Browsing by Author "Kuo, CT"

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Anodic aluminum oxide template assisted growth of vertically aligned carbon nanotube arrays by ECR-CVD
(2004-11-01)
Chen, PL
;
Chang, JK
;
Kuo, CT
;
Pan, FM
;
材料科學與工程學系
Highly aligned carbon nanorubes (CNTs) have been successfully grown in vertical channels of the anodic aluminum oxide (AAO) template by microwave plasma electron cyclotron resonance chemical vapor deposition (ECR-CVD). Nanoporous AAO templates with hexagonal pore pattern were prepared by the two-step anodization of A] films. Following the electroplating of Co catalyst into the pore bottom, multiwalled CNTs were synthesized in the ECR-CVD system using a gas mixture of CH4 and H-2. The microstructure of the CNTs was studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The CNTs with a very high packing density and a uniform size distribution are well graphitized, and Co particles embedded at their tips implies the tip growth mechanism. The segments of CNTs stretching out of the AAO nanopores still maintain relatively good alignment, and have a very slow growth rate, which allows us to obtain reproducible tube length by tuning the growth time. Field emission measurements of the CNTs showed derivable electron emission properties, attributed to their uniformity in size, good alignment, and good graphitization properties. (C) 2004 Elsevier B.V. All rights reserved.
Application of heat treatment and dispersive strengthening concept in interlayer deposition to enhance diamond film adherence
(1997-10-31)
Lin, CR
;
Kuo, CT
;
Chang, RM
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Two different deposition processes were carried out to enhance adherence of diamond films on WC + 3 similar to 5%Co substrate with Ti-Si as the interlayer. One process can be called two-step diamond deposition process. Another process can be called interlayer heat treatment process. Diamond films were deposited by a microwave plasma chemical vapor deposition system. Ti and Si interlayer are deposited by DC sputter and an E-gun, respectively. Film morphologies, interface structure and film qualify were examined by SEM, XRD, Auger electron spectroscopy and Raman spectroscopy. The residual stresses and adhesion strengths of the films were determined by Raman spectroscopy and indentation adhesion testing, respectively. Comparing the regular one-step diamond deposition process with the present two different new processes, the average dP/dX values, which are a measure of the adherence of the film, are 354 kgf/mm, 494 kgf/mm and 787 kgf/mm, respectively. In other words, the interlayer heat treatment process gives the best film adherence on average. For the two-step diamond deposition process, the interlayer thickness and the percent diamond surface coverage of the first diamond deposition step are the main parameters, and there exists an optimum Ti thickness and percent diamond coverage for the best film adherence. The main contribution to better film adherence is not a large difference in residual stress, but is due to the following reasons. The interlayer heat treatment can transform amorphous Si to polycrystalline Si, and may form strong TiC and SiC bonding. The polycrystalline Si and the diamond particles from the first diamond deposition step can be an effective seeds to enhance diamond nucleation. Published by Elsevier Science S.A.
Brazing characteristics of diamond on various substrates with different brazing alloys
(1995)
Kuo, CT
;
Lin, CR
;
Lien, HM
;
材料科學與工程學系
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Department of Materials Science and Engineering
Carrier capture and relaxation of self-assembled ZnTe/ZnSe quantum dots prepared under Volmer-Weber and Stranski-Krastanow growth modes
(2005-02-01)
Lee, ME
;
Yeh, YC
;
Chung, YH
;
Wu, CL
;
Yang, CS
The carrier capture and relaxation of type II ZnTe/ZnSe quantum dots have been investigated with ultrafast time-resolved photo luminescence upconversion. The carrier capture times were 7 and 38 ps for the Volmer-Weber mode and Stranski-Krastanow mode, respectively. We found that the carrier relaxation of QDs exhibits faster decay under the Volmer-Weber growth mode than under the Stranski-Krastanow growth mode. We attribute the difference of carrier relaxation to the wetting layer formed in the Stranski-Krastanow growth mode. (C) 2004 Elsevier B.V. All rights reserved.
Comparisons on properties and growth mechanisms of carbon nanotubes fabricated by high-pressure and low-pressure plasma-enhanced chemical vapor deposition
(2004-11-01)
Lin, CH
;
Lee, SH
;
Hsu, CM
;
Kuo, CT
;
材料科學與工程學系
Effects of plasma pressure and the presence of nitrogen on growth of carbon nanotubes (CNTs) and their properties were studied by using microwave plasma chemical vapor deposition (MPCVD) (pressure=600-3300 Pa) and electron cyclotron resonance chemical vapor deposition (ECR-CVD) (pressure=0.3-0.6 Pa) systems. CH4/H-2 and CH4/N-2 were used as source gases, and Co as the catalyst. The structures and properties of CNTs were characterized by using field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Raman spectra, and field emission I-V measurements. The results show that. CNTs made by higher plasma pressure system have a higher growth rate (typically 1-3 mum/min), smaller tube diameter, better field emission properties, and better tube quality. The growth rate is related to the availability of carbon source. The morphology change from spaghetti-like to well-aligned CNTs is discussed in terms of directed ions. The change in field emission properties is reasoned in terms of geometric enhancement factor and screening effect for different tube morphologies. The presence of nitrogen plasma can have the following effects: increasing tube diameter, increasing straightness of CNTs, forming of bamboo-like CNTs, deterioration of field emission properties, and shifting of Raman peak toward lower-frequency side (or increasing residual tensile stress). (C) 2004 Elsevier B.V. All rigths reserved.
Crystalline SiCN: a hard material rivals to cubic BN
(1999-11-01)
Chen, LC
;
Chen, KH
;
Wei, SL
;
Kichambare, PD
;
Wu, JJ
Growth and mechanical properties of SiCN materials prepared by microwave plasma enhanced chemical vapor deposition (CVD) as well as electron cyclotron resonance plasma CVD are reported. Large (several tens of microns), well-faceted ternary SiCN crystals were grown by microwave plasma-enhanced chemical vapor deposition. whereas amorphous SiCN films were deposited by ECR-CVD. The ternary crystalline compound (C; Si)(x)N-y exhibits a hexagonal structure and consists of a network wherein the Si and C are substitutional elements. While the N content of the crystalline compound is about 50 at.%, the extent of Si substitution varies and can be as low as 10 at.%. The amorphous SIGN films contain only about 30 at.% N. Nano-indentation studies were employed to investigate the mechanical properties of the SiCN materials. From the load versus displacement curves. we estimated the hardness and the effective modulus of the SIGN crystals to be around 30 and 321.7 GPa, respectively. The corresponding values for the amorphous SiCN were around 22 and 164.4 GPa, respectively. These values are well above most reported values for CN films. (C) 1999 Elsevier Science S.A. All rights reserved.
Deposition of silicon carbon nitride films by ion beam sputtering
(1999-11-01)
Wu, JJ
;
Wu, CT
;
Liao, YC
;
Lu, TR
;
Chen, LC
Silicon carbon nitride films have been successfully synthesized at a temperature below 100 degrees C from an adenine(C5N5H5)-silicon-mixed target sputtered by Ar ion beam. The effects of Ar ion sputtering voltage, area ratio of Si to adenine in the mixed target and nitrogen atom addition during deposition on the film growth are investigated. XPS, XRD, and ellipsometry were employed to characterize the composition, chemical bonding, structure, and optical property of the films. The growth characteristic and film properties of the silicon carbon nitride films are also compared with those of the carbon nitride films deposited from an adenine target to elucidate the effect of silicon incorporation. The silicon content of the resultant films increased significantly as the area ratio of Si to adenine increased, whereas a higher Ar ion voltage led to a lower level of silicon incorporation, presumably due to differential sputtering yield of Si and adenine. XPS chemical stare analysis revealed multiple bonding structures for every element in the SiCN films, of which possible implications are given. XRD studies showed that only amorphous films for Si-rich SiCN were obtained, while the films with low Si incorporation and deposited at high Ar ion beam voltage contained nanocrystallites. Furthermore, the: refractive index of the SiCN films increased with increasing silicon content. The appearance of the nanocrystalline structure in the films led to a reduction in the refractive index. (C) 1999 Elsevier Science S.A. All rights reserved.
Determination of 1-hydroxypyrene in children urine using column-switching liquid chromatography and fluorescence detection
(2004-06-15)
Kuo, CT
;
Chen, HW
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Chen, JL
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環境工程研究所
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Institute of Environmental Engineering
This study developed an acid hydrolysis method instead of using enzyme extraction, equipped with column-switching system for the pretreatment of samples, in the determination of 1-hydroxypyrene in the urine from children and pyrene in airborne particulates. We collected both types of samples from areas near a petrochemical industry and rural areas as reference. Samples were first treated with acid hydrolysis and followed by solvent extraction prior to being injected into the separation system for the determination with high performance liquid chromatography and fluorescence. A column-switching system was on-line with a C-18 separation column to remove matrix interference and obtain a stable baseline of the chromatogram. The eluent used to separate the 1-hydroxypyrene was 60% (v/v) aqueous acetonitrile solution. A fluorescence detector was used to monitor 1-hydroxypyrene at lambda(ex) = 348 nm and lambda(em) = 388nm, and pyrene at lambda(ex) = 331 nm and lambda(em) = 390 nm. Both calibration graphs were linear with very good correlation coefficients (r > 0.999) and the detection limits were ca. 2 pg (5 ng/l). Results showed that there was a significant association between 1-hydroxypyrene levels in urine specimens and pyrene levels in airborne particulate samples (r = 0.68, P < 0.05). The average levels of pyrene in the particulates (0.18 versus 0.09 ng/m(3)) and of 1-hydroxypyrene in urine specimens (155.9 versus 110.2 ng/g creatinine) were higher for the petrochemical area than for the rural area. This method is stable and sensitive for measuring polycyclic aromatic hydrocarbons in environmental samples. (C) 2003 Elsevier B.V. All rights reserved.
Effect of silane flowing time on W volcano and plug formation
(2002-05-01)
Chang, HL
;
Juang, FL
;
Kuo, CT
;
交大名義發表
;
National Chiao Tung University
W volcano is one of the defects in semiconductor devices. The presence of defects causes metal line bridges and thus device malfunction. The decomposition of SiH4 gas into Si atoms as nucleation sites is crucial for W film deposition. Here, we investigate the phenomenon in which the flowing time of SiH4 gas appears to dominate both W volcano formation and the degree of W film filling in a hole; the density of W volcanoes is increased with an increase of SiH4 flowing time. The volcano-free process and step-coverage of a W plug with various SiH4 flowing times are evaluated, and a formation mechanism is also proposed.
Effect of substrate orientation on arsenic precipitation in low-temperature-grown GaAs
(2005-09-01)
Lee, WN
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Chen, YF
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Huang, JH
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Guo, XJ
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Kuo, CT
Arsenic precipitation in "superlattice" structures of alternately undoped and [Si] = 3 x 10(18) cm(-3)-doped GaAs grown at 250 degrees C on (100), (311)A, and (311)B GaAs substrates has been studied using transmission electron microscopy. It is found that upon postgrowth annealing at 800 degrees C, As precipitates are nearly confined in the Si-doped regions, forming two-dimensional cluster arrays located approximately at the center of each Si-doped layer. The results also show that the As precipitates in the (311)B substrate are slightly denser and larger than those in the (311)A substrate and both are markedly denser and larger than those in the (100) substrate. This can be attributed to the varying excess arsenic incorporations in differently orientated substrates.
Effect of target materials on crystalline carbon nitride film preparation by ion beam sputtering
(1999-08-01)
Kuo, CT
;
Chen, LC
;
Chen, KH
;
Chen, TM
;
Lu, TR
In order to provide abundant chemical information, two novel bio-molecular target materials, instead of the conventional graphite target, were successfully developed to determine the possible formation mechanisms of carbon nitride during ion beam deposition. The azaadenine and adenine targets consist of carbonitro bonding, high N/C ratio as well as a six-fold carbonitro ring structure similar to that in hypothetical C3N4. Mass spectroscopy was used to determine the possible mechanisms of these two target materials. A lower electron beam energy at 75 eV was adopted to generate as abundant fragmental ions during the decomposition of these targets. Mass spectroscopy study on these two different targets indicates that the adenine target exhibits a more complex decomposition mechanism than the azaadenine target. However, the seven common hydrogenated carbonitro-species may suggest the same predominant mechanism during the decomposition of these two targets under the present deposition condition. The good correlation is one reason why two different targets can make almost the same quality crystalline carbon nitride films, including bonding, composition and structure. (C) 1999 Elsevier Science S.A. All rights reserved.
Effects of buffer layer materials and process conditions on growth mechanisms of forming networks of SWNTs by microwave plasma chemical vapor deposition
(2005-11-01)
Wang, WH
;
Peng, YR
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Kuo, CT
;
材料科學與工程學系
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Department of Materials Science and Engineering
This study investigates the growth mechanism of 1C compatible processes and to the feasibility of synthesizing networks of single-walled carbon nanotubes (SWNT-) at lower temperatures (similar to 610 degrees C) on Si wafer using microwave plasma chemical vapor deposition (MPCVD) with CH4 and H-2 as source gases. The effects of the buffer layer materials (ZnS-SiO2, Al2O3, AlON, and AlN) and process conditions on growth of carbon nanostructures with Co as catalyst were also examined, where the buffer layers and Co catalyst were deposited in sequence by physical vapor deposition (PVD), followed by H-plasma pretreatment before deposition of carbon nanostructures. Additionally, the morphologies and bonding structures of carbon nanostructures were characterized by field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), and Raman Spectroscopy. Analytical results demonstrate that networks of SIANTs are more favorable to be synthesized by selecting proper buffer layer material (e.g., AION), and under higher temperatures, thinner catalyst thickness (e.g., 5 run) and lower CH4/H-2 ratio (e.g., 5/100 sccm/sccm). The networks of SWNTs can be fabricated at temperatures as low as similar to 610 degrees C by manipulating these parameters. In conclusion, the growth mechanism determines the conditions for the formation of nano-sized extrusions on catalyst particles surface. (c) 2005 Elsevier B.V. All rights reserved.
Effects of doping type and concentration on precipitation of nanometer arsenic clusters in low-temperature-grown GaAs
(2005-11-01)
Lee, WN
;
Chen, YF
;
Huang, JH
;
Guo, XJ
;
Kuo, CT
In this study, the effects of doping type and concentration on arsenic precipitation in low-temperature-grown GaAs upon postgrowth annealing at 600, 700. and 800 degrees C were investigated. Three undoped/Si-doped/undoped (i-n-i) regions and three undoped/Be-doped/ undoped (i-p-i) regions were grown by low-temperature Molecular beam epitaxy, The results show that arsenic precipitation is dependent on doping type and doping concentration. Arsenic depletion was observed in all Be-doped layers for all annealing temperatures. However, a "dual" arsenic precipitation behavior was observed in Si-doped layers: As accumulates in [Si]=2 X 10(18) cm(-3) doped layers, while it depletes in [Si]=2 X 10(16) and 2 X 10(17) cm(-3) doped layers, We attribute this "dual" As precipitation phenomenon in Si-doped layers to the different depletion depths. (c) 2005 American Vacuum Society.
Effects of substrate pretreatments and catalyst applications on Si-C-N films and nanotube formations
(2001-12-01)
Chang, HL
;
Kuo, CT
;
材料科學與工程學系
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Department of Materials Science and Engineering
The Si-C-N films were synthesized on Si substrates by a microwave plasma chemical vapor deposition (MPCVD) system with CH4, H-2 and N-2 as the source gases. Metal coating on Si columns were placed around the specimen and acted as catalyst and additional source of Si. Some of the Si substrates were mechanically polished or chemically etched with HF-KIO3-H2O solutions to obtain different surface roughness before film depositions. Effects of the substrate pretreatment and the action of catalysts on surface morphologies, compositions, band structure, field emission of the films were examined. Nanotubes or nanowires structures were found for films deposited on no-treatment substrate using Fe, Co and Pt catalysts. However, chemical etching substrate can enhance formation of crystals and film nucleation with or without the addition of catalyst. This was the first work to demonstrate the possibility of fabricating the Si-C-N nanotubes through use of the catalysts and by controlling the deposition conditions by MPCVD. Under the present deposition conditions and by using Fe catalyst, the lowest turn-on voltage of the films can be as low as 1.3 V/mum, while the corresponding emission current density at field strength of 20 V/mum can go beyond 2000 muA/cm(2).
Effects of the Sb2Te3 crystallization-induced layer on crystallization behaviors and properties of phase change optical disk
(2004-01-30)
Wang, WH
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Chung, LC
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Kuo, CT
;
材料科學與工程學系
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Department of Materials Science and Engineering
The conventional phase-change optical disk is generally fabricated by the sputtering process, which has a drawback of requiring an initialization process to change the as-deposited recording layer in the disk from amorphous to crystalline phases before the disk can be used for reading or writing. In order to develop an initialization-free process, the Sb2Te3, alloy was used as an additional layer below or above the recording Ge2Sb2Te5 layer to study its effect on crystallization behaviors of the recording layer. The layer structures were deposited on substrates of Si wafer, Cu-mesh to examine crystal structure (XRD), amorphous-to-crystal transformation (DSC) and microstructure (TEM). The complete disk specimens were prepared on PC board to measure their dynamic properties, such as reflectivity, jitter and modulation (dynamic tester); and to examine the effects of laser pulse duration time, position and thickness of Sb2Te3, layer on static reflectivity of the disk (static tester), where Avrami coefficient 'q' in J-M-A rate equation can be derived. The results show that effect of Sb2Te3 layer is essentially to induce crystallization of Ge2Sb2Te5, recording layer from (110) plane of Sb2Te3 crystals. This is due to the fact that the crystallization temperature of Sb2Te3 crystal is 85 degreesC below that of Ge2Sb2Te5 crystal, in addition to a lower lattice mismatch between two crystals. The is in agreement with the J-M-A kinetic analyses that the rate controlling step for amorphous-crystal transformation in disk specimens with Sb2Te3 layer over 15-nm thickness is mainly governed by nucleation with q = 2.53-2.79 > 2.5 in J-M-A equation. Regarding the effects of Sb2Te3 layer on disk properties, the results show that under the 10 nm Ge2Sb2Te5, layer thickness, the Sb2Te3 assisted disks with lower Sb2Te3 layer thickness between 13 and 20 nm show the best combination of reflectivity and modulation. The most important advantage of this process is that the Sb2Te3-assisted disks require no initialization process, because the as-deposited disks can be directly written and erased. (C) 2003 Elsevier B.V. All rights reserved.
Electrical properties of ZnO varistors prepared by microwave sintering process
(1996-09-01)
Chen, CS
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Kuo, CT
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Lin, IN
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機械工程學系
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材料科學與工程學系
Microwave sintering processes were observed to substantially enhance the densification rate for ZnO varistor materials. Samples microwave sintered at 900-1200 degrees C for 10 min reached the same high density as those conventionally sintered at the same temperature for 60 min. A similar tendency was observed for the grain size. Prolonged microwave sintering, however, resulted in fast grain growth and degraded electric field-current density (E-J) properties. Capacitance-voltage (C-V) analysis indicated that the degradation in E-J behavior primarily resulted from the decrease in grain boundary barrier height. The modification of the grain boundary electrical properties, in turn, is ascribed to the loss of volatile Bi species along the grain boundaries.
Fabrication and field emission characteristics of highly ordered titanium oxide nanodot arrays
(2005)
Chen, PL
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Huang, WJ
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Chang, JK
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Kuo, CT
;
Pan, FM
A field emission triode device has been fabricated using self-organized nanodot arrays as the electron emission source. Uniform nanodot arrays of titanium oxide were prepared from the Al/Ti film stack on silicon substrates by electrochemical anodization. The field emission triodes with titanium oxide nanodot emitters exhibited a low gate turn-on voltage of 45 V and high emission current density of 25 mA/cm(2) at 120 V. The excellent electric properties and easily controllable fabrication process of the nanodot triodes show potential applications for field emission displays and vacuum microelectronics. (c) 2005 The Electrochemical Society.
Feasibility studies of magnetic particle-embedded carbon nanotubes for perpendicular recording media
(2003-03-01)
Kuo, CT
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Lin, CH
;
Lo, AY
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材料科學與工程學系
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Department of Materials Science and Engineering
Nano-sized magnetic particles were successfully used as the catalysts to synthesize magnetic metal-encapsulated carbon nanotubes (CNTs) or nanoparticles on Si wafers in a microwave plasma electron cyclotron resonance chemical vapor deposition (ECR-CVD) system with CH4 and/or H-2 as source gases. The magnetic catalyst materials, including Fe-Pt, Co-Pt, Nd2Fe14B, Fe and Fe-Ni, were first deposited on Si wafers by a physical vapor deposition (PVD) method, with subsequent plasma treatment for nanoparticle transformation. The main process parameters include catalyst materials, hydrogen plasma catalyst pretreatment and deposition temperature. For applications in magnetic media, the process has the following advantages: perpendicularly aligned CNTs or nanoparticles; tip-growth CNTs; well-distributed magnetic particles; detectable magnetic field in each particle; high tube number density (up to 134 Gtubes/inch(2) for Fe-assisted CNTs); favorable catalyst size; higher shape and induced anisotropy; and nanostructures that can be manipulated. The catalyst particle sizes of Fe, Nb2Fe14B and Fe-Pt (35-40 mn in diameter) are uniform and greater than but close to the critical optimum size or single domain size, which favor a higher coercive force. The greatest coercive force can reach 750 Oe for Fe-assisted CNTs at a deposition temperature of 715 degreesC, which is comparable with values reported in the literature. The coercive force difference between the vertical and horizontal directions can reach 300 Oe for Fe-assisted CNTs, and 355 Oe for Nb2Fe14B-assisted CNTs. (C) 2002 Elsevier Science B.V. All rights reserved.
Field emission of carbon nanotubes on anodic aluminum oxide template with controlled tube density
(2005-03-21)
Chen, PL
;
Chang, JK
;
Kuo, CT
;
Pan, FM
;
材料科學與工程學系
The tube number density of aligned carbon nanotubes (CNTs) grown over the nanoporous anodic aluminum oxide (AAO) template can be directly controlled by adjusting the CH4/H-2 feed ratio during the CNT growth. We ascribe the variation of the tube density as a function of the CH4/H-2 feed ratio to the kinetic competition between outgrowth of cobalt-catalyzed CNTs from the AAO pore bottom and deposition of the amorphous carbon (a-C) overlayer on the AAO template. A pore-filling ratio of 18% to 82% for the nanotubes overgrown out of nanopores on the AAO template can be easily achieved by adjusting the CH4/H-2 feed ratio. Enhanced field emission properties of CNTs were obtained by lowering the tube density on AAO. However, at a high CH4 concentration, a-C by-product deposit on the CNT surface can degrade the field emission property due to a high energy barrier and significant potential drop at the emission site. (C) 2005 American Institute of Physics.
Field emission, structure, cathodoluminescence and formation studies of carbon and Si-C-N nanotubes
(2002-03-01)
Chang, HL
;
Lin, CH
;
Kuo, CT
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Catalyst growth carbon and Si-C-N nanotubes have been synthesized successfully by microwave plasma chemical vapor deposition (MPCVD) method using CH4 + H-2 or CH4 + N-2 as gas sources, Si columns as additional Si solid sources, and Fe, Fe-Y, Co-Ni as catalysts. Nanotubes consisting of Si, C and N were made under process gases of CH4 + N-2, and with or without additional Si columns. Well-aligned and nested nanotubes were observed dependent on the catalyst materials. Besides, Si-C-N nanotubes were observed as bamboo-Eke structure. The as-grown nanotubes were purified in an air furnace to investigate their CL signal shift for potential application involving blue light emission. The field emission results indicate that the emission current densities can be above 10 mA/cm(2) at 10 V/mum, and aligned nanotubes belong to better current stability at a constant electric field than nested nanotubes. Nanotubes with a low I-D/I-G ratio (=0.23) via Raman analysis are achieved. The mechanisms of formation for carbon nanotubes and Si-C-N nanotubes are also discussed. (C) 2002 Elsevier Science B.V. All rights reserved.