Showing papers by "Michael H. Huang published in 2009"

Synthesis of Submicrometer-Sized Cu2O Crystals with Morphological Evolution from Cubic to Hexapod Structures and Their Comparative Photocatalytic Activity

Abstract: We report a facile method for the synthesis of cuprous oxide nanocrystals with systematic morphological evolution. Cubic, truncated cubic, cuboctahedral, truncated octahedral, octahedral, and short hexapod structures have been synthesized in an aqueous solution of CuCl2, NaOH, sodium dodecyl sulfate (SDS) surfactant, and hydroxylamine (NH2OH·HCl) reductant by simply varying the volume of hydroxylamine added to the reaction mixture. A slight modification in the volume of some reagents produced the extended hexapods. The order of the introduction of the reagents is important to the formation of these crystals with distinct morphologies and sharp faces. The sizes of these particles fall mostly in the range of 400−700 nm. Clear transition in the relative intensities of the (111) and the (200) reflection peaks in their XRD patterns was observed. Scattering bands dominate the UV−vis absorption spectra of these crystals. Crystal model analysis revealed that the {111} face contains surface copper atoms with dangl...

Plasmonic-enhanced polymer photovoltaic devices incorporating solution-processable metal nanoparticles

Abstract: We have explored the effect of gold nanoparticle (Au NP)-induced surface plasmons on the performance of organic photovoltaic devices (OPVs). The power conversion efficiency of these OPVs was improved after blending the Au NPs into the anodic buffer layer. The addition of Au NPs increased the rate of exciton generation and the probability of exciton dissociation, thereby enhancing the short-circuit current density and the fill factor. We attribute the improvement in device performance to the local enhancement in the electromagnetic field originating from the excitation of the localized surface plasmon resonance.

Seed-Mediated Synthesis of Palladium Nanorods and Branched Nanocrystals and Their Use as Recyclable Suzuki Coupling Reaction Catalysts

Abstract: In this study, we have used a simple seed-mediated synthesis process to prepare uniform Pd nanorods with average lengths of ∼200 and 300 nm through the addition of 50−100 μL of 0.004 M copper acetate solution into the growth solution for the first time. Because of their long lengths, they nicely settled to the bottom of the reaction vial and can easily be separated from the suspended faceted particles. The nanorods have an average diameter of ∼20 nm, so they have high aspect ratios of 10−15 or more. They can readily self-assemble into high-density packing structures on substrates. By increasing the volume of the copper acetate solution added to 250 μL, extensively branched Pd nanocrystals were obtained. The crystal structures of both particle morphologies have been examined. The nanorods possess a penta-twinned structure. Different growth directions have been found for the branched nanocrystals. The growth mechanism of these nanostructures was studied in great detail. A mixture of short Pd rods and facete...

Au Nanocrystal-Directed Growth of Au-Cu2O Core-Shell Heterostructures with Precise Morphological Control

Abstract: Formation of metal-semiconductor core-shell heterostructures with precise morphological control of both components remains challenging. Heterojunctions, rather than core-shell structures, were typically produced for metal-semiconductor composites. Furthermore, growth of semiconductor shells with systematic shape evolution using the same metal particle cores can also present a significant challenge. Here, we have synthesized Au-Cu(2)O core-shell heterostructures using gold nanoplates, nanorods, octahedra, and highly faceted nanoparticles as the structure-directing cores for the overgrowth of Cu(2)O shells by a facile aqueous solution approach. The gold nanoparticle cores guide the growth of Cu(2)O shells with morphological and orientation control. Systematic shape evolution of the shells can be easily achieved by simply adjusting the volume of reductant added. For example, truncated cubic to octahedral Cu(2)O shells were produced from octahedral gold nanocrystal cores. Unusual truncated stellated icosahedral and star column structures have also been synthesized. The heterostructures were found to be formed via an unusual hollow-shell-refilled growth mechanism not reported before. The approach has potential toward the preparation of other complex Cu(2)O structures with well-defined facets.

Seed-Mediated Synthesis of Branched Gold Nanocrystals Derived from the Side Growth of Pentagonal Bipyramids and the Formation of Gold Nanostars

Abstract: We report the first synthesis of elongated penta-branched gold nanocrystals with a shape resembling that of a star fruit but with sharp ends by a seeding growth approach. Cetyltrimethylammonium bromide (CTAB) capping surfactant was used, and AgNO3 was added to the last growth solution to promote the formation of the five side branches. Through an investigation of the products collected by adding AgNO3 into first, second, third, or fourth growth solution, the penta-branched nanocrystals were found to be derived from pentagonal bipyramid-shaped nanocrystals. Side growth over the twin boundaries results in the formation of five elongated branches with the highest point of each branch bisecting the branch into two halves. Smaller penta-branched nanocrystals with sizes of 70−110 nm and more fully developed larger nanocrystals with sizes of 200−350 nm can be readily prepared. The branches possess single-crystalline {111} faces. The intermediate products obtained at various time points were examined and their UV...

Formation of Hollow Gallium Nitride Spheres via Silica Sphere Templates

Abstract: We report the formation of hollow GaN spheres using silica sphere templates. First, silica spheres with an average diameter of ∼130 nm were synthesized. A mixture of GaCl3, silica spheres, water, and urea in 2-propanol was prepared and heated to 100 °C for 24 h to generate silica spheres with γ-Ga2O3 nanoparticle shells. Decomposition of urea and its reaction with water slowly increased the solution pH to ∼8; this controlled reaction is the key to forming uniform γ-Ga2O3 shells with a thickness of about 13 nm. The amounts of urea and water have been varied to find the optimal conditions for the preparation of the oxide shells. Transfer of the colloidal particle solution to silicon substrates and ammonolysis at 850 °C for 6 h produced the SiO2−GaN core−shell nanostructures. Immersion of the silicon substrates in an HF solution removed the silica cores, and hollow GaN spheres with a shell thickness of around 8 nm were formed. The morphologies and crystal structures of the oxide and nitride shells have been ...

Formation of Hexabranched GeO2 Nanoparticles via a Reverse Micelle System

Abstract: We report the first synthesis of GeO2 nanoparticles with six symmetrically arranged branches running along the long axis of each particle. The nanoparticles have a shape resembling that of a star fruit. A reverse micelle system with Triton X-100 serving as the capping surfactant for the aqueous phase and n-hexanol as the cosurfactant was adopted. Ge(OEt)4 was selected as the germanium source. Using the optimal synthesis procedure by reacting the mixture at room temperature for 3 h, hexabranched GeO2 particles with an average length of 185 nm were produced. The products have been examined by FE-SEM, TEM, X-ray diffraction, and FT-IR techniques. GeO2 nanoparticles with structually well-developed branches were gnereated only with solution pH values in the range of 0.9−1.1. At a low [H2O]/[Ge(OEt)4] molar ratio of 45, particles having a hexagonal bipyramidal shape but without branch formation were observed. Increasing this ratio to 90, branches begin to appear from the six side edges of the particles. By simp...

Growth of Core-Shell Ga-GaN Nanostructures via a Conventional Reflux Method and the Formation of Hollow GaN Spheres

Abstract: We report the growth of core−shell Ga−GaN nanostructures by simple refluxing of a mixture of GaCl3 and lithium bis(trimethylsilyl)amide (LiHMDS) in trioctylamine at 380 °C for 24 h under nitrogen flow. The resulting spherical Ga−GaN nanostructures had diameters of ∼550 nm. By immersing the nanostructures in aqua regia, the gallium cores could be removed, and hollow GaN spheres with thicknesses of 15−25 nm were produced. The shells consisted of connected GaN nanocrystals of both cubic and hexagonal phases. Infrared spectroscopy confirmed the presence of silica or silicate in the GaN shells. The silicon source likely comes from the pyrolysis of LiHMDS. The growth process was studied by examining the intermediate products formed. Gallium metal cores appeared below 380 °C, followed by the slow formation of GaN nanocrystals on the core surfaces. The slow growth of the GaN shells is related to the gradual supply of the nitrogen source from the thermal decomposition of LiHMDS. Thinner shells with a thickness of ...

Method of fabricating nanostructure and nanowire and device fabricated therefrom

Abstract: PROBLEM TO BE SOLVED: To obtain one-dimensional nanostructures having a diameter along the longitudinal axis which does not vary more than approximately 10% in the section exhibiting the maximum change in the diameter, and having a diameter of less than approximately 200 nm at the point of the maximum diameter. SOLUTION: One-dimensional nanostructures have uniform diameters of less than approximately 200 nm. These new nanostructures, which are referred to as "nanowires", include single-crystal homostructures as well as heterostructures of at least two single-crystal materials having different chemical compositions. Because single-crystal materials are used to form the heterostructure, the resultant heterostructure will be single-crystal as well. The nanowire heterostructures are generally based on a semiconducting wire wherein the doping and composition are controlled in either the longitudinal or radial directions, or in both directions, to yield a wire that comprises different materials. Examples of resulting nanowire heterostructures include a longitudinal heterostructure nanowire (LOHN) and a coaxial heterostructure nanowire (COHN). COPYRIGHT: (C)2010,JPO&INPIT