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Now showing 1 - 10 of 17

Carbonaceous Anodes Derived from Sugarcane Bagasse for Sodium-Ion Batteries
(2019-05-21)
Rath, Purna Chandra
;
Patra, Jagabandhu
;
Huang, Hao-Tzu
;
Bresser, Dominic
;
Wu, Tzi-Yi
To realize the sustainability of Na-ion batteries (NIBs) for large-scale energy storage applications, a resource-abundant and cost-effective anode material is required. In this study, sugarcane bagasse (SB), one of the most abundant types of biowaste, is chosen as the carbon precursor to produce a hard carbon (HC) anode for NIBs. SB has a great balance of cellulose, hemicellulose, and lignin, which prevents full graphitization of the pyrolyzed carbon but ensures a sufficiently ordered carbon structure for Na+ transport. Compared with HC derived from waste apples, which are pectin-rich and have less cellulose than SB, SB-derived HC (SB-HC) has fewer defects and a lower oxygen content. SB-HC thus has a higher first-cycle sodiation/desodiation coulombic efficiency and better cycling stability. In addition, SB-HC has a unique flake-like morphology, which can shorten the Na+ diffusion length, and higher electronic conductivity (owing to more sp(2)-hybridized carbon), resulting in superior high-rate charge-discharge performance to apple-derived HC. The effects of pyrolysis temperature on the material characteristics and electrochemical properties, evaluated by using chronopotentiometry, cyclic voltammetry, and electrochemical impedance spectroscopy, are systematically investigated for both kinds of HC.
Porous Polyimide and Carbon Nanotubes: Solvent Vapor-Induced Transformation in the Nanochannels of Anodic Aluminum Oxide Templates
(2019-04-01)
He, Hung-Chieh
;
Tu, Yi-Hsuan
;
Li, Jia-Wei
;
Lin, Yu-Liang
;
Chen, Jiun-Tai
Polyimides (PIs) have attracted wide attention because of their exceptional thermal stability and applications in areas such as printed circuit boards and multichip modules. It remains a great challenge, however, to control the morphologies and properties of PI-based nanomaterials, especially porous PI-based nanotubes. In this work, a versatile method to fabricate porous PI nanotubes via the template method is developed, with a solvent vapor-induced transformation process. First, polyamic acid (PAA) solutions are used as precursors and infiltrated into the nanochannels of anodic aluminum oxide templates, forming PAA nanotubes. After the samples are annealed in tetrahydrofuran or dimethylformamide vapors, depression of the PAA tubes occurs, causing the formation of pores. The porous PAA nanotubes can be further converted to porous PI and carbon nanotubes by imidization and carbonization processes, respectively. The pore sizes of the porous nanomaterials can be controlled by changing the type of the annealing solvent and the solvent annealing time.
Supercapacitive Properties of Micropore- and Mesopore-Rich Activated Carbon in Ionic-Liquid Electrolytes with Various Constituent Ions
(2019-01-24)
Quoc Dat Nguyen
;
Patra, Jagabandhu
;
Hsieh, Chien-Te
;
Li, Jianlin
;
Dong, Quan-Feng
Ionic-liquid (IL) electrolytes, characterized by large potential windows, intrinsic ionic conductivity, low environmental hazard, and high safety, are used for micropore- and mesopore-rich activated-carbon (AC(micro) and AC(meso)) supercapacitors. IL electrolytes consisting of various cations [1-ethyl-3-methylimidazolium (EMI+), N-propyl-N-methylpyrrolidinium (PMP+), and N-butyl-N-methylpyrrolidinium (BMP+)] and various anions [bis(trifluoromethylsulfonyl)imide (TFSI-), BF4-, and bis(fluorosulfonyl)imide (FSI-)] are investigated. The electrolyte conductivity, viscosity, and ion transport properties at the AC(micro) and AC(meso) electrodes are studied. In addition, the capacitance, rate capability, and cycling stability of the two types of AC electrodes are systematically examined and post-mortem material analyses are conducted. The effects of IL composition on the charge-discharge capacitances of the AC(micro) electrodes are more pronounced than those for the AC(meso) electrodes. The FSI-based IL electrolytes, for which electrochemical properties are cation dependent, are found to be promising. Incorporating EMI+ with FSI- results in a low electrolyte viscosity and a fast ion transport, giving rise to optimized electrode capacitance and rate capability. Replacing EMI+ with PMP+ increases the cell voltage (to 3.5 V) and maximum energy density (to 42 Wh kg(-1)) of the AC(micro) cell at the cost of cycling stability.
Effects of NH3 Flow Rate During AlGaN Barrier Layer Growth on the Material Properties of AlGaN/GaN HEMT Heterostructure
(2017-10-01)
Lumbantoruan, Franky J.
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Wong, Yuen-Yee
;
Huang, Wei-Ching
;
Yu, Hung-Wei
;
Chang, Edward-Yi
NH3 flow rate during AlGaN barrier layer growth not only affects the growth efficiency and surface morphology as a result of parasitic reactions but also influences the concentration of carbon impurity in the AlGaN barrier. Carbon, which decomposes from metal precursors, plays a role in electron compensation for AlGaN/GaN HEMT. No 2-dimensional electron gas (2-DEG) was detected in the AlGaN/GaN structure if grown with 0.5 slm of NH3 due to the presence of higher carbon impurity (2.6 x 10(19) cm(-2)). When the NH3 flow rate increased to 6.0 slm, the carbon impurity reduced to 2.10 x 10(18) atom cm(-3) and the 2 DEG electron density recovered to 9.57 x 10(12) cm(-2).
Growth mechanism and properties of the large area well-aligned carbon nano-structures deposited by microwave plasma electron cyclotron resonance chemical vapor deposition
(2002-03-01)
Lin, CH
;
Chang, HL
;
Tsai, MH
;
Kuo, CT
;
材料科學與工程學系
Large area (4-inch diameter) well-aligned carbon nano-structures on Si substrate were successfully synthesized by using a catalyst-assisted microwave plasma electron cyclotron resonance chemical vapor deposition (ECR-CVD) system with CH4 as source gas. The catalysts include Fe, Co and Ni. The catalysts and the deposited nano-structures were characterized by scanning electron microscopy (SEM) transmission electron microscopy (TEM), Raman and field emission I-V measurements. Effects of process parameters on morphologies, structures and properties of the nano-structures were examined. The results show that the deposited nano-structures can include normal nano-tubes, split catalyst nano-tubes, seaweed-like nano-sheets and carbon film, depending mainly on substrate temperature and bias, catalyst materials and their application methods. Deposition mechanisms for different nano-structures, especially, the unique split catalyst nano-tubes and seaweed-like nano-sheets, were proposed. The differences in oxidation resistance and field emission proper-ties between different nano-structures will be compared and discussed. (C) 2002 Elsevier Science B.V. All rights reserved.
Growth of the large area horizontally-aligned carbon nanotubes by ECR-CVD
(2002-12-02)
Hsu, CM
;
Lin, CH
;
Chang, HL
;
Kuo, CT
;
材料科學與工程學系
For potential applications of carbon nanotubes (CNTs) as connectors in microelectronic devices, the process to synthesize the large area horizontally-aligned CNTs on 100 mm (4 inch) Si wafers was developed, using electron cyclotron resonance chemical vapor deposition, with CH, and H, as the source gases and Co as the catalyst. The results show that vertical and horizontal CNTs can be obtained by manipulating the electric field applied on the substrate and flow direction of the gases. In the present deposition conditions, the horizontal CNTs show better field emission properties than vertical CNTs. This may be due to the blocking effect of catalysts at the tips and to the diminishment of the effective emission area from defects of vertical CNTs body. (C) 2002 Elsevier Science B.V. All rights reserved.
Iron and cobalt silicide catalysts-assisted carbon nanostructures on the patterned Si substrates
(2002-12-02)
Chang, HL
;
Lin, CH
;
Kuo, CT
;
材料科學與工程學系
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Department of Materials Science and Engineering
Catalyst-assisted carbon nanotubes (CNTs) and carbon nano-rods were synthesized on the patterned or un-patterned Si wafer by microwave plasma chemical vapor deposition, using iron or cobalt silicide catalysts. Controllable carbon nanostructures were achieved by manipulating carbon and nitrogen concentration in the source gases, catalyst materials, and patterned wafer application. CNTs were synthesized under a high ratio of CH4/H-2 = 0.1, while carbon nano-rods were synthesized under a low ratio of CH4/H-2=0.01. Introducing N-2 gas into CH4/H-2 source gases gives rise to bamboo-like CNTs formation. Selective CNTs depositions were applied on (a) parallel Fe-coated line arrays, (b) CoSix-coated hole arrays. This is a novel method that is compatible with Si microelectronic device manufacturing. The field emission results indicate that the emission current density can be above 1 mA/cm(2) at 3.97 V/mum, and hollow like CNTs belong to better emission current than bamboo-like CNTs. Growth models of different carbon nanostructures are proposed. (C) 2002 Elsevier Science B.V. All rights reserved.
Physical and barrier properties of plasma-enhanced chemical vapor deposited alpha-SiC : H films from trimethylsilane and tetramethylsilane
(2003-07-01)
Chiang, CC
;
Chen, MC
;
Ko, CC
;
Wu, ZC
;
Jang, SM
This work investigates the thermal stability and physical and barrier properties of two species of plasma-enhanced chemical vapor deposited (PECVD) alpha-SiC:H silicon carbide films (with k-values less than 5) deposited using trimethylsilane, (CH3)(3)SiH (3MS) and tetramethylsilane, (CH3)(4)Si (4MS) organosilicate gases. It is found that the 4MS alpha-SiC:H film contains a higher content of carbon and has a lower dielectric constant. Both of the 3MS and 4MS alpha-SiC:H films are thermally stable at temperatures up to 500degreesC. However, degraded barrier property and moisture resistance were observed for the 4MS alpha-SiC:H film; this is attributed to the porosity enrichment caused by the film's high carbon content. The 3MS alpha-SiC:H film, which exhibits a superior Cu-barrier property, is a potential candidate for replacing the higher dielectric constant Si3N4 film as a Cu-cap barrier and etching stop layer in the Cu damascene structure.
Physical and barrier properties of plasma enhanced chemical vapor deposition alpha-SiC : N : H films
(2003-07-01)
Chiang, CC
;
Wu, ZC
;
Wu, WH
;
Chen, MC
;
Ko, CC
In this work, we investigate the thermal stability and physical and barrier properties of three species of plasma enhanced chemical vapor deposition (PECVD) alpha-SiC:N:H silicon carbide films with different carbon and nitrogen contents and dielectric constants less than a value of 5.5. For comparison, one species of alpha-SiN:H film with a k value of 7.2 is also studied. It is found that the dielectric constant decreases with increasing content of carbon and decreasing content of nitrogen in the alpha-SiC:N:H film. All of the three species of alpha-SiC:N:H and the one species of alpha-SiN:H films are thermally stable at temperatures up to 500degreesC. However, degraded barrier capability and moisture resistance were observed for the alpha-SiC:N:H film with a k value of 3.5, which has a C/Si atomic ratio of 0.875. This is presumably due to the poorly crosslinked molecular structure and porosity enhancement caused by the abundant amount of carbon in the alphaSiC:N:H film.
Catalyzed growth model of carbon nanotubes by microwave plasma chemical vapor deposition using CH4 and CO2 gas mixtures
(2003-10-01)
Chen, M
;
Chen, CM
;
Koo, HS
;
Chen, CF
;
材料科學與工程學系
Catalyst growth carbon nanotubes (CNTs) have been synthesized successfully by microwave plasma chemical vapor deposition using CH4-CO2 gas sources, and Fe, Ti, Fe/Ti as catalysts. Significant difference of morphology in the carbon deposition was observed between Fe and Ti catalyst. By adjusting growth parameters of CH4 to CO2, a high yield of vertically aligned CNTs can be found in an Fe-deposited substrate. Ti is shown to be not suitable as a catalyst in CNT production. In the present work, we investigated the effect of H-2 plasma pretreatment on the CNT growth from the viewpoint of catalyst morphology, using Fe as the catalyst. After the H-2 pretreatment, significant catalyst particle sintering was observed and resulted in a broad size distribution of catalyst particles. The diameter of CNTs was governed by the catalyst particle size. The diameter of CNTs thus increased as the H-2 plasma pretreated time increased. The CNT diameters were distributed in the range approximately 10-20 nm when Fe-deposited substrate was not pretreated. However, the diameter of CNTs increased from 30 to 300 nm when Fe-deposited substrate was pretreated from 1 to 15 min. The CNT growth model in catalysts, as a function of a gas environment of CH4-CO2 gas mixture, was investigated. (C) 2003 Elsevier Science B.V. All rights reserved.

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