Browsing by Author "Lai, YJ"

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Effect of hydrating liquid on the hydraulic properties of geosynthetic clay liners
(2002-02-01)
Shan, HY
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Lai, YJ
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土木工程學系
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Department of Civil Engineering
The engineering properties of geosynthetic clay liners (GCLs) are closely related to the chemistry of pore liquid. For applications in lining systems or cover systems of landfills, covers for remediation sites, and secondary containment systems, GCLs are likely to be permeated by more than one type of liquid. In this study, GCL specimens were hydrated and permeated with different liquids. The hydraulic conductivity of these GCL specimens was determined. The results showed that the hydraulic conductivity of GCLs was controlled by both hydrating and permeating liquid. In addition, even if GCLs were hydrated with aqueous phase liquids other than fresh water, they still have the ability to retard infiltration effectively. (C) 2002 Elsevier Science Ltd. All rights reserved.
Growth mode transfer of self-assembled CdSe quantum dots grown by molecular beam epitaxy
(2006-01-15)
Lai, YJ
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Lin, YC
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Fu, CP
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Yang, CS
;
Chia, CH
Self-assembled CdSe/ZnSe quantum dots (QDs) were grown at various growth temperatures on GaAs (0 0 1) by molecular beam epitaxy. An optimum growth temperature for CdSe/ZnSe QDs was found to be 260 degrees C. The Stranski-Krastanow (SK) growth mode was confirmed clearly by atomic force microscopy images. The coherent SK QDs were observed from 2.5 monolayers (MLs). Two types of QDs were found with the CdSe coverage of 3.0 MLs. It was attributed to a growth mode change from the coherent SK growth mode to the ripening growth mode. A schematic diagram of the growth mechanism of self-assembled CdSe QDs was presented. Moreover, the photoluminescence spectra of samples with various thicknesses were investigated. A dramatic change of optical properties confirmed that the QD structure formed with thickness above 2.5 MLs. Finally, the dot size and the density distributions were controlled after growth by in-chamber thermal annealing. For the sample grown at 3.0 MLs, the distribution of dot sizes was controlled from 6.0 to 6.5 x 10(3) nm(3) at an annealing temperature of 400 degrees C. (c) 2005 Published by Elsevier B.V.
Optical properties of self-assembled ZnTe quantum dots grown by molecular-beam epitaxy
(2005-02-01)
Yang, CS
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Lai, YJ
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Chou, WC
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Chen, WK
;
Lee, MC
The morphology and the size-dependent photoluminescence (PL) spectra of the type-II ZnTe quantum dots (QDs) grown in a ZnSe matrix were obtained. The coverage of ZnTe varied from 2.5 to 3.5 monolayers (MLs). The PL peak energy decreased as the dot size increased. Excitation power and temperature-dependent PL spectra are used to characterize the optical properties of the ZnTe quantum dots. For 2.5- and 3.0-ML samples, the PL peak energy decreased monotonically as the temperature increased. However, for the 3.5-ML sample, the PL peak energy was initially blueshifted and then redshifted as the temperature increased above 40 K. Carrier thermalization and carrier transfer between QDs are used to explain the experimental data. A model of temperature-dependent linewidth broadening is employed to fit the high-temperature data. The activation energy, which was found by the simple PL intensity quenching model, of the 2.5, 3.0, and 3.5 MLs were determined to be 6.35, 9.40, and 18.87 meV, respectively. (C) 2005 American Institute of Physics.
Optical properties of Zn1-xCdxSe epilayers grown on (100)GaAs by molecular beam epitaxy
(2004-08-01)
Kuo, MC
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Chiu, KC
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Shih, TH
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Lai, YJ
;
Yang, CS
Zn1-xCdxSe epilayers were grown on (100) GaAs substrates by molecular beam epitaxy. Lattice constants of the epilayers were measured by (004) rocking curve X-ray diffraction. A full width at half maximum of 475 to 2100 arcsec was obtained. The dependence of the energy gap on temperature, measured by the photoluminescence (PL) spectra, was fitted by Varshni's [Y. P. Varshni: Physica 34 149 (1967)] and O'Donnell's [R. P. O'Donnell and X. Chen: Appl. Phys. Lett. 58 2924 (1991)] models. The fitting parameters beta (161 K to 368K) and (hv) (13 meV to 24 meV), related to phonon energy, were obtained from Varshni and O'Donnell fits, respectively. The activation energies calculated from the integrated PL intensity versus inverse temperature decrease as the Cd content increases. The broadening of the PL linewidth with temperature was fitted by Gamma(T) = Gamma(0) + Gamma(a)T + Gamma(LOI)/[exp(homega(LOI)/kT) - 1] + Gamma(LO2)/[exp(homega(LO2)/kT) - 1] + Gamma(i)exp(-/kT). The impurity binding energy, (E-b), was found to decrease as the Cd composition increases.