a high modulus of ∼17 GPa. Removing hemicellulose and lignin from the SFC significantly reduces its modulus to ∼0.487 GPa, demonstrating the critical role of adhesives hemicellulose and lignin in affecting the mechanical properties of the SFCs. This finding sheds light on designing novel bio-inspired high-performance composite nanomaterials with aligned nanofibers, such as using hemicellulose and lignin as adhesive in making carbon nanotube fibers.

    Article link

  • FU Xuewen, GUO Wanlin and YU Dapeng, et al. Exciton Drift in Semiconductors under Uniform Strain Gradients: Application to Bent ZnO Microwires. ACS Nano 2014, 8, 3412–3420.

    Exciton Drift in Semiconductors under Uniform Strain Gradients: Application to Bent ZnO Microwires

    Xuewen Fu †, Gwenole Jacopin ‡, Mehran Shahmohammadi ‡, Ren Liu †, Malik Benameur §, Jean-Daniel Ganière ‡, Ji Feng , Wanlin Guo , Zhi-Min Liao †, Benoit Deveaud ‡*, and Dapeng Yu †*
    † State Key Laboratory for Mesoscopic Physics, and Electron Microscopy Laboratory, Department of Physics, Peking University, 209 Chengfu Road, Beijing 100871, China
    ‡ Laboratoire d’Optoélectronique Quantique, École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland
    § Attolight AG, EPFL Innovation Square, PSE D, 1015 Lausanne, Switzerland
    International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
    State Key Laboratory of Mechanics and Control of Mechanical Structures and Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, 29 Yudao Street, Nanjing 210016, China

    ACS Nano, 2014, 8 (4), pp 3412–3420
    DOI: 10.1021/nn4062353
    Publication Date (Web): March 21, 2014
    Copyright © 2014 American Chemical Society
    *Address correspondence to benoit.deveaud-pledran@epfl.ch; yudp@pku.edu.cn.

    Abstract
    Optimizing the electronic structures and carrier dynamics in semiconductors at atomic scale is an essential issue for innovative device applications. Besides the traditional chemical doping and the use of homo/heterostructures, elastic strain has been proposed as a promising possibility. Here, we report on the direct observation of the dynamics of exciton transport in a ZnO microwire under pure elastic bending deformation, by using cathodoluminescence with high temporal, spatial, and energy resolutions. We demonstrate that excitons can be effectively drifted by the strain gradient in inhomogeneous strain fields. Our observations are well reproduced by a drift-diffusion model taking into account the strain gradient and allow us to deduce an exciton mobility of 1400 ± 100 cm2/(eV s) in the ZnO wire. These results propose a way to tune the exciton dynamics in semiconductors and imply the possible role of strain gradient in optoelectronic and sensing nano/microdevices.

    Keywords: ZnO microwire; time-resolved cathodoluminescence; pure bending strain; exciton dynamics; strain gradient

    Article link

  • LI Xuemei, YIN Jun, ZHOU Jianxin and GUO Wanlin. Large area hexagonal boron nitride monolayer as efficient atomically thick insulating coating against friction and oxidation. Nanotechnology 2014, 25, 105701.

    Nanotechnology Volume 25 Number 10
    Xuemei Li et al 2014 Nanotechnology 25 105701 doi:10.1088/0957-4484/25/10/105701

    Large area hexagonal boron nitride monolayer as efficient atomically thick insulating coating against friction and oxidation
    Xuemei Li1, Jun Yin1, Jianxin Zhou and Wanlin Guo

    wlguo@nuaa.edu.cn
    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, People's Republic of China
    1 These authors contributed equally to this work.

    Dates
    Issue 10 (14 March 2014)
    Received 16 August 2013, revised 20 November 2013, accepted for publication 25 November 2013
    Published 14 February 2014

    Abstract

    Coating is the most widely applied technology to improve surface properties of substrates, and nanotechnology has been playing an important role in enhancing the coating performance. However, the tunability of surface properties by a single atomic layer remains poorly understood. Here we demonstrate that a chemical vapor deposited hexagonal boron nitride (h-BN) monolayer of large area and high quality can serve as a perfect coating to significantly improve friction, oxidation and electric resistance of the substrates. The exceptional low friction and insulation of h-BN monolayer coating facilitate the characterization of the h-BN film vividly by atomic force microscopy, showing the h-BN monolayer consists of domains with size within a few micrometers. This excellent coating performance together with the exceptional high thermal and chemical stability make the h-BN monolayer a promising coating material.

    LINK

  • GUO Yufeng and GUO Wanlin. Insulating to metallic transition of an oxidized boron nitride nanosheet coating by tuning surface oxygen adsorption. Nanoscale 2014, 6(7):3731-6.

    Nanoscale. 2014 Apr 7;6(7):3731-6. doi: 10.1039/c3nr06227a.

    Insulating to metallic transition of an oxidized boron nitride nanosheet coating by tuning surface oxygen adsorption.
    Guo Y1, Guo W.

    Author information

    1State 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. yfguo@nuaa.edu.cn.

    Received 24 Nov 2013, Accepted 06 Jan 2014
    First published online 16 Jan 2014

    Abstract
    Surface modification and functionalization are of fundamental importance in actual application of insulating coating, such as hexagon boron nitride (h-BN) nanosheet. Our first-principles calculations reveal that an oxidized h-BN monolayer supported by a Cu substrate exhibits metallic properties when O adatom vertically bonds with the B atom. This is mainly due to the hybridization of the p orbital of the BN layer and O adatom around the Fermi level. Charge transfer from the Cu substrate to the O atom stabilizes the formation of the vertical O-B bond. Injecting negative charges could trigger the migration of the O adatom from the B-N bond to B atom for metal or insulator-supported h-BN monolayer, which will lead to a metallic transition in the oxidized h-BN nanosheet. Our results provide a viable way to tune the electronic properties of surface h-BN coating through charge injection mediated O adsorption.

    ARTICLE LINK