Browsing by Author "Wu, Chung-Lin"

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A gate-free monolayer WSe2 pn diode
(2018-08-07)
Chen, Jhih-Wei
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Lo, Shun-Tsung
;
Ho, Sheng-Chin
;
Wong, Sheng-Shong
;
Vu, Thi-Hai-Yen
Interest in bringing p- and n-type monolayer semiconducting transition metal dichalcogenides (TMD) into contact to form rectifying pn diode has thrived since it is crucial to control the electrical properties in two-dimensional (2D) electronic and optoelectronic devices. Usually this involves vertically stacking different TMDs with pn heterojunction or, laterally manipulating carrier density by gate biasing. Here, by utilizing a locally reversed ferroelectric polarization, we laterally manipulate the carrier density and created a WSe2 pn homojunction on the supporting ferroelectric BiFeO3 substrate. This non-volatile WSe2 pn homojunction is demonstrated with optical and scanning probe methods and scanning photoelectron microspectroscopy. A homo-interface is a direct manifestation of our WSe2 pn diode, which can be quantitatively understood as a clear rectifying behavior. The non-volatile confinement of carriers and associated gate-free pn homojunction can be an addition to the 2D electron-photon toolbox and pave the way to develop laterally 2D electronics and photonics.
Au@Cu2O core@shell nanocrystals as dual-functional catalysts for sustainable environmental applications
(2019-03-01)
Kuo, Ming-Yu
;
Hsiao, Chih-Feng
;
Chiu, Yi-Hsuan
;
Lai, Ting-Hsuan
;
Fang, Mei-Jing
This work reports the synthesis of Au@Cu2O core@shell nanocrystals with controllable shell thicknesses and demonstrates their use as the dual-functional catalyst that can continuously operate under illumination and darkness conditions for efficient E. con inactivation. On account of the peroxidase mimics of the Au core and Fenton reactivity of the Cu2O shell, the Au@Cu2O nanocrystals exhibit intrinsic peroxidase-like property with the reaction kinetics in accordance with the typical Michaelis-Menten mechanism. On the other hand, time resolved photoluminescence spectra suggest the prevalence of pronounced charge separation for Au@Cu2O nanocrystals, an important advantage that is favourable for photocatalysis. By combining the photocatalytic capability with the peroxidase mimics features, Au@Cu2O nanocrystals can perform practical photocatalytic decomposition of E. coil under visible light illumination but still show vital activity towards E. coil inactivation after light illumination was turned off. The current study delivers a new catalyst configuration by exploiting the multiple functionalities of nanosized Au and Cu2O for advanced environmental and energy conversion applications.
Direct spectroscopic evidence of charge reversal at the Pb(Zr(0.2)Ti(0.8))O(3)/La(0.7)Sr(0.3)MnO(3) heterointerface
(2011-01-21)
Wu, Chung-Lin
;
Lee, Pei-Wei
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Chen, Yi-Chun
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Chang, Lo-Yueh
;
Chen, Chia-Hao
At the heterointerface of a top ferroelectric Pb(Zr(0.2)Ti(0.8))O(3) (PZT) ultrathin film and a bottom La(0.7)Sr(0.3)MnO(3) (LSMO) electrode, we used continuous synchrotron-radiation photoelectron spectroscopy to probe in situ and demonstrated that the interfacial charges are reversible and their affected valence-band barrier height becomes modulated upon switching the polarization in the top layer. By monitoring the core-level shifting of the buried LSMO layer under continuous illumination of synchrotron radiation, we directly observed a temporal screening of polarization induced by the photon-generated carriers in the top PZT layer. This dynamic characterization of the core-level shifting of the buried layer demonstrates an effective method to probe the electric conduction and ferroelectric polarization of an ultrathin ferroelectric oxide thin film.
Direct spectroscopic evidence of charge reversal at the Pb(Zr0.2Ti0.8)O-3/La0.7Sr0.3MnO3 heterointerface
(2011-01-21)
Wu, Chung-Lin
;
Lee, Pei-Wei
;
Chen, Yi-Chun
;
Chang, Lo-Yueh
;
Chen, Chia-Hao
At the heterointerface of a top ferroelectric Pb(Zr0.2Ti0.8)O-3 (PZT) ultrathin film and a bottom La0.7Sr0.3MnO3 (LSMO) electrode, we used continuous synchrotron-radiation photoelectron spectroscopy to probe in situ and demonstrated that the interfacial charges are reversible and their affected valence-band barrier height becomes modulated upon switching the polarization in the top layer. By monitoring the core-level shifting of the buried LSMO layer under continuous illumination of synchrotron radiation, we directly observed a temporal screening of polarization induced by the photon-generated carriers in the top PZT layer. This dynamic characterization of the core-level shifting of the buried layer demonstrates an effective method to probe the electric conduction and ferroelectric polarization of an ultrathin ferroelectric oxide thin film.
Energy Band Gap Modulation in Nd-Doped BiFeO3/SrRuO3 Heteroepitaxy for Visible Light Photoelectrochemical Activity
(2019-01-09)
Tan, Kok Hong
;
Chen, Yun-Wen
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Chien Nguyen Van
;
Wang, Hongliang
;
Chen, Jhih-Wei
The ability of band offsets at multiferroic/metal and multiferroic/electrolyte interfaces in controlling charge transfer and thus altering the photoactivity performance has sparked significant attention in solar energy conversion applications. Here, we demonstrate that the band offsets of the two interfaces play the key role in determining charge transport direction in a downward self-polarized BFO film. Electrons tend to move to BFO/electrolyte interface for water reduction. Our experimental and first-principle calculations reveal that the presence of neodymium (Nd) dopants in BFO enhances the photoelectrochemical performance by reduction of the local electron hole pair recombination sites and modulation of the band gap to improve the visible light absorption. This opens a promising route to the heterostructure design by modulating the band gap to promote efficient charge transfer.
Ferroelectric Control of the Conduction at the LaAlO3/SrTiO3 Heterointerface
(2013-06-25)
Vu Thanh Tra
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Chen, Jhih-Wei
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Huang, Po-Cheng
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Huang, Bo-Chao
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Cao, Ye
Graphene On Au-Coated SiOx Substrate: Its Core-Level Photoelectron Microspectroscopy Study
(2012-08-01)
Chen, Jhih-Wei
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Wang, Chiang-Lun
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Shiu, Hung Wei
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Lin, Chi-Yuan
;
Chang, Chen-Shiung
"The core-level electronic structures of exfoliated graphene sheets on a Au-coated SiOx substrate have been studied using synchrotron radiation photoelectron spectroscopy (SR-PES) on a micron scale. The graphene's visibility on the Au-coated SiOx substrate was first demonstrated by micro optical characterization, and then an SR-PES study was conducted. Because of the elimination of charging effect, a precise C 1s core-level characterization shows graphitic and contaminated carbon states of graphene. Different levels of Au-coating-induced p-type doping on single-and double-layer graphene sheets were also examined in the C 1s core-level shift. The Au-coated SiOx substrate can be treated as a simple but high-throughput platform for in situ studying graphene under further hybridization by PES. (C) 2012 The Japan Society of Applied Physics"
Heteroepitaxial approach to explore charge dynamics across Au/BiVO4 interface for photoactivity enhancement
(2015-07-01)
Chien Nguyen Van
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Chang, Wei Sea
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Chen, Jhih-Wei
;
Tsai, Kai-An
;
Tzeng, Wen-Yen
Heterostructure provides a powerful route in manipulating electrical transport, optical response, electrolytic water splitting and water treatment of complex oxides. As a model for noble metal/ complex oxide heterostructures, we have successfully prepared Au/BiVO4 (BVO) heterostructures in which the Au nanoparticles (NPs) with various sizes and densities were uniformly deposited on the {001} facets of epitaxial BVO thin films. The heterostructures exhibit significantly enhanced photoactivities in both dye degradation and electrolytic water splitting. By employing X-ray photoelectron spectroscopy, the energy band alignment of Au/BVO heterojunction suggests a charge separation at their interfaces, that can manipulate the photoexcited electron-hole pairs and photocatalytic efficiency of the heterostructures. Photogenerated carrier injection, which mainly affects the photoactivity of photocatalysis, was detected across Au/BVO interfaces by ultrafast dynamics spectroscopy. This study delivers a general approach to probe and understand the photochemistry of noble metal-complex oxide heterostructures for photoconversion applications. (C) 2015 Elsevier Ltd. All rights reserved.
Tunable photoelectrochemical performance of Au/BiFeO3 heterostructure
(2016)
Huang, Yen-Lin
;
Chang, Wei Sea
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Chien Nguyen Van
;
Liu, Heng-Jui
;
Tsai, Kai-An
Ferroelectric photoelectrodes, other than conventional semiconductors, are alternative photo-absorbers in the process of water splitting. However, the capture of photons and efficient transfer of photo-excited carriers remain as two critical issues in ferroelectric photoelectrodes. In this work, we overcome the aforementioned issues by decorating the ferroelectric BiFeO3 (BFO) surface with Au nanocrystals, and thus improving the photoelectrochemical (PEC) performance of BFO film. We demonstrate that the internal field induced by the spontaneous polarization of BFO can (1) tune the efficiency of the photo-excited carriers\' separation and charge transfer characteristics in bare BFO photoelectrodes, and (2) modulate an extra optical absorption within the visible light region, created by the surface plasmon resonance excitation of Au nanocrystals to capture more photons in the Au/BFO heterostructure. This study provides key insights for understanding the tunable features of PEC performance, composed of the heterostructure of noble metals and ferroelectric materials.
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.