H. P. Wu

Zhejiang University, Hangzhou, Zhejiang Sheng, China

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Publications (14)19.46 Total impact

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    Scientia Silvae Sincae. 06/2011;
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    ABSTRACT: Monodisperse ZnO nanoparticles were successfully prepared through the decomposition of zinc acetylacetonate precursor in oleylamine. The samples were characterized by transmission electron microscope, X-ray diffraction and infrared spectroscopy. The particle size and morphology could be modified through tuning the reaction temperature, reaction period and concentration of zinc acetylacetonate. The grain size of monodisperse ZnO could be obtained at 205 and 300 °C for 1 h with 1:100 molar ratio of acetylacetonate and oleylamine, respectively. The average grain size of ZnO nanoparticles increased and the shape of ZnO particles varied with the reaction period prolonging or reaction temperature increasing. Some ZnO particles had self-aggregated into a belt using a solution of 1:10 molar ratio of zinc acetylacetonate and oleylamine at 250 °C for 1 h. The oleylamine plays an important role in preventing aggregation of ZnO nanoparticles.
    Materials Letters. 04/2007;
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    ABSTRACT: In this study, chemical plating method was used to prepare silver coated carbon nanotubes (SCCNT). Fundamental materials characterizations including X-ray diffraction and transmission electro microscopy (TEM) were conducted on these nanotubes. Two kinds of isotropical conductive adhesives (ICA) were developed by using multi-walled carbon nanotubes (CNT), SCCNT as conductive fillers, respectively. The electrical, mechanical and aging properties of above ICAs were investigated and compared with that of conventional ICA filled with 1 μm average-sized Ag particles. The results indicated that the percolation threshold of bulk resistivity reaches 2.4 × 10−3 Ω cm for ICA filled with 31% CNT and the shear strength reaches the maximum value for ICA filled with 23% CNT. At the same filler volume content of 28%, the ICAs filled with SCCNT shows the lowest conductive resistivity of 2.2 × 10−4 Ω cm and the ICAs filled with both CNT and SCCNT exhibit higher shear strength (19.6 MPa). The testing results of aging properties under conditions of 85 °C, RH85% for 1000 h showed that the shifts of both bulk resistivity and shear strength did not exceed 15% for the ICAs filled with both CNT and SCCNT, while the shifts of conductive resistivity and shear strength were 200% and 35%, respectively, for ICA filled with micro-sized Ag particles.
    Composites Science and Technology. 01/2007;
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    ABSTRACT: Using oleic acid as surfactant, triangle-shape ZnO with an average diameter of 250 nm can be synthesized by thermal decomposition of precursor zinc acetate (Zn(CH3CH2COO)2) in the high boil-point solvent trioctylamine (TOA). Fundamental characterizations including transmission electron microscopy, X-ray diffraction, high-resolution transmission electron microscopy, scanning electron microscopy and photoluminescence were conducted for the as-synthesized ZnO particles. The effects of refluxing time and the content of surfactant on size and morphology of ZnO particles were studied. It is found that the shape of ZnO particles changes from round-shape, disk-shape to triangle-shape. Based on experimental observations and surface and attachment energies simulation for various crystallographic planes, a possible growth mechanism was put forward to explain the formation of triangle-shape ZnO particles.
    Materials Letters - MATER LETT. 01/2007; 61(16):3416-3420.
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    ABSTRACT: By varying the concentration of surfactant in reverse micelle system, Ag particles from 10 to 200 nm in average diameter were synthesized, which have been characterized by X-ray diffraction and transmission electron microscopy. Isotropical conductive adhesives (ICAs) were prepared by using Ag particles as conductive fillers. It was found that the percolation threshold of ICAs depends on the filler size, which reaches to 63 wt.% when the filler average particle diameter is 50 nm. Results obtained by theoretical calculation are in good agreement with the experimental results.
    Composites Science and Technology. 01/2007;
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    ABSTRACT: A simple method was used to prepare monodispersed ZnO nanoparticles, which can be used as seeds for the synthesis of [0001]-oriented ZnO nanorods by refluxing. Based on the observation of shape and size of ZnO nanocrystals at different refluxing times and surface and attachment energies for various crystallographic planes calculated from the BFDH and HP models, a possible growth mechanism for ZnO nanorods was put forward to explain the experimental observations. The synthesized ZnO nanocrystals show green emission, which are correlated with the degree of oxygen vacancies in the samples.
    Journal of Crystal Growth 01/2007; 305(1):162-166. · 1.55 Impact Factor
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    ABSTRACT: Monodisperse iron oxide nanoparticles with 5–20 nm can be synthesized by an inexpensive and simple ultrasonic-assisted method at low temperature. This is based on the decomposition of iron pentacarbonyl in cis–trans decalin. The high energy emitted by ultrasonic irradiation at a short time can promote the crystallization process simultaneously. At low temperature, these crystalline nucleuses can grow to monodisperse nanoparticles. Effects of ultrasonic treatment, the concentration of surfactant and the refluxing time on the size and size distribution of iron oxide nanoparticles were investigated. The morphology and crystal structure of iron oxide nanoparticles obtained at different conditions were characterized by high-resolution transmission electron microscope, X-ray diffraction and selected area electron diffraction.
    Materials Letters - MATER LETT. 01/2007; 61(11):2204-2207.
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    ABSTRACT: Hexagonal CoO nanocrystals are coarsened under hydrothermal conditions to investigate the effect of particle size on phase transformation and stability property. Structural stability and phase transformation of the hexagonal CoO phase have been investigated by X-ray powder diffraction with Rietveld refinement, transmission electron microscopy, X-ray absorption fine structure, and differential scanning calorimeter. It is found that the hexagonal CoO phase is a metastable phase, which increases its grain size from 50 to 250 nm for refluxing times from 1 to 6 h at 200 degrees C. After 12 h, cubic-structured CoO grains with an average grain size of 20 nm are observed, which spread around big hexagonal CoO grains. After about 24 h, only the cubic CoO phase with an average grain size of 25 nm is detected. The onset temperature of hexagonal-to-cubic phase transformation in CoO is estimated to be 378 degrees C by DSC, using a heating rate of 20 deg/min. The results obtained indicate that the hexagonal-to-cubic phase transformation in nanocrystalline CoO is by nucleation and growth mechanism, starting from the surface to the center of the hexagonal grains.
    The Journal of Physical Chemistry B 12/2006; 110(43):21588-92. · 3.61 Impact Factor
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    ABSTRACT: We report here a simple synthesis method for monodisperse Ge nanocrystals by thermal decomposition of precursor TOG at 360 °C, which is obtained by a reaction of GeCl4 with oleylamine at room temperature. The effect of refluxing time on the average dimension of Ge nanocrystals is discussed. Fundamental characterizations including HRTEM and XRD were performed on these Ge nanocrystals. FTIR, DSC and TG were used to explain the mechanism of formation of Ge nanocrystals by thermal decomposition of TOG. Ge nanocrystals with average grain sizes clearly exhibit blue emission, which might result from the hydrocarbon absorbed on the surface Ge nanocrystals, the amorphous oxide layer on the surface of Ge nanocrystals and/or defects in Ge nanocrystals.
    Nanotechnology 10/2006; 17(21):5339. · 3.84 Impact Factor
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    ABSTRACT: We report here a synthesis method for single-crystal monodisperse GeO2 nanocubes in a reverse micelle system. Hydrolysis of germanium tetrachloride (GeCl4) in a micelle system produces GeO2 nanocubes in the presence of oleylamine and cetyltrimethylammonium (CTAB). The average edge length of the cubes varies from 50 to 520 nm depending on the concentration of CTAB in the solution. The perfection and monodispersity of the nanocubes are greatly improved by decreasing the pH value of the water solution. Different morphologies such as capsules can be prepared by using octane as the oil phase. The BFDH and Hartman-Perdok methods were used to predict the morphology evolution during the growth of GeO2 nanocubes.
    Chemistry of Materials 04/2006; 18(7):1817-1820. · 8.24 Impact Factor
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    ABSTRACT: As an alternative to lead-bearing solder, isotropic conductive adhesives (ICA) have been utilized for many years in microelectronic packaging. In this study, silver nitrate (AgNO3) as precursor, N-N-dimethylformamide (DMF) as solvent and reducing agent, preparing silver (Ag) nanowires in the nanoporous templates formed by the controlled hydrolysis and condensation of butyl titanate (Ti(OC4H9)4). The Ag nanowires were characterized by X-ray diffraction and transmission electron microscopy. An isotropic conductive adhesive (ICA) has been developed by adding Ag nanowires as conductive filler. Bulk resistivity and shear strength of the ICA are measured and compared with those of conventional ICA filled with micrometer-sized Ag particles (about 1 μm) and nanometer-sized Ag particles (about 100 nm). It is found that the ICA filled with lower content of Ag nanowires exhibits lower bulk resistivity and higher shear strength than ICA filled with micrometer-sized Ag particles and nanometer-sized Ag particles. Possible conductive mechanisms of the ICA are discussed.
    International Journal of Adhesion and Adhesives. 01/2006;
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    ABSTRACT: Germanium nanocrystals, ranging from 3 to 10 nm with a narrow size distribution, can be synthesized by an inexpensive, simple ultrasonic solution reduction method. This is based on the reduction of GeCl4 by metal hydride or alkaline in ambient condition. Effects of reduction agent, reaction condition and the concentration of GeCl4 on the formation of germanium nanocrystals were investigated. The morphology and the crystal structure of Ge nanocrystals obtained at different conditions were characterised by transmission electron microscope and selected area electron diffraction. Possible mechanisms for the formation of Ge nanocrystals were discussed.
    Materials Letters - MATER LETT. 01/2006; 60(7):986-989.
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    ABSTRACT: The high-pressure behaviour of nanocrystalline alpha-quartz GeO2 (q-GeO2) with average crystallite sizes of 40 and 260 nm has been studied by in situ high-pressure synchrotron radiation x-ray diffraction measurements up to about 51.5 GPa at ambient temperature. Two phase transformations, q-GeO2 to amorphous GeO2 and amorphous GeO2 to monoclinic GeO2, are detected. The onset and end of the transition pressures for the q-GeO2-to-amorphous GeO2 phase transition are found to be approximately 10.8 and 14.9 GPa for the 40 nm q-GeO2 sample, and 9.5 and 12.4 GPa for the 260 nm q-GeO2 sample, respectively. The mixture of amorphous and monoclinic GeO2 phases remains up to 51.5 GPa during compression and even after pressure release. This result strongly suggests that the difference of free energy between the amorphous phase and the monoclinic phase might be small. Consequently, defects in the starting material, which alter the free energies of the amorphous phase and the monoclinic phase, may play a key role for the phase transformation of q-GeO2.
    Journal of Physics Condensed Matter 01/2006; 181:10817-10824. · 2.22 Impact Factor
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    ABSTRACT: Journal article
    Chemical Science 18(2006)1817,1822.