Browsing by Author "Peng, Yu-Yun"

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Dielectric confinement effect in ZnO quantum dots embedded in amorphous SiO2 matrix
(2007-10-07)
Peng, Yu-Yun
;
Hsieh, Tsung-Eong
;
Hsu, Chia-Hung
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The dielectric confinement effect on the blue shift Delta E-g(a) of the ZnO quantum dots (QDs) embedded in the SiO2 matrix is evaluated by applying a multi-shell two-electron system model. The experimental measurement and the calculations of various dielectric structures indicate that the composite matrix structure provides a better estimation of the blue shift of the ZnO QDs-SiO2 system than the multi-shell structure. The proportionality factor x defined in this work exhibits a dependence of the dielectric confinement energy on the specific dimension ratio (the b/a ratio) and the dielectric constant epsilon(matrix) of the outer matrix. The result of the calculation also shows the limit of the two-electron system in estimating the ground-state energy of samples with high dot density. However, the correlation shows the existence of the strong dielectric confinement effect in ZnO QDs-SiO2 thin films and allows a better understanding of the semiconductor QDs-dielectric systems.
Effects of interface bonding configuration on photoluminescence of ZnO quantum dots-SiOxNy nanocomposite films
(2008-04-01)
Peng, Yu-Yun
;
Hsieh, Tsung-Eong
;
Hsu, Chia-Hung
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Nanocomposite films containing ZnO quantum dots (QDs) and SiOxNy matrix were prepared by target-attached radio frequency sputtering. Photoluminescence (PL) dominated by violet and blue emissions was observed from all ZnO QD-SiOxNy nanocomposite films with dot diameters ranging from 2.77 to 6.65 nm. X-ray photoemission spectroscopy (XPS) revealed the formation of nitrogen-correlated bonding configurations in both the SiOxNy matrix and the dot/matrix interfaces. The nitrogen-correlated configuration at the interface produced a substantial polarization effect at dot surface. The suppression of green-yellow emission observed in photoluminescence spectra of all samples was ascribed to the hole-trapping process promoted by the enhancement of the surface polarization.
Method for preparing nanocomposite ZnO-SiO2 fluorescent film by sputtering
(2008-06-05)
Hsieh, Tsung-Eong
;
Peng, Yu-Yun
A method for preparing nanocomposite ZnO—SiO2 fluorescent thin film by magnetron sputtering is proposed. ZnO is formed as nano-sized crystalline particles uniformly dispersed in the amorphous SiO2 matrix after the sputtering. The photoluminescence (PL) revealed that the spectra consisted of three emission bands, violet, blue and green-yellow and the mixed light turns out to be white. By adjusting the ZnO doping concentration, the relative emission intensities of the three bands can be modulated so that white light with different color temperatures can be obtained. By the invention, the whole process comprised of only one single-layer deposition that can be applied on any substrate.
Optical characteristics and microstructure of ZnO quantum dots-SiO2 nanocomposite films prepared by sputtering methods
(2006-11-20)
Peng, Yu-Yun
;
Hsieh, Tsung-Eong
;
Hsu, Chia-Hung
;
材料科學與工程學系
;
Department of Materials Science and Engineering
ZnO quantum dots (QDs)-SiO2 nanocomposite films were prepared using the target-attached radio-frequency sputtering. The transmission electron microscopy revealed the uniform dispersion of ZnO QDs with diameters about 2-7 nm in amorphous SiO2 matrix. The photoluminescence showed that small ZnO QDs are able to emit white light with luminescence spectra similar to those of the present GaN-based light emitting diode (LED). The calculated chromaticity coordinates of emitting light evidenced the feasibility of ZnO QDs-SiO2 nanocomposite films as the fluorescence material in optoelectronic devices. (c) 2006 American Institute of Physics.
The Conductive Property of ZnO QDs-SiO(2) and ZnO QDs-SiO(x)N(y) Nanocomposite Films
(2009-08-01)
Peng, Yu-Yun
;
Hsieh, Tsung-Eong
;
Hsu, Chia-Hung
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The dc and ac conductive properties of ZnO QDs-SiO(2) and ZnO QDs-SiO(x)N(y) nancomposite films prepared by the target-attached sputtering method are investigated. Both two nanocomposite samples reveal a typical characteristic of a metal-oxide varistor (MOV) on the J-E plots with distinct threshold electric fields (E(th)) which are affected by the molecular bonding configurations in the matrix and at the dot/matrix interfaces. The two systems exhibit dissimilar dependences of dc conductivity (sigma(dc)) on the ZnO content, revealing the limitation of conventional percolation models in which the surface interaction term is usually ignored. The ac conduction behaviors of the two nanocomposite systems were also analyzed and their percolation concentrations V(c) (22.75% for ZnO QDS-SiO(2) and 20.78% for ZnO QDs-SiO(x)N(y)) are determined by the construction of master curves. Analytical results illustrated that the dielectric matrix type indeed affects the defect configuration and transport behaviors inside ZnO dots. Hence, manipulation of dielectric matrix type can possibly achieve various optical and electrical properties in ZnO QDs-dielectric nanocomposite systems.
White-light emitting ZnO-SiO2 nanocomposite thin films prepared by sputtering method
(2006)
Peng, Yu-Yun
;
Hsieh, Tsung-Eong
;
Hsu, Chia-Hung
;
材料科學與工程學系
;
Department of Materials Science and Engineering
ZnO-SiO2 nanocomposite thin films were prepared using RF sputtering method without substrate heating. The photoluminance (PL) measurements showed that the ZnO-SiO2 nanocomposite thin films are able to emit white light consisting of violet, blue, and green-yellow band emissions. The blue emission was attributed to the large amount of ZnO/SiO2 interfaces, which enlarges the depletion layer width and then enhances the related transition. Further analyses indicated that the defect structure of samples could be manipulated by the amount and distribution of ZnO nanoparticles in SiO2 matrix to yield distinct luminescence property.