Browsing by Issue Date, starting with "2020-05-19"

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( )Ultrafast Exciton Dynamics in Scalable Monolayer MoS2 Synthesized by Metal Sulfurization
(2020-05-19)
Tsai, Hsu-Sheng
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Huang, Yung-Hung
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Tsai, Po Cheng
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Chen, Yi-Jia
;
Ahn, Hyeyoung
Excitons in monolayer transition metal dichalcogenides (TMDs) have exceptionally large binding energies and dominate the optical properties of materials. Exploring the relaxation behavior of excitons is crucial for understanding the fundamental physics as well as the performance of TMD-based optoelectronic devices. However, ultrafast carrier dynamics is sensitive to the structural defects and surface conditions of TMDs, depending on the growth or transfer process. Here, we utilized pump-probe transient absorption (TA) spectroscopy with a white-light probe to investigate the dynamics of excitons in monolayer MoS2 synthesized by the metal sulfurization method. The sulfurization method was used for the fabrication of large-scale, continuous, and uniform thin films with a controllable number of layers. The excitation dynamics of the wafer-size monolayer MoS2 is found to be comparable to that of monolayer MoS2 flakes grown by chemical vapor deposition (CVD). The dominant processes of carrier relaxation in the monolayer MoS2 are exciton-exciton annihilation (hundreds of femtoseconds), the trapping of the excitons by surface states (a few picoseconds), and interband carrierphonon scattering (tens of picoseconds). Moreover, the induced absorption due to mid-gap defects, which is often observed for samples fabricated by growth methods, such as CVD, is not observed for our continuous and uniform monolayer films. Understanding the charge carrier dynamics of the exciton in the scalable and uniform monolayer MoS2 can provide physical insights that are valuable in the design and development of complex 2D devices.
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.
Structure-mechanics statistical learning unravels the linkage between local rigidity and global flexibility in nucleic acids
(2020-05-21)
Chen, Yi-Tsao
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Yang, Haw
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Chu, Jhih-Wei
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交大名義發表
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生物資訊及系統生物研究所
The mechanical properties of nucleic acids underlie biological processes ranging from genome packaging to gene expression, but tracing their molecular origin has been difficult due to the structural and chemical complexity. We posit that concepts from machine learning can help to tackle this long-standing challenge. Here, we demonstrate the feasibility and advantage of this strategy through developing a structure-mechanics statistical learning scheme to elucidate how local rigidity in double-stranded (ds)DNA and dsRNA may lead to their global flexibility in bend, stretch, and twist. Specifically, the mechanical parameters in a heavy-atom elastic network model are computed from the trajectory data of all-atom molecular dynamics simulation. The results show that the inter-atomic springs for backbone and ribose puckering in dsRNA are stronger than those in dsDNA, but are similar in strengths for base-stacking and base-pairing. Our analysis shows that the experimental observation of dsDNA being easier to bend but harder to stretch than dsRNA comes mostly from the respective B- and A-form topologies. The computationally resolved composition of local rigidity indicates that the flexibility of both nucleic acids is mostly due to base-stacking. But for properties like twist-stretch coupling, backbone springs are shown to play a major role instead. The quantitative connection between local rigidity and global flexibility sets foundation for understanding how local binding and chemical modification of genetic materials effectuate longer-ranged regulatory signals.
Inter- and Intragrain Inhomogeneity in 2D Perovskite Thin Films Revealed by Relative Grain Orientation Imaging Using Low-Frequency Polarized Raman Microspectroscopy
(2020-05-21)
Toda, Shogo
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Yanagita, Naoya
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Jokar, Effat
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Diau, Eric Wei-Guang
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Shigeto, Shinsuke
Two-dimensional (2D) organic-inorganic hybrid lead halide perovskites make up an emerging class of semiconductor materials for optoelectronic applications such as solar cells. The grain structure of polycrystalline 2D perovskites is one of the key factors that dictate their functionality in the devices, but currently available methods for in situ, chemically specific characterization of 2D perovskite grains are scarce. Here we show that ultra-low-frequency polarized Raman microspectroscopy is a facile yet powerful tool for visualizing relative grain orientations within 2D perovskite thin films. We demonstrate this method on the simplest 2D perovskite, (CH3(CH2)(3)NH3)(2)PbI4. Hierarchical clustering and detailed band decomposition analysis of the low-frequency polarized Raman imaging data reveal not only relative grain orientations but also intragrain inhomogeneity. We envisage that with high chemical specificity, this method will find broad applications ranging from other 2D perovskites to perovskite-based optoelectronic devices.
Contributions of Abundant Hydroxyl Groups to Extraordinarily High Photocatalytic Activity of Amorphous Titania for CO2 Reduction
(2020-05-21)
Kharade, Aparna K.
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Chang, Sue-min
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環境工程研究所
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Institute of Environmental Engineering
Despite severe charge recombination occurring within the bulk lattice, sol-gel-derived amorphous TiO2 particles with abundant OH groups (81.6 mg/g) and high surface area (274 m(2)/g) were for the first time demonstrated to exhibit respectively 8-14 and 9 times higher photocatalytic activity for CO2 reduction than their thermally derived anatase crystals and the commercial P25 powder. Moreover, the high density of the OH groups (12.45/nm(2)) enabled the amorphous oxide to exhibit higher specific surface reactivity than the crystals. The OH groups not only converted CO2 molecules into bonded bicarbonate/carbonate species to improve CO2 chemisorption but also trapped holes to form Ti-O-O-Ti species when the OH density was higher than a threshold value of 8.74/nm(2), which synergistically promoted interfacial charge transfer. Bidentate carbonate and center dot CO2- were two active species that were able to underwent CO32- -> Ti-OOCH2 -> Ti-O-CH3 -> CH4 and center dot CO2- -> CO22- -> Ti-COOH -> CO sequences on the hydroxylated surface to produce CH4 and CO products, respectively. High coverage of the chemisorbed carbonate species selected for CO2 reduction rather than H-2 evolution to proceed. Moreover, it led with CH4 as the major product. Oxygen vacancies were the major active sites on the anatase crystals. Their influences on the surface transformations were also characterized to comprehensively understand the surface-controlled activity and selectivity.
One-dimensional photonic bound states in the continuum
(2020-05-21)
Pankin, P. S.
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Wu, B. -R.
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Yang, J. -H.
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Chen, K. -P.
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Timofeev, I. V.
Bound states in the continuum have recently found application to sensing, lasing and optoelectronics, but have not been realised in 1D. Here, destructive interference of electron spin in a tilted magnetic field is shown to give rise to bound states in the continuum of a 1D layered photonic crystal. In 1985 Fridriech and Wintgen proposed a mechanism for bound states in the continuum based on full destructive interference of two resonances which can be easily applied to the two- and three-dimensional wave systems. Here we explicitly show that this mechanism can be realized in one-dimensional quantum potential well, owing to destructive interference of electron paths with different spin in tilted magnetic field. Due to one-by-one correspondence between the spin of the electron and the polarization state of light, we have found numerous bound states in the continuum in the one-dimensional photonic system and experimentally confirmed them. The experimental set-up consists of the one-dimensional photonic crystal conjugated with a liquid-crystalline anisotropic defect layer and covered by metal film.
Binary meta-hologram for a reconfigurable holographic metamaterial antenna
(2020-05-22)
Hwang, Ruey-Bing (Raybeam)
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交大名義發表
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National Chiao Tung University
This research reports a design method for synthesizing the binary meta-hologram pattern implemented in a leaky waveguide that can radiate the feeding signal toward a prescribed direction. In fact, the obtained pattern is not always a uniform array; it is an almost-periodic one. Statistical analysis of the radiation pattern for imperfect array is then conducted to demonstrate that radiating main-beam angle (ensemble average) is dominated by the average period of a non-uniform array subject to a small perturbation. Additionally,the leaky wave of higher-order space harmonic in a periodic structure is employed to accurately predict the directional radiation including main beam as well as grating lobes.
治安數據知多少？
(2020-05-24)
王乃安
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Department of Communication and Technology
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傳播與科技學系
【台灣治安到底好不好？】專題

你覺得台灣的治安如何呢？相比於國外，台灣的治安是相對穩定的，也時常為人稱道。不過事實真的是如此美好嗎？現在，就讓我們用客觀的數據加以探討吧！
從創傷到療癒　促轉會委員彭仁郁
(2020-05-24)
楊詠嵐
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Department of Communication and Technology
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傳播與科技學系
原本篤信自己的一生，就只是在一間公司當一個小秘書，但自從看見了一個人從深淵反彈的力道之大，也努力用自身證明生命的可能性。歷經生命的高低起伏，現今在幫助有過國家集體暴力創傷的人，她是促轉會心理專家委員彭仁郁。
同人世界　入門指南
(2020-05-24)
謝孟如
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Department of Communication and Technology
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傳播與科技學系
【當我們「同」在一起】專題

隨著動漫、輕小說產業的風行，「同人」一詞躍入人們眼簾，同時卻被貼上「宅」、「BL」的標籤。然而同人的世界遠比大眾所認知的廣泛，就讓我們撕下偏見，進入同人的世界一探究竟。
與「共融式遊戲場」為友
(2020-05-24)
周容萱
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Department of Communication and Technology
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傳播與科技學系
【遊戲場不再只屬於你】

你家旁的公園是共融式遊戲場嗎？帶你一起認識共融式遊戲場，讓你立刻認出它！
總編輯的話
(2020-05-24)
李育陞
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Department of Communication and Technology
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傳播與科技學系
本期為喀報第339期，總共有6篇文章。包含四篇資訊圖表，一篇人物專訪，以及一篇文化現象。本期頭題為邱于非的《浪浪跨國送養知多少》，溫暖精緻的作畫以及順暢的內容編排，使閱讀者能夠輕鬆且舒服的獲取資訊，我們能充分的感受記者在創作時的細膩。此外，本期有多篇精彩的資訊圖表，值得大家一探究竟。
浪浪跨國送養知多少
(2020-05-24)
邱于非
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Department of Communication and Technology
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傳播與科技學系
【跨國送養　浪浪遠渡重洋找家】專題

台灣流浪狗認養率逐年減少，許多收容所都處於飽和狀態，為了替浪浪找到更多認養機會，近年來有部分民間機構開始執行跨國送養。
台灣茶農再進化　茶業的轉型
(2020-05-24)
何雨潮
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Department of Communication and Technology
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傳播與科技學系
【茶業新世代】專題

喝茶是台灣很重要的文化。台灣的茶葉從清治時期以來就聞名於世，但隨著市場結構改變，以及手搖杯的竄起，台灣茶農面臨了許多挑戰，而茶農如何迎擊，將是茶葉新世代的重要課題。
Experimental investigation on heat transfer enhancement with twisted tape having various V-cut configurations
(2020-05-25)
Chu, Wen-Xiao
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Tsai, Ching-An
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Lee, Bing-Hung
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Cheng, Kai-Yueh
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Wang, Chi-Chuan
This paper experimentally investigates the thermo-hydraulic performance of tubes with various twisted tapes (TTs) with the Reynolds number ranging from 4000 to 10,000 (at the turbulent transition region). The Nusselt number (Nu) and friction factor (f) of the tested plain tube shows good agreement with the Gnielienski and Filonenko equations. The average deviations are within 9.5% and 2.8%, respectively. For the successive TT tube, the existing correlation which includes the effect of gap between the TT insert and tube can well predict the present measurement, and the deviation upon Nu and f is within +/- 10%. Meanwhile, the successive TT with the twisted ratio of 4 can achieve the highest comprehensive thermal performance (CTP) by 1.08-1.10. Yet the Nu and f will simultaneously drop by 6.7% and 11.6% when raising the gap ratio from 0.043 to 0.135. The CTP is also pronouncedly reduced and can be negatively reversed than the plain tube at the turbulent transition region. On the other hand, it is validated that the U-cut and isosceles V-cut configurations might provide similar improvement on Nu and f compared to the successive TT. The obtuse V-cut configuration shows more pronounced improvement on Nu and f, and yields the highest CTP of 1.18-1.23 within the test range. The existing correlations applicable for the V-cut TTs are unable to predict the present measurements accurately.
Photocatalytic activity enhancement of Bi2WO6 nanoparticles by Ag doping and Ag nanoparticles modification
(2020-05-25)
Nguyen Dang Phu
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Luc Huy Hoang
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Pham Van Hai
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Tran Quang Huy
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Chen, Xiang-Bai
Bi2WO6 nanoparticles doped with Ag, and modified with Ag nanoparticles, were successfully prepared using a two-step microwave assisted and hydrothermal synthesis. With Ag doping, the Bi ions were substituted by the dopant Ag ions in the host lattice structure of Bi2WO6. With Ag nanoparticles modification, the Ag nanoparticles grew on the surface of the Bi2WO6 nanoparticles without changing the host lattice structure. The photocatalytic activities of the samples were studied by visible light irradiation of rhodamine B. Both the Ag doping and the Ag nanoparticles modification enhanced the photocatalytic activity of the Bi2WO6 nanoparticles. Moreover, Ag nanoparticles modification produced a more than two times higher enhancement of the photocatalytic activity than the Ag doping method. Furthermore, a mechanism of the significant photocatalytic activity enhancement by Ag nanoparticles modification is proposed. (C) 2020 Elsevier B.V. All rights reserved.
A thermodynamic and kinetic study of the antioxidant activity of natural hydroanthraquinones
(2020-05-26)
Vo, Quan V.
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Nguyen Minh Thong
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Trinh Le Huyen
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Pham Cam Nam
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Nguyen Minh Tam
Novel hydroanthraquinones isolated from marine algal-derived endophytic fungus Talaromyces islandicus EN-501 exhibited promising antioxidant properties in preliminary studies, raising the prospect of adapting these compounds for therapeutic use in diseases caused by oxidative stress. For medicinal applications it is beneficial to develop a full understanding of the antioxidant activity of these compounds. In this study, the hydroperoxide radical scavenging activity of five natural hydroanthraquinones was evaluated by kinetic and thermodynamic calculations. The results showed that the radical scavenging of these hydroanthraquinones in the gas phase and in lipid solvents was defined by the formal hydrogen transfer mechanism, that for the polar environments was decided by the sequential proton loss electron transfer pathway. The hydroanthraquinones exhibited good hydroperoxide scavenging activity in both polar and non-polar media. The overall rate constant values for the radical scavenging reaction were in the range of 3.42 x 10(1) to 2.60 x 10(5) M-1 s(-1) and 3.80 x 10(6) to 5.87 x 10(7) M-1 s(-1) in pentyl ethanoate and water solvents, respectively. Thus the activity of 8-hydroxyconiothyrinone B (1) is about 2.6 and 444.6 times higher than that of Trolox in the studied solvents, identifying 8-hydroxyconiothyrinone B as a promising antioxidant.
Structural Colors Enabled by Lattice Resonance on Silicon Nitride Metasurfaces
(2020-05-26)
Yang, Jhen-Hong
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Babicheva, Viktoriia E.
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Yu, Min-Wen
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Lu, Tien-Chang
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Lin, Tzy-Rong
Artificial color pixels based on dielectric Mie resonators are appealing for scientific research as well as practical design. Vivid colors are imperative for displays and imaging. Dielectric metasurface-based artificial pixels are promising candidates for developing flat, flexible, and/or wearable displays. Considering the application feasibility of artificial color pixels, wide color gamuts are crucial for contemporary display technology. To achieve a wide color gamut, ensuring the purity and efficiency of nanostructure resonance peaks in the visible spectrum is necessary for structural color design. Low-loss dielectric materials are suitable for achieving vivid colors with structural color pixels. However, high-order Mie resonances prevent color pixels based on dielectric metasurfaces from efficiently generating highly saturated colors. In particular, fundamental Mie resonances (electric/magnetic dipole) for red can result in not only a strong resonance peak at 650 nm but also high-order Mie resonances at shorter wavelengths, which reduces the saturation of the target color. To address these problems, we fabricated silicon nitride metasurfaces on quartz substrates and applied Rayleigh anomalies at relatively short wavelengths to successfully suppress high-order Mie resonances, thus creating vivid color pixels. We performed numerical design, semianalytic considerations, and experimental proof-of-concept examinations to demonstrate the performance of the silicon nitride metasurfaces. Apart from traditional metasurface designs that involve transmission and reflection modes, we determined that lateral light incidence on silicon nitride metasurfaces can provide vivid colors through long-range dipole interactions; this can thus extend the applications of such surfaces to eyewear displays and guided-wave illumination techniques.
SiCxNy-based resistive and threshold switching by using single precursor plasma-enhanced atomic layer deposition
(2020-05-26)
Hsu, Yu-Lin
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Chang, Yao-Feng
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Chung, Wei-Min
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Chen, Ying-Chen
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Lin, Chao-Cheng
In this work, SiCxNy-based resistive switching memory by using a single precursor for the back end of line (BEOL) integration has been investigated. SiCxNy films were deposited on the aluminum (Al) substrates using plasma enhanced atomic layer deposition (PEALD) method. The effects of SiCxNy chemical structure with respect to resistive switching characteristics have been studied, and the results suggest that the resistive switching mechanism is dominated by the interfacial Schottky junction with SiCxNy composition. This work not only demonstrates a PEALD method in fabricating SiCxNy-based electronics active devices but also provides additional insights into the interaction between the electrical and chemical structures in bi-functional resistive switching or threshold switching behavior. A demonstrated PEALD tool with simple single-precursor for SiCxNy deposition shows excellent feasibility to be used as functional memory and selector devices, further giving the potential pathway for advanced BEOL process integration.
Direct observation of dynamic thermal lensing in nanoscale surfaces/interfaces of end-pumped Nd:YVO4 laser
(2020-05-26)
Lin, Shou-Tai
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Hung, Wei-Kuo
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Zhuo, Guan-Yu
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Wang, Hsien-Yi
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Chan, Ming-Che
This work describes non-invasive observations of dynamic thermal lensing in an end-pumped Nd:YVO4 laser. Measurements were obtained with a nanoscale optical ruler created using chromatic aberrations, pinholes, dispersive gratings, and position-sensitive detectors. This study reports on variations in thermally induced oscillations and on underdamping behavior in the regime of high pump power. Dynamic data related to the thermal behavior can be used to study the balance between driving forces (pumping and thermal stresses) and damping losses (cooling and output coupling). The non-invasive nature of the proposed scheme along with its sub-100-nm axial resolution, sub-millisecond time resolution, and simple configuration makes it widely applicable for studying heat-related phenomena within laser crystals. The preliminary results show that such non-invasive methods could be used to detect thermally induced nanoscale deformations in integrated circuits, high-power optoelectronic devices, and optical devices with high-power illumination.