Browsing by Author "Huang, Bo-Han"

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Facile Electrochemical Fabrication of Large-Area ZnO Inverse Opals with Reduced Defects
(2011)
Huang, Yi-Jui
;
Liao, Chen-Hong
;
Huang, Bo-Han
;
Chen, Wan-Ying
;
Wu, Pu-Wei
We demonstrate a facile fabrication scheme to construct large-area ZnO inverse opals on an indium-tin-oxide substrate with significantly reduced defects and improved stoichiometry. The fabrication steps involve the preparation of colloidal template via vertical electrophoresis of polystyrene (PS) microspheres in 720 nm radius, followed by galvanostatic electrodeposition of ZnO in the interstitial voids among the PS microspheres. Subsequently, the sample undergoes a heat-treatment in air at 500 degrees C for different time to remove the colloidal template, leaving an integral ZnO skeleton with thickness adjusted by the electrodeposition time. Since the colloidal template is deliberately designed with desirable thickness and considerable uniformity, the electroplating of ZnO can be achieved in a reduced ethanol/water ratio that allows faster growth rate and improved ZnO structure. Scanning electron microscope images demonstrate negligible microstructural defects for the ZnO inverse opals. X-ray diffraction reveals a wurtzite hexagonal lattice with (002) preferred orientation. In addition, both X-ray photoelectron spectroscopy and photoluminescence spectra suggest improved crystallinity and stoichiometry with increasing heat-treatment time. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3552604] All rights reserved.
Free-standing Au inverse opals for enhanced glucose sensing
(2016-11-05)
Liao, Chen-Hong
;
Hsieh, Yu-Chi
;
Huang, Bo-Han
;
Pai, Chia-Hao
;
Wu, Pu-Wei
We successfully fabricate free-standing gold inverse opals (GIO) with a highly ordered porous structure, adjustable pore size, and large geometric size (2.5 x 2.5 cm(2)). The process involves a vertical electrophoresis to assemble polystyrene (PS) microspheres in a closed-packed form, followed by backfilling of Ni and Au into the interstitial voids among the PS microspheres. Subsequently, the PS microspheres and Ni are removed to render free-standing GIO samples with pore size of 300, 405, and 600 nm, respectively. The free-standing GIO structures reveal a hexagonally-arranged pores with impressive mechanical strength and flexibility. Diffraction patterns from the X-ray diffractometer indicate a strong preferred orientation in the (111) plane. Cyclic voltammetric scans show excessive electrochemical surface area for the GIO samples as compared to that of planar Au in identical footprint. In glucose oxidation, the GIO structures demonstrate apparent current densities that are ten times larger over planar Au. Among the GIO structures, the sample with 300 nm pore size demonstrates the highest specific activity and the largest I-a/I-c value. We believe that the relatively smaller 300 nm pores facilitate the confinement of byproduct intermediates, and thus results in more effective oxidation of glucose. (C) 2016 Elsevier B.V. All rights reserved.
Structural characterization of colloidal crystals and inverse opals using transmission X-ray microscopy
(2014-07-15)
Huang, Bo-Han
;
Wang, Chun-Chieh
;
Liao, Chen-Hong
;
Wu, Pu-Wei
;
Song, Yen-Fang
A nondestructive tomographic technique was used to determine the crystallographic information of colloidal crystals comprising of polystyrene (PS) microspheres, as well as their silver inverse opals. The properties of the colloidal crystals, such as defects, grain size, grain boundaries, stacking sequence, and grain orientation, were determined using the full field transmission X-ray microscopy (TXM) with a spatial resolution of 50 nm. The PS microspheres (500-750 nm) which underwent a vertical electrophoresis process to form a face-centered cubic (fcc) close-packed structure with an ABCABC packing sequence. In addition, the colloidal crystal exhibited multiple grains, and an orientation variation of 6.1 degrees in the stacking direction between two neighboring grains. (C) 2014 Elsevier Inc. All rights reserved.