Browsing by Author "Nguyen, TP"

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Optical and electrical investigations of poly(p-phenylene vinylene)/silicon oxide and poly(p-phenylene vinylene)/titanium oxide nanocomposites
(2005-01-03)
Yang, SH
;
Nguyen, TP
;
Le Rendu, P
;
Hsu, CS
;
應用化學系
Composites made by incorporation of silicon oxide (SiO2) or titanium (TiO2) nanoparticles into poly(p-phenylene vinylene) (PPV) have been fabricated and their electrical and optical properties have been investigated. The UV-vis absorption and Raman spectra showed that SiO2 nanoparticles reduced the conjugation lengths of PPV chains, while TiO2 nanoparticles did not. In the case Of SiO2 nanoparticles, the reduction of conjugation length was more noticeable on increasing the oxide concentration or on decreasing the particle size. Fourier transform infrared (FT-IR) spectra showed that both types of nanoparticles also reduced the formation of carbonyl groups in PPV main chains. Current-voltage characteristics measured in the indium tin oxide (ITO)-composite-MgAg diodes exhibit different electrical behavior to the composites depending on the particle size and the nature of the used oxide. The composite-electrode contact morphology, the polymer-dielectric particle contact, and the change in the polymer chain length are the possible explanations for these changes in behavior of the diodes. (C) 2004 Elsevier B.V. All rights reserved.
Optical and electrical properties Of PPV/SiO2 and PPV/TiO2 composite materials
(2005)
Yang, SH
;
Nguyen, TP
;
Le Rendu, P
;
Hsu, CS
;
應用化學系
Composites made by incorporation of SiO2 or TiO2 nanoparticles into poly (p-phenylene vinylene) (PPV) have been fabricated and their optical and electrical properties have been investigated. The UV-vis absorption band of the composite films showed a large blue-shift with SiO2 nanoparticles, but only little difference with TiO2 nanoparticles. Photoluminescence (PL) spectra showed the same blue-shift trend for SiO2 composites, and in addition, an increase in intensity of the high energy shoulder (515 nm) when the concentration of nanoparticles increased. Raman spectra showed a reduction of the 1547/1625 cm(-1) band ratio in SiO2 composites but not in TiO2 ones. These results suggest that SiO2 nanoparticles reduced the PPV conjugation length, while TiO2 nanoparticles did not. For SiO2 particles, the reduction of conjugation lengths is more pronounced on increasing the oxide concentration or on decreasing the particle size. Fourier-transform Infrared (FT-IR) spectra showed that both types of nanoparticles reduced the formation of carbonyl groups in PPV main chains. Current-voltage characteristics measured in ITO-composite-MgAg diodes exhibit different electrical behavior of the composites depending on the particle size and the nature of the oxide. The composite-electrode contact morphology, the polymer-dielectric particle contact and the change in the polymer chain length are the possible explanations for these changes in behavior of the diodes. (c) 2004 Published by Elsevier Ltd.
Optical properties of nanosize aggregation of phenylene vinylene oligomers
(2005-08-15)
Nguyen, TP
;
Yang, SH
;
Gomes, J
;
Wong, MS
;
應用化學系
In this paper, we report the experimental results on the optical properties of oligo-phenylene vinylenes (OPVs) formed in nanosize pores of porous silicon substrates. Strong modifications of the photoluminescence properties of nanosize aggregation of OPVs were observed at room temperature, such as a blue shift of the PL spectra, whereas the structure of the oligomers is preserved as proved by Raman scattering experiments. However, the penetration of the oligomers into the nanopores was found to depend on the conformation of the chains, which is, in turn, conditioned by the solvents, used to dissolve the oligomer powder. (C) 2005 Published by Elsevier B.V.
Optical properties of poly(2-methoxy-5-(2 '-ethyl-hexyloxy)-phenylene vinylene) deposited on porous alumina substrates
(2005)
Nguyen, TP
;
Yang, SH
;
Le Rendu, P
;
Khan, H
;
應用化學系
Thin films of poly(2-methoxy-5-(2'-ethyl-hexyloxy)-phenylene vinylene) (MEH-PPV) were deposited from solutions prepared with different solvents, on alumina-1%Mg substrates with different pore sizes from 18 to 118 nm to study the effects of the size on the optical properties of the polymer. The photoluminescence (PL) spectra of films cast from solutions using chloroform, toluene or xylene are almost similar, suggesting that the solvents have little effect on the solid films. In the composite systems, a blue shift of the polymer PL spectra was observed when the pore size decreases. Raman spectra recorded on these samples did not show significant changes compared to that of the polymer, suggesting that the structure of the polymer was preserved. The modifications observed in the PL spectra are attributed to the nanosize effect of the polymer deposited in the pores resulted from the chain conformation, which depends on the nature of the solvents used. (c) 2004 Elsevier Ltd. All rights reserved.