Browsing by Author "Hsu, Hsu-Cheng"

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Band gap engineering and stimulated emission of ZnMgO nanowires
(2006-07-03)
Hsu, Hsu-Cheng
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Wu, Chun-Yi
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Cheng, Hsin-Ming
;
Hsieh, Wen-Feng
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光電工程學系
We report a simple method for fabricating heterostructured ZnMgO nanowires by annealing the preformed ZnO/MgO core-shell structure. Photoluminescence from the alloy nanowires shows strong near-band-edge (NBE) emission, reflecting good material quality. A blueshift of the NBE emission at room temperature after the annealing treatment is attributed to the diffusion of Mg from the shell into the core ZnO of the nanowires to form a ternary ZnMgO alloy. Band gap engineering and stimulated emissions of ZnMgO nanowires with different Mg doping concentrations are also demonstrated. (c) 2006 American Institute of Physics.
Bandgap engineering and spatial confinement of optical phonon in ZnO quantum dots
(2006-01-01)
Hsieh, Wen-Fen
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Lin, Kuo-Feng
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Cheng, Hsin-Ming
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Hsu, Hsu-Cheng
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光電工程學系
Upon decreasing size of ZnO quantum dots, the blueshift in bandgap reveals the quantum confinement effect and the diminishing ratio of the second- to first-order resonant Raman intensity reveals reducing the electron-phonon Frohlich interaction.
Capabilities of time-resolved X-ray excited optical luminescence of the Taiwan Photon Source 23A X-ray nanoprobe beamline
(2020-01-01)
Lin, Bi-Hsuan
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Wu, Yu-Hao
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Li, Xiao-Yun
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Hsu, Hsu-Cheng
;
Chiu, Yu-Cheng
Time-resolved X-ray excited optical luminescence (TR-XEOL) was developed successfully for the 23A X-ray nanoprobe beamline located at the Taiwan Photon Source (TPS). The advantages of the TR-XEOL facility include (i) a nano-focused X-ray beam (<60 nm) with excellent spatial resolution and (ii) a streak camera that can simultaneously record the XEOL spectrum and decay time. Three time spans, including normal (30 ps to 2 ns), hybrid (30 ps to 310 ns) and single (30 ps to 1.72 mu s) bunch modes, are available at the TPS, which can fulfil different experimental conditions involving samples with various lifetimes. It is anticipated that TR-XEOL at the TPS X-ray nanoprobe could provide great characterization capabilities for investigating the dynamics of photonic materials.
Correlation between photoluminescence and varied growth pressure of well-aligned ZnO nanorods on fused silica substrate
(2007-11-01)
Yang, Song
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Hsu, Hsu-Cheng
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Liu, Wei-Ren
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Cheng, Hsin-Min
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Hsieh, Wen-Feng
Well-aligned ZnO nanorods with variable diameters were fabricated on fused silica substrates by the simple physical vapor deposition method with and without pre-deposited NiO particles. The diameter control of ZnO nanorods on the fused silica substrates was achieved by varying the growth pressure. The room-temperature photoluminescence spectra of the ZnO nanorods exhibit strong exciton emission at 3.25 eV that reveals good crystal quality. The exciton emission peak shifts toward 3.22 eV for the samples made at the larger growth pressure that is attributed to the influence of the electron-acceptor-level transition. The ZnO nanorods were examined by high resolution transmission electron microscopy and X-ray diffraction to show single crystal quality and preferentially c-axis alignment. Furthermore, we used scanning electron microscope to verify not only the size but also the growth mechanisms of ZnO nanorods. The results show a ZnO buffer layer formed between the flat top-facet nanorods and the substrate. In comparison with the samples without pre-deposited NiO particles on the substrate, the pre-deposited NiO particles act as nucleation centers for Zn vapor during the deposition process that improves the quality of the buffer layer. (C) 2007 Elsevier B.V. All rights reserved.
Defect induced ferromagnetic ordering in epitaxial Zn0.95Mn0.05O films on sapphire (0001)
(2019-12-04)
Liu, Wei-Rein
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Pao, Chih-Wen
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Yu, Doris Weijyun
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Chin, Yi-Ying
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Wu, Wen-Bin
We report the influence of Mn dopant on magnetic properties of Zn0.95Mn0.05O (ZMO)/Al2O3(0001) hetero-epitaxial systems grown by using pulsed-laser deposition. The room temperature (RT) intrinsic ferromagnetic (FM) ordering verified by superconducting quantum interference device magnetometer and x-ray magnetic circular dichroism spectrum of Mn L-2(,3) edges is ascribed to the substitutional Mn atoms in the Zn site of ZnO. Mn in ZMO has a tetrahedral local symmetry instead of the octahedral symmetry of MnO, after verifying the absence of the Mn-related impurities or clusters in ZMO epitaxial film by Mn K-edge and Zn K-edge x-ray absorption spectroscopy spectrum, as well as the analysis of long-range structural ordering on Renninger scan of forbidden (0005) reflection in x-ray diffraction, transmission electron microscopy and Raman spectrum. Comparison of x-ray absorption spectra of ZMO with those of ZnO epilayers at O K-, Zn K-, and L-3-edges indicates that the substitution of the Zn site with Mn enhances the charge-transfer (CT) transition and the presence of Zn vacancies (V-Zn) also dominate the photoluminescence (PL) spectrum, implying that the formation of numerous V-Zn defects plays an important role in activating FM interactions. The strong CT effect and the existence of high-density V-Zn suggest that the intrinsic RT FM ordering of insulating ZMO is a result of the formation of the bound magnetic polarons (BMPs) that interact with each other via intermediate magnetic impurities.
Growth of sparse arrays of narrow GaN nanorods hosting spectrally stable InGaN quantum disks
(2012-07-16)
Chen, Yen-Ting
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Tsai, Wen-Che
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Chen, Wen-Yen
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Hsiao, Ching-Lien
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Hsu, Hsu-Cheng
Wafer-scale production of single InGaN quantum disks (QD) in-a-nanorod array with small rod diameter (> 9 nm) and low rod-density (< 10(8) cm(-2)) has been achieved without extensive processing steps. Excitation power-dependent mu PL spectrum of single QD reveals multi-excitonic peak with 0.75 meV blue-shift for 3 orders of magnitude increasing power, indicating the present system is spectrally stable and nearly free of quantum-confined Stark effects, due possibly to the strain relaxation induced by free surface of small rod diameters. The fully polarized emissions, a high working temperature (180 K), low rod density and good alignment, render this system promising as a potential quantum photon source. (C) 2012 Optical Society of America
Investigation of Cavity Enhanced XEOL of a Single ZnO Microrod by Using Multifunctional Hard X-ray Nanoprobe
(2019-01-18)
Lin, Bi-Hsuan
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Li, Xiao-Yun
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Lin, Dai-Jie
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Jian, Bo-Lun
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Hsu, Hsu-Cheng
The multifunctional hard X-ray nanoprobe at Taiwan Photon Source (TPS) exhibits the excellent ability to simultaneously characterize the X-ray absorption, X-ray excited optical luminescence (XEOL) as well as the dynamics of XEOL of materials. Combining the scanning electron microscope (SEM) into the TPS 23A end-station, we can easily and quickly measure the optical properties to map out the morphology of a ZnO microrod. A special phenomenon has been observed that the oscillations in the XEOL associated with the confinement of the optical photons in the single ZnO microrod shows dramatical increase while the X-ray excitation energy is set across the Zn K-edge. Besides having the nano-scale spatial resolution, the synchrotron source also gives a good temporal domain measurement to investigate the luminescence dynamic process. The decay lifetimes of different emission wavelengths and can be simultaneously obtained from the streak image. Besides, SEM can provide the cathodoluminescence (CL) to be a complementary method to analyze the emission properties of materials, we anticipate that the X-ray nanoprobe will open new avenues with great characterization ability for developing nano/microsized optoelectronic devices.
p-type Mesoscopic Nickel Oxide/Organometallic Perovskite Heterojunction Solar Cells
(2014-04-23)
Wang, Kuo-Chin
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Jeng, Jun-Yuan
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Shen, Po-Shen
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Chang, Yu-Cheng
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Diau, Eric Wei-Guang
In this article, we present a new paradigm for organometallic hybrid perovskite solar cell using NiO inorganic metal oxide nanocrystalline as p-type electrode material and realized the first mesoscopic NiO/perovskite/[6,6]-phenyl C61-butyric acidmethyl ester (PC61BM) heterojunction photovoltaic device. The photo-induced transient absorption spectroscopy results verified that the architecture is an effective p-type sensitized junction, which is the first inorganic p-type, metal oxide contact material for perovskite-based solar cell. Power conversion efficiency of 9.51% was achieved under AM 1.5 G illumination, which significantly surpassed the reported conventional p-type dye-sensitized solar cells. The replacement of the organic hole transport materials by a p-type metal oxide has the advantages to provide robust device architecture for further development of all-inorganic perovskite-based thin-film solar cells and tandem photovoltaics.
Perovskite film-wire transformation: Preparation, characterization and device application
(2019-06-01)
Chen, Yu-An
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Yang, Sheng-Hsiung
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Chen, Po-Chih
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Lin, Li-Jyuan
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Wu, Zong-Yu
In this research, we demonstrate regular-type perovskite solar cells based on tungsten trioxide nanoparticles layer (WO3 NL) as the electron transport layer and methylammonium lead iodide nanowires (MAPbI(3) NWs) as the absorbing layer. By adjusting the amount of the anti-solvent DMF, MAPbI(3) NWs with different diameters ranging from 50 to 100 nm and lengths extending to several micrometers were obtained. [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) and cesium carbonate (Cs2CO3) were introduced between WO3 NL and MAPbI(3) NWs to improve film morphology and charge transfer ability. Meanwhile, spiro-MeOTAD doped with bis(trifluoromethane)sulfonimide lithium salt (Li-TFSI) was utilized to enhance hole transport. Finally, the perovskite solar cells with the configuration of ITO/WO3 NL/Cs2CO3/PCBM/MAPbI(3) NWs/spiro-MeOTAD/Au were fabricated and evaluated. To date, perovskite NWs treating with the proper amount of the anti-solvent DMF possess higher absorption, faster carrier transportation and lower recombination that are responsible for photovoltaic application.
Selective-area growth of single-crystal wurtzite GaN nanorods on SiOx/Si(001) substrates by reactive magnetron sputter epitaxy exhibiting single-mode lasing
(2017-10-05)
Serban, Elena Alexandra
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Palisaitis, Justinas
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Yeh, Chia-Cheng
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Hsu, Hsu-Cheng
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Tsai, Yu-Lin
Selective-area growth (SAG) of single-crystal wurtzite GaN nanorods (NRs) directly onto Si(001) substrates with un-etched native SiOx amorphous layer, assisted by a patterning TiNx mask fabricated by nanosphere lithography (NSL), has been realized by reactive magnetron sputter epitaxy (MSE). The GaN NRs were grown vertically to the substrate surface with the growth direction along c-axis in the well-defined nano-opening areas. A 5-step structural and morphological evolution of the SAG NRs observed at different sputtering times depicts a comprehensive growth model, listed in sequence as: formation of a polycrystalline wetting layer, predominating c-axis oriented nucleation, coarsening and coalescence of multi-islands, single NR evolution, and finally quasi-equilibrium crystal shape formation. Room-temperature cathodoluminescence spectroscopy shows a strong GaN bandedge emission with a uniform luminescence across the NRs, indicating that the SAG NRs are grown with high quality and purity. In addition, single-longitudinal-mode lasing, attributed to well-faceted NR geometry forming a Fabry-Perot cavity, was achieved by optical pumping, paving a way for fabricating high-performance laser optoelectronics using MSE.
Structural and optical properties of ZnMgO nanostructures formed by Mg in-diffused ZnO nanowires
(2007-04-01)
Pan, Ching-Ju
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Hsu, Hsu-Cheng
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Cheng, Hsin-Ming
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Wu, Chun-Yi
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Hsieh, Wen-Feng
ZnMgO nanostructures with wurtzite phase were prepared by thermal diffusion of Mg into the ZnO nanowires. As ZnO light-emitting devices have been operated by using ZnMgO layers as energy barrier layers to confine the carriers, it is essential to realize the characterization of ZnMgO particularly. In this work, the Mg content in Zn1-xMgxO alloy determined by X-ray diffraction (XRD) and photoluminescence (PL) shows a good coincidence. The variation of lattice constant and the blueshift of near-band-edge emission indicate that Zn2+ ions are successfully substituted by Mg2+ ions in the ZnO lattice. In Raman-scattering studies, the change of E-2(high) phonon line shape in ZnO:Mg nanostructures reveals the microscopic substitutional disorder. In addition to the host phonons of ZnO, two additional bands around 383 and 510cm(-1) are presumably attributed to the Mg-related vibrational modes. (C) 2007 Elsevier Inc. All rights reserved.