Browsing by Author "Yang, Jan-Chi"

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A Fast Route Towards Freestanding Single-Crystalline Oxide Thin Films by Using YBa(2)Cu(3)O(7-x)as a Sacrificial Layer
(2020-08-28)
Chang, Yao-Wen
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Wu, Ping-Chun
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Yi, Jhih-Bang
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Liu, Yu-Chen
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Chou, Yi
Researchers have long been seeking multifunctional materials that can be adopted for next-generation nanoelectronics, and which, hopefully, are compatible with current semiconductor processing for further integration. Along this vein, complex oxides have gained numerous attention due to their versatile functionalities. Despite the fact that unbounded potential of complex oxides has been examined over the past years, one of the major challenges lies in the direct integration of these functional oxides onto existing devices or targeted substrates that are inherently incompatible in terms of oxide growth. To fulfill this goal, freestanding processes have been proposed, in which wet etching of inserted sacrificial layers is regarded as one of the most efficient ways to obtain epitaxial high-quality thin films. In this study, we propose using an alternative oxide, YBa2Cu3O7(YCBO), as a sacrificial layer, which can be easily dissolved in light hydrochloric acid in a more efficient way, while protecting selected complex oxides intact. The high epitaxial quality of the selected complex oxide before and after freestanding process using YBCO as a sacrificial layer is comprehensively studied via a combination of atomic force microscopy, X-ray diffraction, transmission electron microscopy, and electrical transports. This approach enables direct integration of complex oxides with arbitrary substrates and devices and is expected to offer a faster route towards the development of low-dimensional quantum materials.
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.
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
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.
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.
Conductive tail-to-tail domain walls in epitaxial BiFeO3 films
(2018-08-20)
Jin, Yaming
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Xiao, Shuyu
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Yang, Jan-Chi
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Zhang, Junting
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Lu, Xiaomei
The complex conductive behavior of ferroelectric domain walls is attracting more and more attention for their potential application as an independent nanoelectronic component. For the (001) epitaxial BiFeO3 films, we find that the domain wall conductivity varies among 71 degrees domain walls, with tail-to-tail (T-T) domain walls more conductive than head-to-head (H-H) and head-to-tail (H-T) ones. Furthermore, it is observed that most of the conductive areas are composed of two parallel lines around the T-T domain walls. These experimental results can be well simulated by our theoretical model based on the polarization configuration and a tunneling mechanism. Our work will help to understand the mechanism of domain wall conductance in ferroelectric materials and further promote the usage of domain walls in advanced nano-devices. Published by AIP Publishing.
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
Deterministic optical control of room temperature multiferroicity in BiFeO3 thin films
(2019-06-01)
Liou, Yi-De
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Chiu, Yu-You
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Hart, Ryan Thomas
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Kuo, Chang-Yang
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Huang, Yen-Lin
Controlling ferroic orders (ferroelectricity, ferromagnetism and ferroelasticity) by optical methods is a significant challenge due to the large mismatch in energy scales between the order parameter coupling strengths and the incident photons. Here, we demonstrate an approach to manipulate multiple ferroic orders in an epitaxial mixed-phase BiFeO3 thin film at ambient temperature via laser illumination. Phase-field simulations indicate that a light-driven flexoelectric effect allows the targeted formation of ordered domains. We also achieved precise sequential laser writing and erasure of different domain patterns, which demonstrates a deterministic optical control of multiferroicity at room temperature. As ferroic orders directly influence susceptibility and conductivity in complex materials, our results not only shed light on the optical control of multiple functionalities, but also suggest possible developments for optoelectronics and related applications.
Domain relaxation dynamics in epitaxial BiFeO3 films: Role of surface charges
(2012-09-01)
Chen, Yi-Chun
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Ko, Cheng-Hung
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Huang, Yen-Chin
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Yang, Jan-Chi
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Chu, Ying-Hao
The thermodynamic parameters of domain relaxation process in the absence of external electric fields are related to the intrinsic electrostatic and stress/strain conditions inside the materials, such as the states at surface, states at interface with the electrode, and the atomic defects in the bulk. In order to perform systematical studies of these intrinsic effects, we investigated domain relaxation in a monodomain environment, which was obtained in strained epitaxial BiFeO3 (BFO)(111) films. Without as-grown domain walls and grain boundaries, the epitaxial BFO (111) film provided an ideal system for the dynamic observation of 180-degree domain wall motion. Nano-domains were initially created by writing voltage pulses under the tip of a scanning force microscope and then relaxed through time. The downward polarized domains exhibited much better retention behaviors than the upward domains. A two-step backswitching process was observed, and the behaviors varied with the initial domain sizes. Surface potential measurement showed the dissipation of surface screen charges with time, which was strongly coupled with the 1st step relaxation. The asymmetry behaviors for upward and downward backswitchings, and the two-stage relaxation processes can be explained by the mobile vacancies and the redistribution of surface charges. This study provides the basic understanding of the role of surface charges during the ferroelectric domain relaxation. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4746077]
Dry lubrication of friction on ferroelectric BiFeO3 film
(2018-11-01)
Yang, Chunbin
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Xiao, Shuyu
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Yang, Jan-Chi
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Lu, Xiaomei
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Chu, Ying-Hao
Epitaxial BiFeO3 film shows excellent ferroelectric properties, which is not only studied extensively in magnetoelectric modulation but also shows good tribological performance. In our experiment, we find that the surface of BiFeO3 film can be more lubricant with the application of bias voltages or stress through the AFM probe with a reduction (up to similar to 40%) of the friction between the sample and the probe tip. Based on the Prandtl-Tomlinson model, the mechanism of the dry lubrication on BiFeO3 film originates from the reduction of van der Waals force between sample surface and probe tip. The findings here could be advantageously used in promoting the performance and durability of Micro/Nano Electromechanical devices based on ferroelectric thin films.
Electric Field Writing of Ferroelectric Nano-Domains Near 71 degrees Domain Walls with Switchable Interfacial Conductivity
(2018-08-01)
Yang, Shuzhen
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Peng, Ren-Ci
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He, Qing
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Huang, Yen-Lin
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Huang, Yijing
Conducting ferroelectric domain walls attract a wide range of research interest due to their promising applications in nanoelectronics. In this study, we reveal an unexpected enhanced conductivity near the well-aligned 71 degrees nonpolar domain walls in BiFeO3. Such an interfacial conductivity is induced by the creation of up-polarized nano-domains near the 71 degrees domain walls, as revealed by the combination of the piezo-response force microscopy (PFM) and conducting atomic force microscopy (c-AFM) imaging techniques, as well as phase-field simulations. The upward polarized domains are suggested to lower the Schottky barrier at the interface between the tip and sample surface, and then give rise to the enhanced interfacial conductivity. The result provides a new strategy to tune the local conductance in ferroelectric materials and opens up new opportunities to design novel nanoelectronic devices.
Electrically enhanced magnetization in highly strained BiFeO3 films
(2016-05)
Yang, Jan-Chi
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Kuo, Chang-Yang
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Liu, Heng-Jui
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Ding, Hang-Chen
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Duan, Chun-Gang
The control of magnetism via an electric field has attracted substantial attention because of potential applications in magnetoelectronics, spintronics and high-frequency devices. In this study, we demonstrate a new approach to enhance and control the magnetization of multiferroic thin film by an electric stimulus. First, to reduce the strength of the antiferromagnetic superexchange interaction in BiFeO3, we applied strain engineering to stabilize a highly strained phase. Second, the direction of the ferroelectric polarization was controlled by an electric field to enhance the Dzyaloshinskii-Moriya interaction in the highly strained BiFeO3 phase. Because of the magnetoelectric coupling in BiFeO3, a strong correlation between the modulated ferroelectricity and enhanced magnetization was observed. The tunability of this strong correlation by an electric field provides an intriguing route to control ferromagnetism in a single-phase multiferroic.
Enhanced Magnetocaloric Effect Driven by Interfacial Magnetic Coupling in Self-Assembled Mn3O4-La0.7Sr0.3MnO3 Nanocomposites
(2015-12-09)
Vandrangi, Suresh K.
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Yang, Jan-Chi
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Zhu, Yuan-Min
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Chin, Yi-Ying
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Lin, Hong-Ji
Magnetic refrigeration, resulting from the magneto caloric effect of a material around the magnetic phase-transition temperature, is a topic of great interest as it is considered to be an alternate energy solution to conventional vapor-compression refrigeration. The viability of a magnetic refrigeration system for magnetic cooling can be tested by exploiting materials in various forms, from bulk to nanostrucutres. In this study, magnetocaloric properties of self-assembled Mn3O4-La0.7Sr0.3MnO3 nanocomposites, with varying doping concentrations of Mn3O4 in the form of nanocrystals embedded in the La0.7Sr0.3MnO3 matrix, are investigated. The temperatures corresponding to the paramagnetic-to-ferromagnetic transitions are higher, and the values of change in magnetic entropy under a magnetic field of 2 T show an enhancement (highest being similar to 130%) for the nanocomposites with low doping concentrations of Mn3O4, compared to that of pure La0.7Sr0.3MnO3 thin films. Relative cooling power remain close to those of La0.7Sr0.3MnO3. The enhanced magnetic phase-transition temperature and magnetocaloric effect are interpreted and evidenced in the framework of interfacial coupling between Mn3O4 and La0.7Sr0.3MnO3. This work demonstrates the potentiality of self-assembled nanostructures for magnetic cooling near room temperature under low magnetic fields.
Enhanced Structural and Magnetic Coupling in a Mesocrystal-Assisted Nanocomposite
(2016-01-20)
Zhu, Yuanmin
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Zhan, Qian
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Yang, Jan-Chi
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Bitla, Yugandhar
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Liu, Pingping
Benefiting from the advances made in well-controlled materials synthesis techniques, nanocomposites have drawn considerable attention due to their enthralling physics and functionalities. In this work, we report a new heteroepitaxial mesocrystalperovskite nanocomposite, (NiFe2O4)(0.33):(La0.67Ca0.33MnO3)(0.67). Elaborate structural studies revealed that tiny NiFe2O4 nanocrystals aggregate into ordered octahedral mesocrystal arrays with {111} facets together with a concomitant structural phase transition of the La0.67Ca0.33MnO3 matrix upon postannealing process. Combined magnetic and X-ray absorption spectroscopic measurements show significant enhancement in the magnetic properties at room temperature due to the structural evolution of magnetic NiFe2O4 and the consequent magnetic coupling at the heterointerfaces mediating via well connected octahedrons of Mn-O-6 in La0.67Ca0.33MnO3 and (Ni,Fe)-O-6 in NiFe2O4. This work demonstrates an approach to manipulate the exciting physical properties of material systems by integrating desired functionalities of the constituents via synthesis of a self-assembled mesocrystal embedded nanocomposite system.
Field enhancement of electronic conductance at ferroelectric domain walls
(2017-11-06)
Vasudevan, Rama K.
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Cao, Ye
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Laanait, Nouamane
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Ievlev, Anton
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Li, Linglong
Ferroelectric domain walls have continued to attract widespread attention due to both the novelty of the phenomena observed and the ability to reliably pattern them in nanoscale dimensions. However, the conductivity mechanisms remain in debate, particularly around nominally uncharged walls. Here, we posit a conduction mechanism relying on field-modification effect from polarization re-orientation and the structure of the reverse-domain nucleus. Through conductive atomic force microscopy measurements on an ultra-thin (001) BiFeO3 thin film, in combination with phase-field simulations, we show that the field-induced twisted domain nucleus formed at domain walls results in local-field enhancement around the region of the atomic force microscope tip. In conjunction with slight barrier lowering, these two effects are sufficient to explain the observed emission current distribution. These results suggest that different electronic properties at domain walls are not necessary to observe localized enhancement in domain wall currents.
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.
Mapping Band Alignment across Complex Oxide Heterointerfaces
(2012-12-12)
Huang, Bo-Chao
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Chiu, Ya-Ping
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Huang, Po-Cheng
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Wang, Wen-Ching
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Vu Thanh Tra
In this study, direct observation of the evolution of electronic structures across complex oxide interfaces has been revealed in the LaAlO3/SrTiO3 model system using cross-sectional scanning tunneling microscopy and spectroscopy. The conduction and valence band structures across the LaAlO3/SrTiO3 interface are spatially resolved at the atomic level by measuring the local density of states. This study directly maps out the electronic reconstructions and a built-in electric field in the polar LaAlO3 layer. Results also clearly reveal the band bending and the notched band structure in the SrTiO3 adjacent to the interface. DOI: 10.1103/PhysRevLett.109.246807
Mesocrystal-embedded functional oxide systems
(2016-09)
Yang, Jan-Chi
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Liu, Heng-Jui
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Chu, Ying-Hao
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材料科學與工程學系
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Department of Materials Science and Engineering
Mesocrystal-a new class of crystals compared with conventional single crystals and randomly distributed nanocrystal systems-has captured significant attention in recent decades. Current studies have been focused on the advanced synthesis as well as the intriguing properties of mesocrystal. In order to create new opportunities upon functional mesocrystals, they can be regarded as a new functional entirety when integrated with unique matrix environments. The elegant combination of mesocrystals and matrices has enabled researchers to realize enthralling tunabilities and to derive new functionalities that cannot be found in individual components. Therefore, mesocrystal-embedded system forms a new playground towards multifunctionalities. This review article delivers a general roadmap that portrays the enhancement of intrinsic properties and new functionalities driven by novel mesocrystal-embedded oxide systems. An in-depth understanding and breakthroughs achieved in mesocrystal-embedded oxide systems are highlighted. This article concludes with a brief discussion on potential directions and perspectives along this research field.
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
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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.
Non-volatile domain nucleation and growth in multiferroic BiFeO(3) films
(2011-06-24)
Chen, Yi-Chun
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Wang, Guang-Fu
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Tai, Hsiang-Hua
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Chen, Jhih-Wei
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Huang, Yen-Chin
We have presented a systematical study of the domain nucleation and growth behaviors in multiferroic BiFeO(3) (BFO) films. Both the ferroelectric and the ferroelastic switching dynamics were investigated. Several environmental parameters, including the polarization orientations, the monodomain-like matrix, and the ordered domain walls as local boundaries, were well controlled by thin-film strain engineering through changing the vicinal angles of the substrates. The tip-based domain dynamics was studied by subsequent piezoresponse force microscope (PFM) imaging of the domain evolution under external voltage pulses. For the nanodomains written in the monodomain-like environment, the domain wall performed the thermal activated motion. The as-grown 71 degrees domain walls can act as pinning centers for the ferroelectric domain growth driven by low fields; moreover, ferroelastic nucleation near a 71 degrees domain wall will cause the deformation of the domain wall. The ferroelastic domain growth possessed relatively small activation fields, and therefore usually performed non-activated motion. This study revealed the effects of local environments on the dynamics forming nanoscale domains, and opened a pathway for applications in novel non-volatile functional devices.