Browsing by Issue Date, starting with "2019-10-21"

Now showing 1 - 20 of 6623

Size and temperature dependence of photoluminescence of hybrid perovskite nanocrystals
(2019-10-21)
Naghadeh, Sara Bonabi
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Sarang, Som
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Brewer, Amanda
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Allen, A'Lester
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Chiu, Yi-Hsuan
In this work, we studied the effects of particles' size and temperature on the photoluminescence (PL) of CH3NH3PbBr3 perovskite nanocrystals (PNCs), with the PNC size controlled by varying the surface passivating ligands. The structural and optical properties of the PNCs were investigated using UV-Vis and PL spectroscopy, revealing strong quantum confinement effects. Temperature dependent PL measurements showed the spectral blue shift of the PL peak for the small PNCs (3.1 +/- 0.2 nm) with decreasing temperature from 300 K to 20 K, which is opposite to the red shift with decreasing temperature observed for large- (9.2 +/- 0.5 nm) and middle-sized (5.1 +/- 0.3 nm) PNCs. The PL lifetime also increased with increasing temperature for the larger PNCs, while it remained about the same for the small and middle-sized PNCs. This increase in lifetime with temperature is attributed to exciton dissociation to free carriers at higher temperatures and to the formation of polar domains in the PNCs. However, the small and middle-sized PNCs did not show such a trend, which may be due to efficient defect passivation as higher concentration of 3-aminopropyl trimethoxysilane (APTMS) was used and to the role of particle size in surface state delocalization. Cryo-X-ray diffraction showed no new peak formation or peak splitting as temperature was varied, which suggests efficient crystal phase stabilization in PNCs of all three sizes controlled by the concentration of APTMS. These results emphasize the importance of size and surface properties of PNCs in their optical properties such as PL quantum yield, PL lifetime, and crystal phase stability. Published under license by AIP Publishing.
Hard X-ray nanoprobe and time-resolved XEOL to observe increasing luminescence of ZnO and GaN epitaxial structures
(2019-10-21)
Lin, Bi-Hsuan
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Wu, Yu-Hao
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Wu, Tai-Sing
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Wu, Yung-Chi
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Li, Xiao-Yun
Hard X-ray excited optical luminescence (XEOL) with a nanofocused beam provides both excellent spatial resolution and high enough peak power density, which makes XEOL mapping and luminescence dynamics study achievable. We present here the time and X-ray intensity dependence of the near-band-edge (NBE) luminescence from the nonpolar a-plane MgZnO/ZnO multiple quantum wells (MQWs): the emission intensity increases more than 10 times after high X-ray irradiation. Different from the well-known NBE emission lifetime of ZnO (less than 1 ns), the long decay time gradually decreases from 130 ns to 35 ns with the increasing X-ray irradiation time. We attribute the observed changes in NBE luminescence to the excitation of the Mg-related energy state by the high energy X-ray nanobeam. This suggestion was further confirmed in the XEOL spectra of the Mg-doped and Si-doped c-plane GaN epi-films. Published under license by AIP Publishing.
Rapid construction of tetrahydropyridine scaffolds via formal imino Diels-Alder reactions of Schiff bases and Nazarov reagents
(2019-10-21)
Wu, Yen-Ku
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Rawal, Viresh H.
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應用化學系
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Department of Applied Chemistry
Described is a one-flask, two-step method for the synthesis of highly functionalized piperidines. The process involves formal [4 + 2] cycloadditions of Schiff bases and Nazarov reagents, followed by facile elaborations of the initial cycloadducts. Notably, these aza-annulations are facilitated by protic solvents and proceed smoothly under ambient conditions, without other additives. The synthetic utility of this annulation protocol is further showcased through a concise, convergent synthesis of (+/-)-tetrabenazine.
Scaling down of cobalt quantum-dots by colloidal route for non-volatile memory device application
(2019-10-23)
Yadav, Manoj
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Velampati, Ravi Shankar R.
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Mandal, Debaprasad
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
The present work details the synthesis of cobalt quantum-dots (Co QDs) with size downscaling to 1-2 nm and their applications in non-volatile memory (NVM) devices. The process of colloidal synthesis is simple and provides the control over a wide range of QDs size. The scaled-down colloidal Co QDs are applied for the NVM device fabrication. Colloidal synthesised Co QDs are spin-coated over silicon dioxide wafer for the fabrication of floating-gate NVM devices. Capacitance-voltage (C-V) and capacitance-time (C-t) measurements of the fabricated NVM device indicate a low voltage operation of device. A sweep voltages as small as 1.2-4 V lead to a flat band voltage shift of 0.35-1.5 V, evidencing the low operating voltage and low power NVM applications. Further, retention characteristics show a robust retention by fabricated NVM device. In addition, C-V measurements are done for the several samples in order to study the process repeatability. The work also is compared with the other processes for the floating gate memory device.
Sandwich-Nanostructured n-Cu2O/AuAg/p-Cu2O Photocathode with Highly Positive Onset Potential for Improved Water Reduction
(2019-10-23)
Lin, Yu-Chang
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Hsu, Liang-Ching
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Lin, Chia-Yu
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Chiang, Chao-Lung
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Chou, Che-Min
An n-Cu2O layer formed a high-quality buried junction with p-Cu2O to increase the photovoltage and thus to shift the turn-on voltage positively. Mott-Schottky measurements confirmed that the improvement benefited from a positive shift in flat-band potential. The obtained extremely positive onset potential, 0.8 V-RHE in n-Cu2O/AuAg/p-Cu2O, is comparable with measurements from water reduction catalysts. The AuAg alloy sandwiched between the homo-junction of n-Cu2O and p-Cu2O improved the photocatalytic performance. This alloy both served as an electron relay and promoted electron-hole pair generation in nearby semiconductors; the charge transfer between n-Cu2O and p-Cu2O in the sandwich structure was measured with X-ray absorption spectra. The proposed sandwich structure can be considered as a new direction for the design of efficient solar-related devices.
Two-Dimensional Cobalt Phosphate Hydroxide Nanosheets: A New Type of High-Performance Electrocatalysts with Intrinsic CoO6 Lattice Distortion for Water Oxidation
(2019-10-23)
Bu, Xiuming
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Chiang, ChaoLung
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Wei, Renjie
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Li, Zebiao
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Meng, You
Despite the recent advances in electrochemical water splitting, developing cost-effective and highly efficient electrocatalysts for oxygen evolution reaction (OER) still remains a substantial challenge. Herein, two-dimensional cobalt phosphate hydroxides (Co-5(PO4)(2)(OH)(4)) nanosheets, a unique stacking-disordered phosphate-based inorganic material, are successfully prepared via a facile and scalable method for the first time to serve as a superior and robust electrocatalyst for water oxidation. On the basis of the detailed characterization (e.g., X-ray absorption near-edge structure and X-ray photoelectron spectroscopy), the obtained nanosheets consist of special zigzag CoO6 octahedral chains along with intrinsic lattice distortion and excellent hydrophilicity, in which these factors contribute to the highly efficient performance of prepared electrocatalysts for OER. Specifically, (Co-5(PO4)(2)(OH)(4)) deposited on glassy carbon electrode (loading amount approximate to 0.553 mg cm -2 ) can exhibit an unprecedented overpotential of 254 mV to drive a current density of 10 mA cm(-2) with a small Tafel slope of 57 mV dec(-1) in alkaline electrolytes, which outperforms the ones of CO3(PO4)(2)(370 mV) and Co(OH)(2) (360 mV) as well as other advanced catalysts. Evidently, this work has opened a new pathway to the rational design of promising metal phosphate hydroxides toward the efficient electrochemical energy conversion.
Optical Control of Hole Wavefunction in Type-II Magnetic Quantum Dot Structures
(2019-10-24)
Zhang, Peiyao
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Norden, Tenzin
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Pientka, James M.
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Oszwaldowski, Rafal
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Najafi, Arman
Unlike the extensively studied, spatially direct, quantum dots (QDs) with type-I band alignment where both electrons and holes are confined in the QD, in ZnTe QDs embedded in a (Zn,Mn)Se matrix only the holes are confined in the QDs. This spatially indirect type-II system provides unexplored opportunities to control the magnetic interactions between the hole spins in the nonmagnetic QDs and the spins of the magnetic ions in the matrix. Photoluminescence (PL) was excited either with photons of energy 3.06 eV [above band gap of the (Zn,Mn)Se matrix] or with photons of energy 2.54 eV [below the (Zn,Mn)Se band gap]. In the presence of an external magnetic field, the saturation red shift of the PL peak under 2.54 eV excitation exhibits an up to three-fold increase compared to the shift observed with 3.06 eV excitation. This increase is attributed to multiple hole occupancy of the QDs and the resulting increased penetration of the hole wavefunction tail further into the (Zn,Mn)Se matrix. The proposed model is supported by calculations which include the hole-hole Coulomb interactions as well as the hole-Mn spin exchange interactions.
Highly Plasmonic Titanium Nitride by Room-Temperature Sputtering
(2019-10-25)
Chang, Chun-Chieh
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Nogan, John
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Yang, Zu-Po
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Kort-Kamp, Wilton J. M.
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Ross, Willard
Titanium nitride (TiN) has recently emerged as an attractive alternative material for plasmonics. However, the typical high-temperature deposition of plasmonic TiN using either sputtering or atomic layer deposition has greatly limited its potential applications and prevented its integration into existing CMOS device architectures. Here, we demonstrate highly plasmonic TiN thin films and nanostructures by a room-temperature, low-power, and bias-free reactive sputtering process. We investigate the optical properties of the TiN films and their dependence on the sputtering conditions and substrate materials. We find that our TiN possesses one of the largest negative values of the real part of the dielectric function as compared to all other plasmonic TiN films reported to date. Two-dimensional periodic arrays of TiN nanodisks are then fabricated, from which we validate that strong plasmonic resonances are supported. Our room-temperature deposition process can allow for fabricating complex plasmonic TiN nanostructures and be integrated into the fabrication of existing CMOS-based photonic devices to enhance their performance and functionalities.
運用想像力減少悲傷的負面效果
(2019-10-27)
曾弘碩
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Department of Communication and Technology
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傳播與科技學系
當我們遇到悲傷的事情後，常常會做出自暴自棄的舉動。比如：失戀後暴飲暴食來減少痛苦。研究發現，原來把悲傷擬人化，會降低悲傷帶來的負面效果。
一眼看穿你！從消費習慣看你的性格
(2019-10-27)
馬鈺絜
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Department of Communication and Technology
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傳播與科技學系
每個人都有不同的個性特徵，會不自覺地在生活中表現出來。你知道嗎？連消費習慣都可以反映人格特質，你有想到類似的例子嗎？
虐你千百遍，你待「減重」如初戀？
(2019-10-27)
黃心姵
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Department of Communication and Technology
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傳播與科技學系
人常在「食」無忌憚後，立志好好減肥，但你想過造成人們「食」無忌憚背後的原因嗎？多項研究結果指出可能暴飲暴食的原因，也找到可以幫助燃燒脂肪的關鍵基因，並提供新奇的方式來增加卡路里的消耗。
看似「高冷」的貓，其實會與人類產生依附關係
(2019-10-27)
蕭蕙崎
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Department of Communication and Technology
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傳播與科技學系
儘管大多數的貓，似乎不太喜歡與人接觸，但跟據發表於《當代生物學》29期的研究顯示，貓咪會與飼主發展出與人類相同的依附關係，其實貓咪的社交認知力比你想像的要高上許多。
總編的話
(2019-10-27)
吳宥芯
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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321期，共計13篇文章，包含三篇社會議題、七篇科技新知、四篇藝文評論。本篇頭題為陳炘瑜的〈宮鬥禁不禁〉，文章分析今年熱度飆漲的宮鬥劇、手遊等，於中國慘遭禁播的風波，去深入探討。
《哪吒之魔童轉世》不信所謂的命中注定
(2019-10-27)
李金福
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Department of Communication and Technology
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傳播與科技學系
歐美那邊有「漫威宇宙」，中國則欲打造「封神宇宙」；《哪吒之魔童轉世》口碑和票房雙雙爆棚，榮登中國內地電影史票房第二名，究竟是什麼原因讓中國內地冷門類型的動畫片突然爆紅？
當自閉《證人》成了唯一目擊者，你會選擇相信嗎？
(2019-10-27)
李旻珊
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Department of Communication and Technology
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傳播與科技學系
當自閉症的孩子是唯一的證人，不被相信，卻是最值得信任的人。
沉默的告別自殺者遺族的心態與關懷
(2019-10-27)
曾冠霖
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Department of Communication and Technology
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傳播與科技學系
自殺，是一種選擇；自殺者遺族，卻無從選擇。活著的人，該如何面對社會的偏見與誤解，又該如何從痛苦的情緒中重新站起？
宮鬥禁不禁？
(2019-10-27)
陳炘瑜
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Department of Communication and Technology
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傳播與科技學系
宮鬥劇的禁播議題在今年頗受關注，而造成禁播背後的原因與影響到底為何？其中又牽扯哪些面向？如果不禁播，又會形成怎樣的現象？本文將帶你一探究竟。
香港年輕人的吶喊：從地下樂團到獨立樂團
(2019-10-27)
詹庭瑄
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周容萱
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Department of Communication and Technology
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傳播與科技學系
台灣的獨立樂團在近十年內猛然崛起，而香港的獨立樂團也從地下樂團逐漸走出外面的世界，他們的努力，在到處開啟了獨立樂團的花。
神秘歌姬—「?te壞特」用音樂買醉
(2019-10-27)
林怡恩
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Department of Communication and Technology
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傳播與科技學系
「?te壞特」用迷幻出世的嗓音，搭配微醺心醉的Lo-Fi曲風，僅用三首歌曲便震撼了近期台灣獨立音樂圈，為華語樂壇注入一股新的力量。
寂寞的邊緣人請小心！研究顯示孤單比肥胖更不健康
(2019-10-27)
徐曼寧
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Department of Communication and Technology
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傳播與科技學系
孤獨不再只是一種情緒，近年來越來越多研究發現，孤獨對人體危害極大。其中又以「老年孤獨」最為各國矚目。即將邁入超高齡社會的台灣，該如何解決「老年孤獨」？