Browsing by Author "Wang, Bo"

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Direct observation of weakened interface clamping effect enabled ferroelastic domain switching
(2019-06-01)
Li, Mingqiang
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Wang, Bo
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Liu, Heng-Jui
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Huang, Yen-Lin
;
Zhang, Jingmin
Reversible switching of non-180 degrees ferroelastic domains that largely alters the local strain distribution enables many electromechanical, electromagnetic and electroacoustic applications. However, in thin films, the ferroelastic domain walls are usually believed to be immobile because of the interface clamping and/or dislocation pinning. Here, using in situ and aberration-corrected transmission electron microscopy, we directly observe reversible switching of individual 90 degrees domains in dislocation-free PbTiO3 thin films and uncover the weakened interface clamping effect. We find the tetragonality is suppressed to similar to 1.017 while the polarization vectors rotate 45 degrees in the a-domain near the interface. These huge structural distortions at the interface is mainly responsible for the weakened clamping effect and thus the ability to switch ferroelastic domains. The switching is fully reversible (i.e., either electric field or mechanical stress can re-establish the erased domain) regardless of polarization orientation of the c-domain matrix. Phase-field modeling also shows excellent agreement with experimental observations. Our study reveals the mechanism of controllable and reversible ferroelastic domain switching, enabling the design of new actuators, sensors, and electromagnetic devices. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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.
Flexible, multifunctional neural probe with liquid metal enabled, ultra-large tunable stiffness for deep-brain chemical sensing and agent delivery
(2019-04-15)
Wen, Ximiao
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Wang, Bo
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Huang, Shan
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Liu, Tingyi ''Leo''
;
Lee, Meng-Shiue
Flexible neural probes have been pursued previously to minimize the mechanical mismatch between soft neural tissues and implants and thereby improve long-term performance. However, difficulties with insertion of such probes deep into the brain severely restricts their utility. We describe a solution to this problem using gallium (Ga) in probe construction, taking advantage of the solid-to-liquid phase change of the metal at body temperature and probe shape deformation to provide temperature-dependent control of stiffness over 5 orders of magnitude. Probes in the stiff state were successfully inserted 2 cm-deep into agarose gel "brain phantoms" and into rat brains under cooled conditions where, upon Ga melting, they became ultra soft, flexible, and stretchable in all directions. The current 30 mu m-thick probes incorporated multilayer, deformable microfluidic channels for chemical agent delivery, electrical interconnects through Ga wires, and high-performance electrochemical glutamate sensing. These PDMS-based microprobes of ultra-large tunable stiffness (ULTS) should serve as an attractive platform for multifunctional chronic neural implants.