Browsing by Author "Tseng, Yi-Tang"

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Atomic-Scale Fabrication of In-Plane Heterojunctions of Few-Layer MoS2 via In Situ Scanning Transmission Electron Microscopy
(1970-01-01)
Tai, Kuo-Lun
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Huang, Chun-Wei
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Cai, Ren-Fong
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Huang, Guan-Min
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Tseng, Yi-Tang
Layered MoS2 is a prospective candidate for use in energy harvesting, valleytronics, and nanoelectronics. Its properties strongly related to its stacking configuration and the number of layers. Due to its atomically thin nature, understanding the atomic-level and structural modifications of 2D transition metal dichalcogenides is still underdeveloped, particularly the spatial control and selective precision. Therefore, the development of nanofabrication techniques is essential. Here, an atomic-scale approach used to sculpt 2D few-layer MoS2 into lateral heterojunctions via in situ scanning/transmission electron microscopy (STEM/TEM) is developed. The dynamic evolution is tracked using ultrafast and high-resolution filming equipment. The assembly behaviors inherent to few-layer 2D-materials are observed during the process and included the following: scrolling, folding, etching, and restructuring. Atomic resolution STEM is employed to identify the layer variation and stacking sequence for this new 2D-architecture. Subsequent energy-dispersive X-ray spectroscopy and electron energy loss spectroscopy analyses are performed to corroborate the elemental distribution. This sculpting technique that is established allows for the formation of sub-10 nm features, produces diverse nanostructures, and preserves the crystallinity of the material. The lateral heterointerfaces created in this study also pave the way for the design of quantum-relevant geometries, flexible optoelectronics, and energy storage devices.
Atomic-Scale Localized Thinning and Reconstruction of Two-Dimensional WS2 Layers through In Situ Transmission Electron Microscopy/Scanning Transmission Electron Microscopy
(2020-07-09)
Tseng, Yi-Tang
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Tai, Kuo-Lun
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Huang, Chun-Wei
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Huang, Chih-Yang
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Wu, Wen-Wei
Subnanometer nanofabrication has been investigated, and electron beam processing has been found to be a suitable strategy to control nanoparticle organization over large areas. Organized nanostructures have demonstrated their potential for technological applications. Here, we focus on the processing of tungsten disulfide (WS2) due to its novelty and promising electronic properties for further development of functional devices. First, we summarize the theory of electron beam irradiation by surveying the dynamic behaviors observed during in situ experiments. In particular, the diverse structures with various numbers of layers derived from localized thinning produce considerable lateral heterointerfaces. The generation of the intriguing tungsten-rich cluster is also consistent with the mechanism of our atomic engineering experiments. These findings suggest a method for the electron beam processing of 2D materials and demonstrate the viability of atomic engineering using electron irradiation.
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
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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
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Lo, Hung-Yang
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Chang, Jeng-Kuei
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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.