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Tsai M.K.,Tungnan University | Huang C.C.,Tungnan University | Lee Y.C.,Tungnan University | Yang C.S.,Tatung University | And 4 more authors.
Journal of Luminescence | Year: 2012

In this study, we present morphology control investigations on zinc oxide (ZnO) nanorods synthesized by microwave heating of a mixture of zinc nitrate hexahydrate and hexamethylenetetramine (HMTA) precursors in deionized water (DI water). To study the morphology and structural variations of the obtained ZnO nanorods in different molar ratio of zinc nitrate hexahydrate to HMTA, X-ray diffraction (XRD), scanning electron microscopy (SEM) images, Raman scattering, and photoluminescence (PL) spectroscopy were measured. XRD and SEM images are utilized to examine the crystalline quality as well as the morphological properties of the ZnO nanorods. It is found that morphology control can be achieved by simply adjusting the reactant concentrations and the molar ratio of zinc nitrate hexahydrate to HMTA. Raman scattering and PL spectroscopy measurements were demonstrated to study the size- and shape-dependent optical response of the ZnO nanorods. The Raman scattering result shows that the intensity of LO mode at around 576 cm-1 decreases with the increase in the molar ratio of zinc nitrate hexahydrate to HMTA, indicating the reduction of defect concentrations in the synthesized ZnO nanorods. Room temperature PL spectrum of the synthesized ZnO nanorods reveals an ultraviolet (UV) emission peak and a broad visible emission. An enhancement of UV emission appears in the PL spectra as the molar ratio of zinc nitrate hexahydrate to HMTA increases, indicating that the defect concentration of the synthesized ZnO nanorods can be reduced by increasing the molar ratio. © 2011 Elsevier B.V. All rights reserved. Source


Chen L.-Y.,National Taiwan University of Science and Technology | Yin Y.-T.,National Taiwan University of Science and Technology | Chen C.-H.,Protrustech Corporation Ltd | Chiou J.-W.,National Taiwan University
Journal of Physical Chemistry C | Year: 2011

In this study, ZnO nanowire arrays were prepared using a hydrothermal method. During growth, polyethyleneimine (PEI) and ammonia were added to adjust the structure and optical properties of the ZnO nanowires. Emission analysis revealed visible photoluminescence emissions from ZnO nanowires produced under various growth conditions. To correlate the relationship between visible emissions and structural defects in ZnO nanowires, we employed X-ray absorption spectroscopy (XAS) to characterize the coordination number and bond length of the ZnO nanowires. On the basis of analytical results, we determined that the red emission is attributed to interstitial zinc defects (Zni) and the yellow emission is attributed to interstitial oxygen defects (Oi). © 2011 American Chemical Society. Source


Lin M.C.,National Taiwan University | Lin M.C.,Taipei Medical University | Nien L.-W.,National Taiwan University | Chen C.-H.,Protrustech Corporation Ltd | And 3 more authors.
Applied Physics Letters | Year: 2012

An approach was proposed to characterize nanoscale ultrathin films using surface enhanced Raman scattering (SERS). Raman spectroscopy of the TiO 2 film as thin as ∼2 nm, which was prepared by atomic layer deposition, was obtained by depositing a nanostructured Au layer on the film surface. Red-shift in the extinction spectrum of the nanostructured Au layer was observed with increasing TiO 2 film thickness, ascribed to the increase in effective refractive index of the substrate slab and coupled plasmon resonance. This SERS technique can be applied to investigate a variety of solid-state ultrathin films in nanosclae materials and devices in future studies. © 2012 American Institute of Physics. Source


Chen L.-Y.,National Taiwan University of Science and Technology | Yang P.-A.,National Taiwan University of Science and Technology | Tseng C.-H.,National Taiwan University of Science and Technology | Hwang B.-J.,National Taiwan University of Science and Technology | And 2 more authors.
Applied Physics Letters | Year: 2012

CdSe xS 1-x quantum dots (QDs) were synthesized by a simple one-injection non-coordinate solvent method. The composition distribution of Se and S and the internal structures of the CdSe xS 1-x QDs can be tuned by the Se/S molar ratio. To investigate the internal structure of CdSe xS 1-x QD, x-ray absorption spectroscopy was used to examine the distribution of Se and S inside CdSe xS 1-x QDs. © 2012 American Institute of Physics. Source


Yin Y.-T.,National Taiwan University of Science and Technology | Wu S.-H.,National Taiwan University of Science and Technology | Chen C.-H.,Protrustech Corporation Ltd | Chen L.-Y.,National Taiwan University of Science and Technology
Journal of the Chinese Chemical Society | Year: 2011

In this article, we reported a low temperature solvothermalmethod to synthesize ZnO nanorods in one pot. In order to study the growth mechanism of ZnO nanorods, various preparative parameters, such as zinc species concentration, the molar concentration ratio of hydroxide [OH-] to zinc species [Zn2+], and surfactants, have been systematically examined. According to the analysis, the aspect ratio of ZnO nanorods was enlarged with the increase of the concentration ratio of [OH-] to [Zn2+]. However, themean diameter only causes subtle change. Additionally, the influence of surfactants was studied by two different kinds of surfactant, ethylenediamine (EDA) and hexadecylamine (HDA). From transmission electron microscopy analysis, the aspect ratio of ZnO nanorods was similar to that without adding surfactant. However, the green emission caused by oxygen defects or others can be omitted while the surfactants were added into the reaction. Herein, the growth mechanism was proposed to relate to the element of coordination polyhedron presented in the interface.When terminal vertex bonds with more growth units, the interface has higher growth rate for the crystal formation. Besides, the reaction mediumalso affects the growth mechanism of ZnO nanorods. In an alkalimedium, the larger hindrance effect of ONaions at the interface of (0001) and (01 1 1)faces, the growth rates of (0001) and (01 1 1)faces have a great hindrance relative to other crystal faces. Source

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