Browsing by Author "Wang, Yu-Ting"

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A more accurate, reliable method to evaluate the photoelectrochemical performance of semiconductor electrode without under/over estimation
(2018-03-20)
Li, Jing-Mei
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Wang, Yu-Ting
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Hsu, Yung-Jung
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材料科學與工程學系
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Department of Materials Science and Engineering
A more accurate and reliable method is proposed to evaluate the photoelectrochemical (PEC) performance of semiconductor toward water splitting. Conventionally, I-t measurements are conducted at a fixed potential relative to the reference electrode, e.g., 0 V vs. Ag/AgCl, to monitor the photocurrent, which has been regarded as a direct indicator for performance comparison among different electrodes. Considering that the open-circuit potential (OCP) varies from electrode to electrode, the photocurrent comparison at a fixed potential may misrepresent the actual differences between samples. Here, we study the PEC performance by applying two distinct external bias values, one at 0 V vs. Ag/AgCI deriving from the conventional practice and the other at 0.1 V vs. OCP representing the exactly fixed applied overpotential. Two experimental groups are designed to address the arguments, including the influence of heat treatment for ZnO nanorod arrays and the global comparison among ZnO, TiO2, Au particle-decorated TiO2, and CdS electrodes. Different trends in photocurrent are observed at the two distinct biases, with the results from 0.1 V vs. OCP conforming to the general considerations. The results suggest that application of a fixed potential relative to the OCP will provide a more fair comparison for accurate PEC performance evaluation without under-or over-estimation. (C) 2018 Elsevier Ltd. All rights reserved.
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
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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
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.
Intermediate-Valence Ytterbium Compound Yb4Ga24Pt9: Synthesis, Crystal Structure, and Physical Properties
(2017-08-07)
Sichevych, Olga
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Prots, Yurii
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Utsumi, Yuki
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Akselrud, Lev
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Schmidt, Marcus
The title compound was synthesized by a reaction of the elemental educts in a corundum crucible at 1200 degrees C under an Ar atmosphere. The excess of Ga used in the initial mixture served as a flux for the subsequent crystal growth at 600 degrees C. The crystal structure of Yb4Ga24Pt9 was determined from single-crystal X-ray diffraction data: new prototype of crystal structure, space group C2/m, Pearson symbol mS74, a = 7.4809(1) angstrom, b = 12.9546(2) angstrom, c = 13.2479(2) angstrom, beta = 100.879(1)degrees, V = 1260.82(6) angstrom(3), R-F = 0.039 for 1781 observed reflections and 107 variable parameters. The structure is described as an ABABB stacking of two slabs with trigonal symmetry and compositions Yb4Ga6 (A) and Ga12Pt6 (B). The hard. X-ray photoelectron spectrum (HAXPES) of Yb4Ga24Pt9 shows both Yb2+ and Yb3+ contributions as evidence of an intermediate valence state of ytterbium The evaluated Yb valence of similar to 2.5 is in good agreement with the results obtained from the magnetic susceptibility measurements. The compound is, a bad metallic conductor.
Mid-infrared chirped-pulse upconversion with four-wave difference frequency generation in gases
(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
Chirped-pulse upconversion of sub-single-cycle mid-infrared pulses with gaseous media has been realized. Single-shot detection of mid-infrared spectra from 250 to 5500 cm(-1) with 5 cm(-1) resolution was demonstrated. (C) 2013 Optical Society of America
Polarization ratio enhancement of a-plane GaN light emitting diodes by asymmetric two-dimensional photonic crystals
(2014-05-21)
Chou, Yen
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Li, Hsiang-Wei
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Yin, Yu-Feng
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Wang, Yu-Ting
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Lin, Yen-Chen
Fabricating photonic crystals (PhCs) on GaN based non-polar light emitting diodes (LEDs) is an effective way to increase light extraction and meanwhile to preserve or improve polarization ratio. In this work, a-plane GaN LEDs with two-dimensional PhCs were demonstrated. With the E // m polarized modes (which mean the optical polarization with the electric field parallel to m-axis) as the target of diffraction, we matched E//m modes to the photonic bands and aligned E//c modes to fall within the photonic band gap. The results show stronger E//m but weaker E//c mode diffractions on both c- and m-axes. At the vertical direction, the polarization ratio is enhanced from 45.8% for the planar device to 52.3% for the LEDs with PhCs. (C) 2014 AIP Publishing LLC.
Single-shot detection of mid-infrared spectra by chirped-pulse upconversion with four-wave difference frequency generation in gases
(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
Synthesis and characterization of a highly two-photon active dendrimer derived from 2,3,8-trifunctionalized indenoquinoxaline units
(2014)
Lin, Tzu-Chau
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Liu, Che-Yu
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Li, May-Hui
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Liu, Yi-You
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Tseng, Sheng-Yang
A dendritic chromophore derived from 2,3,8-trifunctionalized indenoquinoxaline units was synthesized and experimentally shown to manifest very strong and widely-dispersed two-photon absorption (2PA) across the dynamic tuning range of a Ti:sapphire laser. The maximum 2PA of the studied chromophore was found to reach approximate to 31 700 GM, indicating that 2,3,8-trifuctionalized indenoquinoxaline units are useful building moieties for the construction of highly active 2PA-dyes. In addition, this dendritic structure was also demonstrated to effectively regulate the optical power of femtosecond laser pulses at 800 nm.
Synthesis and Characterization of Two-Photon Chromophores Based on a Tetrasubstituted Tetraethynylethylene Scaffold
(2014-06-01)
Lin, Tzu-Chau
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Liu, Yi-You
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Li, May-Hui
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Liu, Che-Yu
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Tseng, Sheng-Yang
A new series of model dye molecules composed of three multibranched analogues based on the tetrasubstituted tetraethynylethylene structural motif have been synthesized and experimentally shown to possess strong and widely dispersed two-photon absorption (2PA) in the near-IR region. It was found that the spectral position of the major 2PA band could be tuned by the electronic nature of the selected substitution units. The studied model fluorophores also exhibited fairly low photodegradation of their fluorescence intensity even under prolonged UV-light irradiation, which is beneficial for the development of fluorescence probes that are needed for long-term light exposure. Furthermore, representative chromophores were selected to demonstrate the power-control properties within the femtosecond and nanosecond time domains.
TiO2 Nanowire-Supported Sulfide Hybrid Photocatalysts for Durable Solar Hydrogen Production
(2019-01-23)
Hsieh, Ping-Yen
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Chiu, Yi-Hsuan
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Lai, Ting-Hsuan
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Fang, Mei-Jing
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Wang, Yu-Ting
As the feet of clay, photocorrosion induced by hole accumulation has placed serious limitations on the widespread deployment of sulfide nanostructures for photoelectrochemical (PEC) water splitting. Developing sufficiently stable electrodes to construct durable PEC systems is therefore the key to the realization of solar hydrogen production. Here, an innovative charge-transfer manipulation concept based on the aligned hole transport across the interface has been realized to enhance the photostability of In2S3 electrodes toward PEC solar hydrogen production. The concept was realized by conducting compact deposition of In2S3 nanocrystals on the TiO2 nanowire array. Under PEC operation, the supporting TiO2 nanowires functioned as an anisotropic charge-transfer backbone to arouse aligned charge transport across the TiO2-In2S3 interface. Because of the aligned hole transport, the TiO2 nanowire-supported In2S3 hybrid nanostructures (TiO2 In2S3) exhibited improved hole-transfer dynamics at the TiO2-In2S3 interface and enhanced hole injection kinetics at the electrode surface, substantially increasing the long-term photostability toward solar hydrogen production. The PEC durability tests showed that TiO2-In2S3 electrodes can achieve nearly 90.9% retention of initial photocurrent upon continuous irradiation for 6 h, whereas the pure In2S3 merely retained 20.8% of initial photocurrent. This double-gain charge-transfer manipulation concept is expected to convey a viable approach to the intelligent design of highly efficient and sufficiently stable sulfide photocatalysts for sustainable solar fuel generation.
Ultrabroadband time-resolved spectroscopy in novel types of condensed matter
(2016-01-20)
Luo, Chih-Wei
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Wang, Yu-Ting
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Yabushita, Atsushi
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Kobayashi, Takayoshi
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電子物理學系
In condensed matter physics, quasi-particle correlations are crucial to understanding a material\'s properties. For example, strong interaction between electrons with metal-like electron configuration produces strongly correlated insulators rather than conductors, which band theory would predict. Therefore, it is important to determine the interaction strength between different degrees of freedom, e.g., electron, phonon, and spin. Time-resolved spectroscopy is a powerful technique for observing energy transfer between quasi-particles and determining the interaction strength. Ultrashort-pulse light sources with extremely broadband spectra have extended exploration of ultrafast dynamics in various materials. Here, novel types of condensed-phase matter are presented to show how several key issues regarding these materials can be resolved by broadband ultrafast time-resolved spectroscopy. (C) 2016 Optical Society of America
Ultrafast Multi-Level Logic Gates with Spin-Valley Coupled Polarization Anisotropy in Monolayer MoS2
(2015-02-06)
Wang, Yu-Ting
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Luo, Chih-Wei
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Yabushita, Atsushi
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Wu, Kaung-Hsiung
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Kobayashi, Takayoshi
The inherent valley-contrasting optical selection rules for interband transitions at the K and K' valleys in monolayer MoS2 have attracted extensive interest. Carriers in these two valleys can be selectively excited by circularly polarized optical fields. The comprehensive dynamics of spin valley coupled polarization and polarized exciton are completely resolved in this work. Here, we present a systematic study of the ultrafast dynamics of monolayer MoS2 including spin randomization, exciton dissociation, free carrier relaxation, and electron-hole recombination by helicity- and photon energy-resolved transient spectroscopy. The time constants for these processes are 60 fs, 1 ps, 25 ps, and, similar to 300 ps, respectively. The ultrafast dynamics of spin polarization, valley population, and exciton dissociation provides the desired information about the mechanism of radiationless transitions in various applications of 2D transition metal dichalcogenides. For example, spin valley coupled polarization provides a promising way to build optically selective-driven ultrafast valleytronics at room temperature. Therefore, a full understanding of the ultrafast dynamics in MoS2 is expected to provide important fundamental and technological perspectives.
Use of Ultrafast Time-Resolved Spectroscopy to Demonstrate the Effect of Annealing on the Performance of P3HT:PCBM Solar Cells
(2015-03-04)
Wang, Yu-Ting
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Chen, Mei-Hsin
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Lin, Chao-Ting
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Fang, Jian-Jhih
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Chang, Che-Jui
The organic solar cells of heterojunction system, ITO/PEDOT:PSS/P3HT:PCBM/Al, with a thermal annealing after deposition of Al exhibit better performance than those with an annealing process before deposition of Al. In this study, ultrafast time-resolved spectroscopy is employed to reveal the underlying mechanism of annealing effects on the performance of P3HT:PCBM solar cell devices. The analyses of all decomposed relaxation processes show that the postannealed devices exhibit an increase in charge transfer, in the number of separated polarons and a reduction in the amount of recombination between excited carriers. Moreover, the longer lifetime for the excited carriers in postannealed devices indicates it is more likely to be dissociated into photocarriers and result in a larger value for photocurrent, which demonstrates the physical mechanism for increased device performance.