Browsing by Author "Chu, Ying-Hao"

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A Fabrication and Measurement Method for a Flexible Ferroelectric Element Based on Van Der Waals Heteroepitaxy
(2018-04-01)
Jiang, Jie
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Bitla, Yugandhar
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Peng, Qiang-xiang
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Zhou, Yi-Chun
;
Chu, Ying-Hao
Flexible non-volatile memories have received much attention as they are applicable for portable smart electronic device in the future, relying on high-density data storage and low-power consumption capabilities. However, the high-quality oxide based nonvolatile memory on flexible substrates is often constrained by the material characteristics and the inevitable high-temperature fabrication process. In this paper, a protocol is proposed to directly grow an epitaxial yet flexible lead zirconium titanate memory element on muscovite mica. The versatile deposition technique and measurement method enable the fabrication of flexible yet single-crystalline non-volatile memory elements necessary for the next generation of smart devices.
A gate-free monolayer WSe2 pn diode
(2018-08-07)
Chen, Jhih-Wei
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Lo, Shun-Tsung
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Ho, Sheng-Chin
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Wong, Sheng-Shong
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Vu, Thi-Hai-Yen
Interest in bringing p- and n-type monolayer semiconducting transition metal dichalcogenides (TMD) into contact to form rectifying pn diode has thrived since it is crucial to control the electrical properties in two-dimensional (2D) electronic and optoelectronic devices. Usually this involves vertically stacking different TMDs with pn heterojunction or, laterally manipulating carrier density by gate biasing. Here, by utilizing a locally reversed ferroelectric polarization, we laterally manipulate the carrier density and created a WSe2 pn homojunction on the supporting ferroelectric BiFeO3 substrate. This non-volatile WSe2 pn homojunction is demonstrated with optical and scanning probe methods and scanning photoelectron microspectroscopy. A homo-interface is a direct manifestation of our WSe2 pn diode, which can be quantitatively understood as a clear rectifying behavior. The non-volatile confinement of carriers and associated gate-free pn homojunction can be an addition to the 2D electron-photon toolbox and pave the way to develop laterally 2D electronics and photonics.
A Metal-Insulator Transition of the Buried MnO2 Monolayer in Complex Oxide Heterostructure
(2016-11-02)
Liu, Heng-Jui
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Lin, Jheng-Cyuan
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Fang, Yue-Wen
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Wang, Jing-Ching
;
Huang, Bo-Chao
A novel artificially created MnO2 monolayer system is demonstrated in atomically controlled epitaxial perovskite heterostructures. With careful design of different electrostatic boundary conditions, a magnetic transition as well as a metal-insulator transition of the MnO2 monolayer is unveiled, providing a fundamental understanding of dimensionality-confined strongly correlated electron systems and a direction to design new electronic devices.
A Nanostructuring Method to Decouple Electrical and Thermal Transport through the Formation of Electrically Triggered Conductive Nanofilaments
(2018-07-12)
Retamal, Jose Ramon Duran
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Kang, Chen-Fang
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Lien, Der-Hsien
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Kuo, Wei-Cheng
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Juang, Zhen-Yu
Transforming thermal energy into electric energy and vice versa needs the decoupling of electrical transport from thermal transport. An innovative strategy is proposed by forming/disrupting electrically triggered conductive nanofilaments within semiconducting thin films to switch thermoelectric properties between two states without further material modification and manufacturing processes. It can also controllably adjust the degree of decoupling, providing a potential resolution and performance adjustability for heat/coldness control or power consumption reduction on demand.
A Strain-Driven Antiferroelectric-to-Ferroelectric Phase Transition in La-Doped BiFeO3 Thin Films on Si
(2017-09-01)
Chen, Deyang
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Nelson, Christopher T.
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Zhu, Xiaohong
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Serrao, Claudy R.
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Clarkson, James D.
A strain-driven orthorhombic (O) to rhombohedral (R) phase transition is reported in La-doped BiFeO3 thin films on silicon substrates. Biaxial compressive epitaxial strain is found to stabilize the rhombohedral phase at La concentrations beyond the morphotropic phase boundary (MPB). By tailoring the residual strain with film thickness, we demonstrate a mixed O/R phase structure consisting of O phase domains measuring tens of nanometers wide within a predominant R phase matrix. A combination of piezoresponse force microscopy (PFM), transmission electron microscopy (TEM), polarization electric field hysteresis loop (P-E loop), and polarization maps reveal that the O-R structural change is an antiferroelectric to ferroelectric (AFE-FE) phase transition. Using scanning transmission electron microscopy (STEM), an atomically sharp O/R MPB is observed. Moreover, X-ray absorption spectra (XAS) and X-ray linear dichroism (XLD) measurements reveal a change in the antiferromagnetic axis orientation from out of plane (R-phaSe) to in plane (O-p hase). These findings provide direct evidence of spin-charge-lattice coupling in La-doped BiFeO3 thin films. Furthermore, this study opens a new pathway to drive the AFE-FE O-R phase transition and provides a route to study the O/R MPB in these films.
Anisotropic superconductivity induced by periodic multiferroic domain patterns
(2019-12-06)
Huang, Yen-Lin
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Huang, Bo-Chao
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Wang, Yan-Ting
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Xue, Fei
;
Lin, Jheng-Cyuan
The competition between order parameters, such as ferroelectricity, ferromagnetism, and superconductivity, is one of the most fascinating topics in condensed matter physics. Here, we report intriguing anisotropic superconductivity in YBa2Cu3O7-x films induced by a multiferroic, BiFeO3, with periodic domain patterns. The anisotropic superconductivity was investigated by transport measurements and supported by phase-field simulations, and then the detailed local electronic structures were revealed by cross-sectional scanning tunneling microscopy. We found that the oxygen redistribution in YBa2Cu3O7-x modulated by the ferroelectric polarization in BiFeO3 was the key mechanism driving this anisotropic superconductivity. The presented heteroarchitecture of a high-temperature superconductor and a domain-engineered multiferroic provides a new approach to tune superconductivity and offers potential advantages for the design of future multifunctional devices.
Anomalous Electronic Anisotropy Triggered by Ferroelastic Coupling in Multiferroic Heterostructures
(2016-02-03)
Ju, Changcheng
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Yang, Jan-Chi
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Luo, Cheng
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Shafer, Padraic
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Liu, Heng-Jui
Antiferromagnetic Interfacial Coupling and Giant Magnetic Hysteresis in La0.5Ca0.5MnO3-SrRuO3 Superlattices
(2018-10-01)
Kumar, Vandrangi Suresh
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Zhou, Shu-Liang
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Liu, Rui-Rui
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Zhu, Yuan-Min
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Liu, Heng-Jui
Superlattices are of great importance due to their potential as new materials genome to synthesize new functional materials. Thus, tuning of the ground state of superlattices is crucial to further control their physical properties. In this study, superlattices (SLs) consisting of alternating layers of SrRuO3 (SRO) (5 nm) and La0.5Ca0.5MnO3 (LCMO) (5 nm) are epitaxially grown on SrTiO3 (STO) and LaAlO3 (LAO) substrates with 10-unit-cell periods. A variation in the substrate-induced-strain for this choice of SLs triggers observation of remarkable properties, such as magnetic anisotropy and large magnetic hysteresis. The strain states experienced by LCMO and SRO in these SLs result in strong ferromagnetic interlayer coupling and weak antiferromagnetic interlayer coupling at low temperatures in SLs of LCMO-SRO/STO and a strong antiferromagnetic interlayer coupling in SLs of LCMO-SRO/LAO. Besides, a large magnetic hysteresis resulting from the predominant magnetic anisotropy of SRO together with the strength of magnetic coupling is observed in SLs of LCMO-SRO/LAO along the out-of-plane direction of the LAO substrate. These four different magnetic behaviors along four different directions of substrate orientations are interpreted in terms of preferential orbital occupation and competing magnetic exchange coupling together with magnetic anisotropy. This study demonstrates the subtleties in controlling the strength of magnetic coupling at the interface and stands as a model system to realize fascinating magnetic phenomena in layer-by-layer hetero-epitaxial oxide films.
Atomic Heterointerfaces and Electrical Transportation Properties in Self-Assembled LaNiO3-NiO Heteroepitaxy
(2018-04-09)
Zhu, Yuan Min
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Thi Hien Do
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Vu Thanh Tra
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Yu, Rong
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Chu, Ying-Hao
Vertical nanostructure heteroepitaxy opens new opportunities for designing next-generation electronic devices due to the enthralling multifunction combinations and the abundant heterointerfaces manipulated effects. In this study, self-assembled heteroepitaxial thin films, vertically aligned metallic LaNiO3 (LNO) and semiconducting NiO with diverse heterointerfaces, are created and systematically investigated by advanced transmission electron microscopy. With the increase of LaNiO3 content, the LaNiO3 phases present as isolated islands encircled by the connected NiO nanoplates and eventually become the continuous matrix with embedded NiO nanopillars. The atomic heterointerface between NiO and LaNiO3 phases is determined to be [NiO2-LaO](LaNiO3)-LaO-[NiO](NiO), in which an extra La-O layer is enriched at the heterointerface. Besides, the formation mechanism of the heterointerface and antiphase boundaries observed in LaNiO3 phase is discussed. The electrical transport properties at room temperature can be tuned gradually by changing the volume ratio of constituents. The correlation among the insulator-to-metal transition, the carrier types associated with transport behaviors, and the heterostructure evolutions are explored. This study offers a desirable platform to design new multifunctional electronic devices based on the oxide heterojunctions.
Atomic mechanism of polarization-controlled surface reconstruction in ferroelectric thin films
(2016-04-01)
Gao, Peng
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Liu, Heng-Jui
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Huang, Yen-Lin
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Chu, Ying-Hao
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Ishikawa, Ryo
At the ferroelectric surface, the broken translational symmetry induced bound charge should significantly alter the local atomic configurations. Experimentally revealing the atomic structure of ferroelectric surface, however, is very challenging due to the strong spatial variety between nano-sized domains, and strong interactions between the polarization and other structural parameters. Here, we study surface structures of Pb(Zr0.2Ti0.8)O-3 thin film by using the annular bright-field imaging. We find that six atomic layers with suppressed polarization and a charged 180 degrees domain wall are at negatively poled surfaces, no reconstruction exists at positively poled surfaces, and seven atomic layers with suppressed polarization and a charged 90 degrees domain wall exist at nominally neutral surfaces in ferroelastic domains. Our results provide critical insights into engineering ferroelectric thin films, fine grain ceramics and surface chemistry devices. The state-of-the-art methodology demonstrated here can greatly advance our understanding of surface science for oxides.
Atomic Visualization of the Phase Transition in Highly Strained BiFeO3 Thin Films with Excellent Pyroelectric Response
(2015-10-01)
Chiu, Chung-Hua
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Liang, Wen-I
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Huang, Chun-Wei
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Chen, Jul-Yuan
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Liu, Yun-Ya
Great attention is paid to that stimulus response of materials, which is a prerequisite for energy harvesting applications. Driven by advances in nanotechnology, the atomic motions, involved in phase transitions and associated with stimulus responses, require detailed investigation on the nanoscale. Recently, strain engineering of BiFeO3 (BFO) has become the subject of broad research interest due to its promising potential in energy conversion applications, such as piezoelectric, pyroelectric and shape memory effect (SME) devices. In this study, an excellent pyroelectric response is associated with reversible phase transitions in mixed-phase BFO films using thermal stimuli. Using an in situ high-resolution transmission electron microscope (HRTEM), we observed that phase transition between rhombohedral-like (R-like) and tetragonal-like (1-like) BFO involved the migration of the phase boundary, which is a prerequisite for the growth of the T-like phase and requires an intermediate phase. Moreover, the origin of the phase transition is attributed to competition between thermodynamic stability and substrate-induced strain, as suggested by phase-field simulations. The results provide a fundamental understanding of the atomic processes that underlie the stimulus response of the strained BFO films and demonstrate the potential of this extraordinary material for novel energy harvesting applications. (C) 2015 Elsevier Ltd. All rights reserved.
Atomic-Scale Evolution of Local Electronic Structure Across Multiferroic Domain Walls
(2011-04-05)
Chiu, Ya-Ping
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Chen, Yu-Ting
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Huang, Bo-Chao
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Shih, Min-Chuan
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Yang, Jan-Chi
Direct evidence of the electronic configurations across domain walls in BiFeO(3) is quantitatively characterized by cross-sectional scanning tunneling microscopy. Atomic-scale band evolution and the asymmetrically built-in potential barrier at domain boundaries are demonstrated. The 109 degrees domain walls register a remarkable decrease in the bandgap, suggesting a new route to control the local conducting channels within 2 nm.
Atomic-scale mechanism of internal structural relaxation screening at polar interfaces
(2018-05-25)
Li, Mingqiang
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Cheng, Xiaoxing
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Li, Ning
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Liu, Heng-Jui
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Huang, Yen-Lin
The effective screening of the polarization bound charge is a prerequisite to stabilize the ferroelectricity in ferroelectric thin films. Here, by combining annular bright field imaging and electron energy-loss spectroscopy (EELS) in an aberration-corrected scanning transmission electron microscope with phase-field simulations, we investigate the screening mechanism by quantitatively measuring the structural relaxation at Pb(Zr0.2Ti0.8)O-3/SrTiO3 interfaces. We find that the thickness of the interfacial layer is similar to 3.5 unit cells (similar to 1.4 nm) in a domain with upward polarization and similar to 5.5 unit cells (similar to 2.2 nm) in a domain with downward polarization. Phase-field simulations, an EELS analysis, and a lattice parameter analysis verify the existence of interfacial oxygen vacancies accounting for the narrower interfacial layer in the domain with upward polarization. Our study indicates the internal structural relaxation at the interface is the dominant mechanism for the polarization charge screening for ferroelectric films grown on insulating substrates and has implications for our understanding of domain switching in ferroelectric devices.
Atomic-Scale Mechanisms of Defect-Induced Retention Failure in Ferroelectrics
(2017-06-01)
Li, Linze
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Zhang, Yi
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Xie, Lin
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Jokisaar, Jacob R.
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Beekman, Christianne
The ability to switch the ferroelectric polarization using an electric field makes ferroelectrics attractive for application in nanodevices such as high-density memories. One of the major challenges impeding this application, however, has been known as retention failure, which is a spontaneous process of polarization back-switching that can lead to data loss. This process is generally thought to be caused by the domain instability arising from interface boundary conditions and countered by defects, which can pin the domain wall and impede the back-switching. Here, using in situ transmission electron microscopy and atomic-scale scanning transmission electron microscopy, we show that the polarization retention failure can be induced by commonly observed nanoscale impurity defects in BiFeO3 thin films. The interaction between polarization and the defects can also lead to the stabilization of novel functional nanodomains with mixed-phase structures and head-to-head polarization configurations. Thus, defect engineering provides a new route for tuning properties of ferroelectric nanosystems.
Atomic-Scale Visualization of Polarization Pinning and Relaxation at Coherent BiFeO3/LaAlO3 Interfaces
(2014-02-01)
Huang, Rong
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Ding, Hang-Chen
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Liang, Wen-I
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Gao, Yong-Chao
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Tang, Xiao-Dong
Complex oxide heterointerfaces, which play host to an incredible variety of interface physical phenomena, are of great current interest in introducing new functionalities to systems. Here, coherent super-tetragonal BiFeO3/LaAlO3 and rhombohedral BiFeO3/LaAlO3 heterointerfaces are investigated by using a combination of high-angle annular dark-field (HAADF) imaging and annular bright-field (ABF) imaging in a spherical aberration (Cs) corrected scanning transmission electron microscope (STEM), and first-principles calculations. The complicated ferroelectric polarization pinning and relaxation that occurs at both interfaces is revealed with atomic resolution, with a dramatic change in structure of BiFeO3, from cubic to super-tetragonal-like. The results enable a detailed explanation to be given of how non-bulk phase structures are stabilized in thin films of this material.
Atomically Resolved Mapping of Polarization and Electric Fields Across Ferroelectric/Oxide Interfaces by Z-contrast Imaging
(2011-06-03)
Chang, Hye Jung
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Kalinin, Sergei V.
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Morozovska, Anna N.
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Huijben, Mark
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Chu, Ying-Hao
Direct atomic displacement mapping at ferroelectric interfaces by aberration corrected scanning transmission electron microscopy (STEM) (a-STEM image, b-corresponding displacement profile) is combined with the Landau-Ginsburg-Devonshire theory to obtain the complete interface electrostatics in real space, including separate estimates for the polarization and intrinsic interface charge contributions.
BiFeO3 Thin Films: A Playground for Exploring Electric-Field Control of Multifunctionalities
(2015-01-01)
Yang, Jan-Chi
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He, Qing
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Yu, Pu
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Chu, Ying-Hao
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材料科學與工程學系
A promising approach to the next generation of low-power, functional, and green nanoelectronics relies on advances in the electric-field control of lattice, charge, orbital, and spin degrees of freedom in novel materials. The possibility of electric-field control of these multiple materials functionalities offers interesting options across a range of modern technologies, including information communication, computing processes, data storage, active components, and functional electronics. This article reviews electric-field control and modulation of various degrees of freedom through the medium of multiferroic BiFeO3. Coexisting order parameters and inherent couplings in this materials system form a potent playground, enabling direct and indirect manipulation to obtain intriguing properties and functionalities with an electric stimulus. An in-depth understanding of those electrically controlled phenomena and breakthroughs is highlighted, paving a new route toward multifunctional nanoelectronics. This article concludes with a brief discussion on foreseeable challenges as well as future directions.
Complex Oxide-Noble Metal Conjugated Nanoparticles
(2013-04-11)
Guo, Jun-Ling
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Chiou, Yao-De
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Liang, Wen-I
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Liu, Heng-Jui
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Chen, Ying-Jiun
Hybrid nanoparticles (NPs) composed of multiple components offer new opportunities for next-generation materials. In this study, a paradigm for the noble metal/ternary complex oxide hybrid NPs is reported by adopting pulsed laser ablation in liquids. As model hybrids, gold-spinel heterodimer (Au-CoFe2O4) and gold-pervoskite heterodimer (Au-SrTiO3) NPs are investigated. This work has demonstrated the diverse playgroup of NP conjugation enlarged by complex oxides.
Complex strain evolution of polar and magnetic order in multiferroic BiFeO3 thin films
(2018-09-21)
Chen, Zuhuang
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Chen, Zhanghui
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Kuo, Chang-Yang
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Tang, Yunlong
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Dedon, Liv R.
Electric-field control of magnetism requires deterministic control of the magnetic order and understanding of the magnetoelectric coupling in multiferroics like BiFeO3 and EuTiO3. Despite this critical need, there are few studies on the strain evolution of magnetic order in BiFeO3 films. Here, in (110)-oriented BiFeO3 films, we reveal that while the polarization structure remains relatively unaffected, strain can continuously tune the orientation of the antiferromagnetic-spin axis across a wide angular space, resulting in an unexpected deviation of the classical perpendicular relationship between the antiferromagnetic axis and the polarization. Calculations suggest that this evolution arises from a competition between the Dzyaloshinskii-Moriya interaction and single-ion anisotropy wherein the former dominates at small strains and the two are comparable at large strains. Finally, strong coupling between the BiFeO3 and the ferromagnet Co0.9Fe0.1 exists such that the magnetic anisotropy of the ferromagnet can be effectively controlled by engineering the orientation of the antiferromagnetic-spin axis.
Concurrent transition of ferroelectric and magnetic ordering near room temperature
(2011-11-01)
Ko, Kyung-Tae
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Jung, Min Hwa
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He, Qing
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Lee, Jin Hong
;
Woo, Chang Su
Strong spin-lattice coupling in condensed matter gives rise to intriguing physical phenomena such as colossal magnetoresistance and giant magnetoelectric effects. The phenomenological hallmark of such a strong spin-lattice coupling is the manifestation of a large anomaly in the crystal structure at the magnetic transition temperature. Here we report that the magnetic Neel temperature of the multiferroic compound BiFeO3 is suppressed to around room temperature by heteroepitaxial misfit strain. Remarkably, the ferroelectric state undergoes a first-order transition to another ferroelectric state simultaneously with the magnetic transition temperature. Our findings provide a unique example of a concurrent magnetic and ferroelectric transition at the same temperature among proper ferroelectrics, taking a step toward room temperature magnetoelectric applications.