Browsing by Author "Chu, Junhao"

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Atomic-Scale Visualization of Polarization Pinning and Relaxation at Coherent BiFeO3/LaAlO3 Interfaces
(2014-02-01)
Huang, Rong
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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.
High Mobilities in Layered InSe Transistors with Indium-Encapsulation-Induced Surface Charge Doping
(2018-11-02)
Li, Mengjiao
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Lin, Che-Yi
;
Yang, Shih-Hsien
;
Chang, Yuan-Ming
;
Chang, Jen-Kuei
Tunability and stability in the electrical properties of 2D semiconductors pave the way for their practical applications in logic devices. A robust layered indium selenide (InSe) field-effect transistor (FET) with superior controlled stability is demonstrated by depositing an indium (In) doping layer. The optimized InSe FETs deliver an unprecedented high electron mobility up to 3700 cm(2) V-1 s(-1) at room temperature, which can be retained with 60% after 1 month. Further insight into the evolution of the position of the Fermi level and the microscopic device structure with different In thicknesses demonstrates an enhanced electron-doping behavior at the In/InSe interface. Furthermore, the contact resistance is also improved through the In insertion between InSe and Au electrodes, which coincides with the analysis of the low-frequency noise. The carrier fluctuation is attributed to the dominance of the phonon scattering events, which agrees with the observation of the temperature-dependent mobility. Finally, the flexible functionalities of the logic-circuit applications, for instance, inverter and not-and (NAND)/not-or (NOR) gates, are determined with these surface-doping InSe FETs, which establish a paradigm for 2D-based materials to overcome the bottleneck in the development of electronic devices.
The preparation, and structural and multiferroic properties of B-site ordered double-perovskite Bi2FeMnO6
(2017-06-14)
Sun, Lin
;
Fang, Yue-Wen
;
He, Jun
;
Zhang, Yuanyuan
;
Qi, Ruijuan
We report the structural, magnetic, and ferroelectric properties of double-perovskite Bi2FeMnO6 in which Fe3+ and Mn3+ cations are present with alternative ordering along the [111] direction. High-flux synchrotron X-ray diffraction and high resolution transmission electron microscopy show that the pseudo-cubic lattice of Bi2FeMnO6 consists of alternatively corner-shared octahedra of FeO6 and MnO6. In the highly ordered Bi2FeMnO6 thin films, the unusual spin-glassy magnetic state is observed below 18 K by a superconducting quantum interference device, and this is ascribed to the magnetic frustration at the [111] Fe3+ and Mn3+ planes as indicated by X-ray magnetic circular dichroism measurements. Combining with the orbital model analysis based on Goodenough-Kanamori-Anderson rules, first-principles calculations and Monte Carlo simulations suggest that magnetic frustration is dominated by the long-range second nearest neighboring antiferromagnetic interactions of Fe3+-Fe3+ and Mn3+-Mn3+ and leads to the surprisingly weak magnetism. On the other hand, robust room-temperature ferroelectricity in Bi2FeMnO6 films is confirmed by piezoelectric force microscopy through electrically switching the polarization state and the ferroelectric retention.