Browsing by Author "Wang, Yi-Ting"

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A delta-doped quantum well system with additional modulation doping
(2011)
Luo, Dong-Sheng
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Lin, Li-Hung
;
Su, Yi-Chun
;
Wang, Yi-Ting
;
Peng, Zai Fong
A delta-doped quantum well with additional modulation doping may have potential applications. Utilizing such a hybrid system, it is possible to experimentally realize an extremely high two-dimensional electron gas (2DEG) density without suffering inter-electronic-subband scattering. In this article, the authors report on transport measurements on a delta-doped quantum well system with extra modulation doping. We have observed a 0-10 direct insulator-quantum Hall (I-QH) transition where the numbers 0 and 10 correspond to the insulator and Landau level filling factor nu = 10 QH state, respectively. In situ titled-magnetic field measurements reveal that the observed direct I-QH transition depends on the magnetic component perpendicular to the quantum well, and the electron system within this structure is 2D in nature. Furthermore, transport measurements on the 2DEG of this study show that carrier density, resistance and mobility are approximately temperature (T)-independent over a wide range of T. Such results could be an advantage for applications in T-insensitive devices.
Electron heating and current scaling in a two-dimensional electron system in close proximity to nanoscale scatterers
(2014-05-01)
Wang, Yi-Ting
;
Yang, Chun-Kai
;
Lin, Sheng-Di
;
Liang, Chi-Te
;
電子工程學系及電子研究所
We have performed magneto-transport measurements on a two-dimensional electron system (2DES) which is in close proximity to nanoscaled scatterers. Weak localization, as evidenced by negative magnetoresistance, is observed. In this work, we use the extracted phase coherence rate as a thermometer to measure the electron\'s effective temperature T (e) in our 2DES when a high driving current I flows through the device. We find that T (e) ae I (similar to 0.52), consistent with 1/tau (ep) similar to T (2) in two dimensions, where 1/tau (ep) is the electron-phonon scattering rate. However, the phase coherence rate 1/tau (phi) similar to T, with a very small offset, is consistent with zero-temperature dephasing. Most importantly, our experimental results are in agreement with the fact that at low temperatures, the dominant phase-breaking mechanism is electron-electron scattering, not electron-phonon scattering. Therefore we are able to investigate both electron-electron scattering and electron-phonon scattering which are, in most cases, difficult to study independently in the linear region. Our data show that the electron heating effect is a very powerful tool for studying semiconductor devices.
Exploiting Parallelism in the H.264 Deblocking Filter by Operation Reordering
(2011)
Weng, Tsung-Hsi
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Wang, Yi-Ting
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Chung, Chung-Ping
;
資訊工程學系
;
Department of Computer Science
In the H.264 video compression standard, the deblocking filter contributes about one-third of all computation in the decoder. With multiprocessor architectures becoming the future trend of system design, computation time reduction can be achieved if the deblocking filter well apportions its operations to multiple processing elements. In this paper, we apply a 16 pixel long boundary, the basic unit for deblocking in the H.264 standard, as the basis for analyzing and exploiting possible parallelism in deblocking filtering. Compared with existing approaches using a macroblock as a basic unit for analysis, a 16 pixel long boundary by having a finer granularity can improve the chances of increasing the degree of parallelism. Moreover, a possible compromise to fully utilize limited hardware resources and hardware architectural requirements for deblocking are also proposed in this paper. Compared with the 2D wave-front method order for deblocking both 1920*1080 and 1080*1920 pixel sized frames, the proposed design gains speedups of 1.57 and 2.15 times given an un-limited number of processing elements respectively. Using this approach, the execution time of the deblocking filter is proportional to the square root of the growth of the frame size (keeping the same width/height ratio), pushing the boundary of practical real-time deblocking of increasingly larger video sizes.
Improvement of the Efficiency of InGaN-GaN Quantum-Well Light-Emitting Diodes Grown With a Pulsed-Trimethylindium Flow Process
(2009-04-01)
Hsueh, Tao-Hung
;
Sheu, Jinn-Kong
;
Lai, Wei-Chi
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Wang, Yi-Ting
;
Kuo, Hao-Chung
This study demonstrated the enhancement of the light output power of InGaN-GaN multiple quantum-well light-emitting diodes (LEDs) that are grown with a pulsed-trimethylindium (pulsed-TMIn) How process by metal-organic vapor-phase epitaxy. At an injection current of 20 mA, the output power of the pulsed-TMIn treated LEDs was improved by 16% as compared to that of the conventional LEDs. In addition, a minor droop (versus injection current) in terms. of external quantum efficiency was also observed in the pulsed-TMIn treated LEDs as compared to conventional LEDs. This improvement could be attributed to the fact that the significant carrier localization effect in the pulsed-TMIn treated LEDs can lead to higher recombination efficiency. This contention is perhaps tentatively evidenced by the temperature-dependent photoluminescence results in which the activation energy of the pulsed-TMIn treated LEDs was increased by 21.8% as compared to that of conventional LEDs.
Insulating state to quantum Hall-like state transition in a spin-orbit-coupled two-dimensional electron system
(2014-07-07)
Lo, Shun-Tsung
;
Hsu, Chang-Shun
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Lin, Y. M.
;
Lin, S-D
;
Lee, C. P.
We study interference and interactions in an InAs/InAsSb two-dimensional electron system. In such a system, spin-orbit interactions are shown to be strong, which result in weak antilocalization (WAL) and thereby positive magnetoresistance around zero magnetic field. After suppressing WAL by the magnetic field, we demonstrate that classical positive magnetoresistance due to spin-orbit coupling plays a role. With further increasing the magnetic field, the system undergoes a direct insulator-quantum Hall transition. By analyzing the magnetotransport behavior in different field regions, we show that both electron-electron interactions and spin-related effects are essential in understanding the observed direct transition. (C) 2014 AIP Publishing LLC.
Multiresolutional Graph Cuts for Brain Extraction from MR Images
(2013)
Chen, Yong-Sheng
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Chen, Li-Fen
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Wang, Yi-Ting
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資訊工程學系
;
Department of Computer Science
This paper presents a multiresolutional brain extraction framework which utilizes graph cuts technique to classify head magnetic resonance (MR) images into brain and non-brain regions. Starting with an over-extracted brain region, we refine the segmentation result by trimming non-brain regions in a coarse-to-fine manner. The extracted brain at the coarser level will be propagated to the finer level to estimate foreground/background seeds as constraints. The short-cut problem of graph cuts is reduced by the proposed pre-determined foreground from the coarser level. In order to consider the impact of the intensity inhomogeneities, we estimate the intensity distribution locally by partitioning volume images of each resolution into different numbers of smaller cubes. The graph cuts method is individually applied for each cube. Compared with four existing methods, the proposed method performs well in terms of sensitivity and specificity in our experiments for performance evaluation.
On the direct insulator-quantum Hall transition in two-dimensional electron systems in the vicinity of nanoscaled scatterers
(2011)
Liang, Chi-Te
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Lin, Li-Hung
;
Chen, Kuang Yao
;
Lo, Shun-Tsung
;
Wang, Yi-Ting
A direct insulator-quantum Hall (I-QH) transition corresponds to a crossover/transition from the insulating regime to a high Landau level filling factor nu > 2 QH state. Such a transition has been attracting a great deal of both experimental and theoretical interests. In this study, we present three different two-dimensional electron systems (2DESs) which are in the vicinity of nanoscaled scatterers. All these three devices exhibit a direct I-QH transition, and the transport properties under different nanaoscaled scatterers are discussed.
Pd/light-induced alkyl-alkenyl coupling reaction between unactivated alkyl iodides and alkenylboronic acids
(2020-05-21)
Huang, Hsin-Ju
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Wang, Yi-Ting
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Wu, Yen-Ku
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Ryu, Ilhyong
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應用化學系
Alkyl-alkenyl coupling reaction between unactivated alkyl iodides and 2-arylalkenylboronic acids utilizing a Pd/light combined system was studied. This reaction provided 2-alkylarylalkenes in good yields. It is proposed that in this reaction alkyl radicals are formed by SET from a Pd catalyst to alkyl iodides, which then undergo addition reactions to form C-C double bonds of alkenyl boronic acids and the subsequent beta-fragmentation of boronyl radicals leads to the formation of alkyl-substituted arylalkenes.
Probing the onset of strong localization and electron-electron interactions with the presence of a direct insulator-quantum Hall transition
(2010-10-01)
Lo, Shun-Tsung
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Chen, Kuang Yao
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Lin, T. L.
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Lin, Li-Hung
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Luo, Dong-Sheng
We have performed low-temperature transport measurements on a disordered two-dimensional electron system (2DES). Features of the strong localization leading to the quantum Hall effect are observed after the 2DES undergoes a direct insulator-quantum Hall transition on increasing the perpendicular magnetic field. However, such a transition does not correspond to the onset of strong localization. The temperature dependences of the Hall resistivity and Hall conductivity reveal the importance of the electron-electron interaction effects for the observed transition in our study. (C) 2010 Elsevier Ltd. All rights reserved.
Probing the onset of strong localization and electron-electron interactions with the presence of a direct insulator-quantum Hall transition
(2010-10-01)
Lo, Shun-Tsung
;
Chen, Kuang Yao
;
Lin, T. L.
;
Lin, Li-Hung
;
Luo, Dong-Sheng
We have performed low-temperature transport measurements on a disordered two-dimensional electron system (2DES). Features of the strong localization leading to the quantum Hall effect are observed after the 2DES undergoes a direct insulator-quantum Hall transition on increasing the perpendicular magnetic field. However, such a transition does not correspond to the onset of strong localization. The temperature dependences of the Hall resistivity and Hall conductivity reveal the importance of the electron-electron interaction effects for the observed transition in our study. (C) 2010 Elsevier Ltd. All rights reserved.
Spin-orbit-coupled superconductivity
(2014-06-25)
Lo, Shun-Tsung
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Lin, Shih-Wei
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Wang, Yi-Ting
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Lin, Sheng-Di
;
Liang, C. -T.
Superconductivity and spin-orbit (SO) interaction have been two separate emerging fields until very recently that the correlation between them seemed to be observed. However, previous experiments concerning SO coupling are performed far beyond the superconducting state and thus a direct demonstration of how SO coupling affects superconductivity remains elusive. Here we investigate the SO coupling in the critical region of superconducting transition on Al nanofilms, in which the strength of disorder and spin relaxation by SO coupling are changed by varying the film thickness. At temperatures T sufficiently above the superconducting critical temperature T-c, clear signature of SO coupling reveals itself in showing a magneto-resistivity peak. When T < T-c, the resistivity peak can still be observed; however, its line-shape is now affected by the onset of the quasi two-dimensional superconductivity. By studying such magneto-resistivity peaks under different strength of spin relaxation, we highlight the important effects of SO interaction on superconductivity.
Stable superhydrophobic polybenzoxazine surfaces over a wide pH range
(2006-09-26)
Wang, Chih-Feng
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Wang, Yi-Ting
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Tung, Pao-Hsiang
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Kuo, Shiao-Wei
;
Lin, Chun-Hung
In this study, we report on a simple two-step casting process designed to create a stable superhydrophobic surface. This method possesses the advantages of being both simple and inexpensive as well as utilizing non-fluorine-containing compounds. Most interestingly, we found that the as-prepared surface possesses superhydrophobic properties not only for pure water but also for corrosive water under both acidic and basic conditions. Furthermore, the superhydrophobic polybenzoxazine surfaces had excellent environmental stability with regard to both heating and organic solvent treatment in terms of the contact angle to water.
Tunable insulator-quantum Hall transition in a weakly interacting two-dimensional electron system
(2013-07-03)
Lo, Shun-Tsung
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Wang, Yi-Ting
;
Lin, Sheng-Di
;
Strasser, Gottfried
;
Bird, Jonathan P.
We have performed low-temperature measurements on a gated two-dimensional electron system in which electron-electron (e-e) interactions are insignificant. At low magnetic fields, disorder-driven movement of the crossing of longitudinal and Hall resistivities (rho (xx) and rho (xy)) can be observed. Interestingly, by applying different gate voltages, we demonstrate that such a crossing at rho (xx) similar to rho (xy) can occur at a magnetic field higher, lower, or equal to the temperature-independent point in rho (xx) which corresponds to the direct insulator-quantum Hall transition. We explicitly show that rho (xx) similar to rho (xy) occurs at the inverse of the classical Drude mobility 1/mu (D) rather than the crossing field corresponding to the insulator-quantum Hall transition. Moreover, we show that the background magnetoresistance can affect the transport properties of our device significantly. Thus, we suggest that great care must be taken when calculating the renormalized mobility caused by e-e interactions.