Browsing by Issue Date, starting with "2016-01-18"

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Abnormal positive bias stress instability of In-Ga-Zn-O thin-film transistors with low-temperature Al2O3 gate dielectric
(2016-01-18)
Chang, Yu-Hong
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Yu, Ming-Jiue
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Lin, Ruei-Ping
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Hsu, Chih-Pin
;
Hou, Tuo-Hung
Low-temperature atomic layer deposition (ALD) was employed to deposit Al2O3 as a gate dielectric in amorphous In-Ga-Zn-O thin-film transistors fabricated at temperatures below 120 degrees C. The devices exhibited a negligible threshold voltage shift (Delta V-T) during negative bias stress, but a more pronounced Delta V-T under positive bias stress with a characteristic turnaround behavior from a positive Delta V-T to a negative Delta V-T. This abnormal positive bias instability is explained using a two-process model, including both electron trapping and hydrogen release and migration. Electron trapping induces the initial positive Delta V-T, which can be fitted using the stretched exponential function. The breakage of residual AlO-H bonds in low-temperature ALD Al2O3 is triggered by the energetic channel electrons. The hydrogen atoms then diffuse toward the In-Ga-Zn-O channel and induce the negative Delta V-T through electron doping with power-law time dependence. A rapid partial recovery of the negative Delta V-T after stress is also observed during relaxation. (C) 2016 AIP Publishing LLC.
Plasmon-Induced Water Splitting Using Metallic-Nanoparticle-Loaded Photocatalysts and Photoelectrodes
(2016-01-18)
Ueno, Kosei
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Oshikiri, Tomoya
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Misawa, Hiroaki
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應用化學系
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應用化學系分子科學碩博班
Visible- and near-infrared-light-driven water splitting, which splits water molecules to generate hydrogen and oxygen gases, is a significant subject in artificial photosynthesis with the goal of achieving a low-carbon society. In recent years, considerable attention has been paid to studies on the development of a plasmon-induced water-splitting system responding to visible light. In this review, we categorized water-splitting systems as gold-nanoparticle-loaded semiconductor photocatalytic particles system and metallic-nanoparticles-loaded semiconductor photoelectrode systems, and introduce the latest studies according to these categories. Especially, we describe the studies that optimize a material or a structural design of metallic-nanoparticle-loaded semiconductor photoelectrodes and consider a whole water-splitting system, including a cathode design. Furthermore, we discuss important points when studying plasmon-induced water splitting, and we describe a methodology that enhances plasmon-induced water-splitting efficiency.
Design of an FMCW radar baseband signal processing system for automotive application
(2016-01-18)
Lin, Jau-Jr
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Li, Yuan-Ping
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Hsu, Wei-Chiang
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Lee, Ta-Sung
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電機資訊學士班
For a typical FMCW automotive radar system, a new design of baseband signal processing architecture and algorithms is proposed to overcome the ghost targets and overlapping problems in the multi-target detection scenario. To satisfy the short measurement time constraint without increasing the RF front-end loading, a three-segment waveform with different slopes is utilized. By introducing a new pairing mechanism and a spatial filter design algorithm, the proposed detection architecture not only provides high accuracy and reliability, but also requires low pairing time and computational loading. This proposed baseband signal processing architecture and algorithms balance the performance and complexity, and are suitable to be implemented in a real automotive radar system. Field measurement results demonstrate that the proposed automotive radar signal processing system can perform well in a realistic application scenario.
Asymmetric valley-resolved beam splitting and incident modes in slanted graphene junctions
(2016-01-18)
Hsieh, S. H.
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Chu, C. S.
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電子物理學系
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Department of Electrophysics
Electron injection into a graphene sheet through a slanted armchair graphene nanoribbon (AGNR) is investigated. An incident mode, or subband, in the AGNR is valley-unpolarized. Our attention is on the valley-resolved nature of the injected electron beams and its connection to the incident mode. It is known for a normal injection that an incident mode will split symmetrically into two valley-resolved beams of equal intensity. We show, in contrast, that slanted injections result in asymmetric valley-resolved beam splitting. The most asymmetric beam splitting cases, when one of the valley-resolved beams has basically disappeared, are found and the condition derived. This is shown not due to trigonal warping because it holds even in the low incident energy regime, as long as collimation allows. These most asymmetric beam splitting cases occur at energies within an energy interval near and include the subband edge of an incident mode. The physical picture is best illustrated by a projection of the slanted AGNR subband states onto that of the 2D graphene sheet. It follows that the disappearing of a valley-resolved beam coincides with the situation that the group velocities of the projected states in the corresponding valley are in backward directions. (C) 2016 AIP Publishing LLC.
Drag and critical velocities in a nonresonantly pumped trapped polariton condensate with a rotating defect
(2016-01-19)
Cheng, Szu-Cheng
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Chen, Ting-Wei
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Jheng, Shih-Da
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Hsieh, Wen-Feng
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物理研究所
We model the superfluid properties of a trapped exciton-polariton condensate under non-resonant excitation subjected to a rotating defect. With increasing the linear velocity of rotating defect, the density modulation can be classified into superfluid-like regime, parabolic-like regime, Cherenkov regime and over-Cherenkov regime. The threshold-like behavior of drag force and the onset of turbulent fringes can define the critical velocity for the superfluidity. Based on the perturbative drag force in the Bogoliubov-type analysis, the rigid modes with gapped excitation spectrum have higher critical velocity than that of the soft modes. (C) 2015 Elsevier Ltd. All rights reserved.
Enhanced Structural and Magnetic Coupling in a Mesocrystal-Assisted Nanocomposite
(2016-01-20)
Zhu, Yuanmin
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Zhan, Qian
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Yang, Jan-Chi
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Bitla, Yugandhar
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Liu, Pingping
Benefiting from the advances made in well-controlled materials synthesis techniques, nanocomposites have drawn considerable attention due to their enthralling physics and functionalities. In this work, we report a new heteroepitaxial mesocrystalperovskite nanocomposite, (NiFe2O4)(0.33):(La0.67Ca0.33MnO3)(0.67). Elaborate structural studies revealed that tiny NiFe2O4 nanocrystals aggregate into ordered octahedral mesocrystal arrays with {111} facets together with a concomitant structural phase transition of the La0.67Ca0.33MnO3 matrix upon postannealing process. Combined magnetic and X-ray absorption spectroscopic measurements show significant enhancement in the magnetic properties at room temperature due to the structural evolution of magnetic NiFe2O4 and the consequent magnetic coupling at the heterointerfaces mediating via well connected octahedrons of Mn-O-6 in La0.67Ca0.33MnO3 and (Ni,Fe)-O-6 in NiFe2O4. This work demonstrates an approach to manipulate the exciting physical properties of material systems by integrating desired functionalities of the constituents via synthesis of a self-assembled mesocrystal embedded nanocomposite system.
交大e-News第202期-歷史建築竹北六張犁忠孝堂修復及再利用工程開工
(2016-01-20)
國立交通大學秘書室
;
Secretariat
Ultrabroadband time-resolved spectroscopy in novel types of condensed matter
(2016-01-20)
Luo, Chih-Wei
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Wang, Yu-Ting
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Yabushita, Atsushi
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Kobayashi, Takayoshi
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電子物理學系
In condensed matter physics, quasi-particle correlations are crucial to understanding a material\'s properties. For example, strong interaction between electrons with metal-like electron configuration produces strongly correlated insulators rather than conductors, which band theory would predict. Therefore, it is important to determine the interaction strength between different degrees of freedom, e.g., electron, phonon, and spin. Time-resolved spectroscopy is a powerful technique for observing energy transfer between quasi-particles and determining the interaction strength. Ultrashort-pulse light sources with extremely broadband spectra have extended exploration of ultrafast dynamics in various materials. Here, novel types of condensed-phase matter are presented to show how several key issues regarding these materials can be resolved by broadband ultrafast time-resolved spectroscopy. (C) 2016 Optical Society of America
Mn vacancy defects, grain boundaries, and A-phase stability of helimagnet MnSi
(2016-01-20)
Ou-Yang, T. Y.
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Shu, G. J.
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Lin, J-Y
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Hu, C. D.
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Chou, F. C.
Mn vacancy defect and grain size are shown to modify the magnetic phase diagram of MnSi significantly, especially near the critical regime of A-phase (skyrmion lattice) formation and the helimagnetic phase transition. Crystals grown using controlled nonstoichiometric initial precursors creates both grain boundaries and intrinsic Mn vacancy defect of various levels in MnSi. The results of combined transport, specific heat, and AC spin susceptibility measurements are compared for MnSi single crystal samples of various manganese deficiency levels and grain sizes. The finite-size effect and Mn vacancy level dependent helical phase transition temperature T-c have been identified and verified. The stability of A-phase in H-T phase space has been examined through AC spin susceptibility data analysis.
The determinants of photovoltaic system costs: an evaluation using a hierarchical learning curve model
(2016-01-20)
Trappey, Amy J. C.
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Trappey, Charles V.
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Tan, Hao
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Liu, Penny H. Y.
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Li, Shin-Je
The uptake of solar power globally as an important alternative energy source to fossil fuels, together with a rapid fall in the cost of photovoltaic (PV) systems, has been phenomenal during the past decade. This trend is widely anticipated to continue for the years to come. The decline in PV installation costs, like many other new technologies through history, has been largely driven by the learning curve effect. However, it is suggested that other factors, such as costs of key production inputs and prices of competing technologies, also impact the costs of PV systems. In this study, we construct a hierarchical learning curve model to quantify the effects that various factors have on installation costs of PV systems based on empirical data from Taiwan. The results show that, in addition to the learning curve effect as underpinned by an increase of cumulative PV capacity, reductions to silicon price have significantly contributed to the decline of the final installation costs of PV systems in Taiwan. By quantifying the effects of critical cost factors, the learning curve effects on PV installation costs in Taiwan are defined which enable a more accurate projection of PV installation costs for governments, PV producers, operators and users. (C) 2015 Published by Elsevier Ltd.
Near-threshold all-digital PLL with dynamic voltage scaling power management
(2016-01-21)
Chang, C. -W.
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Chang, K. -Y.
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Chu, Y. -H.
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Jou, S. -J.
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電子工程學系及電子研究所
A near-threshold all-digital phase-locked loop (ADPLL) with a power management unit (PMU) is presented to make the proposed ADPLL work reliably across variations and power consumption as well is reduced. When operated under near-threshold condition from 0.52 to 0.58 V V-DD, the gated digitally controlled oscillator frequency range is from 90.8 to 245.7 MHz. When the ADPLL is operated at 0.52 V V-DD, a lock-in time of 9.5 mu s at 100 MHz output clock frequency is measured with an rms period jitter of 0.17% UI. With the PMU, the ADPLL power reduction at 130 MHz output frequency is 39% and the buck converter power consumption is nearly 30 mu W. Consequently, the proposed ADPLL with PMU is suitable to event-driven or low-voltage applications.
The generation of stationary pi-electron rotations in chiral aromatic ring molecules possessing non-degenerate excited states
(2016-01-21)
Yamaki, Masahiro
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Teranishi, Yoshiaki
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Nakamura, Hiroki
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Lin, Sheng Hsien
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Fujimura, Yuichi
The electron angular momentum is a fundamental quantity of high-symmetry aromatic ring molecules and finds many applications in chemistry such as molecular spectroscopy. The stationary angular momentum or unidirectional rotation of pi electrons is generated by the excitation of a degenerated electronic excited state by a circularly-polarized photon. For low-symmetry aromatic ring molecules having non-degenerate states, such as chiral aromatic ring molecules, on the other hand, whether stationary angular momentum can be generated or not is uncertain and has not been clarified so far. We have found by both theoretical treatments and quantum optimal control (QOC) simulations that a stationary angular momentum can be generated even from a low-symmetry aromatic ring molecule. The generation mechanism can be explained in terms of the creation of a dressed-state, and the maximum angular momentum is generated by the dressed state with an equal contribution from the relevant two excited states in a simple three-electronic state model. The dressed state is formed by inducing selective nonresonant transitions between the ground and each excited state by two lasers with the same frequency but having different polarization directions. The selective excitation can be carried out by arranging each photon-polarization vector orthogonal to the electronic transition moment of the other transition. We have successfully analyzed the results of the QOC simulations of (P)-2,2\'-biphenol of axial chirality in terms of the analytically determined optimal laser fields. The present findings may open up new types of chemical dynamics and spectroscopy by utilizing strong stationary ring currents and current-induced magnetic fields, which are created at a local site of large compounds such as biomolecules.
Growing GaN LEDs on amorphous SiC buffer with variable C/Si compositions
(2016-01-22)
Cheng, Chih-Hsien
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Tzou, An-Jye
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Chang, Jung-Hung
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Chi, Yu-Chieh
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Lin, Yung-Hsiang
The epitaxy of high-power gallium nitride (GaN) light-emitting diode (LED) on amorphous silicon carbide (a-SixC1-x) buffer is demonstrated. The a-SixC1-x buffers with different nonstoichiometric C/Si composition ratios are synthesized on SiO2/Si substrate by using a low-temperature plasma enhanced chemical vapor deposition. The GaN LEDs on different SixC1-x buffers exhibit different EL and C-V characteristics because of the extended strain induced interfacial defects. The EL power decays when increasing the Si content of SixC1-x buffer. The C-rich SixC1-x favors the GaN epitaxy and enables the strain relaxation to suppress the probability of Auger recombination. When the SixC1-x buffer changes from Si-rich to C-rich condition, the EL peak wavelengh shifts from 446 nm to 450 nm. Moreover, the uniform distribution contour of EL intensity spreads between the anode and the cathode because the traping density of the interfacial defect gradually reduces. In comparison with the GaN LED grown on Sirich SixC1-x buffer, the device deposited on C-rich SixC1-x buffer shows a lower turn-on voltage, a higher output power, an external quantum efficiency, and an efficiency droop of 2.48 V, 106 mW, 42.3%, and 7%, respectively.
Improvement of light quality by ZrO2 film of chip on glass structure white LED
(2016-01-25)
Lin, Huang-Yu
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Ye, Zhi-Ting
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Lin, Chien-Chung
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Chen, Kuo-Ju
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Tu, Hsien-Hao
A novel combination of blue LED chips, transparent glass substrates and phosphors with PDMS thin film is demonstrated. The flip-chip bonding technology is applied to facilitate this design. The ZrO2 nanoparticles are also doped into the PDMS film to increase light scattering. The resultant luminous efficiency shows an 11% enhancement when compared to the regular COG device. The variation of correlated color temperature of such devices is also reduced to 132K. In addition to these changes, the surface temperature is reduced from 121 degrees C to 104 degrees C due to good thermal dissipation brought by ZrO2 nanoparticles. (C) 2015 Optical Society of America
Spectrally efficient polarization multiplexed direct-detection OFDM system without frequency gap
(2016-01-25)
Wei, Chia-Chien
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Zeng, Wei-Siang
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Lin, Chun-Ting
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光電系統研究所
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Institute of Photonic System
We experimentally demonstrate a spectrally efficient direct-detection orthogonal frequency-division multiplexing (DD-OFDM) system. In addition to polarization-division multiplexing, removing the frequency gap further improves the spectral efficiency of the OFDM system. The frequency gap between a reference carrier and OFDM subcarriers avoids subcarrier-to-subcarrier beating interference (SSBI) in traditional DD-OFDM systems. Without dynamic polarization control, the resulting interference after square-law direct detection in the proposed gap-less system is polarization-dependent and composed of linear inter-carrier interference (ICI) and nonlinear SSBI. Thus, this work proposes an iterative multiple-input multiple-output detection scheme to remove the mixed polarization-dependent interference. Compared to the previous scheme, which only removes ICI, the proposed scheme can further eliminate SSBI to achieve the improvement of similar to 7 dB in signal-to-noise ratio. Without the need for polarization control, we successfully utilize 7-GHz bandwidth to transmit a 39.5-Gbps polarization multiplexed OFDM signal over 100 km. (C) 2016 Optical Society of America
Rear interface engineering of hybrid organic-silicon nanowire solar cells via blade coating
(2016-01-25)
Lai, Yi-Chun
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Chang, Yu-Fan
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Tsai, Pei-Ting
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Chang, Jan-Kai
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Tseng, Wei-Hsuan
In this work, we investigate blade-coated organic interlayers at the rear surface of hybrid organic-silicon photovoltaics based on two small molecules: Tris(8-hydroxyquinolinato) aluminium (Alq(3)) and 1,3-bis(2-(4-tert- butylphenyl)-1,3,4-oxadiazol-5-yl) benzene (OXD-7). In particular, soluble Alq3 resulting in a uniform thin film with a root-mean-square roughness < 0.2nm is demonstrated for the first time. Both devices with the Alq3 and OXD-7 interlayers show notable enhancement in the open-circuit voltage and fill-factor, leading to a net efficiency increase by over 2% from the reference, up to 11.8% and 12.5% respectively. The capacitance-voltage characteristics confirm the role of the small-molecule interlayers resembling a thin interfacial oxide layer for the Al-Si Schottky barrier to enhance the built-in potential and facilitate charge transport. Moreover, the Alq3 interlayer in optimized devices exhibits isolated phases with a large surface roughness, in contrast to the OXD-7 which forms a continuous uniform thin film. The distinct morphological differences between the two interlayers further suggest different enhancement mechanisms and hence offer versatile functionalities to the advent of hybrid organic-silicon photovoltaics. (C)2016 Optical Society of America
Automatic and objective oral cancer diagnosis by Raman spectroscopic detection of keratin with multivariate curve resolution analysis
(2016-01-25)
Chen, Po-Hsiung
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Shimada, Rintaro
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Yabumoto, Sohshi
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Okajima, Hajime
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Ando, Masahiro
We have developed an automatic and objective method for detecting human oral squamous cell carcinoma (OSCC) tissues with Raman microspectroscopy. We measure 196 independent Raman spectra from 196 different points of one oral tissue sample and globally analyze these spectra using a Multivariate Curve Resolution (MCR) analysis. Discrimination of OSCC tissues is automatically and objectively made by spectral matching comparison of the MCR decomposed Raman spectra and the standard Raman spectrum of keratin, a well-established molecular marker of OSCC. We use a total of 24 tissue samples, 10 OSCC and 10 normal tissues from the same 10 patients, 3 OSCC and 1 normal tissues from different patients. Following the newly developed protocol presented here, we have been able to detect OSCC tissues with 77 to 92% sensitivity (depending on how to define positivity) and 100% specificity. The present approach lends itself to a reliable clinical diagnosis of OSCC substantiated by the "molecular fingerprint" of keratin.
Direct Synthesis and Practical Bandgap Estimation of Multilayer Arsenene Nanoribbons
(2016-01-26)
Tsai, Hsu-Sheng
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Wang, Sheng-Wen
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Hsiao, Ching-Hung
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Chen, Chia-Wei
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Ouyang, Hao
Single-crystalline aluminum film for ultraviolet plasmonic nanolasers
(2016-01-27)
Chou, Bo-Tsun
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Chou, Yu-Hsun
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Wu, Yen-Mo
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Chung, Yi-Cheng
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Hsueh, Wei-Jen
Significant advances have been made in the development of plasmonic devices in the past decade. Plasmonic nanolasers, which display interesting properties, have come to play an important role in biomedicine, chemical sensors, information technology, and optical integrated circuits. However, nanoscale plasmonic devices, particularly those operating in the ultraviolet regime, are extremely sensitive to the metal and interface quality. Thus, these factors have a significant bearing on the development of ultraviolet plasmonic devices. Here, by addressing these material-related issues, we demonstrate a low-threshold, high-characteristic-temperature metal-oxide-semiconductor ZnO nanolaser that operates at room temperature. The template for the ZnO nanowires consists of a flat single-crystalline Al film grown by molecular beam epitaxy and an ultrasmooth Al2O3 spacer layer synthesized by atomic layer deposition. By effectively reducing the surface plasmon scattering and metal intrinsic absorption losses, the high-quality metal film and the sharp interfaces formed between the layers boost the device performance. This work should pave the way for the use of ultraviolet plasmonic nanolasers and related devices in a wider range of applications.
Control of the Metal-Insulator Transition at Complex Oxide Heterointerfaces through Visible Light
(2016-01-27)
Lin, Jheng-Cyuan
;
Vu Thanh Tra
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Tsai, Dung-Sheng
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Lin, Tai-Te
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Huang, Po-Cheng
The coupling of the localized surface plasmon resonance of Au nanoparticles is utilized to deliver a visible-light stimulus to control conduction at the LaAlO3/SrTiO3 interface. A giant photoresponse and the controllable metal-insulator transition are characterized at this heterointerface. This study paves a new route to optical control of the functionality at the heterointerfaces.