Browsing by Author "Lai, C. H."

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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.
;
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.
COMPARISON OF THE PROPULSION PERFORMANCE OF AEROSPIKE AND BELL-SHAPED NOZZLE USING HYDROGEN PEROXIDE MONOPROPELLANT UNDER SEA-LEVEL CONDITION
(2019-06-01)
Lai, A.
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Wei, S. S.
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Lai, C. H.
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Chen, J. L.
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Liao, Y. H.
This study investigates numerically the performance of applying aerospike nozzle in a hydrogen peroxide mono-propellant propulsion system. A set of governing equations, including continuity, momentum, energy and species conservation equations with extended k-epsilon turbulence equations, are solved using the finite-volume method. The hydrogen peroxide mono-propellant is assumed to be fully decomposed into water vapor and oxygen after flowing through a catalyst bed before entering the nozzle. The aerospike nozzle is expected to have high performance even in deep throttling cases due to its self-compensating characteristics in a wide range of ambient pressure environments. The results show that the thrust coefficient efficiency (C-f,C-eta) of this work exceeds 90% of the theoretical value with a nozzle pressure ratio (PR) in the range of 20 similar to 45. Many complex gas dynamics phenomena in the aerospike nozzle are found and explained in the paper. In addition, performance of the aerospike nozzle is compared with that of the bell-shape nozzle.
Conduction control at ferroic domain walls via external stimuli
(2014)
Yang, J. C.
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Yeh, C. H.
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Chen, Y. T.
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Liao, S. C.
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Huang, R.
Intriguing functionalities at nano-sized domain walls have recently spawned a new paradigmfor developing novel nanoelectronics due to versatile characteristics. In this study, we explore a new scenario to modulate the local conduction of ferroic domain walls. Three controlling parameters, i.e., external electrical field, magnetic field and light, are introduced to the 90 degrees domain walls (90 degrees DWs) of BiFeO3. Electrical modulation is realized by electrical transport, where the mobility of 90 degrees DWs can be altered by gating voltage. We further use the ferromagnetic/antiferromagnetic coupling to reveal the inherent magnetism at the DWs. With an established magnetic nature, magneto-transport has been conducted to introduce magnetic controlling parameter, where a giant positive magnetoresistance change can be observed up to 200%. In addition, light modulated conduction, a core factor for multifunctional applications, is successfully demonstrated (current enhancement by a factor of 2 with 11 W white lamp). These results offer new insights to discover the tunability of domain wall nanoelectronics.
Novel oxynitride layer applied to flash memory using HfO(2) as charge trapping layer
(2007)
Hsieh, C. R.
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Lai, C. H.
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Lin, B. C.
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Lou, J. C.
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Lin, J. K.
When the thickness of tunnel oxide layer is thinner than 7nm, the defects of tunnel oxide will form the leakage path easily. The trapped charges in trapping layer leak out through the leakage path and let we read the wrong data information. Therefore, the novel oxynitride process has been proposed to improve the reliabilities of Flash memory by reducing the interface states and bulk defects. Moreover, the novel oxynitride process is compatible with standard CMOS process today and it is practicable improvement in industry manufacturing. The HfO(2) layer was used as charge trapping layer. At first we found the better PDA conditions of HfO(2) film from the test capacitors and applied the optimum condition in integrated Flash memory devices. Finally, the complete electrical measurements and analysis were carried out. From the result of this study, the oxynitride can promote the reliabilities of Flash memory by improving the quality of tunnel oxide.
Spin and phonon anomalies in epitaxial self-assembled CoFe2O4-BaTiO3 multiferroic nanostructures
(2014-06-23)
Tsai, C. Y.
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Cheng, H. M.
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Chen, H. R.
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Huang, K. F.
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Tsai, L. N.
Temperature dependent magnetic and phonon anomalies in epitaxial self-assembled CoFe2O4 (CFO) rods embedded in BaTiO3 (BTO) matrix nanostructures were investigated. The temperature dependence of A(1)(2TO) phonon frequency of BTO indicates that the BTO matrix experiences structural transformations. The lattice strain produced during the structural transformations drives spin reorientation in CFO rods, resulting in anomalous changes of magnetization. Through correlating the phonon anomalies with the increase of in-plane spin ordering, we show the spin-phonon coupling induces the softening of A(1g) and A(1)(2TO) phonons. It suggests that spin strongly couples with lattice strain and phonons in this nanostructure. (C) 2014 AIP Publishing LLC.
Spin and phonon anomalies in epitaxial self-assembled CoFe2O4-BaTiO3 multiferroic nanostructures
(2014-06-23)
Tsai, C. Y.
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Cheng, H. M.
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Chen, H. R.
;
Huang, K. F.
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Tsai, L. N.
Temperature dependent magnetic and phonon anomalies in epitaxial self-assembled CoFe2O4 (CFO) rods embedded in BaTiO3 (BTO) matrix nanostructures were investigated. The temperature dependence of A(1)(2TO) phonon frequency of BTO indicates that the BTO matrix experiences structural transformations. The lattice strain produced during the structural transformations drives spin reorientation in CFO rods, resulting in anomalous changes of magnetization. Through correlating the phonon anomalies with the increase of in-plane spin ordering, we show the spin-phonon coupling induces the softening of A(1g) and A(1)(2TO) phonons. It suggests that spin strongly couples with lattice strain and phonons in this nanostructure. (C) 2014 AIP Publishing LLC.
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.
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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]