Browsing by Author "Bow, JS"

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Epitaxial growth of the GaN film by remote-plasma metalorganic chemical vapor deposition
(1998-10-01)
Lai, WC
;
Chang, CY
;
Yokoyama, M
;
Guo, JD
;
Tsang, JS
GaN films were successfully grown by the remote-plasma metalorganic chemical vapor deposition (RPMOCVD) system. The composition of the GaN films could be tuned from nitrogen-rich to stoichiometric growth by varying the mole flow rate of trimethylgallium (TMGa). A hypothesis concerning the collisions between excited nitrogen and TMGa was also brought up. The collision between excited nitrogen and TMGa influences the characteristics of surface morphology, composition, growth rate, and growth mechanism. The characteristics of the GaN film were optimized by changing the growth conditions. The narrowest FWHM of the double-crystal X-ray rocking curve is about 0.2 degrees. Under optimized conditions, the composition of the GaN film is almost the same as that of the reference GaN film grown by MOCVD.
Forming gas annealing on physical characteristics and electrical properties of Sr0.8Bi2Ta2O9/Al2O3/Si capacitors
(2003-08-01)
Lan, BC
;
Hsu, JJ
;
Chen, SY
;
Bow, JS
;
材料科學與工程學系
Sr0.8Bi2Ta2O9 (SBT) ferroelectric film constructed on Al2O3/Si to form metal-ferroelectric-insulator-semiconductor (MFIS) was prepared to study the degradation behavior of SBT films under forming gas annealing (FGA). Although the diffusion of hydrogen ions has been detected during FGA treatment, no significant differences in the microstructure and crystalline phase are observed for the SBT film compared to that without FGA treatment. However, the diffusion of hydrogen ions leads to the rapid decrease in the dielectric constant but shows no apparent influence on the memory window of Sr0.8Bi2Ta2O9/Al2O3/Si capacitors. In addition, it was found that FGA shows a positive effect on the leakage current of MFIS in contrast to that of metal/ferroelectric/metal structure. The leakage current density of MFIS dramatically decreases as much as two orders of magnitude after FGA at 500degreesC compared to that without FGA treatment that was attributed to the reduced defects at the interface of Al2O3/Si. (C) 2003 American Institute of Physics.
Structural characterization of nano-sized calcium deficient apatite powders
(2004-01-01)
Liou, SC
;
Chen, SY
;
Lee, HY
;
Bow, JS
;
材料科學與工程學系
Nano-sized calcium-deficient apatitic (CDHA) crystals with Ca/P ratios from 1.5 to 1.67 were synthesized using wet chemical method and of needle-like shape with 5-10 nm in diameter and 40-50 nm in length was observed. The structural environment of the Ca atoms in all the CDHA nano-crystals has been investigated using EXAFS, XANES and EELS. The results reveal that a maximum Fourier transform amplitude occurs at the apatite with a Ca/P ratio of 1.67 and the structural disorder increase following the sequence of 1.67 > 1.5 > 1.6 > 1.55. A similar phenomenon is also observed in both K-edge XANES and L-2,L-3-edge ELNES in the Ca atom. The structural analysis further demonstrates that different chemical and biological properties among these CDHA nano-crystals with Ca/P ratio from 1.5 to 1.67 are primarily due to the effect of stoichiometry and non-stoichiometry as compared to the structural order-disorder. (C) 2003 Elsevier Ltd. All rights reserved.
Structural characterization of room-temperature synthesized nano-sized beta-tricalcium phosphate
(2004-07-01)
Bow, JS
;
Liou, SC
;
Chen, SY
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A simple route for synthesizing nano-sized beta-tricalcium phosphate (beta-TCP) at room temperature has been developed in methanol solvent. The phase evolution from CaHPO4, intermediate amorphous calcium phosphate (ACP) phases (including ACP1 and ACP2 with different structures) to final beta-TCP with increasing aging time was observed. The formation of beta-TCP phase is favored due to the incorporation of carbonate which can suppress the transformation of ACPI phase. High-resolution transmission electron microscopy image along [1-100] zone axis of beta-TCP reveals two types of lattice fringes (straight and wavy fringes) in beta-TCP structure due to structural imperfection. Furthermore, the observations of abnormal diffraction intensity and superlattice diffraction in selected-area diffraction patterns further confirm the chemical order-disorder characteristics in beta-TCP structure and can be used to elucidate the resorbability of beta-TCP in either in vivo or in vitro environment due to the imperfection in beta-TCP crystal. (C) 2003 Elsevier Ltd. All rights reserved.