Browsing by Author "Thi Hien Do"

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Atomic Heterointerfaces and Electrical Transportation Properties in Self-Assembled LaNiO3-NiO Heteroepitaxy
(2018-04-09)
Zhu, Yuan Min
;
Thi Hien Do
;
Vu Thanh Tra
;
Yu, Rong
;
Chu, Ying-Hao
Vertical nanostructure heteroepitaxy opens new opportunities for designing next-generation electronic devices due to the enthralling multifunction combinations and the abundant heterointerfaces manipulated effects. In this study, self-assembled heteroepitaxial thin films, vertically aligned metallic LaNiO3 (LNO) and semiconducting NiO with diverse heterointerfaces, are created and systematically investigated by advanced transmission electron microscopy. With the increase of LaNiO3 content, the LaNiO3 phases present as isolated islands encircled by the connected NiO nanoplates and eventually become the continuous matrix with embedded NiO nanopillars. The atomic heterointerface between NiO and LaNiO3 phases is determined to be [NiO2-LaO](LaNiO3)-LaO-[NiO](NiO), in which an extra La-O layer is enriched at the heterointerface. Besides, the formation mechanism of the heterointerface and antiphase boundaries observed in LaNiO3 phase is discussed. The electrical transport properties at room temperature can be tuned gradually by changing the volume ratio of constituents. The correlation among the insulator-to-metal transition, the carrier types associated with transport behaviors, and the heterostructure evolutions are explored. This study offers a desirable platform to design new multifunctional electronic devices based on the oxide heterojunctions.
Flexible ferroelectric element based on van der Waals heteroepitaxy
(2017-06-01)
Jiang, Jie
;
Bitla, Yugandhar
;
Huang, Chun-Wei
;
Thi Hien Do
;
Liu, Heng-Jui
We present a promising technology for nonvolatile flexible electronic devices: A direct fabrication of epitaxial lead zirconium titanate (PZT) on flexible mica substrate via van der Waals epitaxy. These single-crystalline flexible ferroelectric PZT films not only retain their performance, reliability, and thermal stability comparable to those on rigid counterparts in tests of nonvolatile memory elements but also exhibit remarkable mechanical properties with robust operation in bent states (bending radii down to 2.5 mm) and cycling tests (1000 times). This study marks the technological advancement toward realizing much-awaited flexible yet single-crystalline nonvolatile electronic devices for the design and development of flexible, lightweight, and next-generation smart devices with potential applications in electronics, robotics, automotive, health care, industrial, and military systems.
Flexible Multiferroic Bulk Heterojunction with Giant Magnetoelectric Coupling via van der Waals Epitaxy
(2017-06-01)
Amrillah, Tahta
;
Bitla, Yugandhar
;
Shin, Kwangwoo
;
Yang, Tiannan
;
Hsieh, Ying-Hui
Magnetoelectric nanocomposites have been a topic of intense research due to their profound potential in the applications of electronic devices based on spintronic technology. Nevertheless, in spite of significant progress made in the growth of high-quality nanocomposite thin films, the substrate damping effect still remains a major hurdle in realizing the ultimate magneto electric coupling. To overcome this obstacle, an alternative strategy of fabricating a self-assembled ferroelectric-ferrimagnetic bulk heterojunction on a flexible muscovite via van der Waals epitaxy is adopted. hi this study, we investigated the magnetoelectric coupling in a self-assembled BiFeO3 (BFO)-CoFe2O4 (CFO) bulk heterojunction epitaxially grown on a flexible muscovite substrate. The obtained heterojunction is composed of vertically aligned multiferroic BFO nanopillars embedded in a ferrimagnetic CFO matrix. Moreover, due to the weak interaction between the flexible substrate and bulk heterojunction, the interface is incoherent and, hence, the substrate damping effect is greatly reduced. The phase-field simulation model also complements our results. The magnetic and electrical characterizations highlight the improvement in magnetoelectric coupling of the BFO-CFO bulk heterojunction. A magnetoelectric coupling coefficient of 74 mV/cm.Oe of this bulk heterojunction is larger than the magnetoelectric coefficient reported earlier on flexible substrates. Therefore, this study delivers a viable route of fabricating a remarkable magnetoelectric heterojunction and yet flexible electronic devices that are robust against extreme conditions with optimized performance.
Heteroepitaxial growth and microwave plasma annealing of DC reactive sputtering deposited TiZrN film on Si (100)
(2020-07-25)
Chiu, Kun-An
;
Fu, Chia-Wei
;
Fang, Yu-Siang
;
Thi Hien Do
;
Shih, Fu-Han
Epitaxial TiZrN films were successfully grown on Si (100) substrates at high temperature by using DC magnetron reactive sputtering with a Ti0.68Zr0.32 alloy target. Annealing of a grown TiZrN/Si specimen was performed by applying microwave plasma with a gas mixture of N-2 and H-2 to improve the film quality. The X-ray rocking curve (XRC) width of (200)(TiZrN) reflection can reach a minimum value of 1.18 degrees. The heteroepitaxial relationship of TiZrN with Si is {001}(TiZrN)//{001}(Si) and < 110 >(TiZrN)//< 110 >(Si). The (200)(TiZrN) XRC width of a 20 nm-thick TiZrN film reduces from 1.99 degrees to 0.85 degrees by microwave plasma annealing. As a result of the improvement of the film quality, the annealed film exhibits a much lower resistivity (28 mu Omega.cm) than that of the as-deposited one (44 mu Omega.cm). The surface morphologies of the TiZrN films are smooth with the surface roughness in the range of 1-2 nm.
Heteroepitaxy of Fe3O4/Muscovite: A New Perspective for Flexible Spintronics
(2016-12-14)
Wu, Ping-Chun
;
Chen, Ping-Fan
;
Thi Hien Do
;
Hsieh, Ying-Hui
;
Ma, Chun-Hao
Spintronics has captured a lot of attention since it was proposed. It has been triggering numerous research groups to make their efforts on pursuing spin-related electronic devices. Recently, flexible and wearable devices are in a high demand due to their outstanding potential in practical applications. In order to introduce spintronics into the realm of flexible devices, we demonstrate that it is feasible to grow epitaxial Fe3O4 film, a promising candidate for realizing spintronic devices based on tunneling magnetoresistance, on flexible muscovite. In this study, the heteroepitaxy of Fe3O4/muscovite is characterized by X-ray diffraction, high-resolution transmission electron microscopy, and Raman spectroscopy. The chemical composition and magnetic feature are investigated by a combination of X-ray photoelectron spectroscopy and X-ray magnetic circular dichroism. The electrical and magnetic properties are examined to show the preservation of the primitive properties of Fe3O4. Furthermore, various bending tests are performed to show the tunability of functionalities and to confirm that the heterostructures retain the physical properties under repeated cycles. These results illustrate that the Fe3O4/muscovite heterostructure can be a potential candidate for the applications in flexible spintronics.
Reactive Sputtering Deposition of Epitaxial TiC Film on Si (100) Substrate
(2020-07-01)
Fang, Yu-Siang
;
Thi Hien Do
;
Chiu, Kun-An
;
Chen, Wei-Chun
;
Chang, Li
Epitaxial (100) TiC film deposition on Si (100) substrate by direct current magnetron reactive sputtering of a metallic Ti target with 3%-6% CH4 in Ar gas was investigated. X-ray diffraction and cross-sectional scanning transmission electron microscopy (STEM) reveal that epitaxial cubic TiC can be grown on the Si substrate by domain matching epitaxy in 5/4 ratio with the epitaxial relationship of TiC (100)[0 (1) over bar1] // Si (100)[0 (1) over bar 1]. For sputtering with 3% and 4% CH4, the deposited films are found to consist of both TiC and metallic Ti phases. Increasing the CH4 flow ratio to 5% results in a deposited film completely consisting of TiC without metallic Ti phase. The crystallinity of the deposited TiC is also improved with increasing the CH4 ratio to 5%. X-ray photoelectron spectroscopy shows that the [C]/[Ti] atomic ratio in TiC is nearly close to 1 for growth with 5% CH4 flow ratio and above. The measured electrical resistivities of the deposited films also increase from 41 to 153 mu omega center dot cm with increasing the CH4 ratio from 3% to 6%. With film growth beyond 50 nm thickness, it is shown that some disoriented TiC grains are formed.
Self-Assembled BiFeO3-epsilon-Fe2O3 Vertical Heteroepitaxy for Visible Light Photoelectrochemistry
(2016-09-21)
Le Thi Quynh
;
Chien Nguyen Van
;
Bitla, Yugandhar
;
Chen, Jhih-Wei
;
Thi Hien Do
Self-assembled vertical heterostructure with a high interface-to-volume ratio offers tremendous opportunities to realize intriguing properties and advanced modulation of functionalities. Here, a heterostructure composed of two visible-light photocatalysts, BiFeO3 (BFO) and epsilon-Fe2O3 (epsilon-FO), is designed to investigate its photoelectrochemical performance. The structural characterization of the BFO-FO heterostructures confirms the phase separation with BFO nanopillars embedded in the epsilon-FO matrix. The investigation of band structure of the heterojunction suggests the assistance of photoexcited carrier separation, leading to an enhanced photoelectrochemical performance. The insights into the charge separation are further revealed by means of ultrafast dynamics and electrochemical impedance spectroscopies. This work shows a delicate design of the self-assembled vertical heteroepitaxy by taking advantage of the intimate contact between two phases that can lead to a tunable charge interaction, providing a new confi guration for the optimization of photoelectrochemical cell.
Superior photoelectrochemical activity of self-assembled NiWO4-WO3 heteroepitaxy
(2016-05)
Thi Hien Do
;
Chien Nguyen Van
;
Tsai, Kai-An
;
Le Thi Quynh
;
Chen, Jhih-Wei
Self-assembled nanocomposites with a high interface-to-volume ratio offer tremendous opportunities of tailoring functionalities by a proper combination of components. In this study, we report the first fabrication of self-assembled NiWO4-WO3 heteroepitaxy and its excellent performance on photoel-ectrochemical water splitting. The heteroepitaxy is evidenced by a combination of x-ray diffraction and transmission electron microscopy. The energy band diagram of NiWO4-WO3 heterostructure probed by x-ray photoelectron spectroscopy suggests an efficient charge separation at their interface by injecting photo -generated electrons from NiWO4 to WO3 and holes from WO3 to NiWO4. Therefore, a great improvement in the photoelectrochemical activity of self -assembled NiWO4-WO3 heteroepitaxy was achieved (1400 mu A cm(-2) at 0.7 V vs. Ag/AgCl). This work delivers a new category of composite materials for promising photoelectrode in photoelectrochemical cells. (C) 2016 Elsevier Ltd. All rights reserved.
Van der Waals epitaxy of functional MoO2 film on mica for flexible electronics
(2016-06-20)
Ma, Chun-Hao
;
Lin, Jheng-Cyuan
;
Liu, Heng-Jui
;
Thi Hien Do
;
Zhu, Yuan-Min
Flexible electronics have a great potential to impact consumer electronics and with that our daily life. Currently, no direct growth of epitaxial functional oxides on commercially available flexible substrates is possible. In this study, in order to address this challenge, muscovite, a common layered oxide, is used as a flexible substrate that is chemically similar to typical functional oxides. We fabricated epitaxial MoO2 films on muscovite via pulsed laser deposition technique. A combination of X-ray diffraction and transmission electron microscopy confirms van der Waals epitaxy of the heterostructures. The electrical transport properties of MoO2 films are similar to those of the bulk. Flexible or free-standing MoO2 thin film can be obtained and serve as a template to integrate additional functional oxide layers. Our study demonstrates a remarkable concept to create flexible electronics based on functional oxides. Published by AIP Publishing.
WO3 mesocrystal-assisted photoelectrochemical activity of BiVO4
(2017-03-01)
Chien Nguyen Van
;
Thi Hien Do
;
Chen, Jhih-Wei
;
Tzeng, Wen-Yen
;
Tsai, Kai-An
Self- assembled nanocomposites have gained much attention over the past decade due to their intriguing properties and functionalities. In this work, we developed a self-assembled nanocomposite photoanode composed of an epitaxial BiVO4 matrix embedded with WO3 mesocrystals for photoelectrochemical (PEC) applications in the visible- light regime. The orientation of the crystal facet and interface provides a superior template to understand the intimate contact between the two constituent phases. We demonstrate that the interfacial coupling of the mesocrystal and matrix improves the separation of photoexcited carriers and the properties of charge transfer, resulting in a greatly enhanced PEC performance compared with their parent compounds. The current study demonstrates that the utilization of the interface-to-volume ratio to optimize charge interactions in the nanocomposite is essential for the advanced design of novel mesocrystal-embedded nanocomposite photoelectrodes.