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RISS 인기검색어
- 검색키워드
- 저자 : Heo Yooun (검색결과 4 건)
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Enhanced conductivity at orthorhombic–rhombohedral phase boundaries in BiFeO3 thin films
Heo, Yooun,Hong Lee, Jin,Xie, Lin,Pan, Xiaoqing,Yang, Chan-Ho,Seidel, Jan Nature Publishing Group 2016 NPG Asia Materials Vol.8 No.-
<P>Enhanced properties in modern functional materials can often be found at structural transition regions, such as morphotropic phase boundaries (MPB), owing to the coexistence of multiple phases with nearly equivalent energies. Strain-engineered MPBs have emerged in epitaxially grown BiFeO3 (BFO) thin films by precisely tailoring a compressive misfit strain, leading to numerous intriguing phenomena, such as a massive piezoelectric response, magnetoelectric coupling, interfacial magnetism and electronic conduction. Recently, an orthorhombic-rhombohedral (O-R) phase boundary has also been found in tensile-strained BFO. In this study, we characterise the crystal structure and electronic properties of the two competing O and R phases using X-ray diffraction, scanning probe microscope and scanning transmission electron microscopy (STEM). We observe the temperature evolution of R and O domains and find that the domain boundaries are highly conductive. Temperature-dependent measurements reveal that the conductivity is thermally activated for R-O boundaries. STEM observations point to structurally wide boundaries, significantly wider than in other systems. Therefore, we reveal a strong correlation between the highly conductive domain boundaries and structural material properties. These findings provide a pathway to use phase boundaries in this system for novel nanoelectronic applications.</P>
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Impact of Isovalent and Aliovalent Doping on Mechanical Properties of Mixed Phase BiFeO<sub>3</sub>
Heo, Yooun,Hu, Songbai,Sharma, Pankaj,Kim, Kwang-Eun,Jang, Byung-Kweon,Cazorla, Claudio,Yang, Chan-Ho,Seidel, Jan American Chemical Society 2017 ACS NANO Vol.11 No.3
<P>In this study, we report the effect of doping in morphotropic BiFeO3 (BFO) thin films on mechanical properties, revealing variations in the elasticity across the competing phases and their boundaries. Spectroscopic force-distance (F-D) curves and force mapping images by AFM are used to characterize the structure and elastic properties of three BFO thin-film candidates (pure-BFO, Ca-doped BFO, La-doped BFO). We show that softening behavior is observed in isovalent La-doped BFO, whereas hardening is seen in aliovalent Ca-doped BFO. Furthermore, quantitative F-D measurements are extended to show threshold strengths for phase transitions, revealing their dependence on doping in the system. First-principles simulation methods are also employed to understand the observed mechanical properties in pure and doped BFO thin films and to provide microscopic insight on them. These results provide key insight into doping as an effective control parameter to tune nanomechanical properties and suggest an alternative framework to control coupled ferroic functionalities at the nanoscale.</P>
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Nanoscale mechanical probing of ferroic materials
Heo Yooun 한국물리학회 2024 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.84 No.9
Mechanical probing, that is using the mechanical force of an atomic force microscopy (AFM) tip for materials’ characterization, has provided a plethora of research opportunities in ferroic materials over the past years. Unique mechanical force-based AFM modes with compatible techniques allow for the study of rather scarcely explored nanoscale phenomena and functionalities in ferroic materials. The key aspect of this involves force interactions, as a main stimulus to enable exploration of mechanically induced novel functionalities closely associated with elastic properties. Mechanical force imposed by an AFM tip at the nanoscale also off ers a unique pathway to dynamically control structural phase transitions and ferroic states such as an electric polarization, magnetization, and strain with their associated functionalities from charge dynamics to electrical conduction. Here, we provide a comprehensive overview of nanoscale mechanical probing in ferroic materials with the recent trends and give an outlook on future research opportunities for technological applications.
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