Browsing by Author "Yang, S"

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Orientation-enhanced growth and optical properties of ZnO nanowires grown on porous silicon substrates
(2005-02-01)
Hsu, HC
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Cheng, CS
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Chang, CC
;
Yang, S
;
Chang, CS
ZnO nanowires have been synthesized on porous silicon substrates with different porosities via the vapour-liquid-solid method. The texture coefficient analysed from the XRD spectra indicates that the nanowires are more highly orientated on the appropriate porosity of porous silicon substrate than on the smooth surface of silicon. The Raman spectrum reveals the high quality of the ZnO nanowires. From the temperature-dependent photoluminescence spectra, we deduced the activation energies of free and bound excitons.
Structural and optical properties of ZnO nanosaws
(2006-01-18)
Wu, CY
;
Hsu, HC
;
Cheng, HM
;
Yang, S
;
Hsieh, WF
The randomly oriented ZnO nanosaws were synthesized on Si substrates by a simple vapor transport method. For structure characterization of the products, the SEM micrograph clearly reveals that length of nanosaw exceeds several tens of mu m and the side of sharp teeth of a saw has a length of about 1-5 mu m and diameters of about 100nm. The results of TEM, XRD, and Raman measurements indicate that the ZnO nanosaw is the single-crystal structure with the wurtzite phase. Under low excitation density, this UV emission peak measured at room temperature is attributed to the recombination of free excitons. Several sharp peaks emerge at photon energy around 3.18 eV with FWHM less than 4 meV when the sample is excited above a certain threshold. We refer that the random lasing in ZnO nanosaws results from the multiple coherent scattering in highly random-oriented ZnO nanosaws. (c) 2005 Elsevier B.V. All rights reserved.
The substrate effect on the in-plane orientation of vertically well-aligned ZnO nanorods grown on ZnO buffer layers
(2005-12-01)
Cheng, HM
;
Hsu, HC
;
Yang, S
;
Wu, CY
;
Lee, YC
Vertically well-aligned ZnO nanorods were synthesized without employing any metal catalysts on various substrates including glass, Si(111), 6H-SiC(0001) and sapphire (0001), which were pre-coated with c-oriented ZnO buffer layers, by simple physical vapour deposition. The alignments of the ZnO nanorods on the different substrates depend on the crystallographic alignments of the pre-coated ZnO buffer layers. The ZnO nanorods grown on glass and Si(111) are vertically aligned but randomly oriented in the in-plane direction. In contrast, the vertically aligned ZnO nanorods on 6H-SiC(0001) and sapphire (0001) show an in-plane alignment with azimuthally sixfold symmetry, which indicates the epitaxial relationship between ZnO and the substrate. Similarly, photoluminescence measurements show the distinct appearance of ZnO nanorods on different substrates. Besides the UV band, which was attributed to the recombination of free excitons near the band edge, defect-related visible emissions were also observed for the samples grown on both glass and Si(111) substrates. However, the ZnO nanorods exhibit only strong band edge emission peaks with no noticeable deep level emissions when grown on the 6H-SiC(0001) and sapphire (0001) substrates, which confirms the good crystalline and optical quality of the epitaxial ZnO nanorods.