Browsing by Author "Lai, Yu-Hong"

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Flexible ferroelectric element based on van der Waals heteroepitaxy
(2017-06-01)
Jiang, Jie
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Bitla, Yugandhar
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Huang, Chun-Wei
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Thi Hien Do
;
Liu, Heng-Jui
We present a promising technology for nonvolatile flexible electronic devices: A direct fabrication of epitaxial lead zirconium titanate (PZT) on flexible mica substrate via van der Waals epitaxy. These single-crystalline flexible ferroelectric PZT films not only retain their performance, reliability, and thermal stability comparable to those on rigid counterparts in tests of nonvolatile memory elements but also exhibit remarkable mechanical properties with robust operation in bent states (bending radii down to 2.5 mm) and cycling tests (1000 times). This study marks the technological advancement toward realizing much-awaited flexible yet single-crystalline nonvolatile electronic devices for the design and development of flexible, lightweight, and next-generation smart devices with potential applications in electronics, robotics, automotive, health care, industrial, and military systems.
Flexible Heteroepitaxy Photoelectrode for Photo-electrochemical Water Splitting
(2018-08-01)
Le Thi Quynh
;
Chien Nguyen Van
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Tzeng, W. Y.
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Huang, Chun-Wei
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Lai, Yu-Hong
MICAtronics represents a new research direction by taking the advantages of good mechanical flexibility and optical transparency of muscovite mica, leading to a new platform to use oxide heteroepitaxy for novel transparent soft technology. Here we report a model flexible photoelectrode for photo-electrochemical (PEC) water splitting based on Fe2O3/ZnO/mica heteroepitaxy. The heteroepitaxy was confirmed by a combination of X-ray diffraction and transmission electron microscopy. The PEC performance of this flexible and semitransparent photoelectrode under various bending states was investigated. We found that the photocurrent of the heteroepitaxial system was enhanced by three times relative to pure ZnO and Fe2O3 under visible-light irradiation, and the heteroepitaxial photoelectrodes retain their photocurrent after continuous bending in cycling (>3000 cycles) with a smallest bending radius of 3.5 mm. The energy band alignment and charge dynamics under light excitation were characterized to understand the mechanism of the enhanced PEC performance. This study provides a new platform for design and fabrication of a flexible transparent photoelectrode in the harvest of solar energy based on oxide heteroepitaxy.
Giant Resistivity Change of Transparent ZnO/Muscovite Heteroepitaxy
(2020-05-13)
Yen, Min
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Lai, Yu-Hong
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Zhang, Chun-Li
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Cheng, Hou-Yung
;
Hsieh, Yi-Ting
The piezoresistive effect has shown a remarkable potential for mechanical sensor applications and been sought for its excellent performance. A great attention was paid to the giant piezoresistive effect and sensitivity delivered by silicon-based nanostructures. However, low thermal stability and complicated fabrication process hinder their practical applications. To overcome these issues and enhance the functionalities, we envision the substantial piezopotential in a zinc oxide (ZnO)/muscovite (mica) heteroepitaxy system based on theoretical consideration and realize it in practice. High piezoresistive effect with giant change of resistivity (-80 to 240%) and large gauge factor (>1000) are demonstrated through mechanical bending. The detailed features of heteroepitaxy, electrical transport, and strain are probed to understand the mechanism of such a giant resistivity change. In addition, a bending model is established to reveal the distribution of strain. Finally, we demonstrate a flex sensor featuring high sensitivity, optical transparency, and two-segment sensing with a great potential toward practical applications. Such an oxide heteroepitaxy exhibits excellent piezoresistive properties and mechanical flexibility. In the near future, the importance of flex sensors will emerge because of the precise control in the automation industries, and our results lead to a new design in the field of flex sensors.
Heteroepitaxy of Co-Based Heusler Compound/Muscovite for Flexible Spintronics
(2019-09-25)
Chen, Yi-Cheng
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Yen, Min
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Lai, Yu-Hong
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Markou, Anastasios
;
Zhang, Liguo
Materials with high spin-polarization play an important role in the development of spintronics. Co-based Heusler compounds are a promising candidate for practical applications because of their high Curie temperature and tunable half-metallicity. However, it is a challenge to integrate Heusler compounds into thin film heterostructures because of the lack of control on crystallinity and chemical disorder, critical factors of novel behaviors. Here, muscovite is introduced as a growth substrate to fabricate epitaxial Co2MnGa films with mechanical flexibility. The feature of heteroepitaxy is evidenced by the results of X-ray diffraction and transmission electron microscopy. Moreover, high chemical ordering with superior properties is delivered according to the observation of large Hall conductivity (680 Omega(-1) cm(-1)) and highly saturated magnetic moment (similar to 3.93 mu(B)/f.u.), matching well with bulk crystals. Furthermore, the excellence of magnetic and electrical properties is retained under the various mechanical bending conditions. Such a result suggests that the development of Co2MnGa/muscovite heteroepitaxy provides not only a pathway to the thin film heterostructure based on high-quality Heusler compounds but also a new aspect of spintronic applications on flexible substrates.
Highly flexible, robust, stable and high efficiency perovskite solar cells enabled by van der Waals epitaxy on mica substrate
(2019-06-01)
Jia, Chunmei
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Zhao, Xingyu
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Lai, Yu-Hong
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Zhao, Jinjin
;
Wang, Pei-Chun
Flexible and lightweight solar cells are promising for numerous emerging applications, and organometallic halide perovskites are particularly suitable for flexible solar cell applications. Transferring state of art high efficiency perovskite solar cells (PSCs) processing onto a flexible substrate, however, is challenging, requiring substantial redevelopment of materials compositions, device architectures, and processing conditions. In this work, highly flexible, robust, stable, and high efficiency PSCs based on mica substrate have been successfully developed, exhibiting a champion photovoltaic conversion efficiency (PCE) of 18.0%, retaining more than 91.7% of the original PCE after 5000 cycles of large deformation bending, and being relatively stable against humidity under elevated temperature. Key to such excellent performance is the inorganic and transparent mica substrate that is chemically inert and stable under high temperature, so that processing developed for glass-based high efficiency perovskite solar cells (PSCs) can be readily applied without modification. Furthermore, the layered mica substrate is highly flexible, and van der Waals epitaxial growth of transparent conducing ITO relaxes the mechanical constraint on the PSCs substantially, reducing the strain in the device even under large bending deformation. We believe inorganic flexible mica substrate can be used as a platform for high efficiency PSCs compatible to glass substrate, speeding up the development of flexible PSCs substantially.
Mechanical Modulation of Colossal Magnetoresistance in Flexible Epitaxial Perovskite Manganite
(1970-01-01)
Yen, Min
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Lai, Yu-Hong
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Kuo, Chang-Yang
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Chen, Chien-Te
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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
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Yen, Min
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Lai, Yu-Hong
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Kuo, Chang-Yang
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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.
Oxide Heteroepitaxy-Based Flexible Ferroelectric Transistor
(2019-07-24)
Tsai, Meng-Fu
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Jiang, Jie
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Shao, Pao-Wen
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Lai, Yu-Hong
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Chen, Jhih-Wei
With the rise of Internet of Things, the presence of flexible devices has attracted significant attention owing to design flexibility. A ferroelectric field-effect transistor (FeFET), showing the advantages of high speed, nondestructive readout, and low-power consumption, plays a key role in next-generation technology. However, the performance of these devices is restricted since conventional flexible substrates show poor thermal stability to integrate traditional ferroelectric materials, limiting the compatibility of wearable devices. In this study, we adopt flexible muscovite mica as a substrate due to its good thermal properties and epitaxial integration ability. A flexible FeFET composed of oxide heteroepitaxy on muscovite is realized by combining an aluminum-doped zinc oxide film as the semiconductor channel layer and a Pb(Zro7Ti0.3)03 film as the ferroelectric gate dielectric. The excellent characteristics of the transistor together with superior thermal stability and mechanical flexibility are demonstrated through various mechanical bending and temperature measurements. The on/off current ratio of the FeFET is higher than 103, which based on the field effect in the transfer curve. The smallest bending radius that can be achieved is 5 mm with a cyclability of 300 times and a retention of 100 h. This study opens an avenue to use oxide heteroepitaxy to construct a FeFET for next-generation flexible electronic systems.
Thickness dependence of the anomalous Hall effect in thin films of the topological semimetal Co2MnGa
(2019-08-19)
Markou, Anastasios
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Kriegner, Dominik
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Gayles, Jacob
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Zhang, Liguo
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Chen, Yi-Cheng
Topological magnetic semimetals promise large Berry curvature through the distribution of the topological Weyl nodes or nodal lines and further novel physics with exotic transport phenomena. We present a systematic study of the structural and magnetotransport properties of Co2MnGa films from thin (20 nm) to bulklike behavior (80 nm) in order to understand the underlying mechanisms and the role of topology. The magnetron sputtered Co2MnGa films are L2(1)-ordered showing very good heteroepitaxy and a strain-induced tetragonal distortion. The anomalous Hall conductivity was found to be maximum at a value of 1138 S/cm, with a corresponding anomalous Hall angle of 13%, which is comparatively larger than topologically trivial metals. There is good agreement between the theoretical calculations and the Hall conductivity observed for the 80 nm film, which suggests that the effect is intrinsic. Thus, the Co2MnGa compound manifests as a promising material for topologically driven spintronic applications.
Transparent Antiradiative Ferroelectric Heterostructure Based on Flexible Oxide Heteroepitaxy
(2018-09-12)
Ma, Chun-Hao
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Jiang, Jie
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Shao, Pao-Wen
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Peng, Qiang-Xiang
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Huang, Chun-Wei
In the era of Internet of Things, the demand for flexible and transparent electronic devices has shifted to the forefront of materials science research. However, the radiation damage to key performance of transparent devices under radiative environment remains as a critical issue. Here, we present a promising technology for nonvolatile transparent electronic devices based on flexible oxide heteroepitaxy. A direct fabrication of epitaxial lead lanthanum zirconate titanate on transparent flexible mica substrate with indium tin oxide electrodes is presented. The transparent flexible ferroelectric heterostructures not only retain their superior performance, thermal stability, reliability, and mechanical durability, but also exhibit remarkably robust properties against to a strong radiation exposure. Our study demonstrates an extraordinary concept to realize transparent flexible nonvolatile electronic devices for the design and development of next-generation smart devices with potential application in electronics, automotive, aerospace, and nuclear systems.
Transparent Flexible Heteroepitaxy of NiO Coated AZO Nanorods Arrays on Muscovites for Enhanced Energy Storage Application
(1970-01-01)
Van-Qui Le
;
Phuoc-Anh Le
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Wu, Shu-Chi
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Lai, Yu-Hong
;
Lin, Yan-Gu
Transparent flexible energy storage devices are considered as important chains in the next-generation, which are able to store and supply energy for electronic devices. Here, aluminum-doped zinc oxide (AZO) nanorods (NRs) and nickel oxide (NiO)-coated AZO NRs on muscovites are fabricated by a radio frequency (RF) magnetron sputtering deposition method. Interestingly, AZO NRs and AZO/NiO NRs are excellent electrodes for energy storage application with high optical transparency, high conductivity, large surface area, stability under compressive and tensile strain down to a bending radius of 5 mm with 1000 bending cycles. The obtained symmetric solid-state supercapacitors based on these electrodes exhibit good performance with a large areal specific capacitance of 3.4 mF cm(-2), long cycle life 1000 times, robust mechanical properties, and high chemical stability. Furthermore, an AZO/NiO//Zn battery based on these electrodes is demonstrated, yielding a discharge capacity of 195 mAh g(-1) at a current rate of 8 A g(-1) and a discharge capacity of over 1000 cycles with coulombic efficiency to 92%. These results deliver a concept of opening a new opportunity for future applications in transparent flexible energy storage.
Van der Waals heteroepitaxial AZO/NiO/AZO/muscovite (ANA/muscovite) transparent flexible memristor
(2019-02-01)
Van-Qui Le
;
Thi-Hien Do
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Retamal, Jose Ramon Duran
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Shao, Pao-Wen
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Lai, Yu-Hong
Multifunctional electronics featuring optical transparency, portability, mechanical flexibility, light-weight and environment-friendly are of great demands for next-generation smart electronics. Memristor represents one of the important chains in next-generation devices as the information computing and storage component. Here, we design the transparent flexible structure based on van der Waals heteroepitaxial AZO/NiO/AZO/muscovite (ANA/muscovite) for a memristor application. The (ANA/muscovite) memristor satisfies all the hardest requirements of a transparent soft device such as optical transparency over 80% in visible light and high performance with a ON/OFF resistance ratio > 10(5), stable endurance to 10(3) cycles and long retention time of 10(5) s. In addition, the ANA/muscovite memristor can work at various bending radii down to 5 mm, a mechanical bending after 1000 cycles at a curvature with a radius of 6.5 mm and a high temperature up to 185 degrees C, which deliver a pathway for future applications in flexible transparent smart electronics.