Jun Guo

Soochow University (PRC), Wu-hsien, Jiangsu Sheng, China

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Publications (55)301.11 Total impact

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    ABSTRACT: Growth orientation of silicon (Si) nanowires is the key in tailoring the optical and electrical characteristics of semiconductor devices. To date, however, the distribution and dictator are still unclear. In this work, Si nanowires are grown via thermal annealing of nickel (Ni) coated Si wafers. The morphology, growth orientation and the relation to the seeding Ni catalyst particles are examined via high resolution transmission electron microscopy and selected area electron diffraction pattern. Statistical results show that Si nanowires prefer to be along the <112> orientation, followed by the ones in the <110>, <111>, <001>, <113> and <133> orientations. Besides surface energy that is commonly believed to control the nanowire׳s growth, this work found that the nanowire׳s growth follows certain structure-sensitive principle at the wire/catalyst interface to minimize the mismatch in lattice spacing and dihedral angle.
    No preview · Article · Oct 2014 · Journal of Crystal Growth
  • Feng Ji Li · Sam Zhang · Jun Guo · Bo Li
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    ABSTRACT: Silicon (Si) nanowires are important building blocks in the devices of photonics, quantum-dots, optoelectronics and energy. So far, however, the morphology is yet well studied. In this work, Si/Si-oxide nanowires were grown through thermal annealing of nickel (Ni) coated Si wafers. Side-by-side biaxial, smooth or sinusoidal triple-concentric, fishbone-profiled, Ni-nanosphere entrapped nanowires, and the transitional morphologies were observed co-existing with the most abundant coaxial ones. The relation between the nanowires and the seeding particles is carefully explored via transmission electron microscopy and selected area electron diffraction pattern. In conjunction with the scrutiny of the existing mechanisms, it is found that the morphology of the nanowires is controlled by the diameter, vibration, phase distribution, and the eutectic precipitation of the seeding Ni–Si–O droplets. A detailed growth mechanism is proposed.
    No preview · Article · Jun 2014 · Nanoscience and Nanotechnology Letters
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    ABSTRACT: TiO2 nanorod (NR) and nanotube (NT) arrays grown on transparent conductive substrates are attractive electrode for solar cells. In this paper, TiO2 NR arrays are hydrothermally grown on FTO substrate, and are in situ converted into NT arrays by hydrothermally etching. The TiO2 NR arrays are reported as single crystalline, but the TiO2 NR arrays are demonstrated to be polycrystalline with a bundle of 2-5 nm single crystalline nanocolumns grown along [001] throughout the whole NR from bottom to top. TiO2 NRs can be converted to NTs by hydrothermal selective etching of the (001) core and remaining the inert sidewall of (110) face. A growth mechanism of the NR and NT arrays is proposed. Quantum dot-sensitized solar cells (QDSCs) are fabricated by coating CdSe QDs on to the TiO2 arrays. After conversion from NRs to NTs, more QDs can be filled in the NTs and the energy conversion efficiency of the QDSCs almost double.
    No preview · Article · Sep 2013 · Small
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    ABSTRACT: Growth of crystalline silicon nanowire of controllable diameter directly from Si wafer opens up another avenue for its application in solar cells and optical sensing. Crystalline Si nanowire can be directly grown from Si wafer upon rapid thermal annealing in the presence of the catalyst such as nickel (Ni). However, the accompanying oxidation immediately changes the crystalline Si nanowire to amorphous SiOx. In this study, amorphous carbon layer was sputtered to on top of the catalyst Ni layer to retard the oxidation. Scanning electron microscope, transmission electron microscope, Raman spectroscopy and X-ray photoelectron spectroscopy were employed to characterize the wires and oxidation process. A model was developed to explain the growth and oxidation process of the crystalline Si nanowire.
    No preview · Article · May 2013 · Thin Solid Films
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    ABSTRACT: Large-sized, 2D single crystals of perylene are grown by both solution-cast and physical vapor transport methods. The crystals have a atomically flat parallelogram morphology and the aspect ratios of the lateral extension compared to the thickness are up to 10(3) . The atomically flat feature leads to good interface contact, making a single-crystal field-effect transistor with higher mobility. The mobility of atomically flat crystals can be 10(3) -10(4) times higher than rough crystals.
    Full-text · Article · Apr 2013 · Small
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    ABSTRACT: A hetero-nanostructured photoanode with enhanced near-infrared light harvesting is developed for photoelectrochemical cells by Alfred Iing Yoong Tok, Xiaogang Liu and co-workers on page 1603. The photoanode comprises upconversion nanoparticles on the surface of titanium oxide inverse opal. A nanoshell of titanium oxide is deposited on the nanoparticles, followed by CdSe quantum dots. Upon near infrared excitation, upconversion nanoparticles emit visible light that excites quantum dots for charge separation. Electrons are injected into titanium oxide with minimal carrier losses. This heteronanostructure is envisioned to be applicable to thin film, liquid-junction, and organic solar cells where near-infrared light can be harvested for improved photon-to-electricity conversion efficiency.
    Full-text · Article · Mar 2013 · Advanced Materials
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    ABSTRACT: Unique DNA-promoted Pd nanocrystals on carbon nanotubes (Pd/DNA-CNTs) are synthesized for the first time, in which through its regularly arranged PO(4) (3-) groups on the sugar-phosphate backbone, DNA directs the growth of ultrasmall Pd nanocrytals with an average size of 3.4 nm uniformly distributed on CNTs. The Pd/DNA-CNT catalyst shows much more efficient electrocatalytic activity towards oxygen reduction reaction (ORR) with a much more positive onset potential, higher catalytic current density and better stability than other Pd-based catalysts including Pd nanocrystals on carbon nanotubes (Pd/CNTs) without the use of DNA and commercial Pd/C catalyst. In addition, the Pd/DNA-CNTs catalyst provides high methanol tolerance. The high electrocatalytic performance is mainly contributed by the ultrasmall Pd nanocrystal particles grown directed by DNA to enhance the mass transport rate and to improve the utilization of the Pd catalyst. This work may demonstrate a universal approach to fabricate other superior metal nanocrystal catalysts with DNA promotion for broad applications in energy systems and sensing devices.
    No preview · Article · Dec 2012 · Chemistry - A European Journal

  • No preview · Dataset · Nov 2012
  • Shaozhou Li · Hui Cai · Chee Lip Gan · Jun Guo · Ja Ma
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    ABSTRACT: We report a new synthesis route to form single-crystalline silicide nanowires (NWs) with the assistance of the reaction between SiO2 and Na2O, which has been intensively studied by glass industry for a century. Rare earth silicide NWs epitaxially grown on the clean silicon substrate surface has been well studied while the synthesis of out-of-plane grown rare earth silicide NWs has not been reported before. In this contribution, we demonstrate that by controlling the growth conditions, it is possible to obtain rare earth silicide NWs that were grown epitaxially aligned or free-standing on silicon wafers. The characterizations show that the NWs are catalyst and silica shell free. The growth mechanism was discussed and electrical properties of the obtained silicide NWs were characterized. These NWs are very attractive nanoscale building blocks for interconnects and fully silicided (FUSI) gate applications in nanoelectronics.
    No preview · Article · Sep 2012 · Journal of Materials Chemistry
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    ABSTRACT: Synthesis of nanocrystals with highly symmetric microstructure is a well-known challenge in many fields of science and technology. In this work, Well-defined uniform Co3O4 octahedrons were synthesized via a simple one step microwave reaction, in which different carbon materials were introduced acting not only as secondary heater, but also as morphology directing agent. The crystal-structure and shape of the samples are examined systemically by using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM). The octahedral Co3O4 obtained by carbon nanotubes (CNTs) assisting microwave process exhibited a weak ferromagnetic property. Its saturation magnetization values (Ms) and coercivity (Hc) values are 234.25 emu/g and 73.513 Oe, respectively.
    No preview · Article · Sep 2012 · Materials Letters
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    ABSTRACT: Nanosized hydroxyapatite (nHA) has been proposed as drug delivery vehicles because of its biocompatibility. While the possible risks of nHA inducing inflammation have been highlighted, the specific influence of varying nHA particle morphology is still unclear. In order to establish this understanding, nHA of four different shapes-needle (nHA-ND), plate (nHA-PL), sphere (nHA-SP) and rod (nHA-RD)-were synthesized. The particle effects with the concentration of 10-300 μg/mL on cytotoxicity, oxygen species generation, production of inflammatory cytokines (TNF-α and IL-6), particle-cell association and cellular uptake were evaluated on BEAS-2B and RAW264.7 cells. Results show that nHA-ND and nHA-PL induced the most significant cell death in BEAS-2B cultures compared to nHA-SP and nHA-RD. Necrosis-apoptosis assay by FITC Annexin V and propidium iodide (PI) staining revealed loss of the majority of BEAS-2B by necrosis. No significant cell death was recorded in RAW264.7 cultures exposed to any of the nHA groups. Correspondingly, no significant differences were observed in TNF-α level for RAW264.7 cells upon incubation with nHA of different shapes. In addition, nHA-RD exhibited a higher degree of particle-cell association and internalization in both BEAS-2B and RAW264.7 cells, compared to nHA-ND. The phenomena suggested that higher particle-cell association and increased cellular uptake of nHA need not result in increased cytotoxicity, indicating the importance of particle shape on cytotoxicity. Specifically, needle- and plate-shaped nHA induced the most significant cell-specific cytotoxicity and IL-6 expression but showed the least particle-cell association. Taken collectively, we demonstrated the shape-dependent effects of nHA on cytotoxicity, inflammatory cytokine expression and particle-cell association.
    No preview · Article · Mar 2012 · Archives of Toxicology
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    ABSTRACT: Boron Carbide is one the hardest and lightest material that is also relatively easier to synthesis as compared to other superhard ceramics like cubic boron nitride and diamond. However, the brittle nature of monolithic advanced ceramics material hinders its use in various engineering applications. Thus, strategies that can toughen the material are of fundamental and technological importance. One approach is to use nanostructure materials as building blocks, and organize them into a complex hierarchical structure, which could potentially enhance its mechanical properties to exceed that of the monolithic form. In this paper, we demonstrated a simple approach to synthesize one- and two-dimension nanostructure boron carbide by simply changing the mixing ratio of the initial compound to influence the saturation condition of the process at a relatively low temperature of 1500 degrees C with no catalyst involved in the growing process. Characterization of the resulting nano-structures shows B13C2, which is a superhard phase of boron carbide as its hardness is almost twice as hard as the commonly known B4C. Using ab-initio density functional theory study on the elastic properties of both B12C3 and B13C2, the high hardness of B13C2 is consistent to our calculation results, where bulk modulus of B13C2 is higher than that of B4C. High resolution transmission electron microscopy of the nanoflakes also reveals high density of twinning defects which could potentially inhibit the crack propagation, leading to toughening of the materials.
    No preview · Article · Jan 2012 · Journal of Nanoscience and Nanotechnology
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    ABSTRACT: SnO(2) nanorod arrays have been deposited on 4 inch SiO(2)/Si and Si wafers and stainless steel substrates by plasma-enhanced chemical vapor deposition without any high temperature treatment or additional catalysis. The SnO(2) nanorods grow up from seed nanocrystals along the [110] preferential direction by a self-catalyzed vapor-solid growth mechanism. The surface of the SnO(2) nanorods was modified by ZnO, Pt and Ni nanocrystals. After surface modification, the field emission properties of the SnO(2) nanorod arrays are improved. The Ni nanocrystal with sharp tips and edges act as additional field emission sites to SnO(2) nanorods and thus the Ni/SnO(2)/SiO(2)/Si outperforms other samples due to the synergistic effects of good conductivity and hierarchical sharp apexes. The field enhancement factor of the Ni/SnO(2)/SiO(2)/Si increased around 3 times while the turn-on field of 8.0 V μm(-1) is about one third of the SnO(2)/SiO(2)/Si device.
    No preview · Article · Nov 2011 · Nanoscale
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    ABSTRACT: Organic nanowires of 9,10-dibromoanthracene (DBA) and 9,10-dicyanoanthracene (DCNA) were obtained by adding the THF solution of DBA/DCNA into water containing P123 surfactants. The as-prepared nanowires were characterized by UV-vis, fluorescence spectra, Field Emission Scanning Electron Microscopy (FESEM), and Transmission Electron Microscopy (TEM). We found that DBA and DCNA nanowires emitted green light rather than blue light for molecules in THF solution. The red-shift UV and fluorescent spectra of DBA and DCNA nanowires implied that these nanowires were formed through J-aggregation. The photoconducting study of DBA/DCNA nanowire-based network on rGO/SiO(2)/Si shows different photocurrent behaviors upon irradiation, which displayed that electron transfer from DCNA nanowire to rGO was stronger than that of DBA nanowires to rGO.
    No preview · Article · Nov 2011 · Nanoscale
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    ABSTRACT: Nanoscale phase separation was investigated in epitaxial strained BiFeO 3 thin films on LaAlO 3 single crystal substrate. In biaxial strained thin films, nanoscale mixtures of the tetragonal-like and rhombohedral-like phases occur with a film thickness above 35 nm. For 10-30 nm ultrathin ones, tetragonal-like single phase is confirmed using synchrotron x-ray and the atomic force microscopy studies. However, nanoscale phase separations are still observed in quasi-uniaxial transmission electron microscopy foil specimens for those ultrathin films, indicating the phase separation emerges in a much smaller thickness in uniaxial constraint films than that in biaxial ones.
    No preview · Article · Oct 2011 · Applied Physics Letters
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    ABSTRACT: Nanomaterials that are enclosed by high index, reactive facets exhibit a significantly enhanced chemical reactivity, leading to superior performances in electronics, photonics, energy conversion and storage, as well as interfacing with living cells for various biological purposes. This article investigates the formation of single crystalline rare earth hydroxide nanobelts with selective control of high energy surfaces. Combining experimental and theoretical efforts, a carboxylic group and carbon-carbon double bond of oleic acid molecules are found to reduce the (0001) surface energy by 60%, leading to the growth of nanobelts and the stabilization of their high energy surfaces. These findings shed light on the growth of one-dimensional nanostructures that exhibit a simultaneous control over the crystallographic facets, shapes, and sizes. Our results engender a versatile synthesis method for nanomaterials that exhibit enhanced physical and chemical properties by overcoming their energy barrier to grow with high energy surfaces.
    Full-text · Article · Sep 2011 · CrystEngComm
  • Huili Wang · Sam Zhang · Soon-Eng Ong · Jun Guo
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    ABSTRACT: Carbon nanotube coatings were synthesized by rapid thermal processing of nickel doped amorphous carbon films. During sputter deposition of the films, different ratios of hydrogen/argon gas were used to study the effect of hydrogen on carbon nanotube growth. The results showed only amorphous nanofibers were grown on unhydrogenated films, while the hydrogenated films yield multiwalled carbon nanotubes. Hydrogen is believed to promote catalytic life of the nickel catalyst dots as well as gasifying the inner amorphous core of the nanofibers so as to result in the formation of the nano tubular structures.
    No preview · Article · Aug 2011 · Nanoscience and Nanotechnology Letters
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    ABSTRACT: Uniform SnO2 nanorod arrays have been deposited at low temperature by plasma-enhanced chemical vapor deposition (PECVD). ZnO surface modification is used to improve the selectivity of the SnO2 nanorod sensor to H2 gas. The ZnO-modified SnO2 nanorod sensor shows a normal n-type response to 100 ppm CO, NH3, and CH4 reducing gas whereas it exhibits concentration-dependent n–p–n transitions for its sensing response to H2 gas. This abnormal sensing behavior can be explained by the formation of n-ZnO/p-Zn-O-Sn/n-SnO2 heterojunction structures. The gas sensors can be used in highly selective H2 sensing and this study also opens up a general approach for tailoring the selectivity of gas sensors by surface modification.
    No preview · Article · Jul 2011 · Advanced Functional Materials
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    ABSTRACT: Rod-shaped hydroxyapatite nanoparticles of varying dimensions (≈ 60 ± 10, 120 ± 15, 240 ± 30 nm in length, labeled respectively as nHA60, nHA120 and nHA240) with specific surface areas (47.02, 23.33, 46.12 nm(2), respectively), were synthesized and their effects on cell viability, reactive oxygen species generation and cellular interaction with BEAS-2B, RAW264.7 and HepG2 were investigated. In vitro exposure of these cell lines to rod shape nHA particles within a range of 10-300 μg/ml for 24 h did not significantly alter cell viability studied by the WST-8 assay. A significant increase in reactive oxygen species (ROS) generation was however observed with the dihydrofluorescein diacetate (DFDA) assay after 4 h incubation with these nanoparticles. The lowest level of ROS generation was observed with nHA120 (with the smallest specific surface area); whereas nHA60 and nHA240 exhibited comparable ROS generation. Subsequently, the Alizarin Red-S (ARS) assay indicated a weaker association of calcium with cells compared to nHA60 and nHA240. The results thus suggest that high surface area may increase cell-particle interaction, which in turn influenced ROS generation. The combined results from all the cell lines thus indicated high biocompatibility of rod-shaped nHA.
    No preview · Article · Jun 2011 · Nanotoxicology
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    ABSTRACT: The chemical reaction between Ag nanoparticles (Ag NPs) and 7,7',8,8'- tetracycanoquinodimethane (TCNQ) microparticles (MPs) in aqueous solution for the formation of Ag-NP-decorated Ag-TCNQ nanowires is reported. Based on the results obtained by UV-vis spectroscopy and scanning electron microscopy (SEM), it is proposed that the reaction between Ag NPs and TCNQ MPs includes three stages, namely, aggregation of NPs and MPs, diffusion and reaction between NPs and MPs, and formation of Ag-TCNQ nanowires. The as-synthesized semiconducting Ag-TCNQ nanowires show good performance in nonvolatile memory devices with multiple write-read-erase-read (WRER) cycles in air.
    No preview · Article · May 2011 · Small

Publication Stats

2k Citations
301.11 Total Impact Points


  • 2013-2014
    • Soochow University (PRC)
      Wu-hsien, Jiangsu Sheng, China
  • 2003-2013
    • Nanyang Technological University
      • • School of Materials Science and Engineering
      • • School of Chemical and Biomedical Engineering
      Tumasik, Singapore