Browsing by Author "Lin, Pang"

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A COMPACT CASCADE QUADRUPLET BANDPASS FILTER WITH LOW TEMPERATURE COFIRED CERAMIC TECHNOLOGY
(2008-12-01)
Lin, Hong-Ching
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Lin, Pang
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Tang, Ching-Wen
;
Wang, Sea-Fue
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材料科學與工程學系
In this article, a compact cascade quadruplet bandpass filter has been proposed. This bandpass filter has been realized with the semilumped method and can generate a pair of transmission zeros at the two sides of passband by using the nonadjacent cross coupling. The analysis and design procedures are provided in this article. To miniaturize the size of the circuit and improve its performance, multilayered structure and the low-temperature cofired ceramic technology are employed to design and fabricate the filter. Measurement results agree well with the electromagnetic simulation, which can validate the proposed structure. (c) 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 3218-3220, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23910
Accelerated Degradation of High Power Light-Emitting Diode Resulted from Inhomogeneous Current Distribution
(2011-03-01)
Yang, Shih Chun
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Lin, Pang
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Fu, Han Kuei
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Lee, An Tse
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Chen, Tzung Te
The uniformity of current spreading is one of the key points to inspect the reliability and endurance of InGaN-based light-emitting diodes. In this paper, we propose an effective circuit model to analyze the phenomenon of premature turn-on diodes in the active layer. With the aging tests and novel investigation of failure analyses, the simulating results are good agreement with experimental data. It is found that an inhomogeneous distribution of forward current in light-emitting diode chips, as measured by conductive atomic force microscopes, provides the evidence that V-shaped defects and the associated threading dislocations are electrically active. Furthermore, the results of emission microscopy images and transmission electron microscope reviews support the assumption that the threading dislocations associated with V-shaped defects behave as very small shunt resistors connected across p-n junction. This study provides a degradation mechanism to realized one of the failure modes of high power light-emitting diodes. (C) 2011 The Japan Society of Applied Physics
Assessment of ESD Robustness in High Power Light-Emitting Diodes
(2010)
Yang, Shih-Chun
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Lin, Pang
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Fu, Han-Kuei
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Wang, Chien-Ping
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Chen, Tzung-Te
The capability of high-power nitride-based light-emitting diodes (HPLED) to withstand electrostatic discharge (ESD) is very important key index due to the horizontal structure of the insulating property of the sapphire substrate. However, it is difficult to real-time monitor the damage caused by the ESD stress because it occurred in a very short period. Current-voltage (I-V) curves and electroluminescence (EL) spectrum were applied to study the change during the series ESD stress. Time-resolved optical beam induced current (TR-OBIC) was used to analyze the characteristics of the delay time between normal region and the defect point caused by ESD stress. Transmission electron microscopy (TEM) was used to compare to the difference in the distribution of damage region and investigate the failure modes. During the series ESD stresses, V-shaped pits suffered from the high electrical field and the distance from multi-quantum well (MQW). The bottom of V-shaped defect would be one of index to assess the ESD endurance of LED chips.
Bottom-Contact n-Channel Organic Thin-Film Transistors with Naphthalene-Based Derivatives
(2009)
Kao, Chia-Chun
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Lin, Pang
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Chan, Li-Hsin
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Lee, Cheng-Chung
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Ho, Jia-Chong
We investigated bottom-contact organic thin-film transistors based on n-benzyl naphthalene 1,4,5,8-tetracarboxylic diimides. The electrical characteristics were tested in both air and vacuum environments. n-Type semiconductors which are modified by fluorinated imide can be operated in ambient environment. The close packing of the fluorinated ester imide group leads to carrier mobility as high as 1.6x10(-2) cm(2) V(-1) s(-1). The short distance between each molecule can be found via a single-crystal structure.
Characteristics of electrolyte supported micro-tubular solid oxide fuel cells with GDC-ScSZ bilayer electrolyte
(2014-10-13)
Hsieh, Wen-Shuo
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Lin, Pang
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Wang, Sea-Fue
;
材料科學與工程學系
;
Department of Materials Science and Engineering
In this study, a gadolinia-doped ceria (GDq-supported micro tubular SOFC (T-SOFC) was fabricated using extrusion and dip-coating techniques (Cell A). The effects of inserting a scandium-stabilized zirconia (ScSZ) layer as an electron blocking layer between the GDC layer and the GDC-Ni anode layer were also explored (Cell B). The microstructures and electrochemical performances of Cell A and Cell B were investigated and compared. The layer thicknesses of the GDC and ScSZ bi-layer electrolytes were approximately 285 mu m and 8 mu m respectively. With the inserted ScSZ layer, both the ohmic resistance and the polarization resistance significantly increased at all the operating temperatures. The increase in the ohmic resistance of Cell B was predominantly due to the interfacial resistance, while the substantial escalation in the polarization resistance was mainly because of the low bulk oxygen diffusion process in the ScSZ layer and the smaller charge transfer processes occurring at the interfaces. The OCV of Cell B showed a slight decrease from 1.06 to 0.98 V and that of Cell A experienced an obvious decline from 0.92 to 0.76 V as the temperature rose from 650 to 800 degrees C. The ScSZ layer of Cell B successfully inhibited the OCV loss caused by the electronic conduction in GDC. The maximum power densities (MPDs) of Cell A at 650, 700, 750, and 800 degrees C were 0.20, 0.27, 0.33, and 0.36 Wcm(-2), and those of Cell B 0.16, 0.23, 0.32, and 0.42 Wcm(-2). The MPD of Cell B was improved at temperatures above 750 degrees C but remained inferior to that of Cell A below 750 degrees C. This is due to the fact that, as operating temperature increased above 750 degrees C, the benefit of the higher OCV in Cell B surpassed the deficiency of the higher cell resistance, thereby leading to a higher MPD. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Characterization of the low-curing-temperature silver paste with silver 2-ethylhexanoate addition
(2007-01-01)
Lu, Chun-An
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Lin, Pang
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Lin, Hong-Ching
;
Wang, Sea-Fue
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材料科學與工程學系
In this study, the effects of the solvent and atmosphere on the thermal decomposition behaviors of silver 2-ethylhexanoate and alpha-terpenol are investigated. Low-curing-temperature silver pastes made from Ag flakes, alpha-terpineol and various amounts of silver 2-ethylhexanoate, were prepared and characterized. The microstructures and resistivities of cured films screen-printed from the pastes were examined. The results of thermal analysis in oxidizing and reducing atmospheres revealed that thermal decomposition is the dominating reaction during the heating process of silver 2-ethylhexanoate, even though the differential scanning calorimetry (DSC) result revealed an exothermic reaction for silver 2-ethylhexanoate heated in air due to oxidation. Thermal decomposition left almost pure Ag particles, which is beneficial for bridging between silver flake particles in the films. On the basis of the theological behavior, microstructural evolution and electrical evaluation, it can be concluded that a low-curing-temperature silver paste with 5 wt % silver 2-ethylhexanoate addition is the best formulation, which possesses shear-thinning and thixotropic properties and a resistivity of 7.8 x 10(-6) Omega cm after being cured at 250 degrees C, which is relatively close to the bulk resistivity of Ag.
Current induced localized domain wall oscillators in NiFe/Cu/NiFe submicron wires
(2012-12-10)
Chang, L. J.
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Lin, Pang
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Lee, S. F.
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材料科學與工程學系
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Department of Materials Science and Engineering
We experimentally demonstrate domain wall (DW) oscillators excited by in-plane ac current through permalloy based pseudo-spin valve wires, which contain one pair of artificial protrusions. By measuring the spin-transfer-torque induced resonance of a pinned antiparallel transverse DW, under transverse external fields, we show that the antiparallel transverse DW oscillates with a resonance frequency as high as 2.92 GHz, depending on the widths of protrusions. For DW oscillations induced by injection of dc currents, the observed peaks in dV/dI associated with the reversible change of magnetoresistance are attributed to the reversible motions of the DW. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4770306]
Effect of annealing on the electrodeposited Cu(2)O films for photoelectrochemical hydrogen generation
(2010-10-01)
Liang, Ru-Meng
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Chang, Yun-Min
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Wu, Pu-Wei
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Lin, Pang
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材料科學與工程學系
Cu(2)O films were electrodeposited on stainless steel substrates followed by Ar annealing for photoelectrochemical hydrogen generation. Plating variables including time and pH for the plating bath were explored to obtain desirable film qualities. X-ray diffraction (XRD) patterns indicated that the as-deposited Cu(2)O films exhibited preferred orientations in (200) and (111) planes from the plating bath of pH 9 and pH 11, respectively. Images from scanning electron microscope (SEM) revealed pyramid-like grains in 1 mu m size for the Cu(2)O films from pH 9 plating bath and large plate-like grains in 3-8 mu m size from pH 11 plating bath. Identical results from SEM and XRD were obtained from the Cu(2)O films at longer plating time. After annealing at 350 degrees C for 30 and 60 min, the Cu(2)O phase was nicely maintained but SEM images demonstrated coarser grains. Photoelectrochemical activity for H(2) generation was obtained on the Cu(2)O films before and after annealing by recording relevant photoelectrochemical currents at -0.3 V in 0.5 M aqueous Na(2)SO(4) solution. For the Cu(2)O films from both baths, substantial increments in photoelectrochemical current were observed for the annealed samples as opposed to as-deposited ones. The largest photoelectrochemical current was obtained at 0.143 mA/cm(2) from the Cu(2)O film of pH 9 plating bath with 60 min annealing, which exhibited a 560% increase over the as-deposited sample. We attributed the enhanced photoelectrochemical current to the improved crystallinity and reduced defects for the annealed Cu(2)O films. (C) 2010 Elsevier B.V. All rights reserved.
Effect of annealing on the electrodeposited Cu2O films for photoelectrochemical hydrogen generation
(2010-10-01)
Liang, Ru-Meng
;
Chang, Yun-Min
;
Wu, Pu-Wei
;
Lin, Pang
;
交大名義發表
Cu2O films were electrodeposited on stainless steel substrates followed by Ar annealing for photoelectrochemical hydrogen generation. Plating variables including time and pH for the plating bath were explored to obtain desirable film qualities. X-ray diffraction (XRD) patterns indicated that the as-deposited Cu2O films exhibited preferred orientations in (200) and (111) planes from the plating bath of pH 9 and pH 11, respectively. Images from scanning electron microscope (SEM) revealed pyramid-like grains in 1 mu m size for the Cu2O films from pH 9 plating bath and large plate-like grains in 3-8 mu m size from pH 11 plating bath. Identical results from SEM and XRD were obtained from the Cu2O films at longer plating time. After annealing at 350 degrees C for 30 and 60 min, the Cu2O phase was nicely maintained but SEM images demonstrated coarser grains. Photoelectrochemical activity for H-2 generation was obtained on the Cu2O films before and after annealing by recording relevant photoelectrochemical currents at -0.3 V in 0.5 M aqueous Na2SO4 solution. For the Cu2O films from both baths, substantial increments in photoelectrochemical current were observed for the annealed samples as opposed to as-deposited ones. The largest photoelectrochemical current was obtained at 0.143 mA/cm(2) from the Cu2O film of pH 9 plating bath with 60 min annealing, which exhibited a 560% increase over the as-deposited sample. We attributed the enhanced photoelectrochemical current to the improved crystallinity and reduced defects for the annealed Cu2O films. (C) 2010 Elsevier B.V. All rights reserved.
Effect of anodic dissolution in multi-element nanoparticles on methanol electro-oxidation
(2009-11-03)
Hsieh, Yi-Fan
;
Yeh, Kung-Yu
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Wu, Pu-Wei
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Hsieh, Yu-Chi
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Lin, Pang
Radio frequency sputter deposition was used to deposit multi-element nanoparticles on carbon clothes for methanol electro-oxidation. Results from energy dispersive spectroscope confirmed the composition was Ft(35)Fe(12)Co(12)Ni(20)Cu(12)Ag(9). X-ray diffraction pattern suggested a fcc phase. An electrochemical de-alloying treatment was conducted in an acidic electrolyte with multiple potential sweeps at a scan rate of 20 mV/s for 0-0.3,0-0.5, and 0-0.7 V, respectively. Images from scanning electron microscope after anodic dissolutions demonstrated considerable variations in surface morphologies. Measurements on hydrogen desorption also revealed substantial increase in electrochemical active surface area. Current responses from cyclic voltammetry indicated the sample of 0-0.5 V anodic dissolution with notable enhancement. In mass activities, the same sample exhibited a comparable value to that Of Pt(43)Ru(57) (C) 2009 Elsevier B.V. All rights reserved.
Effect of platinum present in multi-element nanoparticles on methanol oxidation
(2009-06-10)
Tsai, Chih-Fang
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Yeh, Kung-Yu
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Wu, Pu-Wei
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Hsieh, Yi-Fan
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Lin, Pang
Nanoparticles of Pt(x)Fe((100-x)/5)Co((100-x)/5)Ni((100-x)/5)Cu((100-x)/5)Ag((100-x)/5) (x = 22, 29, 52, 56) were prepared by the sputter depositions on pretreated carbon clothes with their electrocatalytic abilities for the methanol oxidation investigated. XRD analysis of the deposited nanoparticles indicated crystalline fcc phases and SEM images revealed apparent growths of nanoparticulate nodules. Their average sizes were found to increase with the deposition time. Cyclic voltammetry of the deposited samples demonstrated enhancements in the current responses with increasing Pt amount and deposition time. In mass activity, the Pt(52)Fe(11)Co(10)Ni(11)Cu(10)Ag(8) exhibited the highest values of 462-504 mA/mg. Identical process was conducted to fabricate electrodes with sputtered Pt and Pt(43)Ru(57). In comparison, the Pt(52)Fe(11) Co(10)Ni(11)Cu(10)Ag(8) showed moderate improvements over that of Pt but was still outperformed by the Pt(43)Ru(57). (C) 2008 Elsevier B.V. All rights reserved.
Effects of cathode materials on the characteristics of electrolyte supported micro-tubular solid oxide fuel cells
(2014-05-01)
Hsieh, Wen-Shuo
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Lin, Pang
;
Wang, Sea-Fue
;
材料科學與工程學系
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Department of Materials Science and Engineering
The effects of the GDC-LSCF (Ce0.8Gd0.2O0-delta-La0.6Sr0.4Co0.2Fe0.8O3-delta) cathode layer and the GDC interlayer on the electrochemical performance of the ScSZ (Zr0.8Sc0.2O2-delta) electrolyte supported (approximate to 270 mu m) micro-tubular SOFC cells are investigated in this study. Material formulation and sintering profile for fabricating the micro-tubular SOFC cells are developed to avoid physical defects caused by the large sintering shrinkage mismatch among the layers. Cell B (with the LSCF-GDC composite cathode layer and the GDC interlayer) reports an ohmic resistance slightly higher than that of Cell A (with the GDC -La0.8Sr0 2MnO3-delta., i.e. LSM, composite cathode), while its polarization resistance emerges to be significantly smaller than that of Cell A. In terms of cell performance, Cell B demonstrates an OCV value (>1.07 V) similar to that of Cell A and a maximum power density (0.26W cm(-2)) 44.4% greater than that of Cell A (0.17 W cm(-2)) at 850 degrees C. It can thus be concluded that using the LSCF-GDC composite-cathode layer and inserting the GDC interlayer help reduce the total cell impedance, thereby improving the power density of the tubular cells. (C) 2013 Elsevier B.V. All rights reserved.
Effects of metallo-organic decomposition agents on thermal decomposition and electrical conductivity of low-temperature-curing silver paste
(2006-09-01)
Lu, Chun-An
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Lin, Pang
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Lin, Hong-Ching
;
Wang, Sea-Fue
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材料科學與工程學系
Six low-temperature-curing silver pastes were prepared from silver flake, alpha-terpineol and, various metallo-organic decomposition (MOD) compounds. The thermal decomposition behaviors of the pastes were determined. The microstructures and resistivities of screen-printed films on alumina substrate after thermal treatment were characterized and discussed. Results indicated that 2-ethylhexanoate possesses the lowest decomposition temperature (190.3 degrees C) among the MOD agents studied, and it forms silver particles to promote the linking of silver flake powders and thus reduces the resistivity to < 13 mu Omega.cm at a temperature as low as 200 degrees C.
Effects of P2+ doping on La4Ti9O24 ceramics
(2006-08-01)
Liu, Yuan-Wen
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Lin, Pang
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Chu, Ming-Wen
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材料科學與工程學系
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Department of Materials Science and Engineering
The kinetic structural evolution of the Pb2+-doped La4Ti9O24 ceramics was investigated. Using electron diffraction and Rietveld analysis of the X-ray powder diffraction patterns, we show that the increase in Pb2+ doping results in the structural transition from La4Ti9O24 to a La2/3TiO3-type phase (Ibmm, No. 74). Further kinetic studies of Pb2+ diffusion into La4Ti9O24 ceramics suggest that the La4Ti9O24-La2/3TiO3 phase transition requires an activation energy of 607 +/- 60 kJ/ mol..
Effects of silver oxalate additions on the physical characteristics of low-temperature-curing MOD silver paste for thick-film applications
(2009-11-01)
Lin, Hong-Ching
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Lin, Pang
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Lu, Chun-An
;
Wang, Sea-Fue
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材料科學與工程學系
In this paper, the effect of silver oxalate addition on physical characteristics of metallo-organic-decomposition (MOD) silver screen-printable paste for thick film technology was investigated. The addition of silver oxalate in the paste not only produces fresh fine silver particles after curing, but also reduces the decomposition temperature of the lubricant coated on the silver flakes. This is an effective route to provide fine silver particles to the paste without significantly changing the theological behavior. At the curing temperature of 225 degrees C, the resistivity decreases from 180.1 to 31.9 mu Omega-cm, as the silver oxalate content increases from 0 to 10 wt%. This is due to the fact that active silver catalysts produced increase the packing density of silver flakes, and also the removal of lubricant from the surface of silver flakes enhances the electrical conductivity, thereby decreasing the resistance of film. (C) 2009 Elsevier B.V. All rights reserved.
Electrical Properties and Reliability of ZnO-Based Nanorod Current Emitters
(2012-07-01)
Yao, I-Chuan
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Lin, Pang
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Huang, Sheng-He
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Tseng, Tseung-Yuen
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材料科學與工程學系
"The fabrication, optical, and field emission properties of ZnO-based nanorod emitters were studied. Ga-doped ZnO nanorods combined with the formation of tip structure on top of a ZnO nanorod by oxygen plasma treatment are employed to improve the field emission properties of the nanorod emitters. By either of these two methods, the nanorod emitters exhibit significantly reduced turn-on field and enhanced field-emission factor. The morphology, crystal structure, and composition of all the nanorods used for making emitters are characterized by a scanning electron microscopy, X-ray diffraction, and energy dispersive X-ray spectrometer. The nanorods exhibit the highly preferred c-axis orientation single crystal structure. The photoluminescence spectra indicate the nanorods have better crystalline structure after doping and oxygen plasma treatment. Combining gallium doping process (Ga/Zn molar ratio of 1% in solution) and oxygen plasma treatment (etching time of 60 s), the tip-structured GZO nanorod emitters with tip angle of 100 degrees have a turn-on field of 1.99 V/mu m under a current density of 1 mu A/cm(2), field enhancement factor of 2465, and stable operation over 2 x 10(4) s. Such improved field emission properties are attributed to decreased work function and sharp nanotips morphology. In addition, the GZO nanorod emitters with tip structure are successively and stably operated between 25 degrees C and 100 degrees C over 3000 s based on the high-temperature field emission measurement results. They have high potential for practical applications in flat panel display and light emitting device in the future."
Electroless deposition of Ru films on Si substrates with surface pretreatments
(2013-02-01)
Chen, Jing-Yu
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Huang, Shiau-Lin
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Wu, Pu-Wei
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Lin, Pang
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材料科學與工程學系
Electroless Ru depositions on Si substrates undergoing surface pretreatments such as hydrogen fluoride (HF) etching, HF etching and activation, as well as HF etching, sensitization, and activation are explored. The plating bath contains K2RuCl5 center dot xH(2)O, NaClO, NaOH, and NaNO2 at appropriate ratios. Continuous electroless Ru film is unable to obtain on the as-received Si wafer because the native oxide inhibits the process of nucleation and growth. In contrast, after surface pretreatments, dense and continuous Ru films are observed at reasonable growth rates. Contact angle measurements indicate a relatively hydrophilic surface after sensitization and activation, which leads to faster Ru film growths and larger surface roughness as compared to the HF-etched sample. X-ray photoelectron spectra confirm the formation of Sn and Pd nuclei and their presence promotes the heterogeneous growth of Ru films as evidenced by images from scanning electron microscope. In addition, depth profiling from Auger electron spectrometer suggests a uniform composition across the film thickness despite part of the Ru exists in an oxidized form. (C) 2012 Elsevier B.V. All rights reserved.
Electrophoretic Fabrication and Characterizations of Manganese Oxide/Carbon Nanotube Nanocomposite Pseudocapacitors
(2011)
Hung, Chung Jung
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Hung, Jeng Han
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Lin, Pang
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Tseng, Tseung Yuen
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材料科學與工程學系
This study reports the electrochemical performance and stability of MnO(x)-multiwall carbon nanotubes (MWCNTs) nanocomposite/Ni pseudocapacitor electrodes fabricated by a modified electrophoretic deposition (EPD) method. The nanocomposite electrode consisting of highly dispersed manganese oxide on MWCNTs was synthesized by a redox titration method at room temperature. The electrochemical properties of the electrode were demonstrated by cyclic voltammetry. The mean specific capacitances at a constant scan rate of 100 mV/s of MnO(x)-MWCNTs nanocomposites without and with heat treatment at temperatures 150, 200, and 250 degrees C for 2 h are 378, 402, 445, and 469 F/g, respectively, which indicate an increase with increasing annealing temperature. During stability tests, the as-grown MnO(x)-MWCNTs nanocomposite electrode can preserve 80% of its original capacitance after 6000 cycles of operation which can be increased to 86% after annealing at 200 degrees C for 2 h. The EPD MnO(x)/MWCNTs coaxial nanocomposite pseudocapacitors with manganese oxide ionized by H(+) ion process exhibit high specific capacitance, fast reaction rate, high stability, and have high potential for practical applications. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3601862] All rights reserved.
Electrophoretic fabrication and pseudocapacitive properties of graphene/manganese oxide/carbon nanotube nanocomposites
(2013-12-01)
Hung, Chung Jung
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Lin, Pang
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Tseng, Tseung Yuen
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材料科學與工程學系
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電子工程學系及電子研究所
Hybrid nanocomposites provided a synergistic improvement on electrochemical performance and stability for pseudocapacitor. Designed graphene/carbon nanotubes (CNTs)/MnO2 nanocomposites with CNTs electrode (in short, GMC + C) with highly nanoporous framework surface structure are fabricated by a modified electrophoretic deposition (EPD) method. Scanning electron microscopy and transmission electron microscopy analysis demonstrate that the flake-like MnO2 thickness (about less than 10 nm) and uniformly distributed on the porous graphene/CNTs framework. X-ray diffraction shows the formation of birnessite-type MnO2. Pseudocapacitances of the GMC + C electrode calculated by cyclic voltammetry having different scan rates of 5, 20, 50, 100, and 300 mV s(-1) exhibit high specific capacitances of 481, 436, 413, 398, and 372 F g, respectively. Sodium ion diffusion coefficients of the GMC + C electrode show a higher intercalation value of 3.647 x 10(-8) cm(2) s(-1) and deintercalation value of 2.899 x 10(-8) cm(2) s(-1) using chronoamperometry. Moreover, the GMC + C electrode maintains a high specific capacitance of 346 F g(-1), and is about 833% of the initial capacitance after 15,000 charge/discharge cycles. The designed hybrid GMC + C nanocomposites pseudocapacitor electrode using EPD route with the high specific capacitance, fast reaction rate, and high stability, exhibits high potential for practical applications. (C) 2013 Elsevier B.V. All rights reserved.
Evaluation on carbon nanocapsules for supercapacitors using a titanium cavity electrode
(2010-08-01)
Wu, Cheng-Yeou
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Wu, Pu-Wei
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Lin, Pang
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材料科學與工程學系
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Department of Materials Science and Engineering
We synthesize carbon nanocapsules (CNCs) by a flame combustion method and evaluate their potential as the electrode material for electrochemical double layer capacitor using a titanium cavity electrode (TCE). Identical process is conducted on commercially available carbonaceous materials such as Vulcan XC72R, Black Pearl 2000 (BP2000), multi-walled carbon nanotubes (MWCNTs), and active carbon (AC1100) for comparison purposes. Images from Scanning electron microscope and Transmission electron microscope on the CNCs demonstrate irregular-shaped particles in average size of 10-20 nm with graphene layers on perimeter compassing a hollow core. Electrochemical characterizations including cyclic voltammetry (CV), current reversal chronopotentiometry (CRC), and impedance spectroscopy are carried out in 1N H(2)SO(4) to determine the specific capacitance and cycle life time. Among these samples, the BP2000 still delivers the highest specific capacitance in F g(-1) but the CNCs demonstrate the largest value in mu F cm(2). In addition, the CNCs exhibit impressive life time for 5000 cycles without notable degradation. Consistent results are obtained by CV, CRC, and impedance measurements, validating the TCE as a facile tool to perform reliable electrochemical evaluations. (C) 2010 Elsevier B.V. All rights reserved.