Browsing by Author "Liang, KS"

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Binding effect of surface-modified cadmium sulfide on the microstructure of PS-b-PEO block copolymers
(2004-06-15)
Jeng, US
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Sun, YS
;
Lee, HY
;
Hsu, CH
;
Liang, KS
CdS nanoparticles with surfaces modified by mercaptoethanol have been synthesized for greater solubility in dimethylformamide (DMF) and the ability to preferentially bind to the poly(ethylene oxide) (PEO) blocks of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) copolymer. The size of the surface-modified CdS nanoparticles (M-CdS) in DMF can be characterized by the Schultz distribution of a mean radius of 18.4 Angstrom and a polydispersity of 0.5, using small-angle X-ray scattering (SAXS). These M-CdS nanoparticles can further disperse in the PS-b-PEO, with a slightly larger mean radius than that observed in DMF. The uptake of M-CdS nanoparticles for the PEO blocks of the PS-b-PEO saturates around 7% in volume fraction. The binding of the nanoparticles promotes a segregation of the PEO/nanoparticles and leads to spherical PEO/M-CdS microdomains in the composite film with a greatly enhanced thermal stability. The structural information obtained from X-ray scattering agrees well with the transmission electron microscopy images and differential scanning calorimetry results.
CdS nanoparticles induce a morphological transformation of poly(styrene-b-4-vinylpyridine) from hexagonally packed cylinders to a lamellar structure
(2005-07-26)
Yeh, SW
;
Wei, KH
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Sun, YS
;
Jeng, US
;
Liang, KS
Mercaptoacetic acid-modified CdS nanoparticles disperse selectively in the poly(4-vinylpyridine) domains of poly(styrene-b-4-vinylpyridine) (S4VP) block copolymer as a result of the formation of hydrogen bonds. This process in turn induces the morphological transformation of S4VP from a hexagonally packed cylinder structure into a lamellar structure, as evidenced from transmission electron microscopy, atomic force microscopy, and small-angle X-ray scattering studies. This transformation is consistent with that suggested by a theoretical prediction of the phase diagram of the mixed diblock copolymer/nanoparticle system.
Composition determination of semiconductor quantum wires by X-ray scattering
(2005-02-28)
Hsu, CH
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Tang, MT
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Lee, HY
;
Huang, CM
;
Liang, KS
Self-assembled semiconductor nano-structures, e.g. quantum dots and wires, have recently attracted intensive interests due to their potential applications in optoelectronic industry. Strain field, compositional profile, size, and shape are the key factors determining the physical properties of these nano-structures. However, due to their mesoscopic size, it is a challenge to accurately determine those geometric and chemical parameters. In this work, we present the structural and compositional investigation of GaAs quantum wires grown on InP(0 0 1) substrates by grazing incidence X-ray scattering. In particular, we applied resonant X-ray scattering to determine the compositional distribution within the wires. With properly chosen diffraction peak and X-ray energy range, the profile of energy scan is highly sensitive to the composition of the region with selected lattice constant. As compared to other composition determination methods, which rely on the intensity ratio either between a strong and a weak diffraction or between the same Bragg diffraction collected at different energies, the profile of energy scan is not affected by the significant intensity modulation introduced by inter-wire correlation. Therefore, this method can be applied to systems of various surface morphologies and ordered structures and still provides compositional information with high accuracy and good resolution. (C) 2004 Elsevier B.V. All rights reserved.
Effect of incorporated CdS nanoparticles on the crystallinity and morphology of poly (styrene-b-ethylene oxide) diblock copolymers
(2005-05-15)
Yeh, SW
;
Wu, TL
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Wei, KH
;
Sun, YS
;
Liang, KS
Surface-modified CdS nanoparticles selectively dispersed in hexagonally packed poly(ethylene oxide) (PEO) cylinders of poly(styrene-b-ethylene oxide) (PSEO) block copolymers were prepared. The photoluminescence and ultraviolet-visible characteristics of the presynthesized CdS nanoparticles in N,N-dimethylformamide and in PEO domains of the PSEO block copolymers were determined. Because of strong interactions between the CdS nanoparticles and PEO chains, as shown by Fourier transform infrared spectroscopy, the incorporation of the CdS nanoparticles prevented the PEO cylinders from properly crystallizing; this was confirmed by differential scanning calorimetry and wide-angle X-ray diffraction measurements. The intercylinder distance between the swollen and reduced-crystallinity CdS/PEO cylinders in turn increased, as confirmed by small-angle X-ray scattering and transmission electron microscopy. At a high CdS concentration (43 wt % or 8.3 vol % with respect to PEO), however, the hexagonally packed cylindrical nanostructure of the PSEO diblock copolymers was destroyed. (c) 2005 Wiley Periodicals, Inc.
Energy-tunable transmission x-ray microscope for differential contrast imaging with near 60 nm resolution tomography
(2006-06-12)
Yin, GC
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Tang, MT
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Song, YF
;
Chen, FR
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Liang, KS
An energy-tunable transmission hard x-ray microscope with close to 60 nm spatial resolution in three dimensions (3D) has been developed. With a cone beam illumination, a zone plate of 50 nm outmost zone width, a stable mechanical design, and software feedback, we obtained tomographic data sets that are close to 60 nm spatial resolution. Meanwhile, the element specific imaging was also obtained by a differential absorption contrast technique used below and above the absorption of the element. Examples of advanced intergraded circuit devices are used to demonstrate the element selectivity and spatial resolution in 3D of the microscope.
Morphological transformation of PS-b-PEO diblock copolymer by selectively dispersed colloidal CdS quantum dots
(2003-10-21)
Yeh, SW
;
Wei, KH
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Sun, YS
;
Jeng, US
;
Liang, KS
Phase behavior in polystyrene-block-poly (ethylene oxide) nanocomposites with colloidal CDS quantum dots upon heating.
(2004-08-22)
Sun, YS
;
Jeng, US
;
Liang, KS
;
Yeh, SW
;
Wei, KH
Transitions of domain ordering and domain size in a spherical-forming polystyrene-block-poly(ethylene oxide) copolymer and its composites with colloidal cadmium sulfide quantum dots
(2006-02-08)
Sun, YS
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Jeng, US
;
Liang, KS
;
Yeh, SW
;
Wei, KH
With specific annealing schemes applied to a neat polystyrene-block-poly(ethylene oxide) (SE) and its composites with cadmium sulfide quantum dots (CdS QD), we have observed microdomain structures and phase transitions in the system using temperature-resolved small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Both TEM images and SAXS results show clearly that incorporation of surfactant-tethered US QD preferentially into PEO blocks leads to increases in thermal stabilities of both bcc-packed lattice (referred as long-range order) and microdomains themselves in the sphere-forming SE/CdS composites. The bcc-packed lattice in the SE/CdS composites sustains better than that in the neat SE, during a temperature elevation to similar to 160 degrees C, at which the bcc-packed SE/CdS spheres start to transform into micelles with a short-range liquid-like order. Quantitative model analysis shows that the PEO/CdS micelles can retain their size in the SE/CdS composites up to 200 degrees C, whereas the PEO micelles shrink after the softening of the PS matrix around 100 degrees C and disassociate largely into the PS matrix of the neat SE at 160 degrees C. (c) 2005 Elsevier Ltd. All rights reserved.
X-ray scattering study of crystallization behavior in homoepitaxial growth of SrTiO3 films
(2002-10-15)
Lee, HY
;
Chang, WD
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Hsu, CH
;
Liang, KS
;
Lee, JY
X-ray reflectivity and grazing incidence crystal truncation rod (CTR) measurements were employed to characterize the microstructure and crystallization behavior of homoepitaxial SrTiO3 (STO) films deposited on polished SrTiO3 (0 0 1) substrates by pulse laser deposition technique. X-ray scattering results indicate that room temperature grown STO film has a density approximately 11.1% lower than that of bulk STO and shows poor epitaxial relation with the substrate. Subsequent annealing at 760 degreesC for 20 s appeared to transform the film into two-layer structure, with the density of the layer right above the substrate approaching to its bulk value, while the density of the top 15.5 Angstrom thick layer reducing to near 45% of bulk STO. The annealing process also leads to an increase of lateral lattice constant together with the growth of domain size. The appearance of interference fringes of the CTR after annealing, which is also observed at the film grown at 760 degreesC, clearly demonstrates the development of epitaxy upon short time annealing. (C) 2002 Elsevier Science B.V. All rights reserved.