Jun Guo

Singapore Institute of Manufacturing Technology (SIMTech), Tumasik, Singapore

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Publications (46)205.33 Total impact

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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.
    Small 04/2013; · 7.82 Impact Factor
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    ABSTRACT: A hetero-nanostructured photoanode with enhanced near-infrared light harvesting is developed for photo-electrochemical cells. By spatially coating upconversion nanoparticles and quantum dot photosensitizers onto TiO(2) inverse opal, this architecture allows direct irradiation of upconversion nanoparticles to emit visible light that excites quantum dots for charge separation. Electrons are injected into TiO(2) with minimal carrier losses due to continuous electron conducting interface.
    Advanced Materials 01/2013; · 14.83 Impact Factor
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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.
    Small 11/2012; · 7.82 Impact Factor
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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.
    Chemistry - A European Journal 10/2012; · 5.93 Impact Factor
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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.
    Journal of Materials Chemistry 09/2012; 22(39):20958-20961. · 6.63 Impact Factor
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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.
    Archives of Toxicology 03/2012; · 5.22 Impact Factor
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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.
    Journal of Nanoscience and Nanotechnology 01/2012; 12(1):596-603. · 1.15 Impact Factor
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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.
    Nanoscale 11/2011; 4(5):1491-6. · 6.73 Impact Factor
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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.
    Nanoscale 11/2011; 3(11):4720-3. · 6.73 Impact Factor
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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.
    Nanotoxicology 06/2011; 5(2):182-94. · 7.84 Impact Factor
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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.
    Advanced Functional Materials 05/2011; 21(14):2680 - 2686. · 10.44 Impact Factor
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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.
    Small 05/2011; 7(9):1242-6. · 7.82 Impact Factor
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    ABSTRACT: With advances of quantum dots (QDs) in bioimaging applications, various materials have been used to coat QDs to reduce their nanotoxicity; however, the coating could introduce new toxic sources and quench the fluorescence in bioimaging applications. In this work, ZrO₂, an excellent ceramic material with low extinction coefficient and good biocompatibility, is utilized to coat CdTe QDs for the first time. Experimental results show that ZrO₂-QD nanocomposites with the size of ~30 nm possess enhanced fluorescence emission, lower nanotoxicity and gradually increased fluorescence under 350 nm light illumination. After functionalization with folic acid, they were applied to label cultured HeLa cells effectively. Therefore, the ZrO₂-QD nanocomposites could be promising biocompatible nanomaterials with strong fluorescence emission to replace or complement QDs in biomedical applications.
    Nanotechnology 04/2011; 22(15):155604. · 3.84 Impact Factor
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    ABSTRACT: Two novel shapes of 9,10-diphenylanthracene (DPA) micro/nanostructures: octahedron and sphere together with microrod and nanowire have been synthesized via a surfactant-assisted self-assembling process. These micro/nanostructures have been characterized by UV−vis, fluorescence spectra, X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), and transmission electron microscope (TEM). Our results indicated that the absorption and emission spectra of as-prepared particles were slightly blue-shift when the shape of DPA particles changed from octahedron to microrod and finally to nanowire. This result could be explained by the different growth directions of DPA micro/nanostructures. To study the relationship between shape and devices’ performance, the heterojunction light emitting diode (LED) devices of quartz/ITO/organic particles/n-SiC/Ti(10 nm)/Au(120 nm) have been prepared. The testing results showed that the different shapes of DPA micro/nanostructures did affect the performance of diodes and the nanowire was the best shape for the heterojunction light emitting diode (LED) devices.
    The Journal of Physical Chemistry C. 03/2011; 115(16):7924–7927.
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    ABSTRACT: Boron carbidenanoparticles and nanoflakes represent nano-building blocks for complex hierarchical assembly of nanoscale structures that exhibit ideal mechanical robustness. These nano-building blocks were synthesized by simply changing the mixing ratio of the solid precursors to influence the saturation condition of the process. As such, the ability to tune the nanostructures of boron carbide was achieved by controlling the concentration of gaseous boron oxide in the process with no catalyst involved in the growing process. The phase of the resulting nanostructures were found to be B13C2, which is a much desired phase because its hardness of close to 60 GPa is twice as hard as B4C. Nanoflakes were found to contain high degree of (101)-type twins with their boundaries likely to pass through the center of icosahedra in the structure. Nanoflakes with twinned microstructure are anticipated as a model nanostructure and can provide opportunities to fundamentally explore their mechanistic nature since twins have the potential in inhibiting the crack propagation, leading to toughening the materials.
    CrystEngComm 02/2011; 13(5):1299-1303. · 3.88 Impact Factor
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    ABSTRACT: Coronenenanowires were prepared through the reprecipitation method. The as-prepared one-dimensional (1D) nanostructures were characterized by UV-vis, fluorescence spectra, X-ray diffraction (XRD), optical microscopy, field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). We found that coronenenanowires in aqueous solution emitted strong green light instead of blue light for coronene molecules in THF solution. Moreover, the thin film of coronenenanowires on rGO/SiO2/Sielectrode produced a strong photocurrent response upon irradiation. In addition, a heterojunction light emitting diode (LED) device with the structure of quartz/ITO/p-coronenenanowires/n-SiC/Ti (10 nm)/Au (120 nm) has been fabricated. The strong electroluminescence (EL) emission centered at 430 nm was detected with a forward bias at 20 V. Our result showed that the use of organic nanowires as the p-type hole injection layer could produce diodes with performance better than those with only inorganic thin-film structures.
    Journal of Materials Chemistry 01/2011; 21(5):1423-1427. · 6.63 Impact Factor
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    ABSTRACT: In this work, Pt nanowire networks supported on high surface area carbon (Pt NWNs/C) are synthesized as electrocatalysts for direct methanol fuel cells (DMFCs). The electrocatalytic behavior of Pt NWNs/C catalysts for the methanol and adlayer CO oxidation reactions is investigated and the results are compared with the Pt nanoparticles (NPs) supported on carbon (Pt NPs/C). The results indicate that Pt NWNs are characterized by interconnected nanoparticles with large number of grain boundaries, downshifted d-band center and reduced oxophilicity, which results in the enhanced surface mobility of oxygen-containing species such as COads and OHads. The enhanced surface mobility of COads and OHads in turn facilitates the removal of intermediate CO species during the methanol oxidation. The activity of the Pt NWNs/C electrocatalyst for the methanol oxidation reaction and electrooxidation of adsorbed CO is also evaluated by cyclic voltammetry, CO stripping, and kinetic analysis. The results show that Pt NWNs/C catalysts have a significantly higher electrocatalytic activity for the methanol oxidation reaction as compared to Pt NPs/C catalysts. The enhanced electrocatalytic activity of Pt NWNs/C catalysts is mainly due to the existence of large number of the grain boundaries of the interconnected nanoparticles of the unique Pt NWN structure.
    Electrochimica Acta. 01/2011; 56(3):1563-1569.
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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.
    CrystEngComm 01/2011; 13(17):5367-5373. · 3.88 Impact Factor
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    ABSTRACT: Although CdTe nanocrystal has been applied in quantum dot (QD)-based solar cells, there is no report on a graphene-CdTe QD hybrid system and its photoresponses. In this work, graphene-CdTe QD composed nanosheets were one-step synthesized in aqueous solution using a hydrothermal method and demonstrated enhanced photoresponses, rendering potentials in optoelectronics applications. This work could provide an environmental-friendly and universal approach to fabricate graphene-based hybrid nanomaterials for various applications.
    Journal of Colloid and Interface Science 10/2010; 353(2):588-92. · 3.55 Impact Factor

Publication Stats

338 Citations
205.33 Total Impact Points

Institutions

  • 2013
    • Singapore Institute of Manufacturing Technology (SIMTech)
      Tumasik, Singapore
    • Soochow University (PRC)
      Wu-hsien, Jiangsu Sheng, China
  • 2012
    • Southwest University in Chongqing
      Pehpei, Chongqing Shi, China
  • 2011
    • Hebei University
      Pao-ting-shih, Hebei, China
  • 2003–2011
    • Nanyang Technological University
      • • School of Chemical and Biomedical Engineering
      • • School of Materials Science and Engineering
      Singapore, Singapore