Browsing by Author "Tu, Chien-Ming"

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Femtosecond Laser- Colorized AZO Films on Flexible Mica Substrates
(2019-01-01)
Yang, Hung
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Yeh, Tien-Tien
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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 time-evolution of mid-infrared spectral line shapes of Dirac fermions in topological insulators
(2020-06-17)
Yeh, Tien-Tien
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Tu, Chien-Ming
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Lin, Wen-Hao
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Cheng, Cheng-Maw
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Tzeng, Wen-Yen
Mid-infrared (MIR) light sources have much potential in the study of Dirac-fermions (DFs) in graphene and topological insulators (TIs) because they have a low photon energy. However, the topological surface state transitions (SSTs) in Dirac cones are veiled by the free carrier absorption (FCA) with same spectral line shape that is always seen in static MIR spectra. Therefore, it is difficult to distinguish the SST from the FCA, especially in TIs. Here, we disclose the abnormal MIR spectrum feature of transient reflectivity changes (Delta R/R) for the non-equilibrium states in TIs, and further distinguish FCA and spin-momentum locked SST using time-resolved and linearly polarized ultra-broadband MIR spectroscopy with no environmental perturbation. Although both effects produce similar features in the reflection spectra, they produce completely different variations in the Delta R/R to show their intrinsic ultrafast dynamics.
Helicity-dependent terahertz emission spectroscopy of topological insulator Sb2Te3 thin films
(2017-11-06)
Tu, Chien-Ming
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Chen, Yi-Cheng
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Huang, Ping
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Chuang, Pei-Yu
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Lin, Ming-Yu
We report on helicity-dependent terahertz emissions that originate from the helicity-dependent photocurrents in topological insulator Sb2Te3 thin films due to ultrafast optical excitation. The polarity of the emitted terahertz radiation is controlled by both the incident angle and the helicity of optical pulses. Using an unprecedented decomposition-recombination procedure in the time domain, the signals of the Dirac fermions are fully separated from bulk contributions. These results provide insights into the optical coupling of topological surface states and open up opportunities for applying helicity-dependent terahertz emission spectroscopy in spintronics.
Helicity-Dependent Terahertz Radiation from Topological Insulator Sb2Te3 Thin Film by Femtosecond Optical Excitation
(2016)
Tu, Chien-Ming
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Chen, Yi-Cheng
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Huang, Ping
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Chuang, Pei-Yu
;
Lin, Ming-Yu
We report on terahertz radiation from topological insulator (TI)Sb2Te3 thin film under ultrafast optical excitation with different helicity. Polarity-reversals of the emitted THz radiation were observed as the helicity of optical pulses reversed. The observed phenomena are coincident with the characteristics of the helicity-dependent photocurrent on TIs. Our work demonstrates the potential applications of surface photocurrents on TIs for opto-spintronics devices.
Manifestation of a Second Dirac Surface State and Bulk Bands in THz Radiation from Topological Insulators
(2015-09-15)
Tu, Chien-Ming
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Yeh, Tien-Tien
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Tzeng, Wen-Yen
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Chen, Yi-Ru
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Chen, Hsueh-Ju
Topological insulators (TIs) are interesting quantum matters that have a narrow bandgap for bulk and a Dirac-cone-like conducting surface state (SS). The recent discovered second Dirac surface state (SS) and bulk bands (BBs) located similar to 1.5 eV above the first SS are important for optical coupling in TIs. Here, we report on the time-domain measurements of THz radiation generated from TIs n-type Cu0.02Bi2Se3 and p-type Bi2Te3 single crystals by ultrafast optical pulse excitation. The observed polarity-reversal of the THz pulse originated from transient current is unusual, and cannot be reconciled with the photo-Dember effect. The second SS and BBs are found to be indispensable for the explanation of the unusual phenomenon. Thanks to the existence of the second SS and BBs, TIs manifest an effective wide band gap in THz generation. The present study demonstrates that time-domain THz spectroscopy provide rich information of the optical coupling and the electronic structure of TIs.
Newborn Screening Healthcare Information System Based on Service-Oriented Architecture
(2010-08-01)
Hsieh, Sung-Huai
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Hsieh, Sheau-Ling
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Chien, Yin-Hsiu
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Weng, Yung-Ching
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Hsu, Kai-Ping
In this paper, we established a newborn screening system under the HL7/Web Services frameworks. We rebuilt the NTUH Newborn Screening Laboratory's original standalone architecture, having various heterogeneous systems operating individually, and restructured it into a Service-Oriented Architecture (SOA), distributed platform for further integrity and enhancements of sample collections, testing, diagnoses, evaluations, treatments or follow-up services, screening database management, as well as collaboration, communication among hospitals; decision supports and improving screening accuracy over the Taiwan neonatal systems are also addressed. In addition, the new system not only integrates the newborn screening procedures among phlebotomy clinics, referral hospitals, as well as the newborn screening center in Taiwan, but also introduces new models of screening procedures for the associated, medical practitioners. Furthermore, it reduces the burden of manual operations, especially the reporting services, those were heavily dependent upon previously. The new system can accelerate the whole procedures effectively and efficiently. It improves the accuracy and the reliability of the screening by ensuring the quality control during the processing as well.
Selenium nanoparticle prepared by femtosecond laser-induced plasma shock wave
(2020-01-06)
Tzeng, Wen-Yen
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Tseng, Ya-Hsin
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Yeh, Tien-Tien
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Tu, Chien-Ming
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Sankar, Raman
A novel approach for the production of both amorphous and crystalline selenium nanoparticles (SeNPs) using femtosecond laser-induced plasma shock wave on the surface of Bi2Se3 topological insulators at room temperature and ambient pressure is demonstrated. The shape and size of SeNPs can be reliably controlled via the kinetic energy obtained from laser pulses, so these are applicable as active components in nanoscale applications. Importantly, the rapid, low-cost and eco-friendly synthesis strategy developed in this study could also be extendable to other systems. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
THz emission from organic cocrystalline salt: 2, 6-diaminopyridinium-4-nitrophenolate-4-nitrophenol
(2016-03-07)
Tu, Chien-Ming
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Chou, Li-Hsien
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Chen, Yi-Cheng
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Huang, Ping
;
Rajaboopathi, M.
We report few-cycle THz pulses emission from a novel organic crystal 2,6-diaminopyridinium-4-nitrophenolate-4-nitrophenol (DAP(+)NP(-)NP). The observed amplitude of the THz electric field from a DAP(+)NP(-)NP crystal is comparable with that from a ZnTesingle crystal under the same optical pumping conditions. Both the waveform and spectra of the THz radiation from DAP(+)NP(-)NP are similar to those from ZnTe. We conclude that a high quality DAP(+)NP(-)NP crystal would be a high potential candidate in THz generation and applications. (C) 2016 Optical Society of America
Ultrafast carrier dynamics in Ge by ultra-broadband mid-infrared probe spectroscopy
(2017-01-11)
Yeh, Tien-Tien
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Shirai, Hideto
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Tu, Chien-Ming
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Fuji, Takao
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Kobayashi, Takayoshi
In this study, we carried out 800-nm pump and ultra-broadband mid-infrared (MIR) probe spectroscopy with high time-resolution (70 fs) in bulk Ge. By fitting the time-resolved difference reflection spectra [Delta R(omega)/R(omega)] with the Drude model in the 200-5000 cm(-1) region, the time-dependent plasma frequency and scattering rate have been obtained. Through the calculation, we can further get the time-dependent photoexcited carrier concentration and carrier mobility. The Auger recombination essentially dominates the fast relaxation of photoexcited carriers within 100 ps followed by slow relaxation due to diffusion. Additionally, a novel oscillation feature is clearly found in time-resolved difference reflection spectra around 2000 cm(-1) especially for high pump fluence, which is the Lorentz oscillation lasting for about 20 ps due to the Coulomb force exerted just after the excitation.