Browsing by Author "Lu, CA"

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Diamond nucleation on Cu by using MPCVD with a biasing pretreatment
(2001-11-01)
Chuang, KL
;
Chang, L
;
Lu, CA
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Bias enhanced nucleation of diamond on polycrystalline Cu substrates has been investigated. With CH4 concentration increased, the nucleation density is increased and saturated at 10% CH4, but the quality of diamond is decreased. Bias voltages also play an important role on the nucleation of diamond. It is found that the nucleation density is highest when the voltage was set at -250 V. (C) 2001 Elsevier Science B.V. All rights reserved.
Growth of diamond films with bias during microwave plasma chemical vapor deposition
(2002-03-01)
Lu, CA
;
Chang, L
;
Huang, BR
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Diamond films on 3-inch diameter (100) silicon wafers were synthesized with bias during microwave plasma vapor deposition (MPCVD). The deposition parameters were as follows: 0.13% CH4 in H-2 pressure at 30 torr; deposition temperature at 768-869 degreesC, and a deposition time of 3-3.5 h. The bias voltage applied to the substrates during diamond growth varied from 0 to -450 V. The deposited films were characterized by Raman spectroscopy and electron microscopy. The results show that the film properties are uniform across the whole 3-inch diameter area. Raman spectra show that the ratio of sp(3) to sp(2) is increased with the bias voltage up to -350 V, while further increases in voltage resulted in a decreased ratio. It was found that column-shaped grains of diamond were directly grown from the substrate surface without grain coalescence in the lateral direction during growth. The nucleation density of diamond with biased growth was of the order of 10(9) cm(-2). (C) 2002 Elsevier Science B.V. All rights reserved.
Microstructural investigation of hexagonal-shaped diamond nanoplatelets grown by microwave plasma chemical vapor deposition
(2005-07-15)
Lu, CA
;
Chang, L
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Diamond crystallites in hexagonal-shaped nanoplatelet morphology were synthesized in microwave plasma chemical vapor deposition (MPCVD) system using a CH4/H-2 gas mixture with a ratio of 0.667%. Diamond nanoplatelets were deposited on (10 0) silicon substrate. The substrate was embedded within the plasma ball close to its center where the high temperature above 1100 degrees C was reached during the deposition. Surface morphologies and crystalline characteristics of the deposited diamond were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM and TEM observations clearly show that the diamond nanoplatelets exhibit hexagonal-shaped morphologies, and the thickness and the length are measured to be around 20-30nm and several hundred nanometers, respectively. Also, SEM shows that the distribution of the nanoplatelet density gradually increases from the center to the corner of the sample. TEM with selected area electron diffraction shows that each platelet is a single crystalline diamond. Both (1 1 0) and (1 1 1) orientations of the diamond platelets are observed. (c) 2005 Elsevier B.V. All rights reserved.
Parametric study and design of rib-reinforced steel moment connections
(2005-04-01)
Chen, CC
;
Lu, CA
;
Lin, CC
;
土木工程學系
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Department of Civil Engineering
Seismic behavior of moment connections used in moment-resisting frames can be improved by adding vertical ribs to beam-to-column joints. A parametric study is conducted here to investigate effects of design parameters of the rib on the connection behavior. Three geometrical parameters were set for the rib characterized with an extension. Moreover, nonlinear finite element analysis was used for the parametric analysis. The stress distribution and plastic strain demand for various combinations of these parameters are also presented and compared. The numerical results indicate that a single lengthened rib can eliminate the concentrations of stresses and strains found in the unreinforced connection, and reduce the potential for brittle fracture of the connection. On the basis of the numerical results and the confirmation of previous experiments, rib design variables are recommended, along with a design procedure. (c) 2005 Elsevier Ltd. All rights reserved.
Synthesis of diamond hexagonal nanoplatelets by microwave plasma chemical vapor deposition
(2004-11-01)
Lu, CA
;
Chang, L
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Variation of diamond deposition with temperature gradient was studied using standing-up substrates embedded within the plasma ball in microwave plasma chemical vapor deposition (MPCVD). The substrate is a polycrystalline diamond coated with a 30-nm thick iron film before deposition. Surface morphologies of the deposits and their crystalline characteristics were characterized by scanning electron microscopy, transmission electron microscopy (TEM), and selected area diffraction. On the upper area of the specimen near the center of the plasma ball where the temperature is the highest (>1100 degreesC, formation of diamond nanoplatelets in hexagonal shape with a thickness of 2060 nm and side length of several hundreds of nanometers is found. In the middle region, diamond nanoplatelets with some iron nanoparticles are observed. Around the bottom region with low temperature near the edge of the plasma ball, nanodiamonds, Fe nanoparticles, and carbon nanotubes coexisted. The relative temperature distributions of diamond and carbon nanotube growth are briefly discussed. (C) 2004 Elsevier B.V. All rights reserved.