Browsing by Author "Luo, Chih-Wei"

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All-Solution-Processed Red and Orange-Red Organic Light-Emitting Diodes with High-Efficiencies: The Effect of Mixed-Host Emissive Layers and Thermal Annealing Treatment
(2019-09-01)
Chang, Yu-Fan
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Yang, Lan-Sheng
;
Su, Hsiao-Tso
;
Liao, Si-Yi
;
Niu, Mu-Chun
The instability of the organic light-emitting diodes (OLEDs) during operation can be attributed to the existence of point defects on the organic layers. In this work, the effect of mixed-host emissive layer and the thermal annealing treatment were investigated to eliminate defects and to boost the device performance. The mixed-host system includes 4,4 ',4 ''-tri (9-carbazoyl) triphenylamine (TCTA) and 2,7-bis(diphenylphosphoryl)-9, 9 '-spirobi[fluorene] (SPPO13). The mixed-host emissive layer with thermal annealing treatment showed low roughness and few pinholes, and the devices fabricated from this emissive layer exhibited high efficiencies, high stabilities, and long lifetimes. The red and orange-red OLEDs exhibited efficiencies of 13.9 cd/A and 24.35 cd/A, respectively. The longest half-lifetime (L-0=500 cd/m(2)) of the red and orange-red OLEDs were 158 h and 180 h, respectively. Efforts were made to solve problems in large-area coating and to reduce the number of defects on in organic layer. Large-active-area (active area=3 cmx4 cm) red phosphorescent OLEDs (PhOLEDs) devices were realized with very high current efficiency up to 9 cd/A.
Anisotropic optical transmission of femtosecond laser induced periodic surface nanostructures on indium-tin-oxide films
(2012-09-03)
Wang, Chih
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Wang, Hsuan-I
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Luo, Chih-Wei
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Leu, Jihperng
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材料科學與工程學系
Two types of periodic nanostructures, self-organized nanodots and nanolines, were fabricated on the surfaces of indium-tin-oxide (ITO) films using femtosecond laser pulse irradiation. Multiple periodicities (approximately 800 nm and 400 nm) were clearly observed on the ITO films with nanodot and nanoline structures and were identified using two-dimensional Fourier transformation patterns. Both nanostructures show the anisotropic transmission characteristics in the visible range, which are strongly correlated with the geometry and the metallic content of the laser-induced nanostructures. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4751983]
Anomalous Electronic Anisotropy Triggered by Ferroelastic Coupling in Multiferroic Heterostructures
(2016-02-03)
Ju, Changcheng
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Yang, Jan-Chi
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Luo, Cheng
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Shafer, Padraic
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Liu, Heng-Jui
Beamlike photon pairs entangled by a 2 x 2 fiber
(2011-08-01)
Lo, Hsin-Pin
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Yabushita, Atsushi
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Luo, Chih-Wei
;
Chen, Pochung
;
Kobayashi, Takayoshi
Polarization-entangled photon pairs have been widely used as a light source of quantum communication. The polarization-entangled photon pairs are generally obtained at the crossing points of the light cones that are generated from a type-II nonlinear crystal. However, it is hard to pick up the photon pairs coming out from the crossing points because of their invisible wavelength and low intensity. In our previous work, we succeeded in generating polarization-entangled photon pairs by overlapping two light paths for the photon-pair generation. The photon pairs could be entangled in all of the generated photon pairs without clipping the crossing points, even with some difficulty in its alignment to overlap the two light paths. In this paper, we have developed an optical system which generates polarization-entangled photon pairs using a beamlike photon pair, without the difficulty in alignment. The measured results show that the photon pairs generated in the system are entangled in their polarizations.
Beamlike photon-pair generation for two-photon interference and polarization entanglement
(2011-02-14)
Lo, Hsin-Pin
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Yabushita, Atsushi
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Luo, Chih-Wei
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Chen, Pochung
;
Kobayashi, Takayoshi
Beamlike photon pairs were generated by spontaneous parametric down-conversion using a type-II beta-BaB2O4 crystal. A pump laser generated photon pairs when it transmitted through the crystal and was reflected back into the crystal by a mirror to generate more photon pairs. The photon pairs generated when the pump laser first transmitted through the crystal (first photon pairs) were also reflected back into the crystal to overlap with the light path of the photon pairs generated in the second transmission of the pump laser through the crystal (second photon pairs). We observed interference between the first and second photon pairs modulated with a half period of the wavelength of the photon pairs, which demonstrates two-photon interference using the beamlike photon pairs. The fringe period confirms that the observed interference is not classical interference but quantum two-photon interference. Through rotating the angles of quarter-wave plates in the light paths of the photon pairs, we generated beamlike photon pairs with entangled polarization. The phase between the first and second photon pairs could be tuned by changing the position of mirrors reflecting the pump pulses and photon pairs. The fringes of coincidence counts showed that the beamlike photon pairs have polarization entanglement.
Carrier-Envelope Phase of Single-Cycle Pulses Generated Through Two-Color Laser Filamentation
(2015-01-01)
Fuji, Takao
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Nomura, Yutaka
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Wang, Yu-Ting
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Yabushita, Atsushi
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Luo, Chih-Wei
Carrier-envelope phase (CEP) of the single-cycle pulses generated through two-color filamentation has been investigated. It has been found that the phase of high frequency components of the generated pulses changes continuously and linearly with the relative phase between the two-color input pulses, whereas the phase of the low frequency components takes only two discrete values. To our knowledge, such behavior of the phase has never been discussed before. The transition of the phase behavior has been clearly observed by using frequency-resolved optical gating capable of CEP determination.
Carrier-envelope phase of ultrashort pulses generated by optical rectification process
(2013-01-01)
Fuji, Takao
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Nomura, Yutaka
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Wang, Yu-Ting
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Yabushita, Atsushi
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Luo, Chih-Wei
Controlling the carrier-envelope phase of single-cycle mid-infrared pulses with two-color filamentation
(2015-02-01)
Nomura, Yutaka
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Wang, Yu-Ting
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Yabushita, Atsushi
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Luo, Chih-Wei
;
Fuji, Takao
Carrier-envelope phase (CEP) of single-cycle pulses generated through two-color filamentation has been investigated. We have observed a particular behavior of the phase: the phase of high-frequency components of the generated pulses changes continuously and linearly with the relative phase between the two-color input pulses, whereas the phase of the low-frequency components takes only two discrete values. The transition of the phase behavior has been clearly observed by using frequency-resolved optical gating capable of CEP determination. We have found out that such a phase behavior is a unique feature of single-cycle pulses generated with a passive CEP stabilization scheme. (C) 2015 Optical Society of America
Creation of 3D Textured Graphene/Si Schottky Junction Photocathode for Enhanced Photo-Electrochemical Efficiency and Stability
(2019-08-01)
Ku, Che-Kuei
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Wu, Po-Hsieh
;
Chung, Cheng-Chu
;
Chen, Chun-Chi
;
Tsai, Kaijie
This work presents a novel photo-electrochemical architecture based on the 3D pyramid-like graphene/p-Si Schottky junctions. Overcoming the conventional transfer technique by which only planar graphene/Si Schottky junctions are currently available, this work demonstrates the 3D pyramid-like graphene/p-Si Schottky junction photocathode, which greatly enhances light harvesting efficiency and exhibits promising photo-electrochemical performance for hydrogen generation. The formation of 3D pyramid-like graphene/p-Si Schottky junctions exhibits enhanced electrochemical activity and promotes charge separation efficiency compared with the bare pyramid Si surface without graphene. The inherent chemical inertness of graphene significantly improves the operational stability of 3D graphene/p-Si Schottky junction photo-electrochemical cells. The 3D pyramid-like graphene/p-Si Schottky junction photocathode delivers an onset potential of 0.41 V and a saturated photocurrent density of -32.5 mA cm(-2) at 0 V (vs RHE) with excellent stability comparable to values reported for textured or nanostructured p-Si photocathodes coated with ultrathin oxide layers by the conventional atomic layer deposition technique. These results suggest that the formation of graphene/Si Schottky junctions with a 3D architecture is a promising approach to improve the performance and durability of Si-based photo-electrochemical systems for water splitting or solar-to-fuel conversion.
Effects of Strain and Ordering of Rare-Earth Element Moments on Magnetic-Reordering in Orthorhombic Multiferroic Manganites
(2013-10-01)
Hsiao, Yen-Fu
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Lai, Jun-Yo
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Lin, Jun-Yu
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Fang, Hau-Wei
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Hung, Yi-Tse
Orthorhombic multiferroic manganite thin films with various orientations and strain states were prepared to show the effects of anisotropic strain and antiferromagnetic (AFM) ordering of rare-earth f-electrons on the orientation of the incommensurate-to-commensurate AFM reordering. Systematic analyses suggest that the low-temperature AFM ordering of the rare-earth f-electrons may have played a decisive role in causing the orientation changes in AFM reordering, although the b-axis strain does have a significant influence on the zero-field magnetization behaviors. (C) 2013 The Japan Society of Applied Physics
Effects of strain on the electronic structure and magnetic properties in SrMn0.5Fe0.5O3
(2016-09-01)
Mi, Chun-Wei
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Chin, Yi-Ying
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Hsiao, Yen-Fu
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Fang, Hau-Wei
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Luo, Chih-Wei
The electronic structure and magnetic properties of SrMn0.5Fe0.5O3 powder and films grown on (100)-SrTiO3 (STO) and (100)-LaAlO3 (LAO) substrates by pulsed laser deposition (PLD) were investigated by temperature dependent magnetization and soft x-ray absorption. The results exhibit characteristics of 3d(5) Fe3+, 3d(5) (L) under bar Fe4+, and 3d(3) + 3d(4) (L) under bar Mn4+ at room temperature in all samples. However, the features of 3d(5) Fe3+ and 3d(3) Mn4+ increased significantly for SMFO/LAO at 35 K, which also displayed substantial competition between antiferromagnetic and ferromagnetic order well-above the Neel temperature of SrFeO3 (T-N similar to 134 K). We attributed this to being caused by charge disproportionation resulting from ligand-hole localization, which is more favorable to take place when the sample is under compressive strain.
Effects of Structural Strain and Rare-Earth Moments on Spin Cycloidal-Plane in Multiferroic Rare-Earth Manganites
(2016-05)
Hsiao, Yen-Fu
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Kuo, Wei-Cheng
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Mi, Chun-Wei
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Chang, Kai-Ting
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Luo, Chih-Wei
A series of orthorhombic multiferroic manganites (o-ReMnO3) thin films with deliberately designed strain states and different rare-earth elements were prepared to unveil the roles played by the strain and 4f-electron moments in determining the magnetic ordering and associated polarizations. The results obtained from temperature-dependent magnetization, dielectric and ferroelectric measurements revealed that the orientations of magnetic reordering and polarization varied with the specific rare-earth element involved. Namely, with the increase of total angular momentum J of the 4f-electrons of rare-earth element the orientation of magnetic reordering was changed from the b-axis (sinusoidal state) for Yb3+ to the a-axis (ab-cycloidal) for Tm3+ and, eventually to the c-axis (bc-cycloidal) for Er3+ and Ho3+. These results indicate that the Re-Mn magnetic exchange interaction plays a more important role than the external strain does in determining the magnetic and hence polarization states in multiferroic o-ReMnO3 manganites. Our results also confirmed the coexistence of different magnetic spin states in o-ReMnO3 thin films.
Effects on Organic Photovoltaics Using Femtosecond-Laser-Treated Indium Tin Oxides
(2016-09-28)
Chen, Mei-Hsin
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Tseng, Ya-Hsin
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Chao, Yi-Ping
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Tseng, Sheng-Yang
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Lin, Zong-Rong
The effects of, femtosecond-laser-induced periodic surface structures (LIPSS) on an indium tin oxide (ITO) surface applied to an organic photovoltaic (OPV), system were investigated. The modifications of ITO induced by LIPPS in OPV devices result in more than 14% increase in power conversion efficiency (PCE) and short-circuit current density relative to-those of the standard device. The basic mechanisms for the enhanced short-circuit current density are attributed to better light harvesting, increased scattering effects, and more efficient charge collection between the ITO and photoactive layers: Results show that-higher PCEs would be achieved by laser-pulse-treated electrodes.
Environment-Dependent Ultrafast Photoisomerization Dynamics in Azo Dye
(2011-10-27)
Hsu, Chun-Chih
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Wang, Yu-Ting
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Yabushita, Atsushi
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Luo, Chih-Wei
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Hsiao, Yi-Nan
Azoaromatic dyes have been extensively investigated over the past decade due to their potential use in a variety of optical devices that exploit their ultrafast photoisomerization processes. Among the azoaromatic dyes, Disperse Red 19 is a commercially available azobenzene nonlinear optical chromophore with a relatively high ground-state dipole moment. In the present study, we used ultrafast time-resolved spectroscopy to clarify the dynamics of a push-pull substituted azobenzene dye. Solution and film samples exhibited different ultrafast dynamics, indicating that the molecular environment affects the photoisomerization dynamics of the dye.
Epitaxial Photostriction-Magnetostriction Coupled Self-Assembled Nanostructures
(2012-08-01)
Liu, Heng-Jui
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Chen, Long-Yi
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He, Qing
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Liang, Chen-Wei
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Chen, Yu-Ze
Self-assembled vertical nanostructures take advantage of high interface-to-volume ratio and can be used to design new functionalities by the choice of a proper combination of constituents. However, most of the studies to date have emphasized the functional controllability of the nanostructures using external electric or magnetic fields. In this study, to introduce light (or photons) as an external control parameter in a self-assembled nanostructure system, we have successfully synthesized oxide nanostructures with CoFe2O4 nanopillars embedded in a SrRuO3 matrix. The combination of photostrictive SrRuO3 and magnetostrictive CoFe2O4 in the intimately assembled nanostructures leads to a light-induced, ultrafast change in magnetization of the CoFe2O4 nanopillars. Our work demonstrates a novel concept on oxide nanostructure design and opens an alternative pathway for the explorations of diverse functionalities in heteroepitaxial self-assembled oxide nanostructures.
Experimental realization of ultrathin, double-sided metamaterial perfect absorber at terahertz gap through stochastic design process
(2015-12-22)
Huang, Tsung-Yu
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Tseng, Ching-Wei
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Yeh, Ting-Tso
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Yeh, Tien-Tien
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Luo, Chih-Wei
We design and demonstrate a flexible, ultrathin and double-sided metamaterial perfect absorber (MPA) at 2.39 terahertz (THz), which enables excellent light absorbance under incidences from two opposite sides. Herein, the MPA is fabricated on a lambda(0)/10.1-thick flexible polyethylene terephthalate substrate of epsilon(r) = 2.75 x (1 + 0.12i), sandwiched by two identical randomized metallic patterns by our stochastic design process. Such an MPA provides tailored permittivity and permeability to approach the impedance of free space for minimizing reflectance and a great imaginary part of the refractive index for reducing transmittance and finally results in high absorbance. Both experimental measurement and numerical simulation are in a good agreement. The flexible, ultrathin and double-sided MPA significantly differs from traditional quarter-wavelength absorbers and other single-sided perfect absorbers, paving a way toward practical THz applications in thermal emission, sensing and imaging, communications, stealth technique, and even energy harvesting.
Experimental violation of Bell inequalities for multi-dimensional systems
(2016-02-26)
Lo, Hsin-Pin
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Li, Che-Ming
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Yabushita, Atsushi
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Chen, Yueh-Nan
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Luo, Chih-Wei
Quantum correlations between spatially separated parts of a d-dimensional bipartite system (d >= 2) have no classical analog. Such correlations, also called entanglements, are not only conceptually important, but also have a profound impact on information science. In theory the violation of Bell inequalities based on local realistic theories for d-dimensional systems provides evidence of quantum nonlocality. Experimental verification is required to confirm whether a quantum system of extremely large dimension can possess this feature, however it has never been performed for large dimension. Here, we report that Bell inequalities are experimentally violated for bipartite quantum systems of dimensionality d=16 with the usual ensembles of polarization-entangled photon pairs. We also estimate that our entanglement source violates Bell inequalities for extremely high dimensionality of d>4000. The designed scenario offers a possible new method to investigate the entanglement of multipartite systems of large dimensionality and their application in quantum information processing.
Fast trapping force calculation by utilizing graphic processing unit
(2012)
Tseng, Sheng-Yang
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Chang, Ai-Tang
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Luo, Chih-Wei
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Hsu, Long
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Kobayashi, Takayoshi
Fast calculation of trapping force provides a more direct way for optimizing designs of optical systems which generate optical traps. In this study, a graphic processing unit (GPU), NVIDIA GTX 275, is used to boost the speed of trapping efficiency calculation under ray optics approximation. The codes of trapping efficiency calculation are implemented in C++. The computing power of GPU is utilized through compute unified architecture device (CUDA) toolkit 4.0. The computing speed is compared with that of central processing unit (CPU), Intel Core 2 Quad Q9550. Over 100x speedup is achieved when single-precision floating-point numbers were used in the calculation.
Femtosecond Laser- Colorized AZO Films on Flexible Mica Substrates
(2019-01-01)
Yang, Hung
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Yeh, Tien-Tien
;
Tu, Chien-Ming
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Luo, Chih-Wei
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電子物理學系
Laser-colorized aluminum-doped zinc oxide (AZO) films are fabricated using femtosecond laser annealing. By varying the laser fluences, ripple-like nanostructures are generated on the surface of AZO films, which produces cyan, yellow and orange colors. (C) 2019 The Author(s)
Femtosecond laser-colorized indium-tin-oxide films for blue light attenuation and image screening
(2017-12-25)
Tseng, Ya-Hsin
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Yang, Hung
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Luo, Chih-Wei
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電子物理學系
;
Department of Electrophysics
Laser-colorized indium-tin-oxide (ITO) films are fabricated using femtosecond laser processing. By varying the laser fluences, nanostructures with cotton, brick and ripple forms are generated on the surface of ITO films, which produces cyan, yellow and orange colors. The fluence-dependent nanostructures on the surface of ITO films also significantly attenuates blue light so these materials are suited to eye protection and the screening of images behind ITO films for information security. (C) 2017 Optical Society of America under the terms of the OSA Open Access Publishing Agreement