Lian-Ming Lyu

National Tsing Hua University, Hsin-chu-hsien, Taiwan, Taiwan

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Publications (9)52.38 Total impact

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    ABSTRACT: We fabricated Au-Cu2O core-shell octahedra, cuboctahedra, and nanocubes having sizes of 90-220 nm using 50 nm octahedral cores. The smaller particle sizes minimize the strong light scattering features from the Cu2O shells and enable the surface plasmon resonance (SPR) absorption band of the gold cores to be clearly identified. Beyond a lower shell thickness limit, the SPR band positions of the gold cores are independent of the shell thickness, but are strongly dependent on the exposed particle surfaces. The plasmonic band red-shifts from Au-Cu2O octahedra to cuboctahedra and nanocubes, and differs by as much as 26 nm between the octahedra and the nanocubes. The same facet-dependent optical effects were observed using larger octahedral gold cores and cubic gold cores. In contrast, simulation spectra show progressively red-shifted SPR band positions with increasing shell thickness. The Cu2O shells are also found to exhibit facet-dependent optical behavior. These nanocrystals can respond to changes in the solvent environment such as solvents with different refractive indices, indicating that the plasmonic field of the gold cores can extend beyond the particle surfaces despite the presence of thick shells. Plane-selective spectral responses to low concentrations of surfactants were also recorded.
    Nanoscale 03/2014; · 6.73 Impact Factor
  • Lian-Ming Lyu, Michael H Huang
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    ABSTRACT: Ag2 O nanocubes, rhombicuboctahedra, octahedra, and hexapods have been employed as templates for the generation of Ag2 O-Ag2 S core-shell structures through a rapid sulfidation process in a basic solution. Addition of an ammonia etching solution quickly removes the Ag2 O cores, thereby resulting in the formation of Ag2 S cages with morphologies that resemble the starting templates. The composition of the Ag2 S shells and cages has been extensively determined by various analytical techniques including X-ray and electron diffraction and X-ray photoelectron spectroscopy. The Ag2 S shells have a monoclinic crystal structure and are polycrystalline with some amorphous and porous regions. The nanocage formation process has been captured by transmission electron microscopy (TEM). Gap spaces are formed initially between the cores and the shells owing to uniform etching of the Ag2 O cores on all of the faces. No linkages connecting the cores to the shells have been observed. Depending on the potential scanning ranges applied, four types of electrochemical redox behavior have been identified for the Ag2 O and Ag2 O-Ag2 S cubes in a basic solution. The ability to easily fabricate thin sheets of Ag2 S over different Ag2 O surfaces should extend the applications of Ag2 S nanostructures.
    Chemistry - An Asian Journal 03/2013; · 4.57 Impact Factor
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    ABSTRACT: In this study, we have developed for the first time a fast and energy-efficient method for the synthesis of PbS nanocrystals with systematic shape evolution from cubic to truncated cubic, cuboctahedral, truncated octahedral, and octahedral structures. The method involves the addition of a small volume of preheated lead acetate and thioacetamide (TAA) mixture to an aqueous growth solution of lead acetate, thioacetamide, cetyltrimethylammonium bromide, and nitric acid. By varying the amount of thioacetamide added to the growth solution, PbS nanocrystals with different morphologies were generated in 2 h at 90 °C. Slight experimental modifications were adopted to generate truncated octahedra. The nanocrystals have very uniform dimensions with average sizes of 32-47 nm. Their structures have been extensively examined by electron microscopy. Nanocube sizes can also be tuned within a range. UV/Vis absorption spectra of PbS cubes, cuboctahedra, and octahedra all show decreasing but continuous absorption from 300 nm to beyond 1000 nm. By monitoring the speed of darkening of solution color, particle growth rate was found to be fastest for nanocubes, followed by truncated cubes, cuboctahedra, and octahedra. These monodisperse nanocrystals can readily form self-assembled structures. Truncated cubes and octahedra that form monolayer and multilayer packing arrangements have also been studied. This green approach to the synthesis of PbS nanocrystals with fine size and shape control should allow for investigations of their facet-dependent properties and the fabrication of novel heterostructures.
    Chemistry - A European Journal 09/2012; 18(45):14473-8. · 5.93 Impact Factor
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    ABSTRACT: We report a simple solvothermal synthesis approach to the growth of CuInS(2) nanocrystals with zincblende- and wurtzite-phase structures. Zincblende nanocrystals with particle sizes of 10-20 nm were produced using oleylamine as the solvent. When ethylenediamine was used as the solvent, similarly sized wurtzite nanocrystals with some degree of particle aggregation were formed. Use of a mixture of these solvents gave products with mixed phases including some polyhedral nanostructures. The crystal phases of these nanocrystals were carefully determined by X-ray diffraction and transmission electron microscopy analysis. All the samples exhibit strong absorption from the entire visible light region to the near-infrared region beyond 1300 nm. Pure-phase zincblende and wurtzite CuInS(2) nanocrystals were employed as ink in the fabrication of solar cells. The spray-coated nanocrystal layer was subjected to a selenization process. A power conversion efficiency of ~0.74% and a good external quantum efficiency profile over broad wavelengths have been measured. The results demonstrate that wurtzite and zincblende CuInS(2) nanocrystals may be attractive precursors to light-absorbing materials for making efficient photovoltaic devices.
    Langmuir 05/2012; 28(22):8496-501. · 4.38 Impact Factor
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    ABSTRACT: In this study, a new series of Cu(2)O nanocrystals with systematic shape evolution from cubic to face-raised cubic, edge- and corner-truncated octahedral, all-corner-truncated rhombic dodecahedral, {100}-truncated rhombic dodecahedral, and rhombic dodecahedral structures have been synthesized. The average sizes for the cubes, edge- and corner-truncated octahedra, {100}-truncated rhombic dodecahedra, and rhombic dodecahedra are approximately 200, 140, 270, and 290 nm, respectively. An aqueous mixture of CuCl(2), sodium dodecyl sulfate, NaOH, and NH(2)OH·HCl was prepared to produce these nanocrystals at room temperature. Simple adjustment of the amounts of NH(2)OH·HCl introduced enables this particle shape evolution. These novel particle morphologies have been carefully analyzed by transmission electron microscopy (TEM). The solution color changes quickly from blue to green, yellow, and then orange within 1 min of reaction in the formation of nanocubes, while such color change takes 10-20 min in the growth of rhombic dodecahedra. TEM examination confirmed the rapid production of nanocubes and a substantially slower growth rate for the rhombic dodecahedra. The rhombic dodecahedra exposing only the {110} facets exhibit an exceptionally good photocatalytic activity toward the fast and complete photodegradation of methyl orange due to a high number density of surface copper atoms, demonstrating the importance of their successful preparation. They may serve as effective and cheap catalysts for other photocatalytic reactions and organic coupling reactions.
    Journal of the American Chemical Society 01/2012; 134(2):1261-7. · 10.68 Impact Factor
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    Lian-Ming Lyu, Michael H. Huang
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    ABSTRACT: Ag2O nanocubes, rhombicuboctahedra, octahedra, and extended hexapods were employed for the examination of the relative stability of different crystal planes to chemical etching through careful face-selective etching. Precise control of the amount of NH3 solution injected into a mixture of Ag2O nanocrystals and NaOH enables this face-selective etching. Ag(NH3)2+ formed from dissolved silver ions should drive the etching process while NaOH tunes the reaction equilibrium to control morphology of the etched nanocrystals. The order of facet stability in this reaction was found to be {111} > {110} > {100}. The {100} faces are most easily etched. By carefully adjusting the volume of NH3 solution introduced, novel Ag2O cubic nanoframes and rhombicuboctahedra with square depressions on all the {100} faces can be fabricated. The {111} facets contain significant terminal silver atoms, so hydroxide ions should interact strongly to maintain these surfaces. Hydroxide ions are less effective at adsorbing on the {100} faces with terminal oxygen atoms, so these faces are more susceptible to etching. ζ potential measurements support the argument of hydroxide ion adsorption. Interestingly, the {100} facets of Ag2O were found to be most stable in a weakly acidic HNO3 solution; octahedral nanocrystals can transform into particles consisted of {100} square terraces.
    The Journal of Physical Chemistry C. 08/2011; 115(36).
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    Pei-Ju Chung, Lian-Ming Lyu, Michael H Huang
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    ABSTRACT: We report the development of a seed-mediated and iodide-assisted method for the synthesis of monodisperse gold nanocrystals with systematic shape evolution from rhombic dodecahedral to octahedral structures. Particle growth is complete in 15 min at room temperature, so the process is fast and energy-efficient. By progressively increasing the volume of KI used in a growth solution while keeping the amount of ascorbic acid added constant, nanocrystals with morphologies that vary from rhombic dodecahedral to rhombicuboctahedral, edge- and corner-truncated octahedral, corner-truncated octahedral, and octahedral structures were synthesized. The nanocrystals are monodisperse in size and readily form self-assembled structures on substrates. By simply adjusting the volume of gold seed solution added to a growth solution, particle sizes of the octahedral gold nanocrystals can be tuned with average opposite corner-to-corner distances of 42, 48, 54, 60, 68, 93, 107, and 125 nm. In the presence of HAuCl(4), iodide may act as a reducing agent. Variation of its volume in the solution may slightly modulate the reduction rate and affect the final crystal morphology. Intermediate structures collected during crystal growth reveal the presence of many twisted structures that surround a developing nanocrystal core. This nanocrystal growth mechanism and the less important role of surfactant in directing the polyhedral nanocrystal morphology is discussed.
    Chemistry - A European Journal 08/2011; 17(35):9746-52. · 5.93 Impact Factor
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    ABSTRACT: Rhombic dodecahedral and highly edge- and corner-truncated octahedral gold nanocrystal cores with entirely or significant {110} faces were employed to investigate the core–shell orientation relationship of Au–Cu2O core–shell heterostructures. By increasing the volume of reductant added, we synthesized Au–Cu2O face-raised cubes, cuboctahedra, and octahedra. TEM characterization indicates a fixed core–shell orientation relationship. The {100}, {110}, and {111} facets of the gold cores align parallel to the corresponding faces of the Cu2O shells. Structural requirements of the gold cores for the preparation of Au–Cu2O stellated icosahedra indicate that icosahedral gold nanocrystals are good candidates. Use of trisoctahedral nanocrystal cores cannot generate stellated icosahedra, but unusual face-raised octahedra with V-shaped {111} edges can be synthesized. Core–shell cubes, face-raised cubes, core–shell octahedra, and face-raised octahedra were examined for their comparative photocatalytic activity toward the photodegradation of methyl orange. Remarkably, all the cubes were found to be photocatalytically inactive because they are bounded by essentially {100} facets. Face-raised octahedra with more {111} facets showed significantly better photocatalytic performance than regular Au–Cu2O core–shell octahedra. The results reveal that gold nanocrystal-enhanced photocatalysis can be achieved only with Cu2O shells exposing proper facets.
    Chemistry of Materials 04/2011; 23(10):2677–2684. · 8.24 Impact Factor
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    ABSTRACT: We report the development of a facile method for the synthesis of Ag(2)O crystals with systematic shape evolution from cubic to edge- and corner-truncated cubic, rhombicuboctahedral, edge- and corner-truncated octahedral, octahedral, and hexapod structures by mixing AgNO(3), NH(4)NO(3), and NaOH at molar ratios of 1:2:11.8. A sufficient volume of NaOH solution was first added to a mixture of AgNO(3) and NH(4)NO(3) solution to promote the formation of Ag(NH(3))(2)(+) complex ions and the growth of Ag(2)O nanocrystals with good morphological control. The crystals are mostly submicrometer-sized. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy characterization has been performed to determine the crystalline surface facets. A band gap value of approximately 1.45 eV has been found for the octahedral Ag(2)O crystals. By changing the molar ratios of AgNO(3)/NH(4)NO(3)/NaOH to 1:2:41.8, corner-depressed rhombicuboctahedra and elongated hexapods were obtained as a result of enhanced crystal growth along the [100] directions. Smaller nanocubes with average sizes of approximately 200 and 300 nm and octapods can also be prepared by adjusting the reagent molar ratios and their added volumes. Both the octahedra and hexapods with largely silver atom-terminated {111} surface facets responded repulsively and moved to the surface of the solution when dispersing in a solution of positively charged methylene blue, but can be suspended in a negatively charged methyl orange solution. The cubes and octapods, bounded by the {100} faces, were insensitive to the molecular charges in solution. The dramatic facet-dependent surface properties of Ag(2)O crystals have been demonstrated.
    Chemistry - A European Journal 10/2010; 16(47):14167-74. · 5.93 Impact Factor