Browsing by Author "Chang, Chun-Fu"

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Deterministic optical control of room temperature multiferroicity in BiFeO3 thin films
(2019-06-01)
Liou, Yi-De
;
Chiu, Yu-You
;
Hart, Ryan Thomas
;
Kuo, Chang-Yang
;
Huang, Yen-Lin
Controlling ferroic orders (ferroelectricity, ferromagnetism and ferroelasticity) by optical methods is a significant challenge due to the large mismatch in energy scales between the order parameter coupling strengths and the incident photons. Here, we demonstrate an approach to manipulate multiple ferroic orders in an epitaxial mixed-phase BiFeO3 thin film at ambient temperature via laser illumination. Phase-field simulations indicate that a light-driven flexoelectric effect allows the targeted formation of ordered domains. We also achieved precise sequential laser writing and erasure of different domain patterns, which demonstrates a deterministic optical control of multiferroicity at room temperature. As ferroic orders directly influence susceptibility and conductivity in complex materials, our results not only shed light on the optical control of multiple functionalities, but also suggest possible developments for optoelectronics and related applications.
Development of a Compact Low-Temperature Co-Fired Ceramic Antenna Front-End Module
(2008-11-01)
Weng, Chia-Chun
;
Chang, Chun-Fu
;
Chung, Shyh-Jong
;
電信工程研究所
;
Institute of Communications Engineering
This study proposes a compact 5-GHz front-end module with embedded antenna on a low-temperature co-fired ceramic substrate, which is to be used for the IEEE 802.11a wireless local area network applications. The module comprises an embedded inverted-F antenna, a bandpass filter, and a low-pass filter. Both the proposed filters possess transmission zeros at out band for suppressing unwanted signals. A double-pole double-throw bare die transmitting/receiving switch is mounted on the surface of the substrate. The interconnection between the bare die switch and the buried circuits is established by bond wires. The effect of the bond wire is considered by incorporating its equivalent inductance into the design of the filters. The overall size of the antenna front-end module is only 6.2 mm x 5.4 mm x 0.98 mm with most of the space (near two-thirds of the volume) reserved for the antenna so as to have a better radiation performance. Also, to avoid the potential close proximity coupling among the buried circuits and the antenna, numerous metal vias connecting the top and bottom grounds in the module are designed for shielding. Since the radiation of a small antenna is influenced by the nearby circuit ground due to induced ground current, the developed antenna front-end module is tested on two FR4 printed circuit boards (PCBs) with different sizes (i.e., 55 mm x 20 mm and 80 mm x 46 mm). It is demonstrated that the antenna module performs well on these two grounded PCBs. The achieved 10-dB return-loss bandwidths are near 900 MHz for the transmitting and receiving paths. The measured radiation patterns are quite omnidirectional with peak gains (including the losses of circuit components) at approximately 0 dBi for the transmitting path and -1.7 dBi for the receiving path.
Directly Probing Intermolecular Structural Change of a Core Fragment of beta(2)-Microglobulin Amyloid Fibrils with Low-Frequency Raman Spectroscopy
(2017-01-26)
Shigeto, Shinsuke
;
Chang, Chun-Fu
;
Hiramatsu, Hirotsugu
;
應用化學系
;
Department of Applied Chemistry
Amyloid fibrils, which are ordered aggregates of proteins or peptides, have attracted keen interest because their deposition causes serious human diseases. Despite many studies utilizing X-ray crystallography, solid-state NMR, and other methods, intermolecular interactions governing the fibril formation remain largely unclear. Here, we used low-frequency Raman (LFR) spectroscopy to investigate the intermolecular beta-sheet structure of a core fragment of beta(2)-microglobulin amyloid fibrils, beta(2)m(21-29), in aqueous buffer solutions. The LFR spectra (approximately 10-200 cm(-1)) of beta(2)m(21-29) amyloid fibrils measured at different pH values (ranging from 6.8 to 8.0) revealed a broad-spectral pattern with a maximum at similar to 80 cm(-1) below pH 7.2 and at similar to 110 cm(-1) above pH 7.4. This observation is attributed to a pH-dependent structural change from an antiparallel to a parallel intermolecular beta-sheet structure. Multivariate curve resolution-alternating least-squares (MCR-ALS) analysis enabled us to decompose the apparently monotonous LFR spectra into three distinctly different contributions: intermolecular vibrations of the parallel and antiparallel beta-sheets and intramolecular vibrations of the peptide backbone. Peak positions of the obtained LFR bands not only exhibit a much more pronounced difference between the two beta-sheets than the conventional amide I band, but they also suggest stronger intermolecular interaction, due presumably to the hydrophobic effect, in the parallel beta-sheet than in the antiparallel beta-sheet. The present results show that LFR spectroscopy in combination with the MCR-ALS analysis holds promise for real-time tracking of the intermolecular dynamics of amyloid fibril formation under physiological conditions.
Dual bandpass filter having serial configuration of coupled-line filters
(2007-11-08)
Chung, Shyh-Jong
;
Lin, Ke-Chiang
;
Chang, Chun-Fu
Two second-order bandpass filter are connected serially to obtain a dual bandpass filter. One is inductive and the other is capacitive. One has a low passband and the other has a high passband. Between them, a finite transmission zero is formed to suppress noise. The present invention achieves a passband as wide as 1 gigahertz so that it can be applied to a wireless local network, communication equipments and electronic devices.
Heteroepitaxy of Fe3O4/Muscovite: A New Perspective for Flexible Spintronics
(2016-12-14)
Wu, Ping-Chun
;
Chen, Ping-Fan
;
Thi Hien Do
;
Hsieh, Ying-Hui
;
Ma, Chun-Hao
Spintronics has captured a lot of attention since it was proposed. It has been triggering numerous research groups to make their efforts on pursuing spin-related electronic devices. Recently, flexible and wearable devices are in a high demand due to their outstanding potential in practical applications. In order to introduce spintronics into the realm of flexible devices, we demonstrate that it is feasible to grow epitaxial Fe3O4 film, a promising candidate for realizing spintronic devices based on tunneling magnetoresistance, on flexible muscovite. In this study, the heteroepitaxy of Fe3O4/muscovite is characterized by X-ray diffraction, high-resolution transmission electron microscopy, and Raman spectroscopy. The chemical composition and magnetic feature are investigated by a combination of X-ray photoelectron spectroscopy and X-ray magnetic circular dichroism. The electrical and magnetic properties are examined to show the preservation of the primitive properties of Fe3O4. Furthermore, various bending tests are performed to show the tunability of functionalities and to confirm that the heterostructures retain the physical properties under repeated cycles. These results illustrate that the Fe3O4/muscovite heterostructure can be a potential candidate for the applications in flexible spintronics.
Imaging molecular crystal polymorphs and their polycrystalline microstructures in situ by ultralow-frequency Raman spectroscopy
(2014-01-01)
Chang, Chun-Fu
;
Okajima, Hajime
;
Hamaguchi, Hiro-o
;
Shigeto, Shinsuke
;
應用化學系
Ultralow-frequency Raman spectroscopy that can measure vibrational bands at as low as +/- 10 cm(-1) has enabled facile in situ imaging of polycrystalline microstructures such as grains and grain boundaries with high polymorph specificity. We demonstrate this method by investigating microcrystals of two distinct polymorphs of 1,1\'-binaphthyl using a microscope.
In Situ Ultralow-Frequency Raman Tracking of the Polymorphic Transformation of Crystalline 1,1 '-Binaphthyl
(2014-02-06)
Chang, Chun-Fu
;
Wang, Szu-Cheng
;
Shigeto, Shinsuke
;
應用化學系
;
Department of Applied Chemistry
Extremely low-frequency (LF) Raman spectroscopy that allows for fast access to lattice vibrations with little hindrance of immense Rayleigh scattering was used to track in situ thermally induced polymorphic transformation of crystalline 1,1'-binaphthyl (BN), a fundamental structural unit of specific chiral ligands. BN occurs in two conformational polymorphs, cisoid and transoid forms, with the former being a racemate and the latter being a conglomerate of chiral crystals. Observed LF Raman spectra (from 200 cm(-1) down to similar to 5 cm(-1), equivalent to 0.15 THz), which arise predominantly from lattice vibrations, show markedly different features between the cisoid and transoid forms, making it possible to study their phase transition. A series of LF Raman spectra measured with slow heating of microcrystalline BN reveal that, in contrast to previous studies, the monoclinic cisoid form transforms directly to the tetragonal transoid form in the solid state without formation of any intermediate phase. The present approach is applicable to various phase transition systems, including pharmaceutical compounds, liquid crystals, and polymer films, which conventional X-ray diffraction analysis may not be able to investigate.
Mechanical Modulation of Colossal Magnetoresistance in Flexible Epitaxial Perovskite Manganite
(1970-01-01)
Yen, Min
;
Lai, Yu-Hong
;
Kuo, Chang-Yang
;
Chen, Chien-Te
;
Chang, Chun-Fu
Heteroepitaxially flexible oxide systems have been intensely developed and considered as the most promising materials for leading the creation of next-generation flexible electronic devices. Among them, perovskite manganites have attracted significant attention with their abundant and novel properties such as colossal magnetoresistance (CMR) and metal-insulator transition. However, the requirement of high quality samples hampers this field, not to mention the advanced nanoengineering. In this study, fluorophlogopite mica (F-mica) is selected as a flexible substrate to fabricate heteroepitaxial Pr0.5Ca0.5MnO3(PCMO) with a nanocolumn structure. Through a precise control of thickness, different morphologies are realized to manipulate the magnetotransport properties (reduction of melting field). Moreover, thanks to the excellent flexibility of F-mica, mechanical modulation of CMR (approximate to 1000%) can be achieved in different flex modes while the magnetic properties remain unaffected. Detailed bending tests are performed to study the behavior of resistive change (approximate to 30%). Through the combination of high flexibility, high quality PCMO, and well-designed nanocolumn structure, the study exhibits the significant controllability of CMR via mechanical bending, and manifests the potential of such a heteroepitaxially flexible oxide system which can be applied on flexible magnetoresistive devices and sensors.
Mechanically tunable exchange coupling of Co/CoO bilayers on flexible muscovite substrates
(2020-02-07)
Thai Duy Ha
;
Yen, Min
;
Lai, Yu-Hong
;
Kuo, Chang-Yang
;
Chen, Chien-Te
The employment of flexible muscovite substrates has given us the feasibility of applying strain to heterostructures dynamically by mechanical bending. In this study, this novel approach is utilized to investigate strain effects on the exchange coupling in ferromagnetic Co and anti-ferromagnetic CoO (Co/CoO) bilayers. Two different Co/CoO bilayer heterostructures were grown on muscovite substrates by oxide molecular beam epitaxy, with the CoO layer being purely (111)- and (100)-oriented. The strain-dependent exchange coupling effect can only be observed on Co/CoO(100)/mica but not on Co/CoO(111)/mica. The origin of this phenomenon is attributed to the anisotropic spin re-orientation induced by mechanical bending. The strain-dependent magnetic anisotropy of the bilayers determined by anisotropic magnetoresistance measurements confirms this conjecture. This study elucidates the fundamental understanding of how magnetic exchange coupling can be tuned by externally applied strain via mechanical bending and, hence, provides a novel approach for implementing flexible spintronic devices.