Browsing by Author "Hsieh, Ying-Hui"

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Constraining Data Mining with Physical Models: Voltage- and Oxygen Pressure-Dependent Transport in Multiferroic Nanostructures
(2015-10-01)
Streloov, Evgheni
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Belianinov, Alexei
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Hsieh, Ying-Hui
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Chu, Ying-Hao
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Kalinin, Sergei V.
Development of new generation electronic devices necessitates understanding and controlling the electronic transport in ferroic, magnetic, and optical materials, which is hampered by two factors. First, the complications of working at the nanoscale, where interfaces, grain boundaries, defects, and so forth, dictate the macroscopic characteristics. Second, the convolution of the response signals stemming from the fact that several physical processes may be activated simultaneously. Here, we present a method of solving these challenges via a combination of atomic force microscopy and data mining analysis techniques. Rational selection of the latter allows application of physical constraints and enables direct interpretation of the statistically significant behaviors in the framework of the chosen physical model, thus distilling physical meaning out of raw data. We demonstrate our approach with an example of deconvolution of complex transport behavior in a bismuth ferrite cobalt ferrite nanocomposite in ambient and ultrahigh vacuum environments. Measured signal is apportioned into four electronic transport patterns, showing different dependence on partial oxygen and water vapor pressure. These patterns are described in terms of Ohmic conductance and Schottky emission models in the light of surface electrochemistry. Furthermore, deep data analysis allows extraction of local dopant concentrations and barrier heights empowering our understanding of the underlying dynamic mechanisms of resistive switching.
Controllable electrical conduction at complex oxide interfaces
(2014-06-01)
Vu Thanh Tra
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Yang, Jan-Chi
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Hsieh, Ying-Hui
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Lin, Jiunn-Yuan
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Chen, Yi-Chun
Oxide interfaces have sparked considerable interest due to their fascinating physical properties and promising possibilities for next-generation nanoelectronics. Three intriguing oxide interfaces, hetero-, homo-, and tubular interfaces, will be discussed in detail in this review. First, the development and fundamental properties of classical heterointerfaces will be elaborated. Using LaAlO3/SrTiO3 as a case study, we present the most generic approach to control the two-dimensional electron conduction at the heterointerface. Secondly, several key issues based on interesting observations on ferroic homointerfaces will be addressed. Multiple controls of fascinating functionalities based on multiferroic BiFeO3 domain walls will be presented as a model system. Finally, as the most challenging task, we review a new type of complex oxide interfaces, the tubular interface. Further insights of recently emerged tubular interfaces in BiFeO3/CoFe2O4 system will be explored, which serve as one of the focal roles in developing new functional interfaces and potentially new type of nanostructures. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Deep Data Analysis of Conductive Phenomena on Complex Oxide Interfaces: Physics from Data Mining
(2014-06-01)
Strelcov, Evgheni
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Belianinov, Alexei
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Hsieh, Ying-Hui
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Jesse, Stephen
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Baddorf, Arthur P.
Spatial variability of electronic transport in BiFeO3-CoFe2O4 (BFO-CFO) self-assembled heterostructures is explored using spatially resolved first-order reversal curve (FOR) current voltage (IV) mapping. Multivariate statistical analysis of FORC-IV data classifies statistically significant behaviors and maps characteristic responses spatially. In particular, regions of grain, matrix, and grain boundary responses are clearly identified, k-Means and Bayesian demixing analysis suggest the characteristic response be separated into four components, with hysteretic-type behavior localized at the BFO-CFO tubular interfaces. The conditions under which Bayesian components allow direct physical interpretation are explored, and transport mechanisms at the grain boundaries and individual phases are analyzed. This approach conjoins multivariate statistical analysis with physics-based interpretation, actualizing a robust, universal, data-driven approach to problem solving, which can be applied to exploration of local transport and other functional phenomena in other spatially inhomogeneous systems.
Deterministic, Reversible, and Nonvolatile Low-Voltage Writing of Magnetic Domains in Epitaxial BaTiO3/Fe3O4 Heterostructure
(2018-09-01)
Zhong, Gaokuo
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An, Feng
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Bitla, Yugandhar
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Wang, Jinbin
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Zhong, Xiangli
The ability to electrically write magnetic bits is highly desirable for future magnetic memories and spintronic devices, though fully deterministic, reversible, and nonvolatile switching of magnetic moments by electric field remains elusive despite extensive research. In this work, we develop a concept to electrically switch magnetization via polarization modulated oxygen vacancies, and we demonstrate the idea in a multiferroic epitaxial heterostructure of BaTiO3/Fe3O4 fabricated by pulsed laser deposition. The piezoelectricity and ferroelectricity of BaTiO3 have been confirmed by macro- and microscale measurements, for which Fe(3)O(4 )serves as the top electrode for switching the polarization. X-ray absorption spectroscopy and X-ray magnetic circular dichroism spectra indicate a mixture of Fe2+ and Fe3+ at O-h sites and Fe3+ at T-d sites in Fe3O4, while the room-temperature magnetic domains of Fe3O4 are revealed by microscopic magnetic force microscopy measurements. It is demonstrated that the magnetic domains of Fe(3)O(4 )can be switched by not only magnetic fields but also electric fields in a deterministic, reversible, and nonvolatile manner, wherein polarization reversal by electric field modulates the oxygen vacancy distribution in Fe3O4, and thus its magnetic state, making it attractive for electrically written magnetic memories.
Electrical Modulation of the Local Conduction at Oxide Tubular Interfaces
(2013-10-01)
Hsieh, Ying-Hui
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Strelcov, Evgheni
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Liou, Jia-Ming
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Shen, Chia-Ying
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Chen, Yi-Chun
Heterointerfaces between complex oxides have sparked considerable interest due to their fascinating physical properties and their offering of new possibilities for next-generation electronic devices. The key to realize practical applications is the control through external stimuli. In this study, we take the self-assembled BiFeO3-CoFe2O4 tubular interface as a model system to demonstrate the nonvolatile electric control of the local conduction at the complex oxide tubular interface. The fundamental mechanism behind this modulation was explored based on static and dynamic conductive atomic force microscopies. We found the movement of oxygen vacancies in the BiFeO3-CoFe2O4 heterostructure is the key to drive this intriguing behavior. This study delivers a possibility in developing next-generation electronic devices.
Electrical polarization induced by atomically engineered compositional gradient in complex oxide solid solution
(2019-04-12)
Wu, Ping-Chun
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Huang, Rong
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Hsieh, Ying-Hui
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Wang, Bo
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Yen, Min
Control of inhomogeneity in materials in order to avoid unexpected effects to the system remains a challenge. In this study, we seek to engineer inhomogeneity in materials and anticipate new properties. Through precise control of composition at the atomic scale, an electrical polarization is induced in the composition-graded LaAIO(3)-SrTiO3 solid solution epitaxially deposited on NdGaO3 substrates. By tailoring the direction of compositional gradient, the relationship between structure and electrical polarization is simulated via phase-field modeling and revealed by a combination of scanning transmission electron microscopy and scanning probe microscopy. The analysis of the results indicates that the induced polarization is due to the flexoelectric effect in the compositional gradient system. The results of this study provide a new pathway for obtaining a new material genome. Moreover, by a suitable design of the new genome, that is, by using different combinations of compositional gradient geometries, local conduction can be obtained and manipulated, providing a new approach to obtain the desired properties.
Epitaxial Photostriction-Magnetostriction Coupled Self-Assembled Nanostructures
(2012-08-01)
Liu, Heng-Jui
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Chen, Long-Yi
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He, Qing
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Liang, Chen-Wei
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Chen, Yu-Ze
Self-assembled vertical nanostructures take advantage of high interface-to-volume ratio and can be used to design new functionalities by the choice of a proper combination of constituents. However, most of the studies to date have emphasized the functional controllability of the nanostructures using external electric or magnetic fields. In this study, to introduce light (or photons) as an external control parameter in a self-assembled nanostructure system, we have successfully synthesized oxide nanostructures with CoFe2O4 nanopillars embedded in a SrRuO3 matrix. The combination of photostrictive SrRuO3 and magnetostrictive CoFe2O4 in the intimately assembled nanostructures leads to a light-induced, ultrafast change in magnetization of the CoFe2O4 nanopillars. Our work demonstrates a novel concept on oxide nanostructure design and opens an alternative pathway for the explorations of diverse functionalities in heteroepitaxial self-assembled oxide nanostructures.
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
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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 of CoFe2O4/Muscovite Bimorph with Large Magnetostriction
(2017-03-01)
Liu, Heng-Jui
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Wang, Chih-Kuo
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Su, Dong
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Amrillah, Tahta
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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
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Bitla, Yugandhar
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Shin, Kwangwoo
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Yang, Tiannan
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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.
Heteroepitaxy of Fe3O4/Muscovite: A New Perspective for Flexible Spintronics
(2016-12-14)
Wu, Ping-Chun
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Chen, Ping-Fan
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Thi Hien Do
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Hsieh, Ying-Hui
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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.
In-situ TEM observation of Multilevel Storage Behavior in low power FeRAM device
(2017-04-01)
Chiu, Chung-Hua
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Huang, Chun-Wei
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Hsieh, Ying-Hui
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Chen, Jui-Yuan
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Chang, Chia-Fu
The quest for non-volatile memories has attracted tremendous attention, especially in mature ferroelectric random access memory (FeRAM) with properties of high read/write speed and low power consumption. Strain engineering of multiferroic BiFeO3 (BFO) has recently become the subject of broad research interest because of its intriguing properties. In this study, we demonstrate the switchable diode characteristics in highly strained BFO thin films. Using a unique in situ electrical transmission electron microscopy (TEM), we verify the correlation between ferroelectric resistive switching with multilevel states and polarization reversal. Structural investigation confirms that the phase transition from mixed phase to pure T-like phase, accompanying with the polarization reversal by external bias, is the origin of the multilevel states. The switchable diode with multilevel resistive switching can be explained in terms of the variation of the barrier height, governed by ferroelectric polarization and polarity of the external bias. This research model, i.e., engineering of the room inside, can offer an approach toward high-density memories.
Large Magnetoresistance in Magnetically Coupled SrRuO3-CoFe2O4 Self-Assembled Nanostructures
(2013-09-14)
Liu, Heng-Jui
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Vu-Thanh Tra
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Chen, Ying-Jiun
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Huang, Rong
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Duan, Chun-Gang
Local Conduction at the BiFeO3-CoFe2O4 Tubular Oxide Interface
(1970-01-01)
Hsieh, Ying-Hui
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Liou, Jia-Ming
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Huang, Bo-Chao
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Liang, Chen-Wei
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He, Qing
"In strongly correlated oxides, heterointerfaces, manipulating the interaction, frustration, and discontinuity of lattice, charge, orbital, and spin degrees of freedom, generate new possibilities for next generation devices. In this study, existing oxide heterostructures are examined and local conduction at the BiFeO3-CoFe2O4 vertical interface is found. In such heteronanostructures the interface cannot only be the medium for the coupling between phases, but also a new state of the matter. This study demonstrates a novel concept on for oxide interface design and opens an alternative pathway for the exploration of diverse functionalities in complex oxide interfaces."
Magnetic Mesocrystal-Assisted Magnetoresistance in Manganite
(2014-11-01)
Yang, Jan-Chi
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He, Qing
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Zhu, Yuan-Min
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Lin, Jheng-Cyuan
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Liu, Heng-Jui
Mesocrystal, a new class of crystals as compared to conventional and well-known single crystals and polycrystalline systems, has captured significant attention in the past decade. Recent studies have been focused on the advance of synthesis mechanisms as well as the potential on device applications. In order to create further opportunities upon functional mesocrystals, we fabricated a self-assembled nanocomposite composed of magnetic CoFe2O4 mesocrystal in Sr-doped manganites. This combination exhibits intriguing structural and magnetic tunabilities. Furthermore, the antiferromagnetic coupling of the mesocrystal and matrix has induced an additional magnetic perturbation to spin-polarized electrons, resulting in a significantly enhanced magnetoresistance in the nanocomposite. Our work demonstrates a new thought toward the enhancement of intrinsic functionalities assisted by mesocrystals and advanced design of novel mesocrystal-embedded nanocomposites.
Orientation-tuning in self-assembled heterostructures induced by a buffer layer
(2014)
Zhu, Yuanmin
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Liu, Pingping
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Yu, Rong
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Hsieh, Ying-Hui
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Ke, Dan
Anisotropic nano-plate structures in self-assembled perovskite-spinel thin films, BiFeO3-NiFe2O4 and BiFeO3-CoFe2O4, which were deposited on (001)(c) SrRuO3/SrTiO3 and DyScO3 substrates, respectively, have been demonstrated using transmission electron microscopy combined with strain analysis. Unlike the unitary cube-on-cube orientation relationship reported widely, the growth direction of the CoFe2O4 and NiFe2O4 plates was tuned to [011](c) while the BiFeO3 matrix kept [001](c) in both systems. In particular, a thin stress-sensitive BiFeO3 buffer layer between the spinel nanostructure and the substrate was introduced for providing a complex strain state in both film systems. The novel orientation tuning and the pattern configuration of the heterostructures are mainly attributed to the strain imposed on the films and the anisotropic ledge growth mechanism of spinels.
Permanent ferroelectric retention of BiFeO3 mesocrystal
(2016-10-26)
Hsieh, Ying-Hui
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Xue, Fei
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Yang, Tiannan
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Liu, Heng-Jui
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Zhu, Yuanmin
Non-volatile electronic devices based on magnetoelectric multiferroics have triggered new possibilities of outperforming conventional devices for applications. However, ferroelectric reliability issues, such as imprint, retention and fatigue, must be solved before the realization of practical devices. In this study, everlasting ferroelectric retention in the heteroepitaxially constrained multiferroic mesocrystal is reported, suggesting a new approach to overcome the failure of ferroelectric retention. Studied by scanning probe microscopy and transmission electron microscopy, and supported via the phase-field simulations, the key to the success of ferroelectric retention is to prevent the crystal from ferroelastic deformation during the relaxation of the spontaneous polarization in a ferroelectric nanocrystal.
Photostriction of CH3NH3PbBr3 Perovskite Crystals
(2017-09-20)
Wei, Tzu-Chiao
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Wang, Hsin-Ping
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Li, Ting-You
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Lin, Chun-Ho
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Hsieh, Ying-Hui
Organic-inorganic hybrid perovskite materials exhibit a variety of physical properties. Pronounced coupling between phonon, organic cations, and the inorganic framework suggest that these materials exhibit strong light-matter interactions. The photoinduced strain of CH3NH3PbBr3 is investigated using high-resolution and contactless in situ Raman spectroscopy. Under illumination, the material exhibits large blue shifts in its Raman spectra that indicate significant structural deformations (i.e., photostriction). From these shifts, the photostrictive coefficient of CH3NH3PbBr3 is calculated as 2.08 x 10(-8) m(2) W-1 at room temperature under visible light illumination. The significant photostriction of CH3NH3PbBr3 is attributed to a combination of the photovoltaic effect and translational symmetry loss of the molecular configuration via strong translation-rotation coupling. Unlike CH3NH3PbI3, it is noted that the photostriction of CH3NH3PbBr3 is extremely stable, demonstrating no signs of optical decay for at least 30 d. These results suggest the potential of CH3NH3PbBr3 for applications in next-generation optical micro-electromechanical devices.
Self-Assembled Ferroelectric Nanoarray
(2019-01-16)
Jiang, Jie
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Yang, Qiong
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Zhang, Yi
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Li, Xiao-Yu
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Shao, Pao-Wen
Self-assembled heteroepitaxial nanostructures have played an important role for miniaturization of electronic devices, e.g., the ultrahigh density ferroelectric memories, and cause for great concern. Our first principle calculations predict that the materials with low formation energy of the interface (E-f) tend to form matrix structure in self-assembled heteroepitaxial nanostructures, whereas those with high E-f form nanopillars. Under the guidance of the theoretical modeling, perovskite BiFeO3 (BFO) nanopillars are swimmingly grown into CeO2 matrix on single-crystal (001)-SrTiO3 (STO) substrates by pulsed laser deposition, where CeO2 has a lower formation energy of the interface (E-f) than BFO. This work provides a good paradigm for controlling self-ssembled nanostructures as well as the application of self-assembled ferroelectric nanoscale memory.
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
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Hu, Zhiwei
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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.