Browsing by Author "Hsu, H. C."

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Crystal symmetry breaking of wurtzite to orthorhombic in nonpolar a-ZnO epi-films
(2009)
Kuo, C. C.
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Liu, W. -R.
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Hsieh, W. F.
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Hsu, C. -H.
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Hsu, H. C.
Crystal symmetry breaking of wurtzite C(6V) to orthorhombic C(2V) due to in-plane anisotropic strain was investigated for nonpolar a-ZnO epi-films grown on R-sapphire.
Crystal symmetry breaking of wurtzite to orthorhombic in nonpolar a-ZnO epifilms
(2009-07-06)
Kuo, C. C.
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Liu, W. -R.
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Hsieh, W. F.
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Hsu, C. -H.
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Hsu, H. C.
Crystal symmetry breaking of wurtzite C-6V to orthorhombic C-2V due to in-plane anisotropic strain was investigated for nonpolar (11 (2) over bar0) ZnO epifilms grown on the R-sapphire. X-ray diffraction results reveal the epilayer is subjected to a compressive strain along the polar c-axis and tensile strains along both a-[11 (2) over bar0] surface normal and in-plane p-[1 (1) over bar 00] axis. The polarized Raman spectra of E-2 modes reveal violation of the C-6V selection rules. Oppositely, the C-2V configuration satisfies the selection rules for the Raman modes. The observed E-1 and E-2 bands in polarized optical reflection and photoluminescence spectra confirm the anisotropic strain causes the structure change to the orthorhombic one. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3159470]
Disrupted long-range spin-spiral ordering and electric polarization in the Zn-substituted quantum helimagnet LiCu(2-x)Zn(x)O(2)
(2010-06-18)
Hsu, H. C.
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Lee, W. L.
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Lin, J. -Y.
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Liu, H. L.
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Chou, F. C.
Long-range spin-spiral ordering in quantum quasi-two-dimensional helimagnet LiCu(2)O(2) is destroyed by similar to 8% Zn(2+) substitution and a magnetic anomaly near similar to 14 K of different character emerges. Zn substitution may have introduced either a magnetic ground state of spin glass in nature, antiferromagnetic ordering with complex easy-plane anisotropy, or a gapped phase which is phase separated and proportional to the Zn substitution level on a short-range ordered background. The magnetic ground state is modified at the same time that the electric polarization disappears.
Disrupted long-range spin-spiral ordering and electric polarization in the Zn-substituted quantum helimagnet LiCu2-xZnxO2
(2010-06-18)
Hsu, H. C.
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Lee, W. L.
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Lin, J. -Y.
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Liu, H. L.
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Chou, F. C.
Long-range spin-spiral ordering in quantum quasi-two-dimensional helimagnet LiCu2O2 is destroyed by similar to 8% Zn2+ substitution and a magnetic anomaly near similar to 14 K of different character emerges. Zn substitution may have introduced either a magnetic ground state of spin glass in nature, antiferromagnetic ordering with complex easy-plane anisotropy, or a gapped phase which is phase separated and proportional to the Zn substitution level on a short-range ordered background. The magnetic ground state is modified at the same time that the electric polarization disappears.
Improvement of Crystalline and Photoluminescence of Atomic Layer Deposited m-Plane ZnO Epitaxial Films by Annealing Treatment
(2012-10-01)
Yang, S.
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Lin, B. H.
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Kuo, C. C.
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Hsu, H. C.
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Liu, W-R
Monocrystalline m-plane ZnO epitaxial films with flat surface morphology were grown on m-plane sapphire by using atomic layer deposition. X-ray diffraction and transmission electron microscopy measurements verify not only the in-plane epitaxial relationship of the as-grown films as (10 (1) over bar0)< 0001 >(ZnO)parallel to(10 (1) over bar0)<(1) over bar2 (1) over bar0 > Al2O3 but also the absence of domains with undesirable orientations, which are generally obtained in the m-plane ZnO films grown by other methods. Experimental results indicate that the basal plane stacking fault (BSF) is the dominant structural defects that contribute to the emission at 3.31 eV in m-plane ZnO films. Exactly how thermal annealing affects the structural and optical properties of ZnO epi-films was also investigated. Additionally, based on time-resolved photoluminescence at 5 K, the decay time of BSF related emission and near-band-edge (NBE) emission were determined. Results of this work further demonstrated that the decay time of NBE emission increases with a higher annealing temperature, accompanied by an improvement in crystal structure.
Magnetic ground state and transition of a quantum multiferroic LiCu(2)O(2)
(2008-08-15)
Huang, S. W.
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Huang, D. J.
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Okamoto, J.
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Mou, C. Y.
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Wu, W. B.
Based on resonant soft x-ray magnetic scattering, we report that LiCu(2)O(2) exhibits a large interchain coupling which suppresses quantum fluctuations along spin chains, and a quasi-2D short-range magnetic order prevails at temperatures above the magnetic transition. These observations unravel the fact that the ground state of LiCu(2)O(2) possesses long-range 2D-like incommensurate magnetic order rather than being a gapped spin liquid as expected from the nature of quantum spin-1/2 chains. In addition, the spin coupling along the c axis is found to be essential for inducing electric polarization.
Magnetic order of LiCu2O2 studied by resonant soft x-ray magnetic scattering
(2008-08-01)
Huang, S. W.
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Huang, D. J.
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Okamoto, J.
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Wu, W. B.
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Chen, C. T.
We present results of resonant soft x-ray magnetic scattering measurements on single crystals of LiCu2O2 to address the magnetic order. LiCu2O2 exhibits a long-range magnetic order incommensurate with the lattice, and the modulation vector is (0.5, zeta, 0) in reciprocal lattice units with zeta similar to 0.174, depending upon the temperature. The spin-spin correlation length along the spin chain deduced from the width of momentum scan is larger than 2100 angstrom. The inter-chain correlation length that lies within the ab plane was discovered to be substantial, similar to 690 angstrom. (c) 2008 Elsevier Ltd. All rights reserved.
Nonmagnetic impurity perturbation to the quasi-two-dimensional quantum helimagnet LiCu(2)O(2)
(2010-09-29)
Hsu, H. C.
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Lin, J. -Y.
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Lee, W. L.
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Chu, M. -W.
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Imai, T.
A complete phase diagram of Zn-substituted quantum quasi-two-dimensional helimagnet LiCu(2)O(2) has been presented. Helical ordering transition temperature (T(h)) of the original LiCu(2)O(2) follows finite size scaling for less than similar to 5.5% Zn substitution, which implies the existence of finite helimagnetic domains with domain boundaries formed with nearly isolated spins. Higher Zn substitution >= 5.5% quenches the long-range helical ordering and introduces an intriguing Zn-level-dependent magnetic phase transition with slight thermal hysteresis and a universal quadratic field dependence for T(c)(Zn > 0.055, H). The magnetic coupling constants of nearest-neighbor J(1) and next-nearest-neighbor J(2) (alpha = J(2)/J(1)) are extracted from high temperature series expansion fitting and N = 16 finite chain exact diagonalization simulation. We have also provided evidence of direct correlation between long-range helical spin ordering and the magnitude of electric polarization in this spin-driven multiferroic material.
Nonmagnetic impurity perturbation to the quasi-two-dimensional quantum helimagnet LiCu2O2
(2010-09-29)
Hsu, H. C.
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Lin, J. -Y.
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Lee, W. L.
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Chu, M. -W.
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Imai, T.
A complete phase diagram of Zn-substituted quantum quasi-two-dimensional helimagnet LiCu2O2 has been presented. Helical ordering transition temperature (T-h) of the original LiCu2O2 follows finite size scaling for less than similar to 5.5% Zn substitution, which implies the existence of finite helimagnetic domains with domain boundaries formed with nearly isolated spins. Higher Zn substitution >= 5.5% quenches the long-range helical ordering and introduces an intriguing Zn-level-dependent magnetic phase transition with slight thermal hysteresis and a universal quadratic field dependence for T-c(Zn > 0.055, H). The magnetic coupling constants of nearest-neighbor J(1) and next-nearest-neighbor J(2) (alpha = J(2)/J(1)) are extracted from high temperature series expansion fitting and N = 16 finite chain exact diagonalization simulation. We have also provided evidence of direct correlation between long-range helical spin ordering and the magnitude of electric polarization in this spin-driven multiferroic material.
Optical properties of one- and two-dimensional excitons in m-plane ZnO/MgZnO multiple quantum wells
(2016-03-09)
Chen, H. R.
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Tsai, C. Y.
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Huang, Y. C.
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Kuo, C. C.
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Hsu, H. C.
Five pairs of ZnO/Zn0.9Mg0.1O multiple quantum wells (MQWs) with fixed barrier thickness of 55 nm and three well widths of 4, 8 and 16 nm have been grown on m-plane sapphires by pulsed laser deposition. Due to 2D quantum confinement with decreasing well width, the emission of excitons bound to the basal-plane stacking faults, which are one-dimensionally confined in MQWs, encounters larger blue shift than that of the near-band edge excitons. Furthermore, remarkably reducing coupling of free excitons with A1 longitudinal optical phonons is closely correlated with increasing exciton binding energy but enhanced coupling of E-2-low phonons is a result of increasing interaction with the interface phonons with decreasing well width.
Recombination dynamics of a localized exciton bound at basal stacking faults within the m-(p)lane ZnO film
(2014-07-07)
Yang, S.
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Hsu, H. C.
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Liu, W-R.
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Lin, B. H.
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Kuo, C. C.
We investigated the carrier dynamics near basal stacking faults (BSFs) in m-plane ZnO epitaxial film. The behaviors of the type-II quantum wells related to the BSFs are verified through time-resolved and time-integrated photoluminescence. The decay time of the emission of BSFs is observed to have a higher power law value and longer decay time than the emission of the donor-bound excitons. The spectral-dependent decay times reveal a phenomenon of carriers migrating among band tail states, which are related to the spatial distribution of the type-II quantum wells formed by the BSFs. A high density of excited carriers leads to a band bending effect, which in turn causes a blue-shift of the emission peak of BSFs with a broadened distribution of band tail states. (C) 2014 AIP Publishing LLC.
The Design of Big Data Analytics for Testing & Measurement and Traffic Flow on an Experimental 4G/LTE Network
(2015)
Lin, Bao-Shuh
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Tung, Li-Ping
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Hsieh, I-Ching
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Liu, Tsai-Hua
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Chou, Shu-Yuan
BML(Broadband Mobile Lab.) at NCTU has been utilized to support the testing & measurement for communication and networking products. It also has proven to be able to develop applications and services in a campus scale experimental networking environment. In the meantime, ITRI in Taiwan is conducting a greater metropolitan (Hsinchu) scale experimental networking environment, called ITRINET under the MOEA national program to improve and speed up the 4G/LTE applications and services. The BML at NCTU will be integrated with ITRINET and merged to become its subnet. With the cloud-enabled 4G/LTE-based ITRINET, we have designed the system to conduct the big data analytics for testing&measurement data and for network traffic and management data through a real-time streaming computing software package, InfoSphere, run on a cloud server platform, Inventec Zion. The testing&measurement data is generated and collected through the industry-academia R&D services while the network traffic and management data is created and collected by engaged a variety of APP\'s on smart devices (SD). This paper addresses the system design methodology and issues related to the data analytics for an experimental network environment.
ZnO nanopowders fabricated by dc thermal plasma synthesis
(2006-09-25)
Ko, T. S.
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Yang, S.
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Hsu, H. C.
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Chu, C. P.
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Lin, H. F.
Ultrafine ZnO nanopowders were successfully synthesized by the de thermal plasma process with a high production rate of 1.2 kg/h. The combination of plasma was found to affect the nanoparticles morphology. Both X-ray diffraction and Raman spectrum analysis confirmed a high quality wurtzite structure of the ZnO nanopowders. Photoluminescence study exhibited strong ultraviolet emission corresponding to the near band edge emission in the ZnO nanopowders. Random laser action observed in the ZnO nanostructures by optical pumping demonstrated high optical and crystal quality of the ZnO nanopowders fabricated by the dc thermal plasma synthesis. (c) 2006 Elsevier B.V. All rights reserved.