Browsing by Issue Date, starting with "2019-02-07"

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Structure and Strain Relaxation of GaN Nanorods Grown on Homoepitaxial Surface via Controlling Irregular Mask
(2019-02-07)
Huang, Chang-Hsun
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Pakzad, Anahita
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Lee, Wei-I
;
Chou, Yi-Chia
;
電子物理學系
We propose a simple and low-cost approach using irregular mask for growing GaN nanorods (NRs) bottom up on a freestanding GaN substrate through hydride vapor-phase epitaxy. The irregular mask consists of uncoalesced SiO2 islands deposited by plasma-enhanced chemical vapor deposition to isolate growth. The selection of the SiO2 amount is investigated to achieve reasonable NR density (high coverage), desired morphology (flat side walls and uniform diameters), and lattice quality (single crystalline; better quality than that of an as-grown layer under the same growth ambient). Using this growth approach with appropriate parameters, we successfully synthesize high coverage of uncoalesced NRs on a homoepitaxial surface in a short growth duration. The morphology, density, and growth rate are controlled by adjusting V/III ratios. The cathodoluminescence and photoluminescence measurements of GaN show that luminescence was obtained near 3.4 eV while the structure was grown with mask but contained defect signals when grown without mask. The residual strain relaxation within the GaN NRs has been confirmed using Raman spectrum and scanning transmission electron microscopy strain mapping. Moreover, we demonstrate the strain distribution between different crystalline qualities and lattice orientations in GaN NR The method provides a quick and inexpensive method for future nanofabrication consideration.
Image-text dual neural network with decision strategy for small-sample image classification
(2019-02-07)
Zhu, Fangyi
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Ma, Zhanyu
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Li, Xiaoxu
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Chen, Guang
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Chien, Jen-Tzung
Small-sample classification is a challenging problem in computer vision. In this work, we show how to efficiently and effectively utilize semantic information of the annotations to improve the performance of small-sample classification. First, we propose an image-text dual neural network to improve the classification performance on small-sample datasets. The proposed model consists of two sub-models, an image classification model and a text classification model. After training the sub-models separately, we design a novel method to fuse the two sub-models rather than simply combine their results. Our image-text dual neural network aims to utilize the text information to overcome the training problem of deep models on small-sample datasets. Then, we propose to incorporate a decision strategy into the image-text dual neural network to further improve the performance of our original model on few-shot datasets. To demonstrate the effectiveness of the proposed models, we conduct experiments on the LabelMe and UIUC-Sports datasets. Experimental results show that our method is superior to other models. (C) 2018 Elsevier B.V. All rights reserved.
Effects of electrostatic environment on the electrically triggered production of entangled photon pairs from droplet epitaxial quantum dots
(2019-02-07)
Ramirez, Hanz Y.
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Chou, Ying-Lin
;
Cheng, Shun-Jen
;
電子物理學系
;
Department of Electrophysics
Entangled photon pair generation is a crucial task for development of quantum information based technologies, and production of entangled pairs by biexciton cascade decays in semiconductor quantum dots is so far one of the most advanced techniques to achieve it. However, its scalability toward massive implementation requires further understanding and better tuning mechanisms to suppress the fine structure splitting between polarized exciton states, which persists as a major obstacle for entanglement generation from most quantum dot samples. In this work, the influence of electrostatic environment arising from electrically biased electrodes and/or charged impurities on the fine structure splitting of GaAs/AlGaAs droplet epitaxial quantum dots is studied, by means of numerical simulations considering a realistic quantum dot confining potential and electron-hole exchange interaction within a multiband k.p framework. We find that reduction of the fine structure splitting can be substantially optimized by tilting the field and seeding impurities along the droplet elongation axis. Furthermore, our results provide evidence of how the presence of charged impurities and in-plane bias components, may account for different degrees of splitting manipulation in dots with similar shape, size and growth conditions.
On possibility of determining neutrino mass hierarchy by the charged-current and neutral-current events of supernova neutrinos in scintillation detectors
(2019-02-12)
Lee, Fei-Fan
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Lee, Feng-Shiuh
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Lai, Kwang-Chang
;
電機學院
;
College of Electrical and Computer Engineering
One of the unresolved mysteries in neutrino physics is the neutrino mass hierarchy. We present a new method to determine neutrino mass hierarchy by comparing the events of inverse beta decays (IBD), e+pn+e+, and neutral current (NC) interactions, ()+p()+p, of supernova neutrinos from accretion and cooling phases in scintillation detectors. Supernova neutrino flavor conversions depend on the neutrino mass hierarchy. On account of Mikheyev-Smirnov-Wolfenstein effects, the full swap of the e flux with the x (,) one occurs in the inverted hierarchy, while such a swap does not occur in the normal hierarchy. In consequence, the ratio of high energy IBD events to NC events for the inverted hierarchy is higher than in the normal hierarchy. Since the luminosity ofe is larger than that of x in accretion phase while the luminosity of e becomes smaller than that of x in cooling phase, we calculate this ratio for both accretion and cooling phases. By analyzing the change of this event ratio from accretion phase to cooling phase, one can determine the neutrino mass hierarchy.
LIGHT EMISSION DIODE WITH FLIP-CHIP STRUCTURE AND MANUFACTURING METHOD THEREOF
(2019-02-14)
RAY-HUA HORNG
;
RAY-HUA HORNG
;
HUAN-YU CHIEN
A light emitting diode device with flip-chip structure includes a transparent protective substrate, a transparent conductor layer, a glue layer, a group III-V stack layer, a first conductivity metal electrode, a second conductivity metal electrode and an insulating layer. The transparent conductor layer is formed on the transparent protective substrate. The glue layer bonds the transparent protective substrate and the transparent conductor layer. The group III-V stack layer and the first conductivity metal electrode are respectively formed on a first portion and a second portion of the transparent conductor layer. The second conductivity metal electrode is formed on a portion of the group III-V stack layer. The insulating layer covers exposed portions of the transparent conductor layer and the group III-V stack layer, and the insulating layer further covers portions of the first and second conductivity metal electrodes, so as to expose the first and second conductivity metal electrodes.
Efficient Electrostatic Particle-into-liquid Sampler Which Prevents Sampling Artifacts
(2019-02-14)
Chuen-Jinn Tsai
;
Chao-Ting Hsu
The present invention discloses an efficient electrostatic particle-into-liquid sampler (EPILS). The EPILS collects an aerosol sample in the dry mode and extracts it in the wet mode to prevent sampling artifacts. In the dry mode, a first stage utilizes carbon brushes as discharge electrodes to charge aerosol particles which are then collected on the cylinder wall by the electric field setup between the high-voltage central metal rod and the grounded cylinder in the second stage. In the wet mode, DI water is injected into the EPILS in a pulsation manner by opening and closing solenoid valves intermittently, which dislodges aerosol particles deposited on the cylinder wall effectively to become a liquid aerosol sample. The liquid aerosol sample is then analyzed for chemical compositions manually or automatically.
Enhanced wavelength-selective photoresponsivity with a MoS2 bilayer grown conformally on a patterned sapphire substrate
(2019-02-14)
Chen, Sung-Wen Huang
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Wang, Sheng-Wen
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Hong, Kuo-Bin
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Medin, Henry
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Chung, Chieh-Han
In the present study, novel MoS2 bilayers with 3D structures were considered for their application as wavelength-sensitive photodetectors. Using e-gun deposition and a CVD process, MoS2 bilayers can be grown conformally on a patterned (cones or pyramids) sapphire substrate without any wrinkles on the 2D film. After the sulfurization process, the MoS2 bilayer is subjected to a local strain in the patterns and its band gap gets enlarged due to the strain. This phenomenon is beneficial for photo-devices to enable the collection of the photocurrent. Measurements revealed a broadband enhancement of the MoS2-based photodetector with a patterned array in terms of both absorption and photocurrent. It is noteworthy that a cone-patterned sapphire substrate (CPSS) is able to generate more photocurrent when illuminated under blue light illumination, whereas the pyramid-patterned sapphire substrate (PPSS) performs best under green and red light illumination. Simulations of the electric field distributions for MoS2 coatings on different substrates, based on 3D models, revealed that the sensitivity of the MoS2-based photodetector can be greatly enhanced by the light-scattering effect.
Second Harmonic Light Manipulation with Vertical Split Ring Resonators
(2019-02-15)
Tsai, Wei-Yi
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Chung, Tsung Lin
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Hsiao, Hui-Hsin
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Chen, Jia-Wern
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Lin, Ren Jie
The second harmonic generation (SHG) of vertical and planar split-ring resonators (SRRs) that are broken centro-symmetry configurations at the interface of metal surface and air is investigated. Strong interactions, better electromagnetic field confinements, and less leakage into the substrate for vertical SRRs are found. Experimental results show a 2.6-fold enhancement of SHG nonlinearity, which is in good agreement with simulations and calculations. Demonstrations of 3D metastructures and vertical SRRs with strong SHG nonlinearity majorly result from magnetic dipole and electric quadrupole clearly provides potential applications for photonics and sensing.
Synthesis, Isolation, and Characterization of Mono- and Bis-norbornene-Annulated Biarylamines through Pseudo-Catellani Intermediates
(2019-02-15)
Annamalai, Pratheepkumar
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Hsiao, Huan-Chang
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Raju, Selvam
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Fu, Yi-Hsuan
;
Chen, Pei-Ling
A palladium-catalyzed C-H functionalization of an external ring of N-acyl 2-aminobiaryl with bicyclo[2.2.1]-hept-2-ene (norbornene) via multiple C-H bond activations was developed. This study is the first report of the formation of bis-norbornene annulated biarylamines isomers (syn-3a'/anti-3a' = 36:64) from multiple C-H bond functionalizations. Additionally, nondirected C-H bond functionalization at the C-4' position with alkenes rendered complete C-H functionalization of five C-H bonds that formed a stable hexasubstituted benzene ring.
Microwave-assisted synthesis of SnO2/mesoporous carbon core-satellite microspheres as anode material for high-rate lithium ion batteries
(2019-02-15)
Chang, Pei-Yi
;
Doong, Ruey-an
;
環境工程研究所
;
Institute of Environmental Engineering
The highly ordered microspheres containing ultrafine SnO2 nanoparticles and mesoporous carbon is fabricated using microwave-assisted hydrothermal method for high-rate and durable Li-ion battery application. The uniformly carbon nanosphere with an average diameter of around 90 nm exhibits large specific surface area and good mechanical stability to minimize the volume expansion of SnO2 during intercalation-deintercalation. The homogeneous coverage with 3-6 nm SnO2 nanoparticle provides sufficient active sites to facilitate the rapid lithiation-delithiation process through the fast ion transfer rates. Remarkably, SnO2/OMCS at Sn/C ratio of 35% exhibits an excellent initial capacity of 1770 mAh g(-1) at a current density of 35 mAg(-1) and can maintain at a stable capacity of 400 mAh g(-1) under an ultrahigh current density of 3500 mA g(-1) after 400 cycles. The intimate contact of SnO2 with ordered mesoporous carbon sphere shortens the electrons transport paths, resulting in the enhancement of stable lithium storage capacity at a high current density. Results obtained in this study clearly demonstrate that SnO2/OMCS nanocomposite is a promising material for lithium-ion battery and can provide an alternative to fabricate novel mesoporous carbon sphere-based nanocomposites for long cycle life and high-rate energy storage application. (C) 2018 Elsevier B.V. All rights reserved.
Electromagnetic field behavior of 3D Maxwell's equations for chiral media
(2019-02-15)
Huang, Tsung-Ming
;
Li, Tiexiang
;
Chern, Ruey-Lin
;
Lin, Wen-Wei
;
應用數學系
This article focuses on numerically studying the eigenstructure behavior of generalized eigenvalue problems (GEPs) arising in three dimensional (3D) source-free Maxwell's equations with magnetoelectric coupling effects which model 3D reciprocal chiral media. It is challenging to solve such a large-scale GEP efficiently. We combine the null-space free method with the inexact shift-invert residual Arnoldi method and MINRES linear solver to solve the GEP with a matrix dimension as large as 5,308,416. The eigenstructure is heavily determined by the chirality parameter gamma. We show that all the eigenvalues are real and finite for a small chirality gamma. For a critical value gamma = gamma*, the GEP has 2 x 2 Jordan blocks at infinity eigenvalues. Numerical results demonstrate that when gamma increases from gamma*, the 2 x 2 Jordan block will first split into a complex conjugate eigenpair, then rapidly collide with the real axis and bifurcate into positive (resonance) and negative eigenvalues with modulus smaller than the other existing positive eigenvalues. The resonance band also exhibits an anticrossing interaction. Moreover, the electric and magnetic fields of the resonance modes are localized inside the structure, with only a slight amount of field leaking into the background (dielectric) material. (C) 2018 Elsevier Inc. All rights reserved.
Exploring elliptical vortex beams with the spatial damping effect
(2019-02-15)
Chen, Y. F.
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Hsieh, M. X.
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Lai, Y. H.
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Hsieh, Y. H.
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Tu, C. W.
A general integral formula is analytically derived to represent the wave function of elliptical vortex modes. The derived formula can be straightforwardly employed to take account of spatial damping to explore vortex structure. Spatial damping is found to cause the central degenerate singularity of the circular vortex mode to be split into several singularities with different topological charges. For the non-circular vortex beam, the influence of spatial damping on the distribution of singularities is not significant. Theoretical analyses are confirmed to agree very well with the experimental measurements. (C) 2019 Optical Society of America
Effects of tube shapes on the performance of recuperative and regenerative heat exchangers
(2019-02-15)
Ngoctan Tran
;
Wang, Chi-Chuan
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機械工程學系
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Department of Mechanical Engineering
In the present work, the effects of tube shapes on the heat transfer and fluid flow characteristics of the shell-and-tube heat exchangers including square, rectangular, circular, elliptical, equilateral- and isosceles-triangular shapes are numerically investigated in detail. Six parameters including (1) rectangular-tube ratios (alpha = tube height/width), (2) triangular-tube ratios (beta= two-side edge/bottom edge), (3) elliptical-tube ratios (gamma = b/a; a: inner semi-major-axis lengths and b: inner semi-minor-axis lengths), (4) the tube lengths from 2 mto 20 m, (5) outer tube diameters from 52 mm to 252 mm, and (6) 500 <= Re <= 8000 are examined variables. For all cases in this study, it is found that at the same boundary conditions, the thermal performance of an elliptical tube is superior to that of a circular tube. A locally thermal optimal triangular tube shape is defined with a maximum effectiveness up to 92.46%. A novel correlation is developed to describe the Nusseltnumbers subject to the examined tube shapes. The proposed correlation is not only in line with the existing round tube correlations but also gives good predictions for other tube geometries with maximum deviation being less than 7.1%. (C) 2018 Elsevier Ltd. All rights reserved.
耐鹼微藻株及使用其減量與再利用二氧化碳的方法
(2019-02-16)
林志生
;
張嘉修
;
郭秋媚
;
林宗賢
本揭露係關於一種透過N-甲基-N-硝基-N-甲基亞硝基胍突變而篩選出的耐鹼微藻株。此外，本揭露更關於一種使用此耐鹼微藻株減量與再利用二氧化碳的方法，包括下列步驟：提供前述之耐鹼微藻株；以及將耐鹼微藻株培養於一鹼性培養液，且於通入二氧化碳的條件下，培養耐鹼微藻株。
How a branded website creates customer purchase intentions
(2019-02-17)
Chang, Kuo-Chien
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Hsu, Chia-Lin
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Chen, Mu-Chen
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Kuo, Nien-Te
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運輸與物流管理系註：原交通所+運管所
This paper aims to investigate whether customers' perceptions of the quality and brand equity of a branded website affect purchase intentions, and to explore the mediating effects of trust and perceived risk in this relationship. Links between purchase intention and both trust and perceived risk, moderated by electronic word of mouth (eWOM), are also examined. A research model for testing relationships among these constructs based on the stimulus-organism-response (S-O-R) framework is outlined. A statistical analysis of the collected questionnaires was computed from the website of a target chain restaurant in Taiwan (T.G.I. Friday's). Structural equation modelling (SEM) was used to examine the hypothesised relationships among the variables. The findings confirm that potential customers' perceptions of both the quality and brand equity of a branded website affect their trust and perceived risk, and, in turn, their purchase intentions. This study also reveals the existence of a moderating effect of eWOM on the links between both trust and perceived risk and purchase intentions. Based on the findings, the implications are discussed, and directions for future research are highlighted.
Role of Cholecystectomy in Choledocholithiasis Patients Underwent Endoscopic Retrograde Cholangiopancreatography
(2019-02-18)
Wang, Chi-Chih
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Tsai, Ming-Chang
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Wang, Yao-Tung
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Yang, Tzu-Wei
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Chen, Hsuan-Yi
There are no clinical guidelines for the timing of cholecystectomy (CCY) after performing therapeutic endoscopic retrograde cholangiopancreatography (ERCP) for choledocholithiasis. We tried to analyze the clinical practice patterns, medical expenses, and subsequent outcomes between the early CCY, delayed CCY, and no CCY groups of patients. 1827 choledocholithiasis patients who underwent therapeutic ERCP were selected from the nationwide population databases of two million random samples. These patients were further divided into early CCY, delayed CCY, and no CCY performed. In our analysis, 1440 (78.8%) of the 1827 patients did not undergo CCY within 60 days of therapeutic ERCP, and only 239 (13.1%) patients underwent CCY during their index admission. The proportion of laparoscopic CCY increased from 37.2% to 73.6% in the delayed CCY group. There were no significant differences (p = 0.934) between recurrent biliary event (RBE) rates with or without early CCY within 60 days of ERCP. RBE event-free survival rates were significantly different in the early CCY (85.04%), delayed CCY (89.54%), and no CCY (64.45%) groups within 360 days of ERCP. The method of delayed CCY can reduce subsequent RBEs and increase the proportion of laparoscopic CCY with similar medical expenses to early CCY in Taiwan's general practice environment.
A potential peptide derived from cytokine receptors can bind proinflammatory cytokines as a therapeutic strategy for anti-inflammation
(2019-02-19)
Jiang, Shinn-Jong
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Tsai, Pei-I
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Peng, Shih-Yi
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Chang, Chun-Chun
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Chung, Yi
Chronic inflammation is a pivotal event in the pathogenesis of cardiovascular diseases, including atherosclerosis, restenosis, and coronary artery disease. The efficacy of current treatment or preventive strategies for such inflammation is still inadequate. Thus, new anti-inflammatory strategies are needed. In this study, based on molecular docking and structural analysis, a potential peptide KCF18 with amphiphilic properties (positively charged and hydrophobic residues) derived from the receptors of proinflammatory cytokines was designed to inhibit cytokine-induced inflammatory response. Simulations suggested that KCF18 could bind to cytokines simultaneously, and electrostatic interactions were dominant. Surface plasmon resonance detection showed that KCF18 bound to both tumor necrosis factor-alpha (TNF-alpha) and interleukin-6, which is consistent with MM/PBSA binding free energy calculations. The cell experiments showed that KCF18 significantly reduced the binding of proinflammatory cytokines to their cognate receptors, suppressed TNF-alpha mRNA expression and monocyte binding and transmigration, and alleviated the infiltration of white blood cells in a peritonitis mouse model. The designed peptide KCF18 could remarkably diminish the risk of vascular inflammation by decreasing plasma cytokines release and by directly acting on the vascular endothelium. This study demonstrated that a combination of structure-based in silico design calculations, together with experimental measurements can be used to develop potential anti-inflammatory agents.
Palladium-Catalyzed Benzofulvenation of o-Arylanilines through C-H Bond Activation by Using Two Diarylacetylenes as an Implicit Benzofulvene
(2019-02-19)
Raju, Selvam
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Hsiao, Huan-Chang
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Thirupathi, Selvakumar
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Chen, Pei-Ling
;
Chuang, Shih-Ching
We report the first example of Pd(II)-catalyzed highly step- and atom-economical benzofulvenation through free amine-directed ortho C-H bond activation of o-arylanilines. This paper presents a novel, simple, and efficient approach for the synthesis of benzofulvene derivatives from o-arylaniline substrates through C-H bond activation with two diarylacetylenes as an implicit benzofulvene unit. The reactivity of synthesized benzofulvenes toward oxidation was investigated, and they were shown to transform into phenanthridines, oxabenzofulvenes, and fluorescent polycyclics.
Detection of Metal-Molecule-Metal Junction Formation by Surface Enhanced Raman Spectroscopy
(2019-02-19)
Wattanavichean, Nungnit
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Gilby, Matthew
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Nichols, Richard J.
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Arnolds, Heike
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應用化學系
Vibrational modes play a key role in characterizing metal-molecule-metal junctions, but their detection currently either requires single-molecule sensitivity or the generation of defect-free large-scale junctions. Here we demonstrate that surface-enhanced Raman scattering (SERS) on nonideal surfaces can provide a significant amount of information despite many defects in the layer. We determine the vibrational signature of the molecular electronic junction for palladium ions complexed and reduced on 4-mercaptopyridine adsorbed on rough gold and gold nanoparticles using SERS and density functional theory. We show that these nonideal surfaces can be used to probe kinetics of metal ion complexation and establish the success of electrochemical metallization. SERS on nonideal surfaces is thus revealed as a useful tool to rapidly establish the key process parameters in making molecular electronic junctions before embarking on more detailed studies on single molecules or single crystal surfaces.
Nine-sector three-stage Fresnel lens concentrator (vol 58, pg 122, 2019)
(2019-02-20)
Chen, Yong-Da
;
Tu, Sheng Han
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Hong, Hwen-Fen
;
Chen, Chun-Yi
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Pan, Jui-Wen