Browsing by Author "Liao, Sheng-Chieh"

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Epitaxial Magnetic Oxide Nanocrystals Via Phase Decomposition of Bismuth Perovskite Precursors
(2012-12-19)
Bogle, Kashinath A.
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Cheung, Jeffrey
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Chen, Yong-Lun
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Liao, Sheng-Chieh
;
Lai, Chih-Hung
The phase instability of bismuth perovskite (BiMO3), where M is a ferromagnetic cation, is exploited to create self-assembled magnetic oxide nanocrystal arrays on oxide supports. Conditions during pulsed laser deposition are tuned so as to induce complete breakdown of the perovskite precursor into bismuth oxide (Bi2O3) and metal oxide (M-Ox) pockets. Subsequent cooling in vacuum volatizes the Bi2O3 leaving behind an array of monodisperse nanocrystals. In situ reflective high energy electron diffraction beam is exploited to monitor the synthesis in real-time. Analysis of the patterns confirms the phase separation and volatization process. Successful synthesis of M-Ox, where M = Mn, Fe, Co, and Cr, is shown using this template-free facile approach. Detailed magnetic characterization of nanocrystals is carried out to reveal the functionalities such as magnetic anisotropy as well as larger than bulk moments, as expected in these oxide nanostructures.
Misorientation Control and Functionality Design of Nanopillars in Self-Assembled Perovskite-Spinel Heteroepitaxial Nanostructures
(2011-05-01)
Liao, Sheng-Chieh
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Tsai, Pei-Yu
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Liang, Chen-Wei
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Liu, Heng-Jui
;
Yang, Jan-Chi
In this study, advanced control of crystallographic orientations and magnetic properties of self-assembled nanostructures via rational selections of substrates is demonstrated. We show that in the perovskite spinel BiFeO(3)-CoFe(2)O(4) model system the crystal orientation of self-assembled CoFe(2)O(4) nanopillars can be tuned among (001), (011), and (111), while that of the BiFeO(3) matrix is fixed in (001). Moreover, the resultant CoFe(2)O(4) nanopIllars appear in various shapes: pyramid, roof, and triangular platform, respectively. The tunable nanostructures through this approach enable the control of material functionality such as the magnetic anisotropy of CoFe(2)O(4). This study opens a new pathway for the engineering of self-assembled heteroepitaxial nanostructures.
Self-Assembled BiFeO3-epsilon-Fe2O3 Vertical Heteroepitaxy for Visible Light Photoelectrochemistry
(2016-09-21)
Le Thi Quynh
;
Chien Nguyen Van
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Bitla, Yugandhar
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Chen, Jhih-Wei
;
Thi Hien Do
Self-assembled vertical heterostructure with a high interface-to-volume ratio offers tremendous opportunities to realize intriguing properties and advanced modulation of functionalities. Here, a heterostructure composed of two visible-light photocatalysts, BiFeO3 (BFO) and epsilon-Fe2O3 (epsilon-FO), is designed to investigate its photoelectrochemical performance. The structural characterization of the BFO-FO heterostructures confirms the phase separation with BFO nanopillars embedded in the epsilon-FO matrix. The investigation of band structure of the heterojunction suggests the assistance of photoexcited carrier separation, leading to an enhanced photoelectrochemical performance. The insights into the charge separation are further revealed by means of ultrafast dynamics and electrochemical impedance spectroscopies. This work shows a delicate design of the self-assembled vertical heteroepitaxy by taking advantage of the intimate contact between two phases that can lead to a tunable charge interaction, providing a new confi guration for the optimization of photoelectrochemical cell.
Self-Assembled Epitaxial Core-Shell Nanocrystals with Tunable Magnetic Anisotropy
(2015-09-02)
Liao, Sheng-Chieh
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Chen, Yong-Lun
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Kuo, Wei-Cheng
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Cheung, Jeffrey
;
Wang, Wei-Cheng
Strong magnetic enhancement in self-assembled multiferroic-ferrimagnetic nanostructures
(2013)
Chen, Ying-Jiun
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Hsieh, Ying-Hui
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Liao, Sheng-Chieh
;
Hu, Zhiwei
;
Huang, Meng-Jie
In the past decade, self-assembled vertical nano-heterostructures have drawn considerable attention because a high interface-to-volume ratio can be used to tailor or create functionalities. We have systematically investigated the magnetic properties of oxide heterostructures consisting of the CoFe2O4 nanopillars embedded in the BiFeO3 matrix using macroscopic magnetization measurements and element-selective soft X-ray absorption magnetic circular dichroism (XMCD) at the Co- and Fe-L-2,L-3 edge. The magnetization and XMCD data show that the total ordered magnetic moment of Co2+ in CoFe2O4-BiFeO3 nano-heterostructures is strongly enhanced. This study clearly indicates that the high interface-to-volume ratio vertical nanostructure creates a strong ferromagnetic and antiferromagnetic magnetic coupling via an interface. Furthermore, the magnetic coupling can be tuned in the multiferroic-ferrimagnetic self-assembled heterostructures by controlling the spacing between nanopillars.
Tuning the formation and functionalities of ultrafine CoFe2O4 nanocrystals via interfacial coherent strain
(2013)
Hsieh, Ying-Hui
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Kuo, Ho-Hung
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Liao, Sheng-Chieh
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Liu, Heng-Jui
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Chen, Ying-Jiun
Complex oxide nanocrystals with a spinel structure show their remarkable optical, electronic, mechanical, thermal, and magnetic properties. In this study, we present a simple yet versatile strategy to grow self-assembled epitaxial CoFe2O4 nanocrystals with well-controlled size (less than 10 nm) and single orientation. CoFe2O4 nanocrystals were fabricated via phase separation in a BiFeO3-CoF2O4 ultrathin film by pulsed laser deposition. The coherent strain at the BiFeO3-CoF2O4 interface suppressed the growth of the nanocrystals regardless of substrate temperatures. This strain also resulted in the ferromagnetic anisotropy and interesting conducting behaviors of ultrafine CFO nanocrystals.
Tuning the functionalities of a mesocrystal via structural coupling
(2015-07-14)
Liu, Heng-Jui
;
Liu, Yun-Ya
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Tsai, Chih-Ya
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Liao, Sheng-Chieh
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Chen, Ying-Jiun
In the past decades, mesocrystal, a kind of nanocrystals with specific crystallographic orientation, has drawn a lot of attention due to its intriguing functionalities. While the research community keeps searching for new mesocrystal systems, it is equally crucial to develop new approaches to tune the properties of mesocrystals. In this work, a self-organized two-dimensional mesocrystal composed of highly oriented CoFe2O4 (CFO) nano-crystals with assistance of different perovskite matrices is studied as a model system. We have demonstrated that the strain state and corresponding magnetic properties of the CFO mesocrystal can be modulated by changing the surrounding perovskite matrix through their intimate structural coupling. Interestingly, this controllability is more strongly correlated to the competition of bonding strength between the matrices and the CFO mesocrystals rather than the lattice mismatch. When embedded in a matrix with a higher melting point or stiffness, the CFO mesocrystal experiences higher out-of-plane compressive strain and shows a stronger magnetic anisotropy as well as cation site-exchange. Our study suggests a new pathway to tailor the functionalities of mesocrystals.
Tuning the magnetic properties of self-assembled BiFeO3-CoFe2O4 heteroepitaxy by magneto-structural coupling
(2016)
Amrillah, Tahta
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Vandrangi, Suresh K.
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Bitla, Yugandhar
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Do, Thi Hien
;
Liao, Sheng-Chieh
Magnetic and multiferroic nanocomposites with two distinct phases have been a topic of intense research for their profound potential applications in the field of spintronics. In addition to growing high-quality phase separated heteroepitaxial nanocomposites, the strain engineering that is conducive to enhance the tunability of material properties, in general, and the magnetic properties, in particular, is of utmost importance in exploring new possibilities. Here, we investigated the magneto-structural coupling between anti-ferromagnetic BiFeO3 (BFO) and ferrimagnetic CoFe2O4 (CFO) in self-assembled vertically aligned nanocomposites grown on LaAlO3 (LAO) and SrTiO3 (STO) substrates. We found that BFO exhibits tetragonal (T) and rhombohedral (R) structures as the stable phases and CFO has high magnetocrystalline anisotropy even in the form of nanocomposites. The temperature and magnetic field dependent magnetizations of T_ BFO-CFO/LAO and R_ BFO-CFO/STO nanocomposites primarily demonstrate the magnetoelastic coupling between these variants.