Browsing by Author "Yu, Pu"

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A nanoscale shape memory oxide
(2013-11-01)
Zhang, Jinxing
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Ke, Xiaoxing
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Gou, Gaoyang
;
Seidel, Jan
;
Xiang, Bin
Stimulus-responsive shape-memory materials have attracted tremendous research interests recently, with much effort focused on improving their mechanical actuation. Driven by the needs of nanoelectromechanical devices, materials with large mechanical strain, particularly at nanoscale level, are therefore desired. Here we report on the discovery of a large shape-memory effect in bismuth ferrite at the nanoscale. A maximum strain of up to similar to 14% and a large volumetric work density of similar to 600 +/- 90 J cm(-3) can be achieved in association with a martensitic-like phase transformation. With a single step, control of the phase transformation by thermal activation or electric field has been reversibly achieved without the assistance of external recovery stress. Although aspects such as hysteresis, microcracking and so on have to be taken into consideration for real devices, the large shape-memory effect in this oxide surpasses most alloys and, therefore, demonstrates itself as an extraordinary material for potential use in state-of-art nanosystems.
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
;
Liu, Heng-Jui
Atomically Resolved Electronic States and Correlated Magnetic Order at Termination Engineered Complex Oxide Heterointerfaces
(2018-02-01)
Huang, Bo-Chao
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Yu, Pu
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Chu, Y. H.
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Chang, Chia-Seng
;
Ramesh, Ramamoorthy
We map electronic states, band gaps, and interface-bound charges at termination-engineered BiFeO3/La0.7Sr0.3MnO3 interfaces using atomically resolved cross-sectional scanning tunneling microscopy. We identify a delicate interplay of different correlated physical effects and relate these to the ferroelectric and magnetic interface properties tuned by engineering the atomic layer stacking sequence at the interfaces. This study highlights the importance of a direct atomically resolved access to electronic interface states for understanding the intriguing interface properties in complex oxides.
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
;
He, Qing
;
Yu, Pu
;
Chu, Ying-Hao
;
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.
Direct spectroscopic evidence of charge reversal at the Pb(Zr(0.2)Ti(0.8))O(3)/La(0.7)Sr(0.3)MnO(3) heterointerface
(2011-01-21)
Wu, Chung-Lin
;
Lee, Pei-Wei
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Chen, Yi-Chun
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Chang, Lo-Yueh
;
Chen, Chia-Hao
At the heterointerface of a top ferroelectric Pb(Zr(0.2)Ti(0.8))O(3) (PZT) ultrathin film and a bottom La(0.7)Sr(0.3)MnO(3) (LSMO) electrode, we used continuous synchrotron-radiation photoelectron spectroscopy to probe in situ and demonstrated that the interfacial charges are reversible and their affected valence-band barrier height becomes modulated upon switching the polarization in the top layer. By monitoring the core-level shifting of the buried LSMO layer under continuous illumination of synchrotron radiation, we directly observed a temporal screening of polarization induced by the photon-generated carriers in the top PZT layer. This dynamic characterization of the core-level shifting of the buried layer demonstrates an effective method to probe the electric conduction and ferroelectric polarization of an ultrathin ferroelectric oxide thin film.
Direct spectroscopic evidence of charge reversal at the Pb(Zr0.2Ti0.8)O-3/La0.7Sr0.3MnO3 heterointerface
(2011-01-21)
Wu, Chung-Lin
;
Lee, Pei-Wei
;
Chen, Yi-Chun
;
Chang, Lo-Yueh
;
Chen, Chia-Hao
At the heterointerface of a top ferroelectric Pb(Zr0.2Ti0.8)O-3 (PZT) ultrathin film and a bottom La0.7Sr0.3MnO3 (LSMO) electrode, we used continuous synchrotron-radiation photoelectron spectroscopy to probe in situ and demonstrated that the interfacial charges are reversible and their affected valence-band barrier height becomes modulated upon switching the polarization in the top layer. By monitoring the core-level shifting of the buried LSMO layer under continuous illumination of synchrotron radiation, we directly observed a temporal screening of polarization induced by the photon-generated carriers in the top PZT layer. This dynamic characterization of the core-level shifting of the buried layer demonstrates an effective method to probe the electric conduction and ferroelectric polarization of an ultrathin ferroelectric oxide thin film.
Electric Field Writing of Ferroelectric Nano-Domains Near 71 degrees Domain Walls with Switchable Interfacial Conductivity
(2018-08-01)
Yang, Shuzhen
;
Peng, Ren-Ci
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He, Qing
;
Huang, Yen-Lin
;
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.
Heteroepitaxy of Fe3O4/Muscovite: A New Perspective for Flexible Spintronics
(2016-12-14)
Wu, Ping-Chun
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Chen, Ping-Fan
;
Thi Hien Do
;
Hsieh, Ying-Hui
;
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.
Interface dipole between two metallic oxides caused by localized oxygen vacancies
(2012-10-11)
Borisevich, Albina Y.
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Lupini, Andrew R.
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He, Jun
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Eliseev, Eugene A.
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Morozovska, Anna N.
Oxygen vacancies are increasingly recognized to play a role in phenomena observed at transition-metal oxide interfaces. Here, we report a study of SrRuO3 and La0.7Sr0.3MnO3 interfaces using a combination of quantitative aberration-corrected scanning transmission electron microscopy, electron energy-loss spectroscopy, and density functional calculations. Cation displacements are observed at the interface, indicative of a dipolelike electric field even though both materials are nominally metallic. The observed displacements are reproduced by theory if O vacancies are present in the near-interface La0.7Sr0.3MnO3 layers. The results suggest that atomic-scale structural mapping can serve as a quantitative indicator of the presence of O vacancies at interfaces.
Manipulate the Electronic and Magnetic States in NiCo2O4 Films through Electric-Field-Induced Protonation at Elevated Temperature
(2019-04-19)
Wang, Meng
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Sui, Xuelei
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Wang, Yujia
;
Juan, Yung-Hsiang
;
Lyu, Yingjie
Ionic-liquid-gating- (ILG-) induced proton evolution has emerged as a novel strategy to realize electron doping and manipulate the electronic and magnetic ground states in complex oxides. While the study of a wide range of systems (e.g., SrCoO2.5, VO2, WO3, etc.) has demonstrated important opportunities to incorporate protons through ILG, protonation remains a big challenge for many others. Furthermore, the mechanism of proton intercalation from the ionic liquid/solid interface to whole film has not yet been revealed. Here, with a model system of inverse spinel NiCo2O4, an increase in system temperature during ILG forms a single but effective method to efficiently achieve protonation. Moreover, the ILG induces a novel phase transformation in NiCo2O4 from ferrimagnetic metallic into antiferromagnetic insulating with protonation at elevated temperatures. This study shows that environmental temperature is an efficient tuning knob to manipulate ILG-induced ionic evolution.
Nanoscale Control of Domain Architectures in BiFeO(3) Thin Films
(2009-04-01)
Chu, Ying-Hao
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He, Qing
;
Yang, Chan-Ho
;
Yu, Pu
;
Martin, Lane W.
We demonstrate an approach to create a one-dimensional nanoscale array of domain walls in epitaxial La-substituted BiFeO(3) films. We have used a DySCO(3) (110)(o) single-crystal substrate to provide an anisotropic strain to exclude two of the possible structural variants. Furthermore, through careful control of electrostatic boundary conditions, such as the thickness of the SrRuO(3) bottom electrode to induce the self-poling effects, we can choose to obtain either 1090 or 710 one-dimensional periodic domain walls. Detailed measurements of the domain structures is shown using piezoresponse force microscopy and X-ray diffraction, which confirms that these periodic structures are the same as those suggested in previous literature.
Nanoscale Control of Domain Architectures in BiFeO3 Thin Films
(2009-04-01)
Chu, Ying-Hao
;
He, Qing
;
Yang, Chan-Ho
;
Yu, Pu
;
Martin, Lane W.
We demonstrate an approach to create a one-dimensional nanoscale array of domain walls in epitaxial La-substituted BiFeO3 films. We have used a DySCO3 (110)(o) single-crystal substrate to provide an anisotropic strain to exclude two of the possible structural variants. Furthermore, through careful control of electrostatic boundary conditions, such as the thickness of the SrRuO3 bottom electrode to induce the self-poling effects, we can choose to obtain either 1090 or 710 one-dimensional periodic domain walls. Detailed measurements of the domain structures is shown using piezoresponse force microscopy and X-ray diffraction, which confirms that these periodic structures are the same as those suggested in previous literature.
Oxide interfaces: pathways to novel phenomena
(2012-07-01)
Yu, Pu
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Chu, Ying-Hao
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Ramesh, Ramamoorthy
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材料科學與工程學系
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Department of Materials Science and Engineering
Novel phenomena and functionalities at artificial heterointerfaces have been attracting extensive scientific attention in both materials science and fundamental condensed matter physics. The interplay between degrees of freedom at interfaces of complex oxides could lead to exotic and unexpected states of matter. In this article, using the model system of BiFeO3 and La0.7Sr0.3MnO3, we review recent progress on our understanding of the novel states formed at this heterointerface. Furthermore, we discuss how emergent interfacial phenomena can be employed to influence the bulk properties of these materials. We summarize by highlighting several possible and promising directions for future study.
Pulsed laser deposition of complex oxide heteroepitaxy
(2019-08-01)
Huang, Yen-Lin
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Liu, Heng-Jui
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Ma, Chun-Hao
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Yu, Pu
;
Chu, Ying-Hao
The modern studies of complex oxides have been mainly driven by the development of advanced growth and characterization techniques, which provide researchers unprecedented access to new insights and functionalities of these materials. Epitaxial growth of thin films and related architectures offers a pathway to the discovery and stabilization of a wide spectrum of new possibilities in conjunction with the availability of high quality materials that produced with larger lateral sizes and being grown constrainedly. Compared with conventional growth techniques, such as sputtering, spin coating, sol-gel processes, metal-organic chemical vapor deposition, molecular beam epitaxy and so on, no other single advance in the creation of oxide materials has had as pronounced an impact as pulsed laser deposition. In pursuit of the fruitful functionalities and exciting physical phenomena among complex oxides, pulsed laser deposition technique has played an important role to fulfill the flurry of complex oxides in recent decades. In this article, we focus on the details of the growth of epitaxial oxide thin films and the related polymorphs, as well as recent advances in control of the oxide heteroepitaxy via pulsed laser deposition.
Strain-Mediated Inverse Photoresistivity in SrRuO3/La0.7Sr0.3MnO3 Superlattices
(2016-02-02)
Liu, Heng-Jui
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Wei, Tzu-Chiao
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Zhu, Yuan-Min
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Liu, Rui-Rui
;
Tzeng, Wen-Yen
In the pursuit of novel functionalities by utilizing the lattice degree of freedom in complex oxide heterostructure, the control mechanism through direct strain manipulation across the interfaces is still under development, especially with various stimuli, such as electric field, magnetic field, light, etc. In this study, the superlattices consisting of colossal-magnetoresistive manganites La0.7Sr0.3MnO3 (LSMO) and photostrictive SrRuO3 (SRO) have been designed to investigate the light-dependent controllability of lattice order in the corresponding functionalities and rich interface physics. Two substrates, SrTiO3 (STO) and LaAlO3 (LAO), have been employed to provide the different strain environments to the superlattice system, in which the LSMO sublayers exhibit different orbital occupations. Subsequently, by introducing light, we can modulate the strain state and orbital preference of LSMO sublayers through light-induced expansion of SRO sublayers, leading to surprisingly opposite changes in photoresistivity. The observed photoresistivity decreases in the superlattice grown on STO substrate while increases in the superlattice grown on LAO substrate under light illumination. This work has presented a model system that demonstrates the manipulation of orbital-lattice coupling and the resultant functionalities in artificial oxide superlattices via light stimulus.
Tailoring Magnetoelectric Coupling in BiFeO3/La0.7Sr0.3MnO3 Heterostructure through the Interface Engineering
(2019-03-15)
Yi, Di
;
Yu, Pu
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Chen, Yi-Chun
;
Lee, Hsin-Hua
;
He, Qing
Electric field control of magnetism ultimately opens up the possibility of reducing energy consumption of memory and logic devices. Electric control of magnetization and exchange bias are demonstrated in all-oxide heterostructures of BiFeO3 (BFO) and La0.7Sr0.3MnO3 (LSMO). However, the role of the polar heterointerface on magnetoelectric (ME) coupling is not fully explored. Here, the ME coupling in BFO/LSMO heterostructures with two types of interfaces, achieved by exploiting the interface engineering at the atomic scale, is investigated. It is shown that both magnetization and exchange bias are reversibly controlled by switching the ferroelectric polarization of BFO. Intriguingly, distinctly different modulation behaviors that depend on the interfacial atomic sequence are observed. These results provide new insights into the underlying physics of ME coupling in the model system. This study highlights that designing interface at the atomic scale is of general importance for functional spintronic devices.
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
;
Feng, Bin
;
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.
Tunable Metallic Conductance in Ferroelectric Nanodomains
(2012-01-01)
Maksymovych, Peter
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Morozovska, Anna N.
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Yu, Pu
;
Eliseev, Eugene A.
;
Chu, Ying-Hao
Metallic conductance in charged ferroelectric domain walls was predicted more than 40 years ago as the first example of an electronically active homointerface in a nonconductive material. Despite decades of research on oxide interfaces and ferroic systems, the metal-insulator transition induced solely by polarization charges without any additional chemical modification has consistently eluded the experimental realm. Here we show that a localized insulator-metal transition can be repeatedly induced within an insulating ferroelectric lead-zirconate titanate, merely by switching its polarization at the nanoscale. This surprising effect is traced to tilted boundaries of ferroelectric nanodomains, that act as localized homointerfaces within the perovskite lattice, with inherently tunable carrier density. Metallic conductance is unique to nanodomains, while the conductivity of extended domain walls and domain surfaces is thermally activated. Foreseeing future applications, we demonstrate that a continuum of nonvolatile metallic states across decades of conductance can be encoded in the size of ferroelectric nanodomains using electric field.
Tuning the Competition between Ferromagnetism and Antiferromagnetism in a Half-Doped Manganite through Magnetoelectric Coupling
(2013-09-18)
Yi, Di
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Liu, Jian
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Okamoto, Satoshi
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Jagannatha, Suresha
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Chen, Yi-Chun
We investigate the possibility of controlling the magnetic phase transition of the heterointerface between a half-doped manganite La0.5Ca0.5MnO3 and a multiferroic BiFeO3 (BFO) through magnetoelectric coupling. Using macroscopic magnetometry and element-selective x-ray magnetic circular dichroism at the Mn and Fe L edges, we discover that the ferroelectric polarization of BFO controls simultaneously the magnetization of BFO and La0.5Ca0.5MnO3 (LCMO). X-ray absorption spectra at the oxygen K edge and linear dichroism at the Mn L edge suggest that the interfacial coupling is mainly derived from the superexchange between Mn and Fe t(2g) spins. The combination of x-ray absorption spectroscopy and mean-field theory calculations reveals that the d-electron modulation of Mn cations changes the magnetic coupling in LCMO, which controls the enhanced canted moments of interfacial BFO via the interfacial coupling. Our results demonstrate that the competition between ferromagnetic and antiferromagnetic instability can be modulated by an electric field at the heterointerface, providing another pathway for the electrical field control of magnetism.