Browsing by Author "Kuo, Cheng-Tzu"

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A High Efficiency Surface Modification Process for Multiwalled Carbon Nanotubes by Electron Cyclotron Resonance Plasma
(2008-11-27)
Tseng, Wen-Shou
;
Tseng, Chyuan-Yow
;
Chuang, Pi-Kai
;
Lo, An-Ya
;
Kuo, Cheng-Tzu
A novel process of surface modification for multiwalled carbon nanotubes (MWCNTs) by using electron cyclotron resonance plasma is proposed. The process uses a H(2)/O(2) gas mixture as etching gas and applies a bias voltage of -250 DCV to the process stage to extract and accelerate hydrogen and oxygen cations. The generated high density and high incident energy cations are employed to create defects on the surface of nanotubes through ion bombardment. The oxygen cations with high reduction potential are simultaneously applied, oxidizing the surface of the nanotubes so as to form functional groups on the side walls most effectively. Additionally, being far from the plasma sheath, the MWCNTs can be maintained at a lower temperature to prevent from being decomposed under the high energy plasma. The efficiency of this method was systematically analyzed using X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and thermogravimetric analysis. The experimental results have shown that the proposed method is a highly effective way to functionalize MWCNTs, resulting in the nanotubes with high concentration of oxygen-containing functional groups and minimal structural damage within very short process time.
A Single-Walled Carbon Nanotube Network Gas Sensing Device
(2011-08-01)
Wang, Li-Chun
;
Tang, Kea-Tiong
;
Teng, I-Ju
;
Kuo, Cheng-Tzu
;
Ho, Cheng-Long
The goal of this research was to develop a chemical gas sensing device based on single-walled carbon nanotube (SWCNT) networks. The SWCNT networks are synthesized on Al(2)O(3)-deposted SiO(2)/Si substrates with 10 nm-thick Fe as the catalyst precursor layer using microwave plasma chemical vapor deposition (MPCVD). The development of interconnected SWCNT networks can be exploited to recognize the identities of different chemical gases by the strength of their particular surface adsorptive and desorptive responses to various types of chemical vapors. The physical responses on the surface of the SWCNT networks cause superficial changes in the electric charge that can be converted into electronic signals for identification. In this study, we tested NO(2) and NH(3) vapors at ppm levels at room temperature with our self-made gas sensing device, which was able to obtain responses to sensitivity changes with a concentration of 10 ppm for NO(2) and 24 ppm for NH(3).
Anodic aluminum oxide as a template for CNT field emitters and AAO-CNT triode structure
(2005)
Lin, Chen-Chun
;
Pan, Fu-Ming
;
Liu, Mei
;
Chang, Kai-Chun
;
Chen, Po-Lin
We have used anodic aluminum oxide (AAO) as the template to grow carbon nanotubes (CNTs) for the application of field-emission display technology. In order to obtain optimal field emission properties, we have tried to control the density and the length of the CNTs grown from AAO pore channels by tuning the growth time and the CH4 concentration of the precursor gas mixture. AAO pore channel arrays were grown in the triode structure, which was fabricated on silicon wafers by conventional integrated circuit processes.
Anodic-aluminum-oxide templated carbon nanotubes in the field emission triode
(2007)
Lin, Chen-Chun
;
Chang, Kai-Chun
;
Pan, Fu-Ming
;
Kuo, Cheng-Tzu
;
Liu, Mei
To fabricate the field-emission triode structure, carbon nanotubes (CNT) were used as field emitters and grown in the anodic aluminum oxide (AAO). AAO thin layer with vertical pore channels was first prepared on the Si (100) substrate and was used to template the following growth of CNTs in an electron cyclotron resonance chemical vapor deposition (ECR-CVD) system. The tetraethoxysilane (TEOS) oxide and At layer were deposited on the CAITs and acted as the dielectric layer and gate electrode layers for the triode structure, respectively. Reactive ion and wet etches were then used to open the field-emission area in the triode. Field-emission characteristics of the CNT emitters have been studied and an anode turn-on field of similar to 8.05 V/mu m was measured.
Effect of Temperature Gradient Direction in the Catalyst Nanoparticle on CNTs Growth Mode
(2010-09-01)
Lo, An-Ya
;
Liu, Shang-Bin
;
Kuo, Cheng-Tzu
;
材料科學與工程學系
;
Department of Materials Science and Engineering
To improve the understanding on CNT growth modes, the various processes, including thermal CVD, MP-CVD and ECR-CVD, have been used to deposit CNTs on nanoporous SBA-15 and Si wafer substrates with C(2)H(2) and H(2) as reaction gases. The experiments to vary process parameter of Delta T, defined as the vector quantities of temperature at catalyst top minus it at catalyst bottom, were carried out to demonstrate its effect on the CNT growth mode. The TEM and TGA analyses were used to characterize their growth modes and carbon yields of the processes. The results show that Delta T can be used to monitor the temperature gradient direction across the catalyst nanoparticle during the growth stage of CNTs. The results also indicate that the tip-growth CNTs, base-growth CNTs and onion-like carbon are generally fabricated under conditions of Delta T > 0, < 0 and similar to 0, respectively. Our proposed growth mechanisms can be successfully adopted to explain why the base- and tip-growth CNTs are common in thermal CVD and plasma-enhanced CVD processes, respectively. Furthermore, our experiments have also successfully demonstrated the possibility to vary Delta T to obtain the desired growth mode of CNTs by thermal or plasma-enhanced CVD systems for different applications.
Effects of Gas Composition on Highly Efficient Surface Modification of Multi-Walled Carbon Nanotubes by Cation Treatment
(2009-03-01)
Tseng, Wen-Shou
;
Tseng, Chyuan-Yow
;
Kuo, Cheng-Tzu
;
材料科學與工程學系
;
Department of Materials Science and Engineering
High incident energy hydrogen and/or oxygen cations are generated by electron cyclotron resonance system, and then used to highly efficiently modify multi-walled carbon nanotubes (MWCNTs). The effects of various H(2)/O(2) gas compositions on the modification process are studied. A systematic characterization method utilizing a combination of X-ray photoelectron spectroscopy (XPS), scanning electron microscopy, Raman spectroscopy, and thermogravimetric analysis (TGA) is used to evaluate the effects of various H(2)/O(2) gas compositions on MWCNT functionalization. The Raman results show that the I (D)/I (G) ratio is directly affected by H(2) concentration in gas mixture, and the treatment applying a H(2)/O(2) gas mixture with ratio of 40/10 (sccm/sccm) can yield the nanotubes with the highest I (D)/I (G) ratio (1.27). The XPS results suggest that the gas mixture with ratio of 25/25 (sccm/sccm) is most effective in introducing oxygen-containing functional groups and reducing amorphous carbon. The TGA suggests that the structural change of the treated nanotubes is marginal by this method with any gas condition.
Evolution of Fluorine Content with Precipitate Formation in Fluorine-Doped Silicon Oxide
(2009-08-01)
Wu, Jun
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Wang, Ying-Lang
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Kuo, Cheng-Tzu
;
Pan, Fu-Ming
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材料科學與工程學系
Precipitates appear on fluorine-doped silicon oxide (SiOF) film when the film surface is exposed to atmospheric air. They are flake-type and hexagonal-shaped and show up rapidly after initiation, clustered at wafer center. It was found that the onset of precipitation is closely related to fluorine concentration of SiOF films, those with higher fluorine content exhibit high propensity, of precipitation, along with more significant fluorine loss. In this study, the microstructural changes of SiOF films in the course of precipitation were examined. The Fourier transform infrared spectra of SiOF films showed the declined intensities of Si-F(n) (n = 1, 2) bonding peaks at time after the formation of precipitates. In the surface analysis by X-ray photoelectron spectroscopy, the binding energy of F 1s reduced similar to 0.5eV. after, precipitation, indicating also decreased Si-F(n) bonding on the surface layer of SiOF films. Meanwhile, analysis by thermal desorption spectroscopy indicated that the unstable fluorine content in the SiOF film is significantly reduced after precipitation. (C) 2009 The Japan Society of Applied Physics
Fabrication of CNTs with controlled diameters and their applications as electrocatalyst supports for DMFC
(2011-03-01)
Lo, An-Ya
;
Yu, Ningya
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Huang, Shing-Jong
;
Hung, Chin-Te
;
Liu, Shou-Heng
A facile synthesis procedure based on chemical vapor deposition (CVD) process has been developed to fabricate carbon nanotubes (CNTs) with controlled diameters and high yields utilizing Fe-containing ordered hexagonal mesoporous silicas (HMSs) such as MCM-41 and SBA-15 having varied pore sizes as the catalysts as well as the templates. It is found that unlike Fe/HMS catalysts prepared by co-precipitation method, samples prepared by the impregnation method gave rise to multi-wall CNTs with uniform diameters, which were largely dictated by the pore size of the Fe/HMS catalysts. Among these uniform MWCNTs, sample with a larger diameter (>= 8 nm) was found to be more favorable as support for Pt catalyst, leading to a homogeneous dispersion of metal nanoparticles. Consequently, the Pt/CNT electrocatalysts so prepared gave rise to superior methanol oxidation activities as well as tolerances for CO poisoning compared to Pt supported on commercial single-wall CNT (Pt/SWCNT) and XC-72 activated carbon (Pt/XC-72) having a similar metal loading. (c) 2011 Elsevier B.V. All rights reserved.
Fabrication of cone-shaped CNF/SiC-coated Si-nanocone composite structures and their excellent field emission performance
(2012)
Teng, I-Ju
;
Hsu, Hui-Lin
;
Jian, Sheng-Rui
;
Kuo, Cheng-Tzu
;
Juang, Jenh-Yih
Novel cone-shaped carbon nanofiber (CNF)/silicon carbide (SiC)-coated Si-nanocone (Si-NC) composite structures with excellent field emission (FE) performance have been fabricated by a simple microwave plasma chemical vapour deposition process. Transmission electron microscopy analyses reveal that the newly developed cone-shaped composite structures are composed of bamboo-like herringbone CNFs grown vertically on the tips of conical SiC layers with a flat-top Si cone embedded underneath. For this CNF/SiC-coated Si-NC composite array, a ultra-low threshold field of 0.32 V mu m(-1) (at 10 mA cm(-2)), a large emission current density of 668 mA cm(-2) at 1.05 V mu m(-1), and a field enhancement factor as high as similar to 48 349 are obtained. In addition, the FE lifetime test performed at a large emission current density of 200 mA cm(-2) under an applied field of 1 V mu m(-1) shows no discernible decay during a period of over 260 minutes. We deduce that this superior FE performance can be attributed to the specific bamboo-like herringbone CNFs with numerous open graphitic edges and a faceted top end, and the conical base SiC/ Si structures with sufficient adhesion to the substrate surface. Such a novel structure with promising emission characteristics makes it a potential material for electron field emitters.
Feasibility study of high performance field emitter pattern with the horizontally oriented carbon nanotubes by electrophoresis
(2009-02-01)
Lin, Chen-Chun
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Chen, Ying-Chun
;
Wang, Terry
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Kuo, Cheng-Tzu
;
材料科學與工程學系
For the field emitter applications, electrophoretic deposition (EPD) followed by post air annealing treatment was developed to selectively deposit the single-walled carbon nanotubes (SWNTs) pattern made of Al and SiO(2) coatings. The EPD was conducted from a solution mixture of SWNTs and various dispersants or surfactants, including sodium dodecyl sulfate (SDS), hexadecyl trimethyl ammonium bromide and trictylphosphine oxide. Effects of the processing parameters of EPD and the post air annealing treatment on SWNTs dispersion, morphology, field emission (FE), and film-substrate adhesion were examined. The results indicate that the SIDS is the best surfactant in terms of SWNTs dispersion and solution stability, and the EPD parameters have no significant effects on their FE and adhesion properties of the deposited films. However. a higher post annealing temperature combined with an optimum annealing time is required to improve the film-substrate adhesion, so to reduce its electrical resistance and to enhance FE properties. The high performance annealed films with negligible internal stress are made of the micro-sized islands with the horizontally oriented SWNTs between them. The results also show that the pattern made of conductive and nonconductive coatings, such as Al and SiO(2), can be successfully used to deposit SWNTs pattern by EPD. (c) 2008 Published by Elsevier B.V.
Functionalizing Multi-Walled Carbon Nanotubes Using ECR Plasma and a Mild Nitric Acid Treatment
(2009-12-01)
Tseng, Wen-Shou
;
Tseng, Chyuan-Yow
;
Kuo, Cheng-Tzu
;
材料科學與工程學系
;
Department of Materials Science and Engineering
In the present work, a two-step process combining electron cyclotron resonance (ECR) plasma and 0.25 M nitric acid treatments is utilized to functionalize multi-walled carbon nanotubes (MWCNTs). In the process, high density and high incident energy hydrogen and oxygen cations generated by using ECR plasma system are used to bombard the MWCNTs for 5 min to break C-C bonds, creating free radical defects on the nanotube surface; the treated nanotubes are subsequently sonicated in the mild acid for 2 h, forming functional groups at the defects. Several characterization techniques, including X-ray photoelectron spectroscopy, scanning electron microscopy, Raman spectroscopy, and thermogravimetric analysis, are utilized to systematically evaluate the effect of the method. The results show that the MWCNTs treated by the presented method can contain a high concentration of oxygen-containing functional groups on the nanotube surface with the added advantage of high thermal stability and minimal destructive effects to the material structure.
Growth of carbon nanotube field emitters in the triode structure using anodic aluminum oxide as the template
(2007-04-01)
Lin, Chen-Chun
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Chang, Kai-Chun
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Pan, Fu-Ming
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Kuo, Cheng-Tzu
;
Liu, Mai
Carbon nanotubes (CNT) were grown in anodic aluminum oxide (AAO) and used as field emitters in a triode structure. To fabricate the field-emission triode structure, nanoporous anodic aluminum oxide (AAO) thin layer was first prepared on the Si(100) substrate, followed by the growth of vertically aligned carbon nanotubes in AAO pore channels by electron cyclotron resonance chemical vapor deposition (ECR-CVD). The SiO2 dielectric and Al gate electrode layers required for the triode structure were directly deposited on the CNTs. Reactive ion and wet etches were then used to open the field-emission area in the triode. Scanning electron microscopy and Raman spectroscopy studies revealed that damage to CNT emitters in the etched area was trivial. Field-emission characteristics of the CNT emitters have been studied and an anode turn-on electric field of similar to 8.05 V/mu m was measured. (C) 2007 Elsevier B.V. All rights reserved.
Highly graphitized laterally interconnected SWCNT network synthesis via a sandwich-grown method
(2011-04-13)
Teng, I-Ju
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Chen, Kai-Ling
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Hsu, Hui-Lin
;
Jian, Sheng-Rui
;
Wang, Li-Chun
We present a sandwich-grown method for growing laterally interconnected single-walled carbon nanotube (SWCNT) networks with a high degree of graphitization by microwave plasma chemical vapour deposition (MPCVD). An Al(2)O(3)-supported Fe catalyst precursor layer deposited on an oxidized Si substrate with an upper Si cover is first pretreated in pure hydrogen, and then exposed to a gas mixture of methane/hydrogen for growth process at a lower growth temperature and a faster rate. The effects of various parameters, such as catalyst film thickness, gas flow rate, working pressure, growth time and plasma power, on the morphologies and structural characteristics of the SWCNT networks are investigated, and therefore provide the essential conditions for direct growth of laterally interconnected SWCNT networks. Analytical results demonstrate that the SWCNT-based lateral architecture comprises a mixture of graphene-sheet-wrapped catalyst particles and laterally interconnected nanotubes, isolated or branched or assembled into bundles. The results also show that the formation of the laterally interconnected SWCNT networks is related to the sandwich-like stack approach and the addition of an Al(2)O(3) layer in the MPCVD process. The successful growth of lateral SWCNT networks provides new experimental information for simply and efficiently preparing lateral SWCNTs on unpatterned substrates, and opens a pathway to create network-structured nanotube-based devices.
Hollowed carbon capsule based Pt-Fe/carbon electrodecatalysts prepared by chemical vapor infiltration method
(2008-07-01)
Lo, An-Ya
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Liu, Shou-Heng
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Huang, Shing-Jong
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Kuo, Cheng-Tzu
;
Liu, Shang-Bin
A new type of hollowed carbon capsule (HCC) material has been fabricated and utilized as a support for Pt-Fe catalyst by means of chemical vapor infiltration (CVI) method. The supported Pt-Fe/HCC catalyst was found to possess cavities with sizes around 20-40 nm and well-dispersed Pt-Fe alloy particles embedded on the internal graphitic carbon walls and hence can be used as potential electrodecatalyst for fuel cells. Preliminary performance tests by cyclic voltammetry revealed that the supported Pt-Fe/HCC catalyst has electrochemical properties compatible to a common commercial catalyst. The formation mechanism of the HCC material is also proposed. (c) 2008 Elsevier B.V. All rights reserved.
Ir Nanocrystals on Asymmetric Si(3)N(4)/SiO(2) Tunneling Layer with Large Memory Window for Nonvolatile Memory Application
(2011-04-01)
Wang, Terry Tai-Jui
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Chen, Chao-Jui
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Teng, I-Ju
;
Hsieh, Ing-Jar
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Kuo, Cheng-Tzu
The capacitance-voltage measurements and microstructures of Iridium-nanocrystals embedded in two main stack devices of "Al/SiO(2)/Ir-NCs/SiO(2)/Si-Sub/Al" and "Al/SiO(2)/Ir-NCs/Si(3)N(4)/SiO(2)/SiSub/Al" have been compared for the application of nonvolatile memory. It has been demonstrated that the device performance of Si(3)N(4)/SiO(2) tunneling bi-layer (former stack) is much better than the single SiO(2) tunneling layer in terms of program/erase (P/E) efficiency and memory window size (up to 12.6 V at +/-10 V sweeping voltages), though 5% degrade in data retentions. Furthermore, endurances of two devices can stand 10(4) cycles without failure under P/E stressing condition of +/-9 V, 100 ms.
Ir Nanocrystals on Asymmetric Si3N4/SiO2 Tunneling Layer with Large Memory Window for Nonvolatile Memory Application
(2011-04-01)
Wang, Terry Tai-Jui
;
Chen, Chao-Jui
;
Teng, I-Ju
;
Hsieh, Ing-Jar
;
Kuo, Cheng-Tzu
The capacitance-voltage measurements and microstructures of Iridium-nanocrystals embedded in two main stack devices of "Al/SiO2/Ir-NCs/SiO2/Si-Sub/Al" and "Al/SiO2/Ir-NCs/Si3N4/SiO2/SiSub/Al" have been compared for the application of nonvolatile memory. It has been demonstrated that the device performance of Si3N4/SiO2 tunneling bi-layer (former stack) is much better than the single SiO2 tunneling layer in terms of program/erase (P/E) efficiency and memory window size (up to 12.6 V at +/-10 V sweeping voltages), though 5% degrade in data retentions. Furthermore, endurances of two devices can stand 10(4) cycles without failure under P/E stressing condition of +/-9 V, 100 ms.
Iridium Nanocrystal Thin-Film Transistor Nonvolatile Memory with Si(3)N(4)/SiO(2) Stack of Asymmetric Tunnel Barrier
(2011-05-01)
Wang, Terry Tai-Jui
;
Lu, Tien-Lin
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Wu, Chien-Hung
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Liu, Yu-Cheng
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Hung, Shih-Wei
Iridium nanocrystals (Ir-NCs) lying on the Si(3)N(4)/SiO(2) tunneling layer have been demonstrated and Ir-NC-assisted thin-film transistor nonvolatile memory devices were successfully developed. Results show that Ir-NCs with a number density of similar to 6 x 10(11) cm(-2) and a particle diameter of 4 to 12 nm can successfully be fabricated as charge trapping centers. Owing to the asymmetric SiO(2)/Si(3)N(4) tunneling layer that increases programming/erasing efficiency, a significant memory window of 5.5 V has potential to be applied to multibit memory devices. Furthermore, after 10(4) s, the memory window is still about 4.0 V in logic states. (C) 2011 The Japan Society of Applied Physics
Iridium Nanocrystal Thin-Film Transistor Nonvolatile Memory with Si3N4/SiO2 Stack of Asymmetric Tunnel Barrier
(2011-05-01)
Wang, Terry Tai-Jui
;
Lu, Tien-Lin
;
Wu, Chien-Hung
;
Liu, Yu-Cheng
;
Hung, Shih-Wei
Iridium nanocrystals (Ir-NCs) lying on the Si3N4/SiO2 tunneling layer have been demonstrated and Ir-NC-assisted thin-film transistor nonvolatile memory devices were successfully developed. Results show that Ir-NCs with a number density of similar to 6 x 10(11) cm(-2) and a particle diameter of 4 to 12 nm can successfully be fabricated as charge trapping centers. Owing to the asymmetric SiO2/Si3N4 tunneling layer that increases programming/erasing efficiency, a significant memory window of 5.5 V has potential to be applied to multibit memory devices. Furthermore, after 10(4) s, the memory window is still about 4.0 V in logic states. (C) 2011 The Japan Society of Applied Physics
Laser, buffer layer and CoCrPtO(x)-assisted low temperature fabrication process of a small-sized-CNT pattern by MPCVD
(2010-10-01)
Teng, I-Ju
;
Hong, Tsai-Hau
;
Hsu, Hui-Lin
;
Jian, Sheng-Rui
;
Wang, Wei-Hsiang
For improving compatibility with IC processes, this work presents a low temperature process (<400 degrees C) to fabricate a small-sized-carbon nanotube (CNT) (<6 graphene layers) pattern by buffer layer (AlN) and CoCrPtO(x) catalyst precursor-assisted microwave plasma chemical vapor deposition (MPCVD). Without high temperature heating on the whole specimen, the low temperature process mainly results from selective local activation laser heating (>= 600 degrees C) to form the catalyst nanostructures, which are beneficial to low temperature H-plasma treatment to form catalyst nanoparticles for CNT growth. The functions of the buffer layer and the catalyst precursor are to help the heat dissipation and the small-sized CNT formation. (C) 2010 Elsevier B.V. All rights reserved.
Laser, buffer layer and CoCrPtOx-assisted low temperature fabrication process of a small-sized-CNT pattern by MPCVD
(2010-10-01)
Teng, I-Ju
;
Hong, Tsai-Hau
;
Hsu, Hui-Lin
;
Jian, Sheng-Rui
;
Wang, Wei-Hsiang
For improving compatibility with IC processes, this work presents a low temperature process (<400 degrees C) to fabricate a small-sized-carbon nanotube (CNT) (<6 graphene layers) pattern by buffer layer (AlN) and CoCrPtOx catalyst precursor-assisted microwave plasma chemical vapor deposition (MPCVD). Without high temperature heating on the whole specimen, the low temperature process mainly results from selective local activation laser heating (>= 600 degrees C) to form the catalyst nanostructures, which are beneficial to low temperature H-plasma treatment to form catalyst nanoparticles for CNT growth. The functions of the buffer layer and the catalyst precursor are to help the heat dissipation and the small-sized CNT formation. (C) 2010 Elsevier B.V. All rights reserved.