Browsing by Author "Wang, Juen-Kai"

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A High-Accuracy Multidomain Legendre Pseudospectral Frequency-Domain Method With Penalty Scheme for Solving Scattering and Coupling Problems of Nano-Cylinders
(2013-03-01)
Wang, Chih-Yu
;
Chung, Shih-Yung
;
Teng, Chun-Hao
;
Wang, Juen-Kai
;
Chen, Chung-Ping
A new multidomain pseudospectral frequency-domain (PSFD) method based on the Legendre polynomials with penalty scheme is developed for numerically modeling electromagnetic wave scattering problems. The primary aim of the proposed method is to more accurately analyzing scattering and coupling problems in plasmonics, in which optical waves interact with nanometer-sized metallic structures. Using light scattering by a silver circular cylinder as a first example, the formulated method is demonstrated to achieve numerical accuracy in near-field calculations on the order of 10(-9) with respect to a unity field strength of the incident wave with excellent exponentially convergent behavior in numerical accuracy. Then, scattering by a dielectric square cylinder and that by several coupled metallic structures involving circular cylinders, square cylinders, or dielectric coated cylinders are examined to provide high-accuracy coupled near-field results.
Investigation of Nanoelectromagnetics Problems Using the Multidomain Legendre Pseudospectral Time-Domain Method
(2012)
Chang, Hung-chun
;
Chung, Shih-Yung
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Wang, Chih-Yu
;
Teng, Chun-Hao
;
Wang, Juen-Kai
Nanoelectromagnetics problems in nanophotonics and plasmonics in the optical-wavelength regime are concerned in this paper. Very often such problems demand more accurate electromagnetic computation and analysis. A multidomain Legendre pseudospectral time-domain (PSTD) method recently developed and demonstrated to provide high numerical accuracy is utilized to study light interaction with sub-wavelength three-dimensional plasmonic structures and associated plasmonic resonances. With the multidomain technique, the simulation region is partitioned into curvilinear hexahedral subdomains with better fitting to the structural shapes and material interfaces so as to achieve high-accuracy near-field calculations. Light scattering by multiple plasmonic nanospheres and light transmission through a metallic thin film perforated with periodic apertures are investigated with the PSTD analysis.
Polymer side-chain substituents elucidate thermochromism of benzodithiophene-dithiophenylacrylonitrile copolymers - polymer solubility correlation of thermochromism and photovoltaic performance
(2017-06-28)
Chen, Hung-Yang
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Lin, Chiao-Wen
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Chen, Chin-Ti
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Chen, Chao-Tsen
;
Golder, Jan
Nine pBCNx polymers based on a donor-p-acceptor benzo[1,2-b:4,5-b']dithiophene-(E)-2,3-di(thiophen-2-yl) acrylonitrile main-chain structure and n-octyl/2-ethylhexyl as the side-chain substituents have been designed and synthesized. The thermochromism of the pBCNx polymers has been carefully examined in both solution and the thin-film state. With additional evidences from Raman spectroscopy and AFM microscopy, we have deciphered the varied colours of nine pBCNx polymers in solution and the pronounced thin-film thermochromism only observed for certain pBCNx polymers, i.e., pBCN4, pBCN5, pBCN6, and pBCN8. The alkyl side-chain, and hence the solubility or aggregation of pBCNx polymers, is a main factor of the varied colour in solution and the varied thermochromism in the thin film. We have identified that a stronger main-chain and main-chain interaction are present on the (E)-2,3-di(thiophen-2-yl) acrylonitrile moiety, whereas the poor to moderate solubility pBCN3, pBCN5', and pBCN7 exhibit pronounced thermochromism in solution, and pBCN4, pBCN5, pBCN6, and pBCN8 are four polymers which have good solubility in solution and show thermochromism in the thin-film state. We took navy blue pBCN3 (poor solubility), magenta pBCN4 (good solubility), and reddish purple pBCN5' (moderate solubility) for the fabrication of bulk heterojunction organic photovoltaics (OPVs). With a solvent annealing treatment, the power conversion efficiency of the OPVs has been improved significantly from 4.7% to 6.2% for the good solubility pBCN4, but there is little and no improvement for the moderate solubility pBCN5' and poor solubility pBCN3, respectively. Our study verifies that the good OPV performance of the pBCNx polymers can be correlated to the pronounced thin-film thermochromism. A good solubility of the polymer is a common characteristic of a material with significant thin-film thermochromism and good OPV performance.
Pseudospectral Modeling of Nano-Optics in Ag Sphere Arrays
(2010-10-01)
Lin, Bang-Yan
;
Teng, Chun-Hao
;
Chang, Hung-Chun
;
Hsiao, Hui-Hsin
;
Wang, Juen-Kai
We report a Legendre pseudospectral modeling of silver sphere arrays illuminated by light waves. A special feature of the present computation is that the dispersive nature of silver is described by a Drude-Lorentz model with model parameters obtained by fitting the frequency-domain complex-valued dielectric constants measured experimentally. Numerical validations are conducted based on solving both the near and far fields of the Mie scattering problem, and we observe good convergence on the numerical fields. The far-field patterns of the Ag sphere arrays are simulated. The results are compared to those obtained by the dipole-coupling-model method, and we observe very good agreement between these results. The near-field patterns are also computed, and localized enhanced electric fields in the inter-particle gap regions due to plasmonic coupling between Ag particles are visualized. As the gap between Ag particles is reduced the strength of the localized enhanced electric field is increased.
Pseudospectral Modeling of Nano-Optics in Ag Sphere Arrays
(2010-10-01)
Lin, Bang-Yan
;
Teng, Chun-Hao
;
Chang, Hung-Chun
;
Hsiao, Hui-Hsin
;
Wang, Juen-Kai
We report a Legendre pseudospectral modeling of silver sphere arrays illuminated by light waves. A special feature of the present computation is that the dispersive nature of silver is described by a Drude-Lorentz model with model parameters obtained by fitting the frequency-domain complex-valued dielectric constants measured experimentally. Numerical validations are conducted based on solving both the near and far fields of the Mie scattering problem, and we observe good convergence on the numerical fields. The far-field patterns of the Ag sphere arrays are simulated. The results are compared to those obtained by the dipole-coupling-model method, and we observe very good agreement between these results. The near-field patterns are also computed, and localized enhanced electric fields in the inter-particle gap regions due to plasmonic coupling between Ag particles are visualized. As the gap between Ag particles is reduced the strength of the localized enhanced electric field is increased.
Rapid identification of nicotine in electronic cigarette liquids based on surface-enhanced Raman scattering
(2020-01-01)
Chien, Jun-Yi
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Gu, Yong-Chun
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Tsai, Hsin-Mei
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Liu, Chun-Hao
;
Yen, Chia-Yuan
Nicotine-containing electronic cigarette liquid (e-liquid) is prohibited in many countries, creating requirements for rapid detection approaches for on-site inspection or screening for large amounts of samples. Here, we demonstrate a simple way to identify nicotine using surface-enhanced Raman scattering (SERS) with substrates made of silver nanoparticle arrays imbedded in anodic aluminum oxide nanochannels (Ag/AAO). Compared with the reported colloidal nanoparticle-based SERS, that required serial dilutions to enable colloid aggregation in the viscous e-liquid, a small amount of undiluted e-liquid sample can be directly added onto our solid-phase Ag/AAO substrate without any pre-treatment. The sensitivity of our SERS measurements is 2-3 orders of magnitude higher than that required for identification of nicotine in e-liquid, which is typically around 1000-18,000 ppm. Using such nanoparticle array-based SERS, we have tested 22 commercially available e-liquid products, using the corresponding gas chromatography-mass spectrometry (GC-MS) reports as the reference. The SERS measurements were done within one hour and successfully identified 20 samples. Only 2 samples showed SERS interference from ingredients that were not suitable for SERS analysis.
Unconventional anode interlayer universally improving solar cell efficiency
(2018-08-08)
Golder, Jan
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Lin, Chiao-Wen
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Chen, Huan-Wen
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Lan, Yu-Bing
;
Chen, Chin-Ti
Organic photovoltaic cells typically employ an interlayer sandwiched between the active donor or acceptor materials and the respective electrodes. Conventionally, the employed anode interlayer (AIL) adjacent to the anode has a wide optical band gap and a significantly higher lowest unoccupied molecular orbital (LUMO) energy level, compared to the adjunct electron donor material, such as boron subphthalocyanine chloride (SubPc) studied here. In this report, we synthesized three novel AIL materials, NP-beta-PCN, NPAPMLI and NPAPMLI, having narrow optical band gaps but matching the LUMO energy levels of SubPc in a planar heterojunction solar cell of ITO/SubPc/C-60/BCP/Al. Upon insertion of an ultrathin (2 nm) AIL, the device power conversion efficiency is increased from 3.98% to as high as 4.92%, mainly due to the significant increase of short-circuit current density (J(SC)) from 5.97 to 7.11-7.65 mA cm(-2). From the detailed morphological and photophysical studies, we have demonstrated that the employed unconventional materials of AIL are effective in exciton (of SubPc) blocking, thereby enhancing exciton diffusion towards the charge-separating interface of SubPc/C-60 and hence J(SC). Since these AIL materials all have a LUMO energy level very close to that of SubPc, the study reported here clarifies that the electron blocking is not a necessary property of an AIL material.
Unified assay of adverse effects from the varied nanoparticle hybrid in polymer fullerene organic photovoltaics
(2013-09-01)
Huang, Yu-Jui
;
Lo, Wei-Chun
;
Liu, Shun-Wei
;
Cheng, Chao-Han
;
Chen, Chin-Ti
Nanoparticles (NPs) having different surface capping agent, variant electrical conductivity and sunlight absorption have been studied for the ternary hybrid containing poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) in bulk heterojunction (BHJ) organic photovoltaics (OPVs). These NPs are composed of conducting gold, semiconducting CdS or PbS, or insulating cage-like molecular silica (FOSS). We use a series of microscopic methods including TEM, AFM, SEM, optical, and fluorescence microscopy to estimate NP size and to probe the agglomeration and/or aggregation of NPs in P3HT/PCBM blends. Surface capping agent aromatic thiophenol (SPh) was found to be poor in the dispersion of NPs in P3HT/PCBM blends. The light harvesting of these NPs ranges from transparent (POSS NP), near transparent (CdS NP), visible light absorbing (Au NP), to near-infrared absorbing (PbS NP)., Nevertheless, the absorbance of these NPs is all too small relative to that of P3HT polymer. Concerning the charge separation of P3HT exciton, the LUMO energy levels of these NPs have been determined by the combination of optical band-gap energy and HOMO energy levels. By the transient photocurrent time-of-flight method, charge carrier mobility of P3HT/PCBM/NP(CdS-SPh) ternary hybrid was found to be improved, although fluorescence quenching studies imply insufficient or ineffective contact between P3HT and all NPs in the present study. NPs hybrid P3HT/PCBM BHJ OPVs were fabricated by solution process. Regardless of conductivity or sunlight absorbance, all NPs show no improvement on power conversion efficiency of ternary hybrid OPVs, which is 3.03-3.91% less than 4.0-4.1% of P3HT/PCBM OPVs without NPs. Based on the present study, a few problems that associate with the inferior performance of NPs hybrid P3HT/PCBM BHJ OPVs are delineated. (C) 2013 Elsevier B.V. All rights reserved.