Browsing by Author "Liang, Wen-I"

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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
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Seidel, Jan
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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.
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
;
Chen, Jul-Yuan
;
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 Visualization of Polarization Pinning and Relaxation at Coherent BiFeO3/LaAlO3 Interfaces
(2014-02-01)
Huang, Rong
;
Ding, Hang-Chen
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Liang, Wen-I
;
Gao, Yong-Chao
;
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.
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
;
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.
Concurrent transition of ferroelectric and magnetic ordering near room temperature
(2011-11-01)
Ko, Kyung-Tae
;
Jung, Min Hwa
;
He, Qing
;
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.
Directed assembly of nano-scale phase variants in highly strained BiFeO3 thin films
(2012-09-15)
Zhou, Jian
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Trassin, Morgan
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He, Qing
;
Tamura, Nobumichi
;
Kunz, Martin
The delicate balance between elastic energy and electrostatic energy in highly strained BiFeO3 (BFO) thin films results in complex mixed-phase patterns, which poses significant challenges for theoretical understanding and complicates the realization of its full potential in magnetoelectric, electromechanical, and photovoltaic devices. In this letter, we explore in-plane electric field induced phase transition in strain engineered BFO thin films and elucidate the mechanism behind the assembly behavior of complex nano-scale phase domains. Our approach enables deterministic control of phase variants with well-defined structures and orientation, paving the way for designing novel data storage devices based on mixed phase BFO. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4752395]
Dynamics of Nanoscale Dendrite Formation in Solution Growth Revealed Through in Situ Liquid Cell Electron Microscopy
(2018-10-01)
Hauwiller, Matthew R.
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Zhang, Xiaowei
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Liang, Wen-I
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Chiu, Chung-Hua
;
Zhang, Qian
Formation mechanisms of dendrite structures have been extensively explored theoretically, and many theoretical predictions have been validated for micro- or macroscale dendrites. However, it is challenging to determine whether classical dendrite growth theories are applicable at the nanoscale due to the lack of detailed information on the nanodendrite growth dynamics. Here, we study iron oxide nanodendrite formation using liquid cell transmission electron microscopy (TEM). We observe "seaweed"-like iron oxide nanodendrites growing predominantly in two dimensions on the membrane of a liquid cell. By tracking the trajectories of their morphology development with high spatial and temporal resolution, it is possible to explore the relationship between the tip curvature and growth rate, tip splitting mechanisms, and the effects of precursor diffusion and depletion on the morphology evolution. We show that the growth of iron oxide nanodendrites is remarkably consistent with the existing theoretical predictions on dendritic morphology evolution during growth, despite occurring at the nanoscale.
Effect of processing kinetics on the structure of ferromagnetic-ferroelectric-ferromagnetic interfaces
(2012-11-15)
Krishnan, P. S. Sankara Rama
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Ramasse, Q. M.
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Liang, Wen-I
;
Chu, Ying-Hao
;
Nagarajan, V.
Trilayer heterostructures consisting of a ferroelectric bismuth ferrite (BFO) film sandwiched between ferromagnetic lanthanum strontium manganese oxide (LSMO) films were fabricated using pulsed laser deposition. Both BFO thicknesses (20 nm, 5 nm) and cooling rates were varied to investigate the role of processing parameters on the chemistry of the interfaces. The interfaces were investigated using a dedicated aberration corrected scanning transmission electron microscope (STEM) operated at 100 kV via STEM-high angle annular dark field (STEM-HAADF) and STEM-electron energy loss spectroscopy (STEM-EELS) modes. Combined analysis through STEM-HAADF and STEM-EELS revealed the formation of lattice distortion in certain regions of the BFO layer for the similar to 5 nm film. Piezoresponse force microscopy (PFM) studies of the similar to 5 nm BFO sample revealed weak ferroelectric domain switching. Stacking fault defects with mixed valence manganese (Mn-B site cation) were formed in the top LSMO layer when the heterostructure was cooled at a slower rate irrespective of BFO thickness, thereby demonstrating the effect of processing kinetics on the physical integrity of the heterostructure. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4765045]
Electrical Control of Multiferroic Orderings in Mixed-Phase BiFeO3 Films
(2012-06-12)
Chen, Yi-Chun
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He, Qing
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Chu, Feng-Nan
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Huang, Yen-Chin
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Chen, Jhih-Wei
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
;
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
;
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.
In Situ Study of Fe3Pt-Fe2O3 Core-Shell Nanoparticle Formation
(2015-12-02)
Liang, Wen-I
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Zhang, Xiaowei
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Zan, Yunlong
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Pan, Ming
;
Czarnik, Cory
We report an in situ study of Fe3Pt-Fe2O3 coreshell nanoparticle growth using liquid cell transmission electron microscopy. By controlling the Fe-to-Pt ratio in the precursor solution, we achieved the growth of nanoparticles with the formation of an ironplatinum alloy core followed by an iron oxide shell in the electron beam-induced reactions. There was no substantial change in the growth kinetics of the iron oxide shell after the FePt alloy core stopped growing. The core growth was arrested by depletion of the Pt precursor. Heteroepitaxy of Fe3Pt [101] (core)||alpha-Fe2O3 [111] (shell) was observed in most of the nanoparticles, while a polycrystalline iron oxide shell is developed eventually for strain relaxation. Our studies suggest that Pt atoms catalyze the reduction of Fe ions to form the Fe3Pt alloy core, and when Pt is depleted, a direct precipitation of iron oxide results in the core-shell nanostructure formation.
In Situ Study of Spinel Ferrite Nanocrystal Growth Using Liquid Cell Transmission Electron Microscopy
(2015-12-08)
Liang, Wen-I
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Zhang, Xiaowei
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Bustillo, Karen
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Chiu, Chung-Hua
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Wu, Wen-Wei
We report transition metal oxide nanocrystal formation in a liquid cell using. transmission electron microscopy (TEM). The growth of M-Fe-oxide (M = Ni, Mn, Co, or Zn) nanoparticles from a growth solution of metal acetylacetonates dissolved in oleylamine, oleic acid, and benzyl ether was studied. Nickel iron oxide nanocrystals with spinel structure were obtained under electron beam irradiation of the Ni-Fe growth solution, whereas iron oxide nanocrystals were achieved with Mn remaining in the Mn-Fe growth solution. Similarly, we achieved cobalt iron oxide nanocrystals in the Co-Fe precursor solution, while iron oxide nanoparticles were obtained in the Zn-Fe solution. By tracking nanoparticle size evolution as a function of time along the Ni-Fe oxide nanoparticle growth trajectories, we found the growth kinetics follow a Lifshitz-Slyozov-Wagner (LSW) model suggesting surface reaction-limited growth. Ex situ characterization shows elemental distribution and structural and valence state of the different nanoparticles. The trend of nanoparticle growth in a liquid cell shares many similarities with those in "one-pot" flask synthesis by thermal heating. We compare reduction potentials (E-r) of the metal ions and thermal decomposition temperatures (T-d) of the precursors and correlate them with nanoparticle growth in a liquid cell under TEM. We found a tendency to form mixed metal ion oxide nanoparticles instead of single metal ion (iron) oxides when the two precursors have similar values of T-d and metal ion reduction potential. The higher T-d and smaller E-r values of Mn and Zn precursors than those of Fe precursor, as well as Ni and Co precursors, may have resulted in the single metal ion (iron) oxide formation in M-Fe (M = Mn and Zn) precursor systems. This study sheds light on nanoparticle growth mechanisms by liquid cell TEM. In situ study of oxide nanocrystal growth using liquid cell TEM provides the opportunity to explore solution chemistry during nanocrystal growth beyond the nanoparticle growth that occurs in a TEM cell.
In-situ Multimodal Imaging and Spectroscopy of Mg Electrodeposition at Electrode-Electrolyte Interfaces
(2017-02-10)
Wu, Yimin A.
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Yin, Zuwei
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Farmand, Maryam
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Yu, Young-Sang
;
Shapiro, David A.
We report the study of Mg cathodic electrochemical deposition on Ti and Au electrode using a multimodal approach by examining the sample area in-situ using liquid cell transmission electron microscopy (TEM), scanning transmission X-ray microscopy (STXM) and X-ray absorption spectroscopy (XAS). Magnesium Aluminum Chloride Complex was synthesized and utilized as electrolyte, where non-reversible features during in situ charging-discharging cycles were observed. During charging, a uniform Mg film was deposited on the electrode, which is consistent with the intrinsic non-dendritic nature of Mg deposition in Mg ion batteries. The Mg thin film was not dissolvable during the following discharge process. We found that such Mg thin film is hexacoordinated Mg compounds by in-situ STXM and XAS. This study provides insights on the non-reversibility issue and failure mechanism of Mg ion batteries. Also, our method provides a novel generic method to understand the in situ battery chemistry without any further sample processing, which can preserve the original nature of battery materials or electrodeposited materials. This multimodal in situ imaging and spectroscopy provides many opportunities to attack complex problems that span orders of magnitude in length and time scale, which can be applied to a broad range of the energy storage systems.
Nanoscale Control of Phase Variants in Strain-Engineered BiFeO(3)
(2011-08-01)
Vasudevan, Rama K.
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Liu, Yunya
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Li, Jiangyu
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Liang, Wen-I
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Kumar, Amit
Development of magnetoelectric, electromechanical, and photovoltaic devices based on mixed-phase rhombohedral-tetragonal (R-T) BiFeO(3) (BFO) systems is possible only if the control of the engineered R phase variants is realized. Accordingly, we explore the mechanism of a bias induced phase transformation in this system. Single point spectroscopy demonstrates that the T -> R transition is activated at lower voltages compared to T -> - T polarization switching. With phase field modeling, the transition is shown to be electrically driven. We further demonstrate that symmetry of formed R-phase rosettes can be broken by a proximal probe motion, allowing controlled creation of R variants with defined orientation. This approach opens a pathway to designing next-generation magnetoelectronic and data storage devices in the nanoscale.
Nanoscale Control of Phase Variants in Strain-Engineered BiFeO3
(2011-08-01)
Vasudevan, Rama K.
;
Liu, Yunya
;
Li, Jiangyu
;
Liang, Wen-I
;
Kumar, Amit
Development of magnetoelectric, electromechanical, and photovoltaic devices based on mixed-phase rhombohedral-tetragonal (R-T) BiFeO3 (BFO) systems is possible only if the control of the engineered R phase variants is realized. Accordingly, we explore the mechanism of a bias induced phase transformation in this system. Single point spectroscopy demonstrates that the T -> R transition is activated at lower voltages compared to T -> - T polarization switching. With phase field modeling, the transition is shown to be electrically driven. We further demonstrate that symmetry of formed R-phase rosettes can be broken by a proximal probe motion, allowing controlled creation of R variants with defined orientation. This approach opens a pathway to designing next-generation magnetoelectronic and data storage devices in the nanoscale.
PROBING MULTIFERROIC HETEROSTRUCTURES OF BiFeO3-LiMn2O4 USING MAGNETIC, PIEZOELECTRIC AND PIEZOMAGNETIC FORCE MICROSCOPIES
(2014-01-01)
Eshghinejad, Ahmadreza
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Liang, Wen-I
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Chen, Qian Nataly
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Ma, Feiyue
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Chu, Ying-Hao
In this study magnetic force microscopy (MFM), piezore-sponse force microscopy (PFM), and the newly developed piezomagnetic force microscopy (PmFM) techniques are used to probe the ferroelectric and ferromagnetic properties of BiFeO3-LiMn2O4 (BFO-LMO) heterostructures at nano-scale. The PmFM technique is also used to probe the ferromagnetic properties of CoFe2O4 (CFO) as a case study. The PFM and PmFM mappings of the BFO-LMO heterostructures clearly distinguish the BFO matrix and LMO nanopillars while the MFM mapping is ambiguous. The relatively high piezomagnetic response of BFO matrix is believed to be due to the Mn doping while the piezoelectric-like response of LMO nanopillars is due to the ionic activities and the vertical geometry of its heterostructure. Lastly, limitations of the PmFM technique are discussed.
Self-assembled vertical heteroepitaxial nanostructures: from growth to functionalities
(2014-06-01)
Liu, Heng-Jui
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Liang, Wen-I
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Chu, Ying-Hao
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Zheng, Haimei
;
Ramesh, Ramamoorthy
Self-assembled vertical heteroepitaxial nanostructures (VHN) in the complex oxide field have fascinated scientists for decades because they provide degrees of freedom to explore in condensed matter physics and design-coupled multifunctionlities. Recently, of particular interest is the perovskite-spinel-based VHN, covering a wide spectrum of promising applications. In this review, fabrication of VHN, their growth mechanism, control, and resulting novel multifunctionalities are discussed thoroughly, providing researchers a comprehensive blueprint to construct promising VHN. Following the fabrication section, the state-of-the-art design concepts for multifunctionalities are proposed and reviewed by suitable examples. By summarizing the outlook of this field, we are excitedly expecting this field to rise with significant contributions ranging from scientific value to practical applications in the foreseeable future.
Strain-driven phase boundaries in BiFeO(3) thin films studied by atomic force microscopy and x-ray diffraction
(2012-01-17)
Liu, Heng-Jui
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Liang, Chen-Wei
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Liang, Wen-I
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Chen, Hsiang-Jung
;
Yang, Jan-Chi
We report a detailed study on the strain-driven phase transition between the tetragonal-like and rhombohedral-like phases in epitaxial BiFeO(3) (BFO) thin films which focuses on their structural nature, thermodynamic stability, and ferroelectric/piezoelectric properties. We first show that the tetragonal-like phase, which has a large c/a ratio (similar to 1.2), in the compressively strained BFO is thermodynamically more favorable at high temperature and high strain state (small thickness). We also report a phase transition between two monoclinic phases at 150 degrees C. The two monoclinic phases are differentiated by their c-axis parameters and tilting angles: The low-temperature phase (M(C)) has a c-axis parameter of 4.64 angstrom and a tilting angle (beta = 88.5 degrees) along the a axis, while the high-temperature phase (M(A)) has a c-axis parameter of 4.66 angstrom and a tilting angle (beta = 86.8 degrees) along both of the a and b axes. We further show that samples undergoing the M(C)-M(A) phase transition exhibit ferroelectric polarization rotation and piezoelectric enhancement. Our findings directly unveil the close links between structural changes, polarization rotation, and large piezoelectricity at morphotropic phase boundaries in BiFeO(3).
Strain-driven phase boundaries in BiFeO3 thin films studied by atomic force microscopy and x-ray diffraction
(2012-01-17)
Liu, Heng-Jui
;
Liang, Chen-Wei
;
Liang, Wen-I
;
Chen, Hsiang-Jung
;
Yang, Jan-Chi
We report a detailed study on the strain-driven phase transition between the tetragonal-like and rhombohedral-like phases in epitaxial BiFeO3 (BFO) thin films which focuses on their structural nature, thermodynamic stability, and ferroelectric/piezoelectric properties. We first show that the tetragonal-like phase, which has a large c/a ratio (similar to 1.2), in the compressively strained BFO is thermodynamically more favorable at high temperature and high strain state (small thickness). We also report a phase transition between two monoclinic phases at 150 degrees C. The two monoclinic phases are differentiated by their c-axis parameters and tilting angles: The low-temperature phase (M-C) has a c-axis parameter of 4.64 angstrom and a tilting angle (beta = 88.5 degrees) along the a axis, while the high-temperature phase (M-A) has a c-axis parameter of 4.66 angstrom and a tilting angle (beta = 86.8 degrees) along both of the a and b axes. We further show that samples undergoing the M-C-M-A phase transition exhibit ferroelectric polarization rotation and piezoelectric enhancement. Our findings directly unveil the close links between structural changes, polarization rotation, and large piezoelectricity at morphotropic phase boundaries in BiFeO3.