Browsing by Author "Tsai, W. C."

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Anisotropic strain, magnetic properties, and lattice dynamics in self-assembled multiferroic CoFe2O4-PbTiO3 nanostructures
(2014-04-07)
Tsai, C. Y.
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Chen, H. R.
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Chang, F. C.
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Kuo, H. H.
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Cheng, H. M.
We investigate the anisotropic stress dependent magnetic and phonon behaviors in self-assembled CoFe2O4-PbTiO3 (CFO-PTO) nanostructures deposited on SrRuO3 buffered SrTiO3 substrates of various thickness. The increased vertical compressed stress with increasing thickness enhances the vertical magnetic anisotropy of CFO while gradually reducing the vertical polarization of PTO. By applying the magnetic-field dependent Raman scattering, the CFO-A(1g) and T-2g(1) phonon frequencies shift oppositely because of the magnetostriction. Moreover, the PTO-A(1) mode intensities anomalously enhance and the A(1) and E mode frequencies, respectively, increase and decrease, which prove the existence of the stress-mediated magnetoelectric (ME) effect. This study shows that the ME transmission process is dominated by interfacial stress, which is critical for enhancing the ME efficiency. (C) 2014 AIP Publishing LLC.
Characteristics of Zinc Oxide Thin Film Transistors Fabricated by Location-Controlled Hydrothermal Method
(2010)
Yang, P. Y.
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Wang, J. L.
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Tsai, W. C.
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Wang, S. J.
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Chen, P. C.
In this paper, high-performance Zinc oxide (ZnO) thin-film transistors (TFTs) with bottom-gate (BG) structure and artificially location-controlled lateral grain growth have been prepared by low-temperature hydrothermal method. As the proper design of source/drain structure of ZnO/Ti/Pt thin films, the lateral grain growth can be artificially controlled in the desired location and the vertical grain boundary perpendicular to the current flow in the channel region can be reduced to single one. As compared with the conventional sputtered ZnO BG-TFTs, the proposed location-controlled hydrothermal ZnO BG-TFTs (W/L = 250 mu m/10 mu m) demonstrated the higher field-effect mobility of 6.09 cm(2)/V.s, lower threshold voltage of 3.67 V, larger on/off current ratio above 10(6), and superior current drivability, which can be attributed to the high-quality ZnO thin films with the reduced vertical grain boundaries in the channel region.
Impacts of ammonia background flows on structural and photoluminescence properties of InN dots grown on GaN by flow-rate modulation epitaxy
(2006-12-25)
Ke, W. C.
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Lee, L.
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Chen, C. Y.
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Tsai, W. C.
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Chang, W. -H.
Structural and photoluminescence (PL) properties of InN dots grown on GaN by metal organic vapor phase epitaxy using the flow-rate modulation technique, and their dependence on growth conditions, were investigated. An ammonia (NH3) background flow was intentionally supplied during indium deposition periods to control the kinetics of adatoms and hence the morphology of InN dots. Samples prepared under lower NH3 background flows generally exhibit narrower and more intense PL signals peaked at lower emission energies. The authors point out that the NH3 background flow is an important parameter that controls not only the nucleation process but also the emission property of InN dots. (c) 2006 American Institute of Physics.
Preheating-temperature effect on structural and photoluminescent properties of sol-gel derived ZnO thin films
(2014-04-01)
Chia, C. H.
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Tsai, W. C.
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Chou, W. C.
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電子物理學系
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Department of Electrophysics
We investigated he evolution of structural and low-temperature photoluminescence properties of sol-gel derived ZnO thin films, as a function of pre-heating temperature between 300 degrees C and 600 degrees C. The pre-heating crystallization plays an important role in the lineshape of PL spectra. The increase in pre-heating temperature enables rearrangement of atoms at the pre-heating stage, leading to c-axis oriented growth of films, modification in lineshape of impurity-detect emission, and reduction of deep-level emission intensity. (C) 2013 Elsevier B.V. All rights reserved
Stress-mediated magnetic anisotropy and magnetoelastic coupling in epitaxial multiferroic PbTiO3-CoFe2O4 nanostructures
(2013-04-01)
Tsai, C. Y.
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Chen, H. R.
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Chang, F. C.
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Tsai, W. C.
;
Cheng, H. M.
This study reports a self-assembled multiferroic nanostructure, composed of PbTiO3 (PTO) pillars embedded in a CoFe2O4 (CFO) matrix, deposited on MgO(001) by pulsed laser deposition. The epitaxial relationship in the PTO-CFO nanostructure is (100) [101](PTO) parallel to (001) [101](CFO) parallel to (001) [101](MgO), confirming the in-plane aligned polarization of PTO. The perpendicular magnetic anisotropy of this thin film results from the magnetoelastic anisotropy that exceeds the shape anisotropy. The increased frequency and the enhanced intensity of the tetrahedral (T-) site phonon modes by increasing the magnetic field indicate strong magnetoelastic coupling through magnetostriction in this multiferroic nanostructure. The anisotropic Raman strength enhancement of the T-site phonon along different directions suggests the magnetoelastic coupling is most efficient in the in-plane direction. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4800069]
The structural and optical properties of InN nanodots grown with various V/III ratios by metal-organic chemical vapor deposition
(2009-07-22)
Fu, S. F.
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Wang, S. M.
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Lee, L.
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Chen, C. Y.
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Tsai, W. C.
Self-assembled InN nanodots have been prepared at 650 degrees C with various V/III ratios from 500 to 30 000 by metal-organic chemical vapor deposition (MOCVD). It is found that the dot density and morphological size as well as the optical properties all display drastic changes at V/III = 12000. Generally, denser and smaller InN nanodots with higher emission energy and narrower linewidth were obtained when growth was conducted at V/III ratios slightly lower than 12 000 as compared to those at higher V/III ratios. The physical properties of our MOCVD-grown InN nanodots are sensitive to the surface structure and the morphology is very similar to molecular beam epitaxially grown GaN and InN films, which may be used as a guide to optimize the InN growth.