Weigang Lu

Baylor University, Waco, Texas, United States

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Publications (17)104.87 Total impact

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    ABSTRACT: Recently, rutile nanotwins were synthesized using high temperature organic solvent methods, yielding two kinds of common high-quality rutile twinned nanocrystals, (101) and (301) twins, accompanied by minor rutile nanorods (Lu et al 2012 CrystEngComm 14 3120-4). In this report, the atomic structures of the rutile and anatase nanocrystals are directly resolved with no need for calculation or image simulation using atomic resolution STEM techniques. The locations of the oxygen rows in the rutile twins' boundaries are directly determined from both HAADF images and ABF images. To the best of our knowledge, this is the first time oxygen columns have been distinguished in rutile twin boundaries using HAADF and BF imaging.
    Full-text · Article · Aug 2012 · Nanotechnology
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    ABSTRACT: V-shaped rutile twinned nanorods (VRTNs) with different aspect ratios were synthesized on large scale using a one-pot organic solvothermal method. Although several different types of VRTNs were produced, (101) twinned nanorods were the major product with minor amounts of (301) twins and straight nanorods. STEM, TEM and XRD characterizations show that [001] is the growth direction of VRTNs, with surfaces dominated by {110} facets. Intermediate formation of both brookite and anatase nanorods provides dual pathways to VRTNs' growth: one path in which anatase seeds trigger and promote brookite nanorod growth; and a second path in which anatase nanorods are formed by oriented attachment. Subsequent dissolution of both brookite and anatase nanorods provides titania to support VRTNs growth.
    No preview · Article · Apr 2012 · CrystEngComm
  • Yiping Fang · Welley S Loc · Weigang Lu · Jiye Fang
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    ABSTRACT: In(2)O(3)@SiO(2) core-shell nanoparticles were prepared using an organic solution synthesis approach and reverse-microemulsion technique. In order to explore the availability of various silica encapsulations, a partial phase diagram for this ternary system consisting of hexane/cyclohexane (1:29 wt), surfactant (polyoxyethylene(5)nonylphenyl ether, i.e., Igepal CO-520), and aqueous solution containing ammonium hydroxide was also established. It is realized that the shell-thickness can be tuned by several parameters such as the concentration of In(2)O(3) nanocrystal suspension and the dose of the Si-precursor, tetraethyl orthosilicate. It was observed that the deeper energy level emissions of In(2)O(3) were apparently enhanced when In(2)O(3) was confined by the silica-shell in such core-shell nanoparticles. However, this enhancement could be degraded by increasing the shell-thickness.
    No preview · Article · Dec 2011 · Langmuir
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    ABSTRACT: The three-dimensional self-assembly of a nanocrystal superlattice, i.e., a super crystal, has attracted increasing attention. The small building blocks for assemblies are usually spherical nanocrystals. Recent progress indicates that it is possible to achieve a super crystal using cubic nanocrystals. We further analyze and describe two-dimensional and some three-dimensional assemblies of uniform cubic-phase In2O3 nanocrystals with an octahedral shape. In this article, we demonstrate our amazing observations on these kinds of super crystals (or superlattices) as a model system, report their scale in at least tens of microns, and show other interesting features such as steps, terraces, kinks, and vacancies which are similar to those from a single crystal. Based on electron microscopy observations, three types of well-defined octahedral nanocrystal packed structures in such super crystal systems are also identified. The investigation of octahedral super crystal systems provides an alternate direction in research that may extend the interest of superlattice study to a broad spectrum by enriching and varying the shape of elemental building blocks. This may potentially result in new concepts and more challenging applications such as soft X-ray photonics.
    Full-text · Article · Jul 2008 · Journal of the American Chemical Society
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    Bing Guan · Weigang Lu · Jiye Fang · Richard B Cole
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    ABSTRACT: Titania represents an important material that has wide applications. The bactericidal efficiency of TiO(2) has been shown to be dependent on the size of the nanoparticles, so it is important to be able to reliably estimate their dimensions. In this study, a stable TiO(2) cluster suspension is produced by the thermal solvent process, and ultrasmall clusters (<1 nm) with different sizes are obtained by size-selection treatment. MALDI-TOF-MS and LDI-TOF-MS are shown to be useful for characterization of these ultrasmall nanoparticles. Peak maxima are found to correlate with nanoparticle size, and the possibility of using these mass spectrometry-based approaches to estimate nanoparticle size is affirmed. The size distributions of TiO(2) nanoparticles obtained from MALDI- and LDI-TOF-MS are in good agreement with parallel TEM observations. Finally, PSD analysis of inorganic nanomaterials is performed and valuable information about the structure of analytes has been obtained.
    Preview · Article · Apr 2007 · Journal of the American Society for Mass Spectrometry
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    ABSTRACT: Nanocrystals of Ag, PbSe, and PbTe were prepared via a high-temperature organic solution approach, respectively. Using a size-selection technique, the size-distribution of each set of nanocrystals could be fine-tuned and finally monodisperse products were achieved. Superlattice structure of binary self-assemblies in low size-ratio were also explored and characterized by transmission electron microscopy. It is realized that a success of achieving binary self-assembly pattern is greatly dependent on several key factors including particle size-distributions, relative concentrations of both components, as well as the size-ratios between Ag and PbSe (or PbTe) nanocrystals.
    Full-text · Article · Jul 2006 · Journal of Nanoscience and Nanotechnology
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    Masih Darbandi · Weigang Lu · Jiye Fang · Thomas Nann
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    ABSTRACT: Spherical PbSe@SiO2 nanoparticles have been successfully synthesized within reverse micelles via metal alkoxide hydrolysis and condensation within a microemulsion system. These core-shell nanoparticles were characterized by transmission electron microscopy (TEM), NIR absorption spectroscopy, energy-dispersive X-ray analysis, and TEM electron diffractions. It shows that the obtained core-shell structures have a spherical shape with narrow size distribution (average size approximately 35 nm) and smooth surfaces. The size of the particles and the thickness of the shells can be controlled by manipulating the relative rates of the hydrolysis and condensation reactions of tetraethoxysilane (TEOS) within the microemulsion.
    Full-text · Article · May 2006 · Langmuir
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    W. B. Jian · Weigang Lu · Jiye Fang · M. D. Lan · J. J. Lin
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    ABSTRACT: A high-temperature organic solution approach was applied to prepare crystalline PbSe quantum dots. It is diamagnetic with an atomic susceptibility of ∼ −1.0×10−4 emu/mol Oe for bulk PbSe. The core diamagnetism of bulk PbSe was subtracted from our raw data. While transforming into the nanophase, orbital susceptibility including finite-size corrections to the Landau susceptibility has been observed. A paramagnetic zero-field peak with a large diamagnetic susceptibility in high fields exhibit in the field dependent susceptibility as characteristics of the Landau orbital susceptibility. At low temperatures and fields the paramagnetism dominates the contribution of magnetization of quantum dots while the diamagnetism dominates at high temperatures and fields. All these measurements, showing paramagnetism at low fields, indicate the existence of spontaneous magnetization in the quantum dot. In addition, we have observed profound hysteresis loops implying ferromagnetism among the quantum dots even at room temperature, which is spontaneous magnetization in the quantum dot and of the ferromagnetic order among these quantum dots.
    Full-text · Article · Apr 2006 · Journal of Applied Physics
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    W B Jian · Weigang Lu · Jiye Fang · S J Chiang · M D Lan · CY Wu · ZY Wu · F R Chen · J J Kai
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    ABSTRACT: Different sizes of three-dimensional PbSe quantum dots have been synthesized for the study of orbital magnetic susceptibilities. Two types of orbital susceptibilities have been found, including the Curie susceptibility and finite-size corrections to the Landau susceptibility. The Curie term of a quantum dot manifests itself in the temperature dependence of magnetic susceptibility at low temperatures, while the field dependence of differential susceptibility at high temperatures shows finite-size corrections to the Landau susceptibility. Both of the two kinds of orbital susceptibility, estimated per quantum dot, show linear dependence on the size.
    Full-text · Article · Mar 2006 · The Journal of Chemical Physics
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    Weigang Lu · Jiye Fang · Yong Ding · Zhong Lin Wang
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    ABSTRACT: In this paper we report an electron microscopic observation of crystal shape development when PbSe nanocrystals were synthesized using a dynamic injection technique at different temperatures in the presence of oleic acid. A two-step evolution mechanism was proposed, indicating that the shape evolution of PbSe nanocrystals is dependent on the growth time, whereas the crystalline size can be tuned by varying the growth temperature under the studied conditions. It also implies that a higher growth rate in the 111 direction compared to that in the 100 direction results in the formation of nanocubes.
    Preview · Article · Nov 2005 · The Journal of Physical Chemistry B
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    Weigang Lu · Yong Ding · Yuxi Chen · Zhong Lin Wang · Jiye Fang
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    ABSTRACT: We report a synthesis of discrete, single-crystal, defect-free, and hexagonal Bi2Te3 nanoplatelets using a high-temperature organic solution approach, and we demonstrate a two-step epitaxial growth of the cylindrical strings of Bi2Te3 nanoplatelets on the surface of the Te rod by packing them along c-axis in a top-bottom-top-bottom sequence. This type of building-up provides additional opportunity for the exploration of novel thermoelectric properties from such quantum-confined materials, in which the boundary scattering of phonons is anticipated to enhance.
    Preview · Article · Aug 2005 · Journal of the American Chemical Society
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    Qingsheng Liu · Weigang Lu · Aihui Ma · Jinke Tang · Jun Lin · Jiye Fang
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    ABSTRACT: In this communication, we report a successful synthesis of quasi-monodisperse In2O3 nanocrystals with high crystallinity in a high-temperature organic solution. The average size of nanocrystals can be tuned using a dynamic injection technique. TEM and XRD investigations indicate that each nanocrystal is a single crystal. The optical determination implies that the photoluminescence behavior of these In2O3 nanocrystals is different from that of the bulk, probably due to the combination of weak quantum-confinement-effects and the nature of high crystallinity in nanocrystals.
    Full-text · Article · May 2005 · Journal of the American Chemical Society
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    ABSTRACT: We descried a method to synthesize single crystalline Fe3O4 nanotubes by wet-etching the MgO inner cores of MgO/Fe3O4 core-shell nanowires. Homogeneous Fe3O4 nanotubes with controllable length, diameter, and wall thickness have been obtained. Resistivity of the Fe3O4 nanotubes was estimated to be approximately 4 x 10-2 Omega cm at room temperature. Magnetoresistance of approximately 1% was observed at T = 77 K when a magnetic field of B = 0.7 T was applied. The synthetic strategy presented here may be extended to a variety of materials such as YBCO, PZT, and LCMO which should provide ideal candidates for fundamental studies of superconductivity, piezoelectricity, and ferromagnetism in nanoscale structures.
    Preview · Article · Feb 2005 · Journal of the American Chemical Society
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    ABSTRACT: We demonstrate a novel approach for the large-scale, shape-controlled synthesis of one-dimensional (1D) corrugated nanoarrays of Pb(1-x)Mn(x)Se nanocrystals (0.002 < or = x < or = 0.008) through an in-situ self-assembly without using either capping polymer or ionic surfactant. The one-step-prepared 1D nanoarrays exhibit a well-defined morphology, single-crystal orientation, and clean surface without amorphous contamination. The average diameter of the 1D nanoarrays can be controlled and varied from <10 to 80 nm by finely tuning the assembly temperature and the growth time. Four growth models were suggested to explain the in-situ self-assembly processes based on the fundamental building blocks of octahedral nanocrystals by sharing [111] facets.
    Full-text · Article · Nov 2004 · Journal of the American Chemical Society
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    Weigang Lu · J. Jiye Fang · Kevin L Stokes · Jun Lin
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    ABSTRACT: In this communication, we report our recent achievement in synthesis and self-assembly of both spherical and cubic PbTe nanocrystals using a high-temperature solution-phase synthesis approach. The possible mechanism of nanocrystalline evolution from spherical to cubic structure has also been discussed. It is possible to use the highly orientated PbTe nanocrystals as building blocks to achieve thickness-controlled film for further manipulation into thermoelectric devices.
    Full-text · Article · Oct 2004 · Journal of the American Chemical Society
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    ABSTRACT: We report a chemical approach for the in situ synthesis of conducting polymer-magnetic inorganic nanomaterials with the integration of a high temperature organometallic method and a new microemulsion system containing organic, surfactant and aqueous phases that were established to enable the formation of our host nanocomposite materials. Polypyrrole-based γ-Fe2O3 nanocomposites were prepared through this colloidal system. These organic–inorganic nanocomposites were characterized using X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, electrical resistivity and magnetization measurements. It was observed that the blocking temperature increases with increasing the γ-Fe2O3 nanocomponent in these samples. The resistivity and the temperature variation of resistivity have also been investigated.
    Preview · Article · Oct 2004 · Materials Letters
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    ABSTRACT: We report a chemical approach for the in situ synthesis of conducting polymer-magnetic inorganic nanomaterials with the integration of a high temperature organometallic method and a new microemulsion system containing organic, surfactant and aqueous phases that were established to enable the formation of our host nanocomposite materials. Polypyrrole-based g-Fe 2 O 3 nanocomposites were prepared through this colloidal system. These organic – inorganic nanocomposites were characterized using X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, electrical resistivity and magnetization measurements. It was observed that the blocking temperature increases with increasing the g-Fe 2 O 3 nanocomponent in these samples. The resistivity and the temperature variation of resistivity have also been investigated. D 2004 Elsevier B.V. All rights reserved.
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