Browsing by Author "Su, Dong"

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Flexible Heteroepitaxy of CoFe2O4/Muscovite Bimorph with Large Magnetostriction
(2017-03-01)
Liu, Heng-Jui
;
Wang, Chih-Kuo
;
Su, Dong
;
Amrillah, Tahta
;
Hsieh, Ying-Hui
A bimorph composed of ferrimagnetic cobalt ferrite (CoFe2O4, CFO) and flexible muscovite was fabricated via van der Waals epitaxy. The combination of X-ray diffraction and transmission electron microscopy was conducted to reveal the heteroepitaxy of the CFO/muscovite system. The robust magnetic behaviors against mechanical bending were characterized by hysteresis measurements and magnetic force microscopy, which maintain a saturation magnetization (M-s) of similar to 120-150 emu/cm(3) under different bending states. The large magnetostrictive response of the CFO film was then determined by digital holographic microscopy, where the difference of magnetostrction coefficient (Delta lambda) is -104 ppm. The superior performance of this bimorph is attributed to the nature of weak interaction between film and substrate. Such a flexible CFO/muscovite bimorph provides a new platform to develop next-generation flexible magnetic devices.
Flexible Multiferroic Bulk Heterojunction with Giant Magnetoelectric Coupling via van der Waals Epitaxy
(2017-06-01)
Amrillah, Tahta
;
Bitla, Yugandhar
;
Shin, Kwangwoo
;
Yang, Tiannan
;
Hsieh, Ying-Hui
Magnetoelectric nanocomposites have been a topic of intense research due to their profound potential in the applications of electronic devices based on spintronic technology. Nevertheless, in spite of significant progress made in the growth of high-quality nanocomposite thin films, the substrate damping effect still remains a major hurdle in realizing the ultimate magneto electric coupling. To overcome this obstacle, an alternative strategy of fabricating a self-assembled ferroelectric-ferrimagnetic bulk heterojunction on a flexible muscovite via van der Waals epitaxy is adopted. hi this study, we investigated the magnetoelectric coupling in a self-assembled BiFeO3 (BFO)-CoFe2O4 (CFO) bulk heterojunction epitaxially grown on a flexible muscovite substrate. The obtained heterojunction is composed of vertically aligned multiferroic BFO nanopillars embedded in a ferrimagnetic CFO matrix. Moreover, due to the weak interaction between the flexible substrate and bulk heterojunction, the interface is incoherent and, hence, the substrate damping effect is greatly reduced. The phase-field simulation model also complements our results. The magnetic and electrical characterizations highlight the improvement in magnetoelectric coupling of the BFO-CFO bulk heterojunction. A magnetoelectric coupling coefficient of 74 mV/cm.Oe of this bulk heterojunction is larger than the magnetoelectric coefficient reported earlier on flexible substrates. Therefore, this study delivers a viable route of fabricating a remarkable magnetoelectric heterojunction and yet flexible electronic devices that are robust against extreme conditions with optimized performance.
In situ evolution of highly dispersed amorphous CoOx clusters for oxygen evolution reaction
(2017-09-07)
Chen, Dawei
;
Dong, Chung-Li
;
Zou, Yuqin
;
Su, Dong
;
Huang, Yu-Cheng
Electrocatalytic water splitting is a key technique to produce hydrogen fuels, which can be considered as an efficient strategy to store renewable energy. Oxygen evolution reaction (OER) that occurs at the anode side requires a four-electron transfer under highly oxidizing conditions. OER has a large overpotential and therefore determines the overall efficiency. Certain electrocatalysts can efficiently help to improve the reaction kinetics. Owing to the high cost of precious metals such as Pt, Ru, and Ir, non-precious metal oxide catalysts have been vigorously investigated under alkaline conditions. Herein, we synthesized novel highly dispersed amorphous CoOx for the first time in the form of a cluster favorable to enhance the OER activity using a facile method via the air dielectric barrier discharge (DBD) plasma. Compared with the pristine biopolymer-cobalt complex, the amorphous CoOx cluster exhibits a much higher current density and a lower overpotential for OER, e.g., the overpotential of 290 mV at 10 mA cm(-2) and the overpotential of only 350 mV at 300 mA cm(-1). The excellent electrocatalytic OER activity was attributed to the unsaturated catalytic sites on the amorphous CoOx cluster. In addition, we studied the reaction mechanism, and it was observed that pure O-2 DBD plasma could lead to the evolution of crystalline CoOx; however, the presence of N-2 and O-2 in DBD plasma could ensure the facile evolution of amorphous CoOx clusters. This study provides a new strategy to design amorphous materials for electrocatalysis and beyond.
Strain Coupling of Conversion-type Fe3O4 Thin Films for Lithium Ion Batteries
(2017-06-26)
Hwang, Sooyeon
;
Meng, Qingping
;
Chen, Ping-Fan
;
Kisslinger, Kim
;
Cen, Jiajie
Lithiation/delithiation induces significant stresses and strains into the electrodes for lithium ion batteries, which can severely degrade their cycling performance. Moreover, this electrochemically induced strain can interact with the local strain existing at solid-solid interfaces. It is not clear how this interaction affects the lithiation mechanism. The effect of this coupling on the lithiation kinetics in epitaxial Fe3O4 thin film on a Nb-doped SrTiO3 substrate is investigated. In situ and ex situ transmission electron microscopy (TEM) results show that the lithiation is suppressed by the compressive interfacial strain. At the interface between the film and substrate, the existence of LixFe(3)O(4) rock-salt phase during lithiation consequently restrains the film from delamination. 2D phase-field simulation verifies the effect of strain. This work provides critical insights of understanding the solid-solid interfaces of conversion-type electrodes.