Browsing by Author "Chen, Chia-Chun"

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Electroluminescence from a conjugated polymer grafted with CdSe/ZnS: High brightness and improved efficiency
(2006-09-15)
Chen, Kuei-Bai
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Chen, Ming-Hwey
;
Yang, Sheng-Hsiung
;
Hsieh, Chao-Hsiang
;
Hsu, Chain-Shu
A new series of sulfide-substituted poly(1,4-phenylene vinylene) derivatives (S1PPV-S3PPV) with different composition ratios were successfully synthesized,via the Gilch route. The CdSe/ZnS were grafted to the sulfur atoms by ligand exchange reaction. The grafted CdSe/ZnS contents were determined from TGA analysis to be from 4.6 to 37.8%. A new peak at 1151 cm(-1) formed in FT-IR after ligand exchange, which is attributed to the force formation between sulfur and CdSe. The GPC results show that the molecular weights of final polymers became higher after ligand exchange. Thin films of obtained polymers emitted bright green and yellow light with the max emission peak located from 546 to 556 nm. Double-layer LEDs with an ITO/PEDOT/polymer/Ca/Al configuration were fabricated to evaluate the potential use of these polymers. The turn-on voltages of the devices were about 4-5 V As the CdSe/ZnS content increased in grafted polymers, the device performance was significantly enhanced as compared to pristine polymers. In the case of S3PPV, the double-layer device showed a maximum luminance of 6073 cd/m(2) with a current yield of 0.82 cd/A. The maximum luminance and current yield was enhanced to 13,390 cd/m(2) and 2.25 cd/A by grafting CdSe/ZnS onto polymers. (c) 2006 Wiley Periodicals, Inc.
Low operation voltage macromolecular composite memory assisted by graphene nanoflakes
(2013)
Lai, Ying-Chih
;
Wang, Di-Yan
;
Huang, I-Sheng
;
Chen, Yu-Ting
;
Hsu, Yung-Hsuan
The trend towards simple and low-cost processing is one of the most important for macromolecular memory development. Here, bistable memory devices using a solution-processable active material, a mixture of graphene nanoflakes (GNFs) and insulating poly(vinyl alcohol) (PVA), are investigated, which serve as the first example for the direct integration of as-prepared nanoscale graphene into macromolecular memory devices through a one-step low-temperature processing method. Bistable electrical switching behavior and nonvolatile rewritable memory effects are realized by using an indium-tin-oxide/GNF-PVA/silver (ITO/GNF-PVA/Ag) sandwich structure. The resulting device exhibits low operation voltages of +1.4 V (turn-on) and -1.3 V (turn-off), which is promising for memory cells with low power consumptions. The programmable ON- and OFF-states possess a retention time of over 10(4) s and endure up to 10(7) read pulses. The carrier transport in the OFF- and ON-states follows the typical trap-limited space charge limited current and Ohmic laws, respectively. The asymmetric electrical switch behavior is therefore attributed to conducting filaments formed in the PVA layer assisted by the charged GNFs that induce the transition of the conductivity. Our study provides a potential approach for integrating as-prepared graphene into macromolecular memory devices with excellent performances through a simple solution-process.
Low-Frequency Contact Noise of GaN Nanowire Device Detected by Cross-Spectrum Technique
(2011-06-01)
Li, Liang-Chen
;
Huang, Kuo-Hsun
;
Wei, Jia-An
;
Suen, Yuen-Wuu
;
Liu, Ting-Wei
We report the properties of low-frequency contact noise of multielectrode GaN nanowire (NW) devices. A two-port cross-spectrum technique is used to discriminate the noise of the ohmic contact from that of the NW section. The diameter of the GaN NW is around 100 nm. The Ti/Al electrodes of the NWs are defined by e-beam lithography. The typical resistance of a NW section with a length of 800nm is about 5.5 k Omega and the two-wire resistance is below 100 k Omega. The results show that the low-frequency excess noise of the GaN NW is much smaller than that of the current-flowing contact, indicating that the contact noise dominates the noise behavior in our GaN NW devices. A careful study of the noise amplitude (A) of the 1/f noise of different types of NW and carbon nanotube devices, both in our work and in the literature, yields an empirical formula for estimating A from the two-wire resistance of the device. (C) 2011 The Japan Society of Applied Physics
POLY 162-Electroluminescence from a conjugated polymer grafted with CdSe/ZnS quantum dots: High brightness and improved efficiency
(2006-09-10)
Chen, Kuei-Bai
;
Chen, Ming-Hwey
;
Yang, Sheng-Hsiung
;
Hsu, Chain-Shu
;
Chen, Chia-Chun
Vitalizing fuel cells with vitamins: pyrolyzed vitamin B12 as a non-precious catalyst for enhanced oxygen reduction reaction of polymer electrolyte fuel cells
(2012-01-01)
Chang, Sun-Tang
;
Wang, Chen-Hao
;
Du, He-Yun
;
Hsu, Hsin-Cheng
;
Kang, Chih-Ming
The limited natural abundance and high cost of Pt has been a major barrier in its applications for hydrogen or methanol fuel cells. In this work, based on the pyrolyzed corrin structure of vitamin B12 (py-B12/C), it is reported to produce superior catalytic activity in the oxygen reduction reaction (ORR) with an electron transfer number of 3.90, which is very close to the ideal case of 4. The H-2-O-2 fuel cell using py-B12/C provides a maximum power density of 370 mW cm(-2) and a current density of 0.720 A cm(-2) at 0.5 V at 70 degrees C. Calculations based on density functional theory suggests that the corrin complex with a low-symmetric structure offers a much preferable path for the ORR, which is not applicable to the porphyrin with a high-symmetric structure. The long-term stability and high ORR activity of py-B12/C make it a viable candidate as a Pt-substitute in the ORR.