Our Publications

  • Tunable magnetism on Si(111)-(2×1) via chemisorption of graphene nanoribbons. Zhuhua Zhang, Wanlin Guo, and Xiao Cheng Zeng. Phys. Rev. B, 2010, 82, 235423.

    Tunable magnetism on Si(111)-(2×1) via chemisorption of graphene nanoribbons

    Phys. Rev. B 82, 235423 (2010) [6 pages]

    Zhuhua Zhang1,2, Wanlin Guo1,*, and Xiao Cheng Zeng2,†
    1Institute of Nanoscience, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
    2Department of Chemistry, Nebraska Center for Materials and Nanoscience, University of Nebraska–Lincoln, Lincoln, Nebraska 68588, USA

    Received 12 November 2010; published 13 December 2010

    We demonstrate from density-functional theory calculations that strong spin polarization can be achieved on a silicon surface via chemisorption of graphene nanoribbons (GNRs). The net electron spins are due to the unique silicon dangling-bond states induced by the chemisorption of GNRs and further localized by the well-aligned Si-C bonds between the silicon surface and the GNRs. The induced magnetic moment on the silicon surface depends on the width of GNRs and is thus tunable through controlling lateral separation among GNRs. We show that the silicon surface magnetization can even sustain large vertical compression to the GNRs and thus can be used as a functional switch upon high deformation of GNR. Similar magnetic behavior can be also achieved via chemisorption of certain organic molecules on the silicon surface. Our finding points to a viable nanofabrication approach to achieve intrinsic spin polarization on silicon nanostructure, thereby having implications in the emerging field of silicon-based spintronics.

  • “White Graphenes”: Boron Nitride Nanoribbons via Boron Nitride Nanotube Unwrapping. Haibo Zeng*, Chunyi Zhi, Zhuhua Zhang, Xianlong Wei, Xuebin Wang, Wanlin Guo, Yoshio Bando, and Dmitri Golberg. Nano Lett., 2010, 10 (12), 5049–5055.

    “White Graphenes”: Boron Nitride Nanoribbons via Boron Nitride Nanotube Unwrapping

    Haibo Zeng*†, Chunyi Zhi†, Zhuhua Zhang‡, Xianlong Wei†, Xuebin Wang†, Wanlin Guo*‡, Yoshio Bando†, and Dmitri Golberg*†
    † International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan
    ‡ Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
    Nano Lett., 2010, 10 (12), pp 5049–5055
    DOI: 10.1021/nl103251m

    Publication Date (Web): October 28, 2010

    * To whom correspondence should be addressed. E-mail: (H.Z.) ZENG.Haibo@nims.go.jp, hbzeng@issp.ac.cn; (W.G) wlguo@nuaa.edu.cn; (D.G.) GOLBERG.Dmitri@nims.go.jp.

    Inspired by rich physics and functionalities of graphenes, scientists have taken an intensive interest in two-dimensional (2D) crystals of h-BN (analogue of graphite, so-called “white” graphite). Recent calculations have predicted the exciting potentials of BN nanoribbons in spintronics due to tunable magnetic and electrical properties; however no experimental evidence has been provided since fabrication of such ribbons remains a challenge. Here, we show that few- and single-layered BN nanoribbons, mostly terminated with zigzag edges, can be produced under unwrapping multiwalled BN nanotubes through plasma etching. The interesting stepwise unwrapping and intermediate states were observed and analyzed. Opposed to insulating primal tubes, the nanoribbons become semiconducting due to doping-like conducting edge states and vacancy defects, as revealed by structural analyses and ab initio simulations. This study paves the way for BN nanoribbon production and usage as functional semiconductors with a wide range of applications in optoelectronics and spintronics.

    Keywords: “White graphene”; boron nitride (BN); nanoribbon; nanosheet; two-dimensional crystal

  • Opening carbon nanotubes into zigzag graphene nanoribbons by energy-optimum oxidation. Yufeng Guo, Lai Jiang, and Wanlin Guo. Phys. Rev. B, 2010, 82, 115440.

    Yufeng Guo, Lai Jiang, and Wanlin Guo.

    Phys. Rev. B, 2010, 82, 115440.

    Received 19 May 2010; revised 17 August 2010; published 21 September 2010

    Narrow zigzag graphene nanoribbons are found to have exceptional electronic and magnetic properties but difficult to fabricate. We show by density-functional calculations and an elastic mechanical model that oxygen atoms have strong energetic favorability to adsorb on small-diameter carbon nanotubes and form unzipped C-O-C epoxy chains along a direction of minimum angle to the tube axis. With other oxygen atoms further attacking, the unzipping epoxy chain formed on the energy-optimum direction of the nanotube is broken into carbonyl pairs. These results promise that unique zigzag graphene nanoribbons could be fabricated by oxidization of small-diameter carbon nanotubes with arbitrary chiralities according to the minimum energy principle.

  • Electronic and magnetic properties of zigzag graphene nanoribbons with periodic protruded edges. Wenzhi Wu, Zhuhua Zhang, Peng Lu, and Wanlin Guo. Phys. Rev. B, 2010, 82, 085425.

    Electronic and magnetic properties of zigzag graphene nanoribbons with periodic protruded edges

    Wenzhi Wu, Zhuhua Zhang, Peng Lu, and Wanlin Guo*
    Institute of Nanoscience, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

    Received 22 March 2010; published 17 August 2010

    The electronic and magnetic properties of zigzag graphene nanoribbons with protruded steps along their edges (ZS-GNRs) are investigated by extensive density-functional theory calculations. We show that the electronic and magnetic properties are determined by an interesting interplay between the length of the protruded step and the distance of two adjacent steps along the ribbon edge. With a small length of the protruded steps along the edge, the system can be converted from a nonmagnetic semiconductor to metal and then to a magnetic semiconductor by increasing the step-to-step distance. In particular, the energy gap decreases first toward a zero minimum and then gradually increases as the step length increases, accompanying with the rapid increase in the edge magnetization. When the step length exceeds a critical value, the ZS-GNR will be always a magnetic semiconductor regardless of the step-to-step distance. We also reveal that the applied transverse electric field can enlarge the energy gap of nonmagnetic ZS-GNRs, due to the breaking of band degeneration; whereas the field-induced gap change in the magnetic ZS-GNRs is spin dependent, leading to the emergence of amazing half metallicity under certain field strengths. These findings suggest that the ZS-GNRs are promising for designing versatile graphene-based devices and can find novel applications in both electronics and spintronics.

  • Strain-Induced Modulations of Electro-Optic and Nonlinear Optical Properties of ZnO: A First-Principles Study. Chun Li, Fan Yang, and Wanlin Guo. Applied Mechanics and Materials, 2010, 29-32, 1803-1808.

    Strain-Induced Modulations of Electro-Optic and Nonlinear Optical Properties of ZnO: A First-Principles Study

    Chun Li, Fan Yang, and Wanlin Guo

    Applied Mechanics and Materials, 2010, 29-32, 1803-1808.

    Online since August, 2010

    Strain-dependent electro-optic constant r33 and nonlinear optical coefficient d33 of ZnO are investigated systematically using density-functional theory based linear-response perturbation method. Miscellaneous properties, such as dielectric constants, elastic constants, piezoelectric coefficients, nonlinear optical coefficients, and electro-optic constants of other II-VI compound semiconductors (both Wurtzite and Zinc-blende structures) are also calculated for comparison with the results of unstrained ZnO. Extensive first-principles calculations show that both r33 and d33 of ZnO decrease almost linearly with increasing strains, which indicates that appropriate compression along the [0001] direction of ZnO could enhance its electro-optic and nonlinear optical properties, while stretching may weaken the corresponding properties. Among the involved Wurtzite structures, ZnO has the highest elastic constant, piezoelectric coefficient and electro-optic constant, showing practical importance.

    Keywords: Electro-Optic Constant, First Principles Calculation, Nonlinear Optical Coefficient, Strain-Dependence, ZnO

  • Charge carrier separation induced by intrinsic surface strain in pristine ZnO nanowires. Liangzhi Kou, Chun Li, Zi-Yue Zhang, Changfeng Chen, and Wanlin Guo. Appl. Phys. Lett., 2010, 97, 053104.

    Liangzhi Kou,1,2, Chun Li,3, Zi-Yue Zhang,1, Changfeng Chen,2, and Wanlin Guo,1

    1. Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
    2. Department of Physics and High Pressure Science and Engineering Center, University of Nevada, Las Vegas, Nevada 89154, USA
    3. School of Mechanics, Civil Engineering, and Architecture, Northwestern Polytechnical University, Xi’an 710072, China

    Appl. Phys. Lett. 97, 053104 (2010)

    Received 24 May 2010; accepted 29 June 2010; published online 2 August 2010

    We predict by first-principles calculations a spontaneous charge carrier separation mechanism in pristine [0001]-oriented ZnO nanowires. We find that the shrinking strain induced by surface reconstruction causes electrons and holes to separate and move toward the core and surface region, respectively. Such separation can be enhanced by axially applied tensile strain as a result of the enhancement of surface strain induced by the Poisson effect, and be suppressed by compressive axial strain. Similar carrier separations are found in IIB-sulfides. This intrinsic charge separation and tensile strain induced enhancement are expected to shed light on solar cell designs.

  • Bending manipulation induced sp2–sp3 bond transition in carbon nanotubes. Chun Tang, Wanlin Guo,and Changfeng Chen. Journal of Applied Physics, 2010, 108(2), 026108.

    Chun Tang,1,2, Wanlin Guo,1, and Changfeng Chen,2

    1. Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China map
    2. Department of Physics and High Pressure Science and Engineering Center, University of Nevada, Las Vegas, Nevada 89154, USA

    J. Appl. Phys. 108, 026108 (2010)

    Received 21 April 2010; accepted 22 June 2010; published online 29 July 2010

    Introducing sp3 bonds in carbon nanotubes can significantly modify their electronic properties but need high pressure at room temperature. Here we show by molecular dynamics simulations that sp2 to sp3 bond transition can be realized through bending manipulation at the buckling location, resembling that of nanoindented carbon nanostructures but with more convenient operation technique. The capability of sp3 bond formation is sensitive to the thickness and diameter of the carbon nanotubes. This bending induced sp3 structures can serve as tunneling junction for electrons, thus bending manipulation could be a route to tailoring nanocircuits.

  • Carrier-Tunable Magnetic Ordering in Vanadium−Naphthalene Sandwich Nanowires. Zhuhua Zhang, Xiaojun Wu, Wanlin Guo, and Xiao Cheng Zeng. J. Am. Chem. Soc., 2010, 132(30), 10215–10217.

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

    Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China, Department of Chemistry, University of Nebraska—Lincoln, Lincoln, Nebraska 68588, and Department of Materials of Science and Engineering, University of Science and Technology of China, Hefei 230026, China

    J. Am. Chem. Soc., 2010, 132 (30), pp 10215–10217

    Publication Date (Web): July 12, 2010

    We report results of first-principles calculation of novel NpTM2 (Np = naphthalene; TM = V, Mn, Ti, Nb) sandwich nanowires. Most importantly, we find that the magnetic ordering in the NpV2 nanowire can be adjusted by changing its charge state. Its intrinsic antiferromagnetic ordering can be switched to ferromagnetic ordering by injecting electrons, whereas injecting holes to the nanowire can further stabilize the antiferromagnetic state. This carrier-tunable magnetic ordering appears to be unique to the NpV2 nanowire. Moreover, we find that the bonding between the two nearest-neighbor metal atoms plays a key role in controlling the magnetic coupling of charge-neutral NpTM2 nanowires. We predict that the NpMn2 nanowire is ferromagnetic while the NpTi2 and NpNb2 nanowires are antiferromagnetic.

  • Homogeneous nanocables from double-walled boron-nitride nanotubes using first-principles calculations. Zhuhua Zhang, Xiao Cheng Zeng, and Wanlin Guo. Phys. Rev. B, 2010, 82, 035412.

    Homogeneous nanocables from double-walled boron-nitride nanotubes using first-principles calculations

    Zhuhua Zhang1,2, Xiao Cheng Zeng2, and Wanlin Guo1,*
    1Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
    2Department of Chemistry and Nebraska Center for Materials and Nanoscience, University of Nebraska–Lincoln, Lincoln, Nebraska 68588, USA

    Received 23 April 2010; revised 3 June 2010; published 12 July 2010

    Since electrons injected to a homogenous wire always tend to concentrate on its surface, heterogeneous coaxial structures are generally necessary to make nanocables with an insulating sheath. Here we reveal from first-principles calculations that double-walled boron-nitride nanotubes could be natural homogeneous nanocables as injected electrons prefer abnormally to concentrate on the inner semiconducting tube while the outer tube remains insulating. The ratio of extra electrons on the inner tube to total carriers in the double-walled nanotubes can be tuned widely by changing either the tube diameter or the local tube curvature through radial deformation, both attributed to the predominant band filling and weak enhancement in Coulomb interaction within the inner wall where the sublattice asymmetry is strongly attenuated by curvature effect. This exotic charge screening is universal for any form of electron-doping sources.

  • Semiconducting to Half-Metallic to Metallic Transition on Spin-Resolved Zigzag Bilayer Graphene Nanoribbons. Yufeng Guo, Wanlin Guo, and Changfeng Chen. J. Phys. Chem. C, 2010, 114 (30), 13098–13105.

    Semiconducting to Half-Metallic to Metallic Transition on Spin-Resolved Zigzag Bilayer Graphene Nanoribbons

    J. Phys. Chem. C, 2010, 114 (30), pp 13098–13105.

    Publication Date (Web): July 8, 2010

    Yufeng Guo*†‡, Wanlin Guo*† and Changfeng Chen*‡
    Institute of Nanoscience, Nanjing University of Aeronautics and Astronautics, Nanjing, 210016, People’s Republic of China, and Department of Physics and High Pressure Science and Engineering Center, University of Nevada, Las Vegas, Nevada 89154

    Our first-principles calculations show that the electronic properties of spin-resolved zigzag bilayer graphene nanoribbons (ZBGNRs) of antiferromagnetic edges are highly sensitive to the interlayer distance between nanoribbons. The energy gap of the antiferromagnetic ZBGNR decreases and the semiconducting ZBGNR finally becomes a metal with decreasing interlayer spacing. Coupling with a transverse electric field, the ZBGNR exhibits a semiconducting to half-metallic to metallic transition via interlayer distance compression. The charge redistribution of spin-up and spin-down and the change of the density of states on the edge atoms, which are driven by the coupled effect of nanomechanical compression and the electric field, contribute to the exceptional modification on the band structure of the ZBGNR.

  • Equivalent thickness conception for corner cracks. Peishi Yu, Chongmin She, and Wanlin Guo. International Journal of Solids and Structures, 2010, 47(16), 2123-2130.

    Peishi Yu, Chongmin She, and Wanlin Guo

    School of Frontier Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

    International Journal of Solids and Structures, 2010, 47(16), 2123-2130.

    Received 10 December 2009; revised 12 April 2010. Available online 24 April 2010.

    Thickness dependence of the one-parameter-based fracture toughness has been well recognized and widely studied. However, it is still a challenge to predict the fracture of structures with curved cracks from the fracture toughness data obtained from the standard through-the-thickness cracked specimens. The complicated three-dimensional (3D) stress fields near the crack front play a vital role in the fracture strength of materials. Based on a systematical numerical study of the 3D stress fields near the crack tip of quarter elliptic corner cracks and comparison with that of ideal through-the-thickness cracks, an equivalent thickness conception for curved cracks is proposed from the viewpoint of out-of-plane constraint, and a semi-analytical solution for the equivalent thickness of corner cracks is obtained. With the evaluated equivalent thickness, the fracture toughness of corner cracked specimens is predicted efficiently by the plane-strain toughness value of the material obtained from the standard through-the-thickness specimen.

    Keywords: Equivalent thickness; Out-of-plane constraint; Corner crack; Three-dimensional fracture; Through-the-thickness crack

  • Tuning the magnetic and electronic properties of bilayer graphene nanoribbons on Si(001) by bias voltage. Zhuhua Zhang, Changfeng Chen, Xiao Cheng Zeng, and Wanlin Guo. Phys.Rev. B, 2010, 81, 155428.

    Zhuhua Zhang1,2, Changfeng Chen3, Xiao Cheng Zeng2, and Wanlin Guo1,*

    1. Institute of Nanoscience, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
    2. Department of Chemistry, University of Nebraska–Lincoln, Lincoln, Nebraska 68588, USA
    3. Department of Physics and High Pressure Science and Engineering Center, University of Nevada, Las Vegas, Nevada 89154, USA

    Phys. Rev. B 81, 155428 (2010) [9 pages]

    Received 4 December 2009; revised 28 February 2010; published 13 April 2010

    We report on a systematic study of bias-voltage-induced modulation of magnetic and electronic properties of bilayer zigzag graphene nanoribbons (Z-GNRs) on Si(001) substrate by first-principles calculations. We show that the intrinsically nonmagnetic bilayer Z-GNRs exhibit magnetic ordering on the top layer while the bottom layer serves as a nonmagnetic buffer layer when adsorbed on the substrate. Interestingly, the adsorbed bilayers display distinct ribbon-width-dependent magnetoelectric effect under bias voltages. The magnetoelectric coefficient oscillates with increasing ribbon width, which arises from an interesting interplay of the interaction of the bottom ribbon layer with the substrates and the decay length of the localized edge states in Z-GNRs. Moreover, our calculations reveal that the electronic band gap of the top ribbon layer also can be effectively modulated by the applied bias voltage, which can lead to a semiconductor-to-metal transition in the top magnetic semiconductor layer. These results provide insights into the intriguing behaviors of Z-GNRs on substrates and raise the prospects of developing an innovative path toward graphene-based electronic and spintronic devices by integrating the emerging nanoscale graphene systems with existing silicon technology.

  • Inorganic salt-induced phase control and optical characterization of cadmium sulfide nanoparticles. Guo’an Tai, Jianxin Zhou, and Wanlin Guo. Nanotechnology, 2010, 21, 175601.

    Guo’an Tai, Jianxin Zhou and Wanlin Guo

    Institute of Nanoscience, Nanjing University of Aeronautics and Astronautics, 29 Yudao Street, Nanjing 210016, People’s Republic of China

    Nanotechnology, 2010, 21, 175601.

    Received 21 February 2010 , in final form 25 February 2010
    Published 1 April 2010

    Phase-controlled synthesis of CdS nanoparticles from zinc-blende to wurtzite has been successfully realized by an inorganic salt-induced process with no use of surfactants or other ligands in an ultrasound-assisted microwave synthesis system. Pure zinc-blende CdS nanoparticles were produced without adding NaCl, while mixed zinc-blende and wurtzite nanoparticles were obtained by adding NaCl/Cd2 + molar ratios below 1, and pure wurtzite nanoparticles were produced at a molar ratio of 1. The energy bandgap (Eg) of the CdS nanoparticles calculated from optical absorption spectra increases as the phase transformation from zinc-blende to wurtzite occurs. Additionally, the CdS nanoparticles showed a 489 nm band-edge emission without adding NaCl, and a 501 nm emission when the molar ratios of NaCl to Cd2 + are 0.25, 0.5 and 1. It was found that the phase transformation originates from the effect of the halide ion Cl − . We also found that some other halide ions such as Br − and I − can induce the phase transformation. It is shown that the phase, size and optical properties of the anisotropic nanoparticles can be well tuned by varying the concentration of the halide ions.

  • Hydration valve controlled non-selective conduction of Na+ and K+ in the NaK channel. Rong Shen, Wanlin Guo, and Wenyu Zhong. Biochimica et Biophysica Acta - Biomembranes, 2010, 1798(8), 1474-1479.

    Rong Shen,1, Wanlin Guo,1, and Wenyu Zhong,1

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

    Biochimica et Biophysica Acta - Biomembranes, 2010, 1798(8), 1474-1479.

    Received 28 June 2009; revised 20 March 2010; accepted 7 April 2010. Available online 11 April 2010.

    The Na+ and K+ channels are essential to neural signaling, but our current knowledge at the atomic level is mainly limited to the conducting mechanism of K+. Unlike a K+ channel having four equivalent K+-binding sites in its selectivity filter, a NaK channel has a vestibule in the middle part of its selectivity filter, and can conduct both Na+ and K+ ions. However, the underlying mechanism for non-selective ion conduction in NaK remains elusive. Here we find four small grottos connecting with the vestibule of the NaK selectivity filter, which form a vestibule-grotto complex perpendicular to the filter pore with a few water molecules within it. It is shown that two or more of the water molecules coming to the vestibule to coordinate the cation are necessary for conducting both Na+ and K+ ions, while only one water molecule in the vestibule will obstruct ion permeation. Thus, the complex with the aid of interior water movement forms a dynamic hydration valve which is flexible in conveying different cations through the vestibule. Similar exquisite hydration valve mechanisms are expected to be utilized by other non-selective cation channels, and the results should shed new light on the importance of water in neural signaling.

    Keywords: Hydration valve; Ion permeation; NaK channel; Water dynamics

  • Transport Properties of Single-File Water Molecules inside a Carbon Nanotube Biomimicking Water Channel. Guangchao Zuo, Rong Shen, Shaojie Ma and Wanlin Guo. ACS Nano, 2010, 4(1), 205-210.

    Guangchao Zuo, Rong Shen, Shaojie Ma and Wanlin Guo

    ACS Nano, 2010, 4 (1), pp 205–210

    Abstract

    The single-file water transport through a biomimic water channel consisting of a (6,6) carbon nanotube (CNT) with different types of external point charges is studied using molecular dynamics simulations. It is demonstrated that, as in the aquaporins, asymmetrically positioned charges cannot generate robust unidirectional water flow in the CNT. Thermal fluctuation in bulk water competes with charge affinity to steer the water transport, resulting in nonmonotonic flow with intermittent reversal of transport direction. The energetic analysis suggests that the water−water interaction, determined by dipole orientation configuration, influences the transport rate significantly. These findings can provide correct biomimic understanding of water transport properties and will benefit the design of efficient functional nanofluidic devices.

    Keywords: transport property; carbon nanotube; water channel; free energy; molecular dynamics simulation

  • Magnetism in armchair BC2N nanoribbons. Peng Lu, Zhuhua Zhang, and Wanlin Guo. Appl. Phys. Lett., 2010, 96, 133103.

    Peng Lu, Zhuhua Zhang, and Wanlin Guo

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

    Appl. Phys. Lett. 96, 133103 (2010)

    Received 20 October 2009; accepted 27 February 2010; published online 29 March 2010

    We show by first-principles calculations that H-terminated armchair BC2N nanoribbons (a-BC2NNRs) have exceptional electronic and magnetic properties. In particular, a-BC2NNRs with the B and N atoms uncoordinated can be either p- or n-doped semiconductors, and the wide ones own spontaneous magnetization. It is shown that the magnetism is induced by the localization of acceptor or donor levels from unpaired B or N atoms, and the magnetic moment increases with further increasing ribbon width. The a-BC2NNRs with B and N atoms coordinated have band gaps decreasing with increasing ribbon width.

  • Thermal vibration of carbon nanotubes predicted by beam models and molecular dynamics. Lifeng Wang, Haiyan Hu, and Wanlin Guo. Proc. R. Soc. A, 2010, 466, 2325-2340.

    Lifeng Wang,1, Haiyan Hu,1, and Wanlin Guo,2

    1. MOE Key Laboratory of Mechanics and Control of Aerospace Structures, Nanjing University of Aeronautics and Astronautics, 210016 Nanjing, People's Republic of China
    2. Institute of Nanoscience, Nanjing University of Aeronautics and Astronautics, 210016 Nanjing, People's Republic of China

    Proc. R. Soc. A 8 August 2010 vol. 466 no. 2120 2325-2340

    Published online before print March 10, 2010

    The paper presents a detailed study on the thermal vibration of a single-walled carbon nanotube by using different beam models of continuum mechanics, together with the law of energy equipartition, and the molecular dynamics simulations. The basic finding of the study is the relation, derived by using the Timoshenko beam model and the law of energy equipartition, between the temperature and the root-of-mean-squared (RMS) amplitude of thermal vibration at any cross section of the carbon nanotube. The molecular dynamics simulations show that both the Euler beam model and the Timoshenko beam model can roughly predict the thermal vibration of lower order modes for a relatively long carbon nanotube. However, the Timoshenko beam model, compared with the Euler beam model, offers a much better prediction of the RMS amplitude of the thermal vibration near the fixed end of the carbon nanotube. For the thermal vibration of a relatively short carbon nanotube or higher order models of a relatively long carbon nanotube, the difference between the Timoshenko beam and the Euler beam in dynamic prediction becomes obvious, and the Timoshenko beam model works much better than the Euler beam model.

  • Ultrasound-assisted microwave preparation of Ag-doped CdS nanoparticles. Jun Ma, Guo’an Tai, and Wanlin Guo. Ultrasonics Sonochemistry, 2010, 17(3), 534-540.

    Jun Ma,1, Guo’an Tai,1, and Wanlin Guo,1

    1. Institute of Nanoscience, Nanjing University of Aeronautics and Astronautics, No. 29, Yudao Street, Nanjing 210016, PR China

    Ultrasonics Sonochemistry, 2010, 17(3), 534-540.

    Received 28 September 2009; revised 9 November 2009; accepted 13 November 2009. Available online 18 November 2009.

    Ag-doped CdS nanoparticles were synthesized by an ultrasound-assisted microwave synthesis method. The X-ray diffraction patterns reveal a structural evolution from cubic to hexagonal with increasing molar ratios of Ag+/Cd2+ from 0% to 5%. It shows that the Ag-doped hexagonal CdS nanoparticles are polycrystal. The X-ray photoelectron spectroscopy of the CdS nanoparticles doping with 5% Ag+ shows that the doped Ag in CdS is metallic. Simultaneously, the characteristic Raman peaks of the CdS nanoparticles enhance with increasing Ag+ concentrations. The photocatalytic activity of different Ag-doped samples show a reasonable change due to different ratios of Ag which doped into CdS.

    Keywords: Ultrasound; Microwave; Ag–CdS; Phase evolution; Raman enhanced; Photocatalysis

  • Dynamic and energetic mechanisms for the distinct permeation rate in AQP1 and AQP0. Hu Qiu, Shaojie Ma, Rong Shen and Wanlin Guo. Biochim Biophys Acta, 2010, 1798(3), 318-326.

    Hu Qiu, Shaojie Ma, Rong Shen and Wanlin Guo

    Biochim Biophys Acta. 2010 Mar;1798(3):318-26.

    Abstract

    Despite sharing overall sequence and structural similarities, water channel aquaporin 0 (AQP0) transports water more slowly than other aquaporins. Using molecular dynamics simulations of AQP0 and AQP1, we find that there is a sudden decrease in the distribution profile of water density along the pore of AQP0 in the region of residue Tyr23, which significantly disrupts the single file water chain by forming hydrogen bond with permeating water molecules. Comparisons of free-energy and interaction-energy profiles for water conduction between AQP0 and AQP1 indicate that this interruption of the water chain causes a huge energy barrier opposing water translocation through AQP0. We further show that a mutation of Tyr23 to phenylalanine leads to a 2- to 4-fold enhancement in water permeability of AQP0, from (0.5 ± 0.2) × 10− 14 cm3s− 1 to (1.9 ± 0.6) × 10− 14 cm3s− 1. Therefore, Tyr23 is a dominate factor leading to the low water permeability in AQP0.

    Keywords: Aquaporin; Molecular dynamics; Water conduction; Energetic mechanism

  • Chemical-mechanical stability of the hierarchical structure of shell nacre. Jinmei Sun, and Wanlin Guo. Science China (Physics,Mechanics & Astronomy), 2010, 53(2), 380-388.

    Jinmei Sun, and Wanlin Guo

    Science China (Physics,Mechanics & Astronomy), 2010, 53(2), 380-388.

    The hierarchical structure and mechanical property of shell nacre are experimentally investigated from the new aspects of chemical stability and chemistry-mechanics coupling. Through chemical deproteinization or demineralization methods together with characterization techniques at micro/nano scales,it is found that the nacre of abalone,haliotis discus hannai,contains a hierarchical structure stacked with irregular aragonite platelets and interplatelet organic matrix thin layers. Yet the aragonite platelet itself is a nanocomposite consisting of nanoparticles and intraplatelet organic matrix framework. The mean diameter of the nanoparticles and the distribution of framework are quite different for different platelets. Though the interplatelet and in-traplatelet organic matrix can be both decomposed by sodium hydroxide solution,the chemical stability of individual aragonite platelets is much higher than that of the microstructure stacked with them. Further,macroscopic bending test or nanoindentation experiment is performed on the micro/nanostructure of nacre after sodium hydroxide treatment. It is found that the Young's modulus of both the stacked microstructure and nanocomposite platelet reduced. The reduction of the microstructure is more remark than that of the platelet. Therefore the chemical-mechanical stability of the nanocomposite platelet itself is much higher than that of the stacked microstructure of nacre.

  • Mechanical properties and thermal stability of stacked microstructure of nacre. Jinmei Sun, and Wanlin Guo. SCIENTIA SINICA Phys, Mech & Astron, 2010, 40(8), 1044-1053.

    Mechanical properties and thermal stability of stacked
    microstructure of nacre

    Jinmei Sun,1, and Wanlin Guo,2

    1 Mechanical and Electrical Engineering Department, Qingdao Technological University Qindao College, Qingdao,
    266106, China;
    2 Institute of Nanoscience, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

    SCIENTIA SINICA Phys, Mech & Astron, 2010, 40(8), 1044-1053.

    Large amount of effort has been invested in nacre of mollusc shells because of its stacked microstructure with
    aragonite platelets and thin organic matrix interlayers and excellent mechanical properties. However, the contribution
    to the mechanical properties by the interplatelet and intraplatelet organic matrixs in nacre is poorly understood. In this
    work, the structure-mechanical property relationship of nacre from Haliotis discus hannai was studied by mechanical
    tests coupling with thermal loads. It is found the thermal decomposition of interplatelet organic matrix effectively
    decreases the strength and toughness of nacre and makes its layer-stacked microstructure destroyed completely at
    250°C. However, at 250°C organic matrix of about 1.7 wt% is decomposed, which is only 40% of total organic
    matrix. And mechanical properties tests show that the thermal stability of the stacked microstructure of nacre is much
    worse than its primary element—the nanocomposite structure of aragonite platelet. Besides we propose that the
    structural design mechanism of layer-by-layer stacked form is the determinative factor of nacre stiffness, and the
    adhesives effect of organic matrix interlayers is also significant.
    Keywords: nacre, stacked microstructure, organic matrix, mechanical properties, thermal stability

  • Electric Field and Hydrogen Passivation Induced Band Modulations in Armchair ZnO Nanoribbons. Liangzhi Kou, Chun Li, Zhuhua Zhang and Wanlin Guo. J. Phys. Chem. C, 2010, 114 (2), 1326–1330.

    Electric-Field- and Hydrogen-Passivation-Induced Band Modulations in Armchair ZnO Nanoribbons

    Liangzhi Kou†, Chun Li‡, Zhuhua Zhang† and Wanlin Guo*†
    Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China, and School of Mechanics, Civil Engineering and Architecture, Northwestern Polytechnical University, Xi’an 710072, People’s Republic of China

    J. Phys. Chem. C, 2010, 114 (2), pp 1326–1330
    DOI: 10.1021/jp909584j
    Publication Date (Web): December 10, 2009

    We report on the electric-field- and H chemical-absorption-induced band manipulations of armchair ZnO nanoribbons using first-principles calculations. It is shown that the band gap of a semiconducting armchair nanoribbon can be reduced monotonically with increasing transverse field strength, demonstrating a giant Stark effect. The critical field strength to completely close the band gap decreases with increasing ribbon width, while it is almost independent of the stacking thickness. On the other hand, the nanoribbon with the edges fully passivated shows an enhanced gap but a slightly weaker Stark effect. We also observe hydrogen-termination-induced metallization of the ribbons when only the edge O atoms are passivated, which results from an n-type doping effect. These findings suggest potential ways of band engineering in armchair ZnO nanoribbons.

  • Tuning magnetism in zigzag ZnO nanoribbons by transverse electric fields. Liangzhi Kou, Chun Li, Zhuhua Zhang, and Wanlin Guo. ACS Nano, 2010, 4, 2124–2128.

    Liangzhi Kou†, Chun Li‡, Zhuhua Zhang† and Wanlin Guo*†

    † Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China, and School of Mechanics, Civil Engineering and Architecture
    ‡ Northwestern Polytechnical University, Xi’an 710072, People’s Republic of China

    J. Phys. Chem. C, 2010, 114 (2), pp 1326–1330

    Publication Date (Web): December 10, 2009

    We report on the electric-field- and H chemical-absorption-induced band manipulations of armchair ZnO nanoribbons using first-principles calculations. It is shown that the band gap of a semiconducting armchair nanoribbon can be reduced monotonically with increasing transverse field strength, demonstrating a giant Stark effect. The critical field strength to completely close the band gap decreases with increasing ribbon width, while it is almost independent of the stacking thickness. On the other hand, the nanoribbon with the edges fully passivated shows an enhanced gap but a slightly weaker Stark effect. We also observe hydrogen-termination-induced metallization of the ribbons when only the edge O atoms are passivated, which results from an n-type doping effect. These findings suggest potential ways of band engineering in armchair ZnO nanoribbons.