Browsing by Issue Date, starting with "2017-09-11"

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Effect of barrier layer on switching polarity of ZrO2-based conducting-bridge random access memory
(2017-09-11)
Chandrasekaran, Sridhar
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Simanjuntak, Firman Mangasa
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Tsai, Tsung-Ling
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Lin, Chun-An
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Tseng, Tseung-Yuen
In this study, metal diffusion barrier-dependent switching polarity in ZrO2-based conducting-bridge random access memory was investigated. The device without the barrier layer (BL) exhibited nonpolar switching characteristics. However, inserting TiW BL resulted in positive reset failure. This phenomenon depends on the size and shape of the conducting bridge and also on the defects that contribute to the formation and rupture of the bridge. Consequently, the properties of the conducting bridge govern the device switching performance. Cu- and oxygen vacancy-based conducting bridge during N-Set for a device with and without the BL was proposed. The effect of the insertion of BL on the switching performance was also discussed. The absence of BL resulted in switching instability and poor nonvolatility. By contrast, a device with BL exhibited enhanced uniformity and nonvolatility, and the retention was more than 10(5) s at 200 degrees C. Published by AIP Publishing.
An Affordable Wet Chemical Route to Grow Conducting Hybrid Graphite-Diamond Nanowires: Demonstration by A Single Nanowire Device
(2017-09-11)
Shellaiah, Muthaiah
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Chen, Tin Hao
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Simon, Turibius
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Li, Liang-Chen
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Sun, Kien Wen
We report an affordable wet chemical route for the reproducible hybrid graphite-diamond nanowires (G-DNWs) growth from cysteamine functionalized diamond nanoparticles (ND-Cys) via pH induced self-assembly, which has been visualized through SEM and TEM images. Interestingly, the mechanistic aspects behind that self-assembly directed G-DNWs formation was discussed in details. Notably, above self-assembly was validated by AFM and TEM data. Further interrogations by XRD and Raman data were revealed the possible graphite sheath wrapping over DNWs. Moreover, the HR-TEM studies also verified the coexistence of less perfect sp(2) graphite layer wrapped over the sp3 diamond carbon and the impurity channels as well. Very importantly, conductivity of hybrid G-DNWs was verified via fabrication of a single G-DNW. Wherein, the better conductivity of G-DNW portion L2 was found as 2.4 +/- 1.92 x 10(-6) mS/cm and revealed its effective applicability in near future. In addition to note, temperature dependent carrier transport mechanisms and activation energy calculations were reported in details in this work. Ultimately, to demonstrate the importance of our conductivity measurements, the possible mechanism behind the electrical transport and the comparative account on electrical resistivities of carbon based materials were provided.
Significant color space blue-shift of green OLED emitter with sustaining lifetime and substantial efficiency enhancement (vol 111, 093301, 2017)
(2017-09-11)
Li, Jung-Yu
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Chen, Shih-Pu
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Siao, Huei-Jhen
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Wu, Jin-Han
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Chen, Guan-Yu
Approaching confinement structure for light quarks in a holographic soft wall QCD model
(2017-09-12)
Li, Meng-Wei
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Yang, Yi
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Yuan, Pei-Hung
;
電子物理學系
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物理研究所
We study the confinement-deconfinement phase transition in a holographic soft-wall QCD model. By solving the Einstein-Maxwell-scalar system analytically, we obtain the phase structure of the black hole backgrounds. We then impose probe open strings in such a background to investigate the confinement-deconfinement phase transition from different open string configurations under various temperatures and chemical potentials. Furthermore, we study the Wilson loop by calculating the minimal surface of the probing open string world sheet and obtain the Cornell potential in the confinement phase analytically.
Characterization of a heat-tolerant Chlorella sp GD mutant with enhanced photosynthetic CO2 fixation efficiency and its implication as lactic acid
(2017-09-12)
Lee, Tse-Min
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Tseng, Yu-Fei
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Cheng, Chieh-Lun
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Chen, Yi-Chuan
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Lin, Chih-Sheng
Background: Fermentative production of lactic acid from algae-based carbohydrates devoid of lignin has attracted great attention for its potential as a suitable alternative substrate compared to lignocellulosic biomass. Results: A Chlorella sp. GD mutant with enhanced thermo-tolerance was obtained by mutagenesis using N-methyl-N'-nitro-N-nitrosoguanidine to overcome outdoor high-temperature inhibition and it was used as a feedstock for fermentative lactic acid production. The indoor experiments showed that biomass, reducing sugar content, photosynthetic O-2 evolution rate, photosystem II activity (F-v/F-m and F-v'/F-m'), and chlorophyll content increased as temperature, light intensity, and CO2 concentration increased. The mutant showed similar DIC affinity and initial slope of photosynthetic light response curve (a) as that of the wild type but had higher dissolved inorganic carbon (DIC) utilization capacity and maximum photosynthesis rate (P-max). Moreover, the PSII activity (F-v'/F-m') in the mutant remained normal without acclimation process after being transferred to photobioreactor. This suggests that efficient utilization of incident high light and enhanced carbon fixation with its subsequent flux to carbohydrates accumulation in the mutant contributes to higher sugar and biomass productivity under enriched CO2 condition. The mutant was cultured outdoors in a photobioreactor with 6% CO2 aeration in hot summer season in southern Taiwan. The harvested biomass was subjected to separate hydrolysis and fermentation (SHF) for lactic acid production with carbohydrate concentration equivalent to 20 g/L glucose using the lactic acid-producing bacterium Lactobacillus plantarum 23. The conversion rate and yield of lactic acid were 80% and 0.43 g/g Chlorella biomass, respectively. Conclusions: These results demonstrated that the thermo-tolerant Chlorella mutant with high photosynthetic efficiency and biomass productivity under hot outdoor condition is an efficient fermentative feedstock for large-scale lactic acid production.
Carbodicarbenes: Unexpected pi-Accepting Ability during Reactivity with Small Molecules
(2017-09-13)
Chen, Wen-Ching
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Shih, Wei-Chih
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Jurca, Titel
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Zhao, Lili
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Andrada, Diego M.
An investigation of carbodicarbenes, the less explored member of the carbenic complex/ligand family has yielded unexpected electronic features and concomitant reactivity. Observed 1,2-addition of E-H bonds (E = B, C, Si) across the carbone central carbon and that of the flanking N-heterocyclic carbene (NHC) fragment, combined with single-crystal X-ray studies of a model Pd complex strongly suggests a significant level of pi-accepting ability at the central carbon of the NHC moiety. This feature is atypical of classic NHCs, which are strong sigma-donors, with only nominal pi-accepting ability. The unanticipated pi-acidity is critical for engendering carbodicarbenes with reactivity more commonly observed with frustrated Lewis pairs (FLPs) rather than the more closely related NHCs and cyclic (alkyl)(amino)carbenes (CAACs).
Directional Solution Coating by the Chinese Brush: A Facile Approach to Improving Molecular Alignment for High-Performance Polymer TFTs
(2017-09-13)
Lin, Fang-Ju
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Guo, Cheng
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Chuang, Wei-Tsung
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Wang, Chien-Lung
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Wang, Qianbin
Directional solution coating by the Chinese brush provides a facile approach to fabricate highly oriented polymer thin films by finely controlling the wetting and dewetting processes under directional stress. The biggest advantage of the Chinese brush over the normal western brush is the freshly emergent hairs used, whose unique tapered structure renders a dynamic balance of the liquid within the brush by multiple forces when interacting with the liquid. Consequently, the liquid is steadily held within the brush without any unexpected leakage, making the liquid transfer proceed in a well-controllable manner. It is demonstrated that the Chinese brush coating enables the crystallization of the polymer and the self-assembly of conjugated backbones to proceed in a quasi-steady state via a certain direction, which is attributed to the controllable receding of the three-phase contact line during the dewetting process by the multiple parallel freshly emergent hairs. The as-prepared polymer thin films exhibit over six times higher charge-carrier mobility compared to the spin-coated films, which therefore provides a general approach for high-performance organic thin-film transistors.
Energy transfer within small molecule/conjugated polymer blends enhances photovoltaic efficiency
(2017-09-14)
Lin, Yu-Che
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Su, Yu-Wei
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Li, Jia-Xing
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Lin, Bo-Hsien
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Chen, Chung-Hao
In this study, we employed ternary blends capable of energy transfer-a synthesized high-band-gap small molecule (SM-4OMe) comprising benzodithiophene (BDT) and rhodanine units (a molecular structure that was designed for energy transfer), a low-band-gap polymer (PTB7-TH) comprising BDT and thienothiophene units with desired packing orientation, and a fullerene-as active layers for singlejunction photovoltaic devices. The light absorption of the small molecule and the polymer was partially complementary, owing to their band gap difference, thereby broadening the absorption spectrum of solar light while maintaining the energy band structures that facilitated energy and charge transfer. The synthesized small molecule SM-4OMe and the PTB7-TH had somewhat similar chemical structureswith the same planar BDT donor units-and thus allowed sufficient mixing between them for energy transfer to take place. The power conversion efficiency of a device incorporating a ternary blend of PTB7-TH:SM-4OMe:PC71BM (0.9 :0.1 :1.5, w/w/w) as the active layer, processed with diiodooctane (2 vol%) in chlorobenzene, was 10.4%, which is higher than the value of 8% of the corresponding device incorporating PTB7-TH:PC71BM (1 :1.5, w/w)-an increase of 30%. We attribute this enhancement to the energy transfer from the high-band-gap small molecule SM-4OMe to the low-band-gap polymer PTB7-TH and to the optimal phase-separated bulk heterojunction morphology that comprises a mean PC71BM cluster size of 6 nm, which is lower than 12 nm for the PTB7-TH and PC71BM binary blends, and slightly better in-plane packing, arising from the inducements of the presence of SM-4OMe. This approach provides a facile and effective way to enhance the power conversion efficiency of single junction organic photovoltaics.
Theoretical study of the substituent effect controlling the radiative and non-radiative decay processes of platinum(II) complexes
(2017-09-14)
Shen, Wei
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Zhang, Wenting
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Zhu, Chaoyuan
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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
Six platinum complexes bearing different electron-withdrawing groups (-CN, -NO2, -o-carborane, -SF5 and -CF2CF2CF3) have been designed to explore the electron-withdrawing capability and the conjugative effect of the substituents, and density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations have been performed to determine their electronic structures and phosphorescent properties. Three factors, including the oscillator strength mu(S-n) for S-0-S-n excitations, the energy gap between the triplet and singlet states DE(Sn-T1) and the spin-orbital coupling < T-1|(H) over cap (SOC)| S-n >, have been calculated to analyze the radiative processes. In addition, temperature-independent, temperature-dependent and triplet-triplet annihilation (TTA) have been analyzed to determine the non-radiative decay processes. Introducing strong electron-withdrawing groups into phosphorescent transition-metal complexes has a significant impact on the phosphorescent properties and some regularity besides the inductive effect (the electron-withdrawing capability) and the conjugative effect of the substituents. The stronger electron-withdrawing capability and smaller conjugative effect can give rise to blue-shifted emission behavior and give larger radiative decay rate constants. The results demonstrate that complex 4 (-NO2 substituted) and complex 2 (-o-carborane) are possible candidates for blue-emitting materials.
Threading dislocation reduction in three-dimensionally grown GaN islands on Si (111) substrate with AlN/AlGaN buffer layers
(2017-09-14)
Chang, Shane
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Wei, Lin Lung
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Luong, Tien Tung
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Chang, Ching
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Chang, Li
Three-dimensional GaN island growth without any masks was first introduced under high pressure in metalorganic chemical vapor deposition after the growth of AlN and AlGaN buffer layers on Si ( 111) substrate, followed by two-dimensional GaN growth to form a continuous GaN film with improvement of the crystalline quality and surface smoothness. X-ray diffraction and cross-sectional scanning transmission electron microscopy analyses show that a high-quality GaN film can be achieved by bending of edge threading dislocations (TDs) and the formation of dislocation half-loops. It is observed that most of edge TDs bend 90 degrees from the growth direction along c-axis, whereas mixed TDs bend about 30 degrees towards the inclined sidewall facets of the islands. Consequently, a 1.2 mu m thick GaN epitaxial film with a low threading dislocation density of 2.5 x 10 8 cm(-2) and a smooth surface of 0. 38 nm roughness can be achieved on Si substrate. Published by AIP Publishing.
Selective antibody activation through protease-activated pro-antibodies that mask binding sites with inhibitory domains
(2017-09-14)
Chen, I-Ju
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Chuang, Chih-Hung
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Hsieh, Yuan-Chin
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Lu, Yun-Chi
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Lin, Wen-Wei
Systemic injection of therapeutic antibodies may cause serious adverse effects due to on-target toxicity to the antigens expressed in normal tissues. To improve the targeting selectivity to the region of disease sites, we developed protease-activated pro-antibodies by masking the binding sites of antibodies with inhibitory domains that can be removed by proteases that are highly expressed at the disease sites. The latency-associated peptide (LAP), C2b or CBa of complement factor 2/B were linked, through a substrate peptide of matrix metalloproteinase-2 (MMP-2), to an anti-epidermal growth factor receptor (EGFR) antibody and an anti-tumor necrosis factor-alpha (TNF-alpha) antibody. Results showed that all the inhibitory domains could be removed by MMP-2 to restore the binding activities of the antibodies. LAP substantially reduced (53.8%) the binding activity of the anti-EGFR antibody on EGFR-expressing cells, whereas C2b and CBa were ineffective (21% and 9.3% reduction, respectively). Similarly, LAP also blocked 53.9% of the binding activity of the anti-TNF-alpha antibody. Finally, molecular dynamic simulation showed that the masking efficiency of LAP, C2b and CBa was 33.7%, 10.3% and -5.4%, respectively, over the binding sites of the antibodies. This strategy may aid in designing new protease-activated pro-antibodies that attain high therapeutic potency yet reduced systemic on-target toxicity.
Study of the wave packet treatment of neutrino oscillation at Daya Bay
(2017-09-14)
An, F. P.
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Balantekin, A. B.
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Band, H. R.
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Bishai, M.
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Blyth, S.
The disappearance of reactor (v) over bar (e) observed by the Daya Bay experiment is examined in the framework of a model in which the neutrino is described by a wave packet with a relative intrinsic momentum dispersion sigma(rel). Three pairs of nuclear reactors and eight antineutrino detectors, each with good energy resolution, distributed among three experimental halls, supply a high-statistics sample of (v) over bar (e) acquired at nine different baselines. This provides a unique platform to test the effects which arise from the wave packet treatment of neutrino oscillation. The modified survival probability formula was used to fit Daya Bay data, providing the first experimental limits: 2.38 x 10(-1)7 < sigma(rel) < 0.23. Treating the dimensions of the reactor cores and detectors as constraints, the limits are improved: 10-(14) less than or similar to sigma(rel) < 0.23, and an upper limit of sigma(rel) < 0.20 (which corresponds to sigma(x) greater than or similar to 10(-11) cm) is obtained. All limits correspond to a 95% C. L. Furthermore, the effect due to the wave packet nature of neutrino oscillation is found to be insignificant for reactor antineutrinos detected by the Daya Bay experiment thus ensuring an unbiased measurement of the oscillation parameters sin(2) 2 theta(13) and Delta m(32)(2) within the plane wave model.
Eco-friendly luminescent solar concentrators with low reabsorption losses and resistance to concentration quenching based on aqueous-solution-processed thiolate-gold nanoclusters
(2017-09-15)
Huang, H. Y.
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Cai, K. B.
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Chang, L. Y.
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Chen, P. W.
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Lin, T. N.
Heavy-metal-containing quantum dots (QDs) with engineered electronic states have been served as luminophores in luminescent solar concentrators (LSCs) with impressive optical efficiency. Unfortunately, those QDs involve toxic elements and need to be synthesized in a hazardous solvent. Recently, biocompatible, eco-friendly gold nanoclusters (AuNCs), which can be directly synthesized in an aqueous solution, have gained much attention for promising applications in 'green photonics'. Here, we explored the solid-state photophysical properties of aqueoussolution- processed, glutathione-stabilized gold nanoclusters (GSH-AuNCs) with a ligand-tometal charge-transfer (LMCT) state for developing 'green' LSCs. We found that such GSH-AuNCs exhibit a large Stokes shift with almost no spectral overlap between the optical absorption and PL emission due to the LMCT states, thus, suppressing reabsorption losses. Compared with GSH-AuNCs in solution, the photoluminescence quantum yields (PL-QYs) of the LSCs can be enhanced, accompanied with a lengthened PL lifetime owing to the suppression of non-radiative recombination rates. In addition, the LSCs do not suffer from severe concentration-induced PL quenching, which is a common weakness for conventional luminophores. As a result, a common trade-off between light-harvesting efficiency and solid-state PL-QYs can be bypassed due to nearly-zero spectral overlap integral between the optical absorption and PL emission. We expect that GSH-AuNCs hold great promise for serving as luminophores for 'green' LSCs by further enhancing solid-state PL-QYs.
Electrocatalytic performance of Pt nanoparticles sputter-deposited on indium tin oxide toward methanol oxidation reaction: The particle size effect
(2017-09-15)
Ting, Chao-Cheng
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Chao, Chih-Hsuan
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Tsai, Cheng Yu
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Cheng, I-Kai
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Pan, Fu-Ming
We sputter-deposited Pt nanoparticles with an average size ranging from 2.0 nm to 8.5 nm on the indium tin oxide (ITO) glass substrate, and studied the effect of the size of Pt nanoparticles on electrocatalytic activity of the Pt/ITO electrode toward methanol oxidation reaction (MOR) in acidic solution. X-ray photoelectron spectroscopy (XPS) reveals an interfacial oxidized Pt layer present between Pt nanoparticles and the ITO substrate, which may modify the surface electronic structure of Pt nanoparticles and thus influences the electrocatalytic properties of the Pt catalyst toward MOR. According to electrochemical analyses, smaller Pt nanoparticles exhibit slower kinetics for CO electrooxidation and MOR. However, a smaller particle size enables better CO tolerance because the bifunctional mechanism is more effective on smaller Pt nanoparticles. The electrocatalytic activity decays rapidly for Pt nanoparticles with a size smaller than 3 nm and larger than 8 nm. The rapid activity decay is attributed to Pt dissolution for smaller nanoparticles and to CO poisoning for larger ones. Pt nanoparticles of 5-6 nm in size loaded on ITO demonstrate a greatly improved electrocatalytic activity and stability compared with those deposited on different substrates in our previous studies. (C) 2017 Elsevier B.V. All rights reserved.
Change in the structure and function of lectin by photodissociation of NO
(2017-09-16)
Kurota, T.
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Sato, I.
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Kuroi, K.
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Hiramatsu, H.
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Nakabayashi, T.
We have shown here that the structure and sugar-binding activity of lectin can be changed by the photodissociation of NO. Intramolecular S-S bonds are photogenerated from SNO in the protein, which can be used to photo-control the structure and function of proteins.
Exploring the self-mode locking and vortex structures of nonplanar elliptical modes in selectively end-pumped Nd: YVO4 lasers: manifestation of large fractional orbital angular momentum
(2017-09-18)
Tung, J. C.
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Omatsu, T.
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Liang, H. C.
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Huang, K. F.
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Chen, Y. F.
An end-pumped Nd: YVO4 laser under selective pumping is used to excite lasing modes with transverse patterns performed to exhibit the characteristics of multiple spots arranged on elliptical features near degenerate cavities. The spatial distribution of elliptical lasing modes is clearly revealed to be localized on the nonplanar ray orbits, so-called nonplanar elliptical modes, which possess large fractional orbital angular momentum. Moreover, temporal dynamics for the output emission of nonplanar elliptical modes are verified to obtain self-mode-locked operation. We further numerically manifest not only the influence of radial-asymmetry distributions on the vortex structures of nonplanar elliptical modes, but also the vector field of transverse lasing modes altered with twisting phase structures in the propagation direction. (C) 2017 Optical Society of America
Forward bias operation of silicon photonic Mach Zehnder modulators for RF applications
(2017-09-18)
Chao, Rui Lin
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Shi, Jin Wei
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Jain, Aditya
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Hirokawa, Takako
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Khope, Akhilesh S. P.
In this paper, we demonstrate that forward bias (+ 0.9V) of a high-speed silicon (Si) optical Mach-Zehnder Modulator (MZM) increases the radio-frequency (RF) link gain by 30 dB when compared to reverse bias operation (-8V). RF applications require tunable, narrowband electro-optic conversion with high gain to mitigate noise of the optical receiver and realize high RF spur-free dynamic range. Compared to reverse bias, the forward bias gain rolls off more rapidly but offers higher RF link gain improvement of more than 13.2 dB at 20 GHz. Furthermore, forward bias is shown to result in comparable spurious-free dynamic range (SFDR: 104.5 dB. Hz(2/3)). We demonstrate through an analytical dc transfer curve the existence of simultaneous high gain and OIP3 and verify the theoretical results with measurement under forward bias at a bias point of around + 0.9 V. (C)2017 Optical Society of America
Analysis of a lens-array modulated coaxial holographic data storage system with considering recording dynamics of material
(2017-09-18)
Yu, Yeh-Wei
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Yang, Chi-Hsiang
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Yang, Tsung-Hsun
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Lin, Shiuan-Huei
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Sun, Ching-Cherng
In the first time, a simulation model with considering the recording dynamics of material is built and is used to simulate evolution of the grating strength of the recorded hologram in a coaxial volume holographic memory system. In addition, phase modulation by lens array in the reference is introduced and observed to perform better diffracted signal quality and higher shifting selectivity, in both simulation and experiment. The use of lens array is found to provide multiple advantages in volume holographic memory system. The new simulation model potentially can be used to precisely design the system to obtain higher diffracted signal quality, higher shifting selectivity, and reduction of M# consumption and increase of storage capacity. (C) 2017 Optical Society of America
Competitive profit maximization in social networks
(2017-09-19)
Li, Weian
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Liu, Wenjing
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Chen, Tiantian
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Qu, Xiaoying
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Fang, Qizhi
We study the competitive profit maximization problem in a social network, which can be viewed as the profit maximization problem in a game-theoretic setting. We formulate two models called the profit maximization-agent (PM-A) game and the profit maximization-society (PM-S) game. By reducing them to be valid utility systems, we show that any Nash equilibrium provides an excepted social utility within a factor 1/2 (subject to a function-dependent additive term) of the optimum in the PM-A game and a factor of 1/2 of the optimum in the PM-S game. Furthermore, for the PM-S game, a polynomial-time algorithm is given for each player that can approximate the best response within a factor (1 - 1/e). (C) 2017 Elsevier B.V. All rights reserved.
In Situ TEM Investigation of the Electrochemical Behavior in CNTs/MnO2-Based Energy Storage Devices
(2017-09-19)
Tsai, Tsung-Chun
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Huang, Guan-Min
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Huang, Chun-Wei
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Chen, Jui-Yuan
;
Yang, Chih-Chieh
Transition metal oxides have attracted much interest owing to their ability to provide high power density in lithium batteries; therefore, it is important to understand the electrochemical behavior and mechanism of lithiation-delithiation processes. In this study, we successfully and directly observed the structural evolution of CNTs/MnO2 during the lithiation process using transmission electron microscopy (TEM). CNTs/MnO2 were selected due to their high surface area and capacitance effect, and the lithiation mechanism of the CNT wall expansion was systematically analyzed. Interestingly, the wall spacings of CNTs/MnO2 and CNTs were obviously expanded by 10.92% and 2.59%, respectively. The MnO2 layer caused structural defects on the CNTs surface that could allow penetration of Li+ and Mn4+ through the tube wall and hence improve the ionic transportation speed. This study provided direct evidence for understanding the role of CNTs/MnO2 in the lithiation process used in lithium ion batteries and also offers potential benefits for applications and development of supercapacitors.