Browsing by Author "Lo, Hung-Yang"

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Dynamic observation on the functional metal oxide conversion behaviors in Fe3O4/ZnO heterostructures
(2020-03-01)
Huang, Chih-Yang
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Tai, Kuo-Lun
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Huang, Chun-Wei
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Tseng, Yi-Tang
;
Lo, Hung-Yang
We directly observed the atomic diffusion process of bilayered Fe/ZnO transforming into a Fe3O4/ZnO heterostructure. Significantly, we suggested a unique two-step route in which Fe diffused along [0001](znO) via boundaries of ZnO and then reacted along [(1) over bar2 (1) over bar0](ZnO). The specific orientation relationship of [0001(]ZnO)//[11 (1) over bar ]Fe3O4 could be precisely controlled. In addition, the formation of a ZnO/Fe3O4 heterostructure can be tuned in terms of reaction depth by controlling the annealing time. This study provided a novel nanofabricated method to produce oriented metal oxide heterostructures while visualizing the atomic mechanism of metal oxide formation, which allows for further investigation of promising devices. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
In situ atomic scale investigation of Li7La3Zr2O12-based Li+-conducting solid electrolyte during calcination growth
(2020-05-01)
Huang, Chih-Yang
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Tseng, Yi-Tang
;
Lo, Hung-Yang
;
Chang, Jeng-Kuei
;
Wu, Wen-Wei
The development of solid-state electrolytes (SSEs) is crucial for realizing next-generation high-energy-density and high-safety lithium-ion batteries (LIBs). The chemical composition design and synthesis route are known to be the determining factors for SSE properties. One of the most promising SSEs for LIB applications is garnet-type Li+-conducting oxide synthesized via a solid-state reaction. This study performs an in situ TEM investigation of Li6.25Ga0.25La3Zr2O12 (Ga-LLZO) growth during a high-temperature calcination process. At 750 degrees C, an intermediate phase, La2Zr2O7 (LZO), is formed through epitaxial growth along the crystallographic orientations of ((1) over bar 11)(LZO)//((1) over bar 11) ZrO2 and [211](LZO)//[101]ZrO2. The incorporation of Li and Ga into LZO is found to occur at 900.C. The LZO transforms into Ga-LLZO via a layer-by-layer diffusion process that takes place along the [01 (1) over bar] direction. The Ga doping can stabilize the cubic structure of Ga-LLZO at a temperature of 900 degrees C (while a temperature of >1100 degrees C is needed to obtain cubic LLZO) and eliminate the formation of the unwanted tetragonal phase. This dynamic microstructure evolution of Ga-LLZO is examined at an atomic scale for the first time. This study opens up a new route to better characterize and understand SSE materials, providing opportunities for further tailoring SSE properties.
Observing topotactic phase transformation and resistive switching behaviors in low power SrCoOx memristor
(2020-06-01)
Lo, Hung-Yang
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Yang, Chih-Yu
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Huang, Guan-Ming
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Huang, Chih-Yang
;
Chen, Jui-Yuan
Recently, complex oxides have been shown to be promising candidate in dielectric materials of resistive random access memory (RRAM). However, the detailed switching information of complex oxide RRAM is still insufficient, and direct observation of the whole switching process is required to figure out the mechanism. In this study, we deposited SrCoOx (SCO) on a niobium-doped SrTiO3 substrate as the dielectric layer via pulsed laser deposition (PLD). The novel SCO device possesses excellent RRAM properties, high cycling endurance, a long data retention time, and uniform distributions of the high resistance state (HRS) and low resistance state (LRS) resistance and Set/Reset voltage. Furthermore, the switching mechanism was investigated by using transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM), which showed that the switching behavior resulted from the topotactic phase transformation. In addition, the whole switching process was observed through in situ TEM, and the results strengthened the findings of the ex situ experiment. The discussion of this switching behavior provides support for a novel aspect of the RRAM switching mechanism and also a new option for the dielectric material in RRAM.