Browsing by Author "Huang, Rong"

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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
;
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.
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
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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.
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.
Control of the Metal-Insulator Transition at Complex Oxide Heterointerfaces through Visible Light
(2016-01-27)
Lin, Jheng-Cyuan
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Vu Thanh Tra
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Tsai, Dung-Sheng
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Lin, Tai-Te
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Huang, Po-Cheng
The coupling of the localized surface plasmon resonance of Au nanoparticles is utilized to deliver a visible-light stimulus to control conduction at the LaAlO3/SrTiO3 interface. A giant photoresponse and the controllable metal-insulator transition are characterized at this heterointerface. This study paves a new route to optical control of the functionality at the heterointerfaces.
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
;
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 integration of a nanoscale BiFeO3 phase boundary with silicon
(2016-01-01)
Liang, Wen-I
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Peng, Chun-Yen
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Huang, Rong
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Kuo, Wei-Cheng
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Huang, Yen-Chin
The successful integration of the strain-driven nanoscale phase boundary of BiFeO3 onto a silicon substrate is demonstrated with extraordinary ferroelectricity and ferromagnetism. The detailed strain history is delineated through a reciprocal space mapping technique. We have found that a distorted monoclinic phase forms prior to a tetragonal-like phase, a phenomenon which may correlates with the thermal strain induced during the growth process.
Epitaxial integration of a nanoscale BiFeO3 phase boundary with silicon
(2016)
Liang, Wen-I
;
Peng, Chun-Yen
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Huang, Rong
;
Kuo, Wei-Cheng
;
Huang, Yen-Chin
The successful integration of the strain-driven nanoscale phase boundary of BiFeO3 onto a silicon substrate is demonstrated with extraordinary ferroelectricity and ferromagnetism. The detailed strain history is delineated through a reciprocal space mapping technique. We have found that a distorted monoclinic phase forms prior to a tetragonal-like phase, a phenomenon which may correlates with the thermal strain induced during the growth process.
High Mobilities in Layered InSe Transistors with Indium-Encapsulation-Induced Surface Charge Doping
(2018-11-02)
Li, Mengjiao
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Lin, Che-Yi
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Yang, Shih-Hsien
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Chang, Yuan-Ming
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Chang, Jen-Kuei
Tunability and stability in the electrical properties of 2D semiconductors pave the way for their practical applications in logic devices. A robust layered indium selenide (InSe) field-effect transistor (FET) with superior controlled stability is demonstrated by depositing an indium (In) doping layer. The optimized InSe FETs deliver an unprecedented high electron mobility up to 3700 cm(2) V-1 s(-1) at room temperature, which can be retained with 60% after 1 month. Further insight into the evolution of the position of the Fermi level and the microscopic device structure with different In thicknesses demonstrates an enhanced electron-doping behavior at the In/InSe interface. Furthermore, the contact resistance is also improved through the In insertion between InSe and Au electrodes, which coincides with the analysis of the low-frequency noise. The carrier fluctuation is attributed to the dominance of the phonon scattering events, which agrees with the observation of the temperature-dependent mobility. Finally, the flexible functionalities of the logic-circuit applications, for instance, inverter and not-and (NAND)/not-or (NOR) gates, are determined with these surface-doping InSe FETs, which establish a paradigm for 2D-based materials to overcome the bottleneck in the development of electronic devices.
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
;
Duan, Chun-Gang
Microstructure evolution determined by the crystalline phases competition in self-assembled WO3-BiVO4 hetero nanostructures
(2018-02-28)
Song, Haili
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Li, Chao
;
Chien Nguyen Van
;
Dong, Wenxia
;
Qi, Ruijuan
A series of self-assembled WO3-BiVO4 nanostructured thin films were grown on the (001) yttria-stabilized zirconia (YSZ) substrate at the substrate temperatures of 400 degrees C, 500 degrees C, 550 degrees C, 600 degrees C, 650 degrees C and 700 degrees C by a pulsed laser deposition method. The microstructures including crystalline phases, epitaxial relationships, surface morphologies and interface structures were investigated by a combination of x-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscopy. The sample grown at 400 degrees C was amorphous due to the low driving forces for nucleation and diffusion. For the samples made at 500 degrees C, 550 degrees C and 600 degrees C, the monoclinic BiVO4 matrix epitaxially grew on YSZ, forming the matrix, where the WO3 nanopillars were embedded in with a specific orientation relationship among BiVO4, WO3 and YSZ. However, in thin films deposited at 650 degrees C and 700 degrees C, the WO3 grains randomly grew on the YSZ substrate, which dominated the microstructures of the resultant thin films. Quantitative analyses of the microstructures revealed that the lateral grain sizes of BiVO4 and WO3 increased and the volume fraction of BiVO4 in the thin films decreased with the increase of the deposition temperature. A three-regime growth mechanism of the WO3-BiVO4 composite thin film was proposed based on the growth dynamics determined by the competition between BiVO4 and WO3. Published by AIP Publishing.
Microstructure evolution with composition ratio in self-assembled WO3-BiVO4 hetero nanostructures for water splitting
(2017-07-01)
Song, Haili
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Li, Chao
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Chien Nguyen Van
;
Liu, Heng-Jui
;
Qi, Ruijuan
A series of self-assembled WO3-BiVO4 nanostructured thin films with 17, 25, 50, 67, and 100 mol% WO3 were grown on the (001) yttria-stabilized zirconia (YSZ) substrate by pulsed laser deposition method. The microstructures including crystalline phases, epitaxial relationship, interface structures, and chemical composition distributions were investigated by a combination of various electron microscopy techniques including scanning electron microscopy, transmission electron microscopy, and X-ray energy dispersive spectroscopy. The monoclinic BiVO4 formed the matrix, in which WO3 nanopillars were embedded with specific epitaxial relationships. In BiVO4-rich sample, orthorhombic Bi2WO6 was formed. However, metastable hexagonal WO3 phase and orthorhombic WO3 phase coexisted in other composite samples. The thin amorphous layer at the film/substrate interface indicated that the mismatch strain between films and substrate is released. The hydrostatic tensile strain due to thermal expansion mismatch between BiVO4 and WO3 as well as the diffusion of Bi into the WO3 stabilized the metastable h-WO3. A WO3-BiVO4 pseudobinary phase diagram was proposed based on the magnitude of the thermal expansion mismatch and the distance of Bi diffusion, which can be applied to design the microstructures of WO3-BiVO4 heterojunctions and optimize their photoelectrochemical properties.
Proton-Mediated Phase Control in Flexible and Transparent Mott Transistors
(1970-01-01)
Deng, Xing
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Zhao, Yi-Feng
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Zhong, Ni
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Yue, Fang-Yu
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Huang, Rong
To meet the development of wearable and energy-efficient flexible electronics, multifunctional oxide film on soft substrate and its versatile phase control are in demand. Here, flexible VO2 film is directly deposited on mica via van der Waals epitaxy, exhibiting pronounced metal-insulator (MI) transition and infrared (IR) switching properties. Using a rubbery solid ionic gel as gate insulator, a fully flexible and transparent VO2-channel Mott transistor is successfully demonstrated. The prototype Mott transistor processes excellent mechanical flexibility and giant on/off current ratio of approximate to 10(5)% even at room temperature. Highly reversible suppression of MI transition is realized by applying small gate voltages and the nonvolatile phase modulation suggests an electrochemical reaction mechanism. X-ray diffraction and secondary-ion mass spectroscopy analyses, together with theoretical calculation, confirm that electrically controlled phase transformation is mainly caused by reversible and nonvolatile proton (H+) doping into VO2 lattices. Significant modulation of IR transmittance (>40%) is observed in the VO2 Mott transistor, which is attributed to electrically driven phase transition between insulating VO2 and metallic HxVO2 phases. The flexible and transparent Mott transistor provides a good platform for proton-mediated Mottronics and realizes novel electric control of optical characteristics, showing a promising application for flexible energy-saving smart windows.
Role of indium tin oxide electrode on the microstructure of self-assembled WO3-BiVO4 hetero nanostructures
(2017-11-07)
Song, Haili
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Li, Chao
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Chien Nguyen Van
;
Dong, Wenxia
;
Qi, Ruijuan
Self-assembled WO3-BiVO4 nanostructured thin films were grown on a (001) yttrium stabilized zirconia (YSZ) substrate by the pulsed laser deposition method with and without the indium tin oxide (ITO) bottom electrode. Their microstructures including surface morphologies, crystalline phases, epitaxial relationships, interface structures, and composition distributions were investigated by scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray energy dispersive spectroscopy. In both samples, WO3 formed nanopillars embedded into the monoclinic BiVO4 matrix with specific orientation relationships. In the sample with the ITO bottom electrode, an atomically sharp BiVO4/ITO interface was formed and the orthorhombic WO3 nanopillars were grown on a relaxed BiVO4 buffer layer with a mixed orthorhombic and hexagonal WO3 transition layer. In contrast, a thin amorphous layer appears at the interfaces between the thin film and the YSZ substrate in the sample without the ITO electrode. In addition, orthorhombic Bi2WO6 lamellar nanopillars were formed between WO3 and BiVO4 due to interdiffusion. Such a WO3-Bi2WO6-BiVO4 double heterojunction photoanode may promote the photo-generated charge separation and further improve the photoelectrochemical water splitting properties. Published by AIP Publishing.
The preparation, and structural and multiferroic properties of B-site ordered double-perovskite Bi2FeMnO6
(2017-06-14)
Sun, Lin
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Fang, Yue-Wen
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He, Jun
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Zhang, Yuanyuan
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Qi, Ruijuan
We report the structural, magnetic, and ferroelectric properties of double-perovskite Bi2FeMnO6 in which Fe3+ and Mn3+ cations are present with alternative ordering along the [111] direction. High-flux synchrotron X-ray diffraction and high resolution transmission electron microscopy show that the pseudo-cubic lattice of Bi2FeMnO6 consists of alternatively corner-shared octahedra of FeO6 and MnO6. In the highly ordered Bi2FeMnO6 thin films, the unusual spin-glassy magnetic state is observed below 18 K by a superconducting quantum interference device, and this is ascribed to the magnetic frustration at the [111] Fe3+ and Mn3+ planes as indicated by X-ray magnetic circular dichroism measurements. Combining with the orbital model analysis based on Goodenough-Kanamori-Anderson rules, first-principles calculations and Monte Carlo simulations suggest that magnetic frustration is dominated by the long-range second nearest neighboring antiferromagnetic interactions of Fe3+-Fe3+ and Mn3+-Mn3+ and leads to the surprisingly weak magnetism. On the other hand, robust room-temperature ferroelectricity in Bi2FeMnO6 films is confirmed by piezoelectric force microscopy through electrically switching the polarization state and the ferroelectric retention.
Thickness dependence of transport behaviors in SrRuO3 /SrTiO3 superlattices
(2020-01-03)
Wu, Ping-Chun
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Song, Haili
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Yuan, Ye
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Feng, Bin
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Ikuhara, Yuichi
Ultrathin oxide films have attracted considerable attention due to the potential for the integration of next-generation devices. However, the transport behaviors of the ultrathin oxide films are yet to be explored due to the high resistance caused by the strong influence of the interface and substrates. In this paper, an attempt is made to engineer the transport behaviors in ultrathin oxides. To exclude the high-resistance issue, conductive SrRuO3 with thickness down to two unit cells is embedded in insulating SrTiO3 in the form of superlattices. With precise control of the thickness in each layer, the transport behaviors, as well as the anomalous Hall effects, in SrRuO3 can be systematically manipulated. The analysis indicates that the diversity of the anomalous Hall effects is attributed to the change of Berry curvatures. The results give a pathway to the control of physical properties in ultrathin oxide systems by thickness engineering.
WO3 mesocrystal-assisted photoelectrochemical activity of BiVO4
(2017-03-01)
Chien Nguyen Van
;
Thi Hien Do
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Chen, Jhih-Wei
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Tzeng, Wen-Yen
;
Tsai, Kai-An
Self- assembled nanocomposites have gained much attention over the past decade due to their intriguing properties and functionalities. In this work, we developed a self-assembled nanocomposite photoanode composed of an epitaxial BiVO4 matrix embedded with WO3 mesocrystals for photoelectrochemical (PEC) applications in the visible- light regime. The orientation of the crystal facet and interface provides a superior template to understand the intimate contact between the two constituent phases. We demonstrate that the interfacial coupling of the mesocrystal and matrix improves the separation of photoexcited carriers and the properties of charge transfer, resulting in a greatly enhanced PEC performance compared with their parent compounds. The current study demonstrates that the utilization of the interface-to-volume ratio to optimize charge interactions in the nanocomposite is essential for the advanced design of novel mesocrystal-embedded nanocomposite photoelectrodes.