Browsing by Author "Chen, HG"

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Characterization of diamond nanoplatelets
(2004-04-01)
Chen, HG
;
Chang, L
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材料科學與工程學系
;
Department of Materials Science and Engineering
Diamond deposition at a temperature above 1000 degreesC was carried out in a microwave plasma chemical vapor deposition reactor using a 3% CH4/H-2 gas mixture. A polycrystalline diamond substrate was coated with a thin film of nickel in 100-nm thickness before deposition. Electron microscopy characterization of electron diffraction, high-resolution imaging, and electron energy loss spectroscopy shows that the diamonds deposited exhibit regular shapes in triangles and parallelogram with well-faceted surfaces. These diamond platelets are single crystallites with a uniform thickness of approximately 30-70 nm and length of several hundred nanometers to a few micrometers. The platelet morphology suggests that it is formed by lateral growth. Also, it was found that the diamonds are covered with a 1 to 2-nm thick graphite films in epitaxy. (C) 2003 Elsevier B.V. All rights reserved.
Diamond deposition on Au/amorphotis Si thin films
(2004-04-01)
Kao, CK
;
Yan, JK
;
Chang, L
;
Cho, SY
;
Chen, HG
Au/amorphous Si/SiO2/Si structure was used as substrate for diamond deposition by microwave plasma CVD. The Au-Si phase diagram shows a eutectic point at 363 degreesC. At deposition temperatures of 700-800 degreesC, the Au and amorphous Si films were alloyed as liquid during deposition, which resulted in formation of an array of single crystalline Si whiskers. Microstructural characterization shows that the Si whiskers have a diameter in the range of 50 nm-5 mum with facet on the top surface. The Si whiskers are shown to be oriented along <311> directions. Diamond particles deposited are found only on top of the Si whiskers. The diamond particles can be either of polycrystalline or single crystalline characteristics. (C) 2004 Elsevier B.V. All rights reserved.
Diamond growth onCoSi(2)/Si by bias-enhanced microwave plasma chemical vapor deposition method
(2001-11-01)
Chen, MR
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Chang, L
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Chang, DF
;
Chen, HG
;
材料科學與工程學系
Diamond was grown on polycrystalline CoSi2/Si substrates by bias-enhanced microwave plasma chemical vapor deposition. Both of the positive and negative biasing effects were investigated by microstructural characterization. It has been found that nucleation density can reach similar to 10(9) cm(-2) with positive biasing, much higher than with negative biasing. Cross-sectional transmission electron microscopy shows that diamond deposited by positive biasing grows on a relatively smooth CoSi2 surface, while the etching effect of ion bombardment during negative biasing results in a rough CoSi2 surface. The diamond morphology obtained with negative bias has a flat surface with a strong (1 0 0) texture. (C) 2001 Elsevier Science B.V. All rights reserved.
Diamond nucleation on Ni3Al substrate using bias enhanced nucleation method
(2005-02-01)
Chen, HG
;
Chang, L
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Diamond deposition with positive and negative bias enhanced nucleation (BEN) pretreatments on mirror-polished polycrystalline Ni3Al substrates has been investigated, respectively. It was found that diamond deposition on the substrates under both biasing exhibited significant variations among grains of different orientations. The substrate surface was found to be rough in the case of negative biasing, whereas it was smooth in the case of positive biasing. Thus, the correlation of the crystallographic orientation of grains on the samples with the diamond nucleation behavior was systematically characterized for the case of positive biasing by electron backscattered diffraction method with scanning electron microscopy. Diamond deposition on Ni3Al grains near (111) orientation results in higher nucleation densities, while the densities are low on (110) and (100) oriented grains. Also, the interfacial microstructure between diamond deposited and Ni3Al was characterized by cross-sectional transmission electron microscopy. (C) 2004 Elsevier B.V. All rights reserved.
Growth and characterization of chemical-vapor-deposited zinc oxide nanorods
(2006-03-01)
Wu, CL
;
Chang, L
;
Chen, HG
;
Lin, CW
;
Chang, TF
ZnO nanorods were grown on Si substrates by metal-organic chemical vapor deposition (CVD). The ZnO nanorods were characterized by scanning electron microscopy, transmission electron microscopy (TEM), and X-ray diffraction. It was found that highly oriented ZnO single-crystalline nanorods were formed only on the substrate coated with a gold film. Without the gold, ZnO was deposited as a continuous film. No Au was observed on top of the ZnO nanorods, implying that the Au plays no role as catalytic metal in vapor-liquid-solid mechanism for formation of ZnO nanorods. In CVD, oriented ZnO nanorods along the c-axis were grown as a result of < 111 > textured Au. High-resolution TEM shows that the gold layer and ZnO are in orientation relationship of Au 111 planes//ZnO (0002) basal planes. (c) 2005 Elsevier B.V. All rights reserved.
Lyapunov-based quantitative analysis of robust stability
(1995-07-01)
Chen, HG
;
Han, KW
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電控工程研究所
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Institute of Electrical and Control Engineering
The robust stability of control systems with perturbation is considered. Using Lyapunov functions, quantitative bounds on the perturbation ave obtained such that the systems remain stable. Foul classes of perturbations are treated and four measures of robust stability are proposed: the nondelay unstructured, delayed unstructured, nondelay structured and delayed structured measures. Examples are given, and comparisons with the results given in current literature are made.
Structural investigation of diamond nanoplatelets grown by microwave plasma-enhanced chemical vapor deposition
(2005-03-01)
Chen, HG
;
Chan, L
;
材料科學與工程學系
;
Department of Materials Science and Engineering
We report a unique morphology of diamond nanoplatelets synthesized by microwave plasma chemical vapor deposition on Ni coated polycrystalline diamond substrates. The diamond nanoplatelets were as thin as approximately 30 nm. Electron microscopy showed that the diamond nanoplatelets appear in a shape consisting of trapezoid and parallelogram tabular crystallites. Furthermore, the diamond nanoplatelets were single crystalline, as shown by electron diffraction. The edges of nanoplatelets were along the < 110 > direction with both the top and bottom tabular surfaces parallel to the {111} plane. Transmission electron microscopy revealed that the twinned planes are parallel to the platelet and side-face structure in ridge shape is bounded by {100} and {111} planes. Lateral growth of diamond nanoplatelet is believed to result from twin and ridge face structure. An oriented thin graphite layer was observed on some diamond nanoplatelets.
The orientation effect of silicon grains on diamond deposition
(2005-11-01)
Su, YH
;
Chang, L
;
Chen, HG
;
Yan, JK
;
Chou, T
Diamond deposition on mirror-polished polycrystalline silicon substrates which have grains in various orientations has been investigated using electron backscatter diffraction (EBSD) method with scanning electron microscopy (SEMI). Diamond was deposited by microwave plasma chemical vapor deposition with application of a negative bias voltage oil the substrate. The evidence from systematic SEM observations shows that silicon orientation determined by EBSD has a strong effect on diamond nucleation. In general, the diamond nucleation density on Si grains oriented close to < 100 > is the highest, while it is the lowest for those grains close to < 111 >, under the same experimental conditions for deposition. The same phenomena have been observed in the range of methane concentration from 2% to 4% in hydrogen. (c) 2005 Elsevier B.V. All rights reserved.