Browsing by Author "Lai, Yu-Ling"

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Effectiveness of organic molecules for spin filtering in an organic spin valve: Reaction-induced spin polarization for Co atop Alq(3)
(2015-01-21)
Tu-Ngoc Lam
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Lai, Yu-Ling
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Chen, Chih-Han
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Chen, Po-Hung
;
Chan, Yuet-Loy
The spin polarization of organic-ferromagnetic interfaces in an organic spin valve critically affects the efficiency of spin injection or detection. We examined the chemical and electronic properties of ferromagnetic Co deposited on organic Alq(3) and the interfacial spin-polarized capability of the electronic states. Our x-ray photoemission spectra and calculations with density-functional theory indicate a sequential and unequal distribution of charge from Co clusters to N and then to O atoms in Alq(3). The preferential orbital hybridization at specific functional sites produces efficient spin polarization of organic molecules. Element-specific measurements of x-ray magnetic circular dichroism demonstrate the preferential spin polarization in the lowest unoccupied molecular orbital state of N atoms at the complex interface for Co atop Alq(3), which agrees satisfactorily with calculation. Our results indicate that an induced interfacial spin polarization on engineering the dominant reaction of Co with mainly N and O atoms in Alq(3) might pave a way for effective spin filtering in organic spintronics.
Enhanced Magnetic Anisotropy via Quasi-Molecular Magnet at Organic-Ferromagnetic Contact
(2013-01-17)
Hsu, Yao-Jane
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Lai, Yu-Ling
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Chen, Chih-Han
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Lin, Ying-Chang
;
Chien, Hsiu-Yun
To realize the origin of efficient spin injection at organic-ferromagnetic contact in organic spintronics, we have implemented the formation of quasi-molecular magnet via surface restructuring of a strong organic acceptor, tetrafluoro-tetracyanoquinodimethane (F4-TCNQ), in contact with ferromagnetic cobalt. Our results demonstrate a spin-polarized F4-TCNQ layer and a remarkably enhanced magnetic anisotropy of the Co film. The novel magnetic properties are contributed from strong magnetic coupling caused by the molecular restructuring that displays an angular anchoring conformation of CN and upwardly protruding fluorine atoms. We conclude that the pi bonds of CN, instead of the lone-pair electrons of N atoms, contribute to the hybridization-induced magnetic coupling between CN and Co and generate a superior magnetic order on the surface.
Fluorene Conjugated Polymer/Nickel Oxide Nanocomposite Hole Transport Layer Enhances the Efficiency of Organic Photovoltaic Devices
(2017-01-25)
Chiou, Guan-Chiun
;
Lin, Ming-Wei
;
Lai, Yu-Ling
;
Chang, Chiao-Kai
;
Jiang, Jian-Ming
A nanocomposite layer comprising the conjugated polymer poly[(9,9-bis(3\'(N,N-dimethylamino)propy1)-2,7-fluorene)-alt-2,7-(9,9-dioctyl)fluorene] (PFN) and nickel oxide (NiOx) has been employed as the hole transport layer (HTL) in organic photovoltaics (OPVs) featuring PBDTTBO-C-8 and [6,6] -phenyl -C-71-butyric acid methyl ester (PC71BM) as the active layer. The optimal device incorporating the PFN:NiOx nanocomposite as the HTLs displayed a power conversion efficiency (PCE) to 6.2%, up from 4.5% for the corresponding device incorporating pristine NiOx as the HTL layer: a nearly 40% improvement in PCE. X-ray photoelectron spectroscopy (XPS) was used to determine the types of chemical bonding, ultraviolet photoelectron spectroscopy (UPS) to measure the change in work function, and atomic force microscopy (AFM) to examine the morphology of the composite layers. The growth of nickel trioxide, Ni2O3, in the PFN:NiOx layer played a key role in producing the p-doping effect and in tuning the work function, thereby improving the overall device performance.
Interfacial symmetry of Co-Alq(3)-Co hybrid structures for effective spin filtering
(2015-11-01)
Lam, Tu-Ngoc
;
Lai, Yu-Ling
;
Chen, Chih-Han
;
Chen, Po-Hung
;
Wei, Der-Hsin
Understanding the interfacial behavior at FM-OSC-FM hybrid structures for both the bottom contact (Alq(3) adsorption on Co, Co/Alq(3)) and the top contact (Co atop Alq(3), Alq(3)/Co) is crucial for efficient spin filtering with transport of spin-polarized charge carriers through these interfaces. X-ray photoelectron spectroscopy (XPS) spectra indicate a symmetry of charge transfer from Co to Alq(3) and the corresponding orbital hybridization to a certain extent at both contacts. The alignment of energy levels at both Alq(3)/Co and Co/Alq(3) heterostructures is depicted with ultraviolet photoelectron spectroscopy (UPS). Through magnetic images acquired with a X-ray photoemission electron microscope (XPEEM), the strong hybridization of the top contact presents no micromagnetic domain but still shows magnetic coupling, to some extent, to the bottom contact in the Co-Alq(3)-Co trilayer structure. Measurements of X-ray magnetic circular dichroism (XMCD) demonstrate the induced spin-polarization of non-magnetic Alq(3) at both contacts, proving Alq(3) a unique and promising organic material for spin filtering in OSV. (C) 2015 Elsevier B.V. All rights reserved.
Interfacial symmetry of Co-Alq(3)-Co hybrid structures for effective spin filtering (vol 354, pg 90, 2015)
(2018-05-31)
Tu-Ngoc Lam
;
Lai, Yu-Ling
;
Chen, Chih-Han
;
Chen, Po-Hung
;
Wei, Der-Hsin
Microscopic evidence for the dissociation of water molecules on cleaved GaN(1(1)over bar00)
(2018-01-14)
Wu, Shih-Yu
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Lang, Liang-Wei
;
Cai, Pei-Yang
;
Chen, Yun-Wen
;
Lai, Yu-Ling
The dissociation of water molecules absorbed on a cleaved non-polar GaN(1(1)over bar00) surface was studied primarily with synchrotron-based photoemission spectra and density-functional-theory calculations. The adsorbed water molecules are spontaneously dissociated into hydrogen atoms and hydroxyl groups at either 300 or 130 K, which implies a negligible activation energy (<11 meV) for the dissociation. The produced H and OH were bound to the surface nitrogen and gallium on GaN(1(1)over bar00) respectively. These results highlight the promising applications of the non-polar GaN(1(1)over bar00) surface in water dissociation and hydrogen generation.
Spin filtering of a termination-controlled LSMO/Alq(3) heterojunction for an organic spin valve
(2017-09-21)
Lam, Tu-Ngoc
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Huang, Yen-Lin
;
Weng, Ke-Chuan
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Lai, Yu-Ling
;
Lin, Ming-Wei
La1-xSrxMnO3 (LSMO) is weLL known as an efficient spin-injection electrode in ferromagnetic organic hybrid-based organic spin valves (OSV). Herein, we examine the influence of three terminating Layers of LSMO fiLms (mixed-, MnO2-, and LaSrO- (LSO-) terminated) on the spin filter at the bottom interface of tri (8-hydroxyquinoLine) aluminum (ALq(3)) deposited on these substrates. Angle-dependent X-ray photoelectron spectra (XPS) demonstrated the presence of SrO segregation at the outermost Layer for three types of LSMO fiLms but in different amounts that might contribute to their magnetic properties. A weak surface coupling between LSMO and Alq(3) was obtained through a small increase of Mn L-edge X-ray magnetic circular dichroism (XMCD) but it does not vary the bulk magnetic properties of LSMO fiLms upon Alq(3) adsorption (LSMO/Alq(3)). The surface dipoles due to the interaction between LSMO fiLms and Alq(3) were found to be 0.5, 0.5, and 0.7 eV for the mixed-ter/Alq(3), MnO2-ter/Alq(3), and LSO-ter/Alq(3) interfaces, respectively. Our results indicate that the segregated SrO Layer Ways an important role in the surface electronic and magnetic properties at LSMO/Alq(3) interfaces, which contributes to a fundamental understanding of the spin injection and transport in LSMO-Alq(3) hybrid-based OSV devices.