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Microstructure control of Fe catalyst films for the growth of multiwalled carbon nanotube arrays
Guo-an Cheng,Hua-ping Liu,Rui-ting Zheng,Yong Zhao,Chang-lin Liang 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.-
Fe catalyst films were deposited on silicon substrates by using a metal vapor vacuum arc (MEVVA) ion deposition system for the growth of aligned multiwalled carbon nanotubes. The effects of deposition angle and film thickness on the morphologies of catalyst films before and after thermal treatment were investigated. The results show that the uniformities of both 5-nm and 10-nm films are enhanced as the deposition angle decreases. With increase from 5 nm to 10 nm, the surface uniformities of pristine films prepared at higher deposition angles (60˚ and 90˚) are increased, while that of the films produced at 30˚ deposition angle is slightly decreased. The uniformity of Fe catalyst particle sizes after thermal treatment on the whole, clearly decreases as the thickness is increased from 5 nm to 10 nm in the case of the same deposition angle. 5-nm films deposited at 30˚ deposition angle show the most uniform features before and after thermal treatment and can be used for the synthesis of high-quality carbon nanotube arrays. Fe catalyst films were deposited on silicon substrates by using a metal vapor vacuum arc (MEVVA) ion deposition system for the growth of aligned multiwalled carbon nanotubes. The effects of deposition angle and film thickness on the morphologies of catalyst films before and after thermal treatment were investigated. The results show that the uniformities of both 5-nm and 10-nm films are enhanced as the deposition angle decreases. With increase from 5 nm to 10 nm, the surface uniformities of pristine films prepared at higher deposition angles (60˚ and 90˚) are increased, while that of the films produced at 30˚ deposition angle is slightly decreased. The uniformity of Fe catalyst particle sizes after thermal treatment on the whole, clearly decreases as the thickness is increased from 5 nm to 10 nm in the case of the same deposition angle. 5-nm films deposited at 30˚ deposition angle show the most uniform features before and after thermal treatment and can be used for the synthesis of high-quality carbon nanotube arrays.
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Key Application Technologies of High Efficiency Power Quality Control Systems
Ding-Guo Liu,Zhi-kang Shuai,Chun-ming Tu,Ying Cheng,An Luo 전력전자학회 2013 JOURNAL OF POWER ELECTRONICS Vol.13 No.3
Large capacity reactive power compensation and harmonic control in the low-voltage grid of an enterprise, are important technical means to improve power quality and reduce power loss. In this paper, the principle of an efficient power quality controller is analyzed. Then, key application technologies of the HPQC which would influence the performances of the HPQC are studied. Based on an analysis of the harmonic shunt problem, a frequency dividing control strategy of the HPQC continuous subsystem is proposed. A parameter design method of the HPQC discrete subsystem and its installation method are also proposed to ensure the system compensation effect. HPQC systems have been designed for a copper foil plant. The effectiveness of this paper has been verified by the simulation and application results.
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Key Application Technologies of High Efficiency Power Quality Control Systems
Liu, Ding-Guo,Shuai, Zhi-Kang,Tu, Chun-Ming,Cheng, Ying,Luo, An The Korean Institute of Power Electronics 2013 JOURNAL OF POWER ELECTRONICS Vol.13 No.3
Large capacity reactive power compensation and harmonic control in the low-voltage grid of an enterprise, are important technical means to improve power quality and reduce power loss. In this paper, the principle of an efficient power quality controller is analyzed. Then, key application technologies of the HPQC which would influence the performances of the HPQC are studied. Based on an analysis of the harmonic shunt problem, a frequency dividing control strategy of the HPQC continuous subsystem is proposed. A parameter design method of the HPQC discrete subsystem and its installation method are also proposed to ensure the system compensation effect. HPQC systems have been designed for a copper foil plant. The effectiveness of this paper has been verified by the simulation and application results.
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Jian-hua Deng,Zhao-xia Ping,Rui-ting Zheng,Guo-an Cheng 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.41
The stability behaviors of multiwalled carbon nanotube arrays during field electron emission are studied. The results indicate that the stability, even at a high emission current density, has been greatly improved by an aging process, and a degradation of about 0.66% in the emission current density at 21.86 mA/cm_2 during a 10-hour stability test has been obtained. A detailed analysis of the deterioration of the field electron emission characteristics is given, and the generation of Joule heat during field emission is found to be able to burn off the extruded carbon nanotubes, which will directly reduce the number of emission sites. On the other hand, the Joule heating effect may induce an annealing of the defects existing in the carbon nanotubes and may influence the distribution of electron energy states, both having a bad influence on the field emission characteristics. An aging process, especially aging at high emission current densities, can greatly reduce the influence of Jouleheating induced current degradation. Hence, an aging process at high emission current densities provides an effective way to realize long-term stable field electron emission from carbon nanotube arrays.
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Lei Guo,Wen-Cheng Zhu,Ya-Ting Liu,Jiu-Yu Wu,An-Qi Zheng,Yan-Li Liu 한국식품과학회 2013 Food Science and Biotechnology Vol.22 No.5
The optimized extraction conditions of total flavonoids from mimenghua were determined by the Box-Behnken design and response surface methodology. The optimal conditions to achieve the maximum yield of flavonoids were determined as follows: ethanol concentration 68%(v/v), extraction temperature 72.4oC, liquid/material ratio 48:1mL/g, and extraction time 2 h. Under the optimized conditions, the extraction ratio of flavonoids was 15.44%. The crude extract was then purified by AB-8 macroporous adsorption resin, the flavonoids content in the purified extract increased to 90.43%. The antioxidant activities of the purified flavonoids were evaluated in vitro by scavenging capabilities of DPPH radical, hydroxyl radical and superoxide radical, reducing power and total antioxidant capacity. The results showed that the flavonoids have significant antioxidant activities, which can be used as a source of potential antioxidant.
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Effect of the microstructure of Ag catalysts in the fabricating process of silicon nanowires
Fei Zhao,Guo-an Cheng,Rui-ting Zheng,Le-yang Xia 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.-
In this paper, well-aligned silicon nanowire (SiNW) arrays have been directly synthesized on single crystal silicon wafer at room temperature via a simple chemical etching method, and the effect of the microstructure of Ag catalysts on the fabricating process of the silicon nanowires has been systematically investigated. The experimental results show that different microstructures of Ag catalysts have been observed with different concentration of AgNO3/HF solution for different deposition times. The diameters of Ag particles and the mean interstitial sizes among Ag particles are relatively small for a short deposition time, and some large particles are formed when the deposition time increases. A much longer deposition time caused the substrate to be covered with a large amount of Ag dendrite. It can be inferred that 4 min is a good deposition time, because of the proportioned structure of particles and interstitial size, according to our experimental results. Nanostructures of Ag catalyst also vary with a change of concentration of AgNO3/HF solution. Ag dendrite may be formed at high concentration and affect the fabrication of SiNWs. In this paper, well-aligned silicon nanowire (SiNW) arrays have been directly synthesized on single crystal silicon wafer at room temperature via a simple chemical etching method, and the effect of the microstructure of Ag catalysts on the fabricating process of the silicon nanowires has been systematically investigated. The experimental results show that different microstructures of Ag catalysts have been observed with different concentration of AgNO3/HF solution for different deposition times. The diameters of Ag particles and the mean interstitial sizes among Ag particles are relatively small for a short deposition time, and some large particles are formed when the deposition time increases. A much longer deposition time caused the substrate to be covered with a large amount of Ag dendrite. It can be inferred that 4 min is a good deposition time, because of the proportioned structure of particles and interstitial size, according to our experimental results. Nanostructures of Ag catalyst also vary with a change of concentration of AgNO3/HF solution. Ag dendrite may be formed at high concentration and affect the fabrication of SiNWs.
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You, Youngmin,An, Cheng-Guo,Lee, Deug-Sang,Kim, Jang-Joo,Park, Soo Young Royal Society of Chemistry 2006 Journal of materials chemistry Vol.16 No.48
<P>In this paper, we present the synthesis and characterization of a new highly phosphorescent cyclometalated Ir(<SMALL>III</SMALL>) complex with a silane-based dendritic substituent. The Ir(<SMALL>III</SMALL>) complex showed 74 ± 3% of absolute phosphorescence quantum efficiency in the film state. In addition, efficient electrophosphorescence (32.8 cd A<SUP>−1</SUP>) employing an Ir(<SMALL>III</SMALL>) complex–poly(<I>N</I>-vinylcarbazole) system device is observed. Study of a series of electroluminescent, spectroscopic, and electrochemical data of the Ir(<SMALL>III</SMALL>) complex and the reference Ir(ppy)<SUB>3</SUB> reveals superior performance of the new Ir(<SMALL>III</SMALL>) complex.</P> <P>Graphic Abstract</P><P>A highly phosphorescent cyclometalated Ir(<SMALL>III</SMALL>) complex having dendritic aryl silane ligands has been synthesized. Absolute phosphorescence quantum yield of the Ir(<SMALL>III</SMALL>) complex film reached 74 ± 3%, and the polymer-based OLED showed a luminous efficiency as high as 32.8 cd A<SUP>−1</SUP>. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=b611288a'> </P>
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Morphology-dependent Optical Properties of One-dimensional Nanostructure-arrayed Silicon
Shao-long Wu,Guo-an Cheng,Rui-ting Zheng,Xiao-ling Wu 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.6
The optical properties of one-dimensional nanostructure-arrayed silicon (1DNSASi), which wasfabricated by the metal assisted electroless chemical etching method under different conditions,were characterized in the wavelength range of 220 - 1000 nm. Whether the optical absorption ofthe 1DNSASi was enhanced relative to that of the polished Si was determined from the detailedmorphology of the 1D nanostructures. For the yellow 1DNSASi prepared at a high etchant concentrationand high temperatures, its optical absorption was relatively nice in the ultraviolet lightregion, while a gradual attenuation was shown in the visible and the near-infrared regions, and theoptical absorption was lower than that of the polished Si at wavelengths above 800 nm. When theeffects of zeroth-order reflectance and zero transmission were combined, the optical absorption ofthe black 1DNSASi prepared at a low etchant concentration and room temperature was very high(> 99%) in the wavelength range of 220 - 1030 nm and displayed a slight decrease at wavelengthsabove 1030 nm. Our results demonstrate that the optical absorption of the black 1DNSASi couldbe further improved by increasing the etching depth and exhibited its measurable maximum valuewhen the etching depth was large enough. These results indicate that the 1DNSASi may be apromising candidate for high-efficiency photovoltaic devices, high-sensitivity sensors and detectors.
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Wei Li,Yuan-ping Cheng,Pin-kun Guo,Feng-hua An,Ming-yi Chen 한국지질과학협의회 2014 Geosciences Journal Vol.18 No.4
The mining of protective coal seams can cause changesin geostress, leading to changes in the permeability of coal rock and creatingfavorable conditions for gas extraction from coal seams. Atthe Haishiwan Coal Mine, field tests using remote protective coalseam mining were performed in the protected layer, which is richin CO2 gas. In remote protective longwall mining, the permeabilityand composition of extracted stress-relief gas can vary. Under theconditions of remote protective longwall mining, the permeabilityof a protected coal seam can be generally described by the Liumodel. During protective layer mining, the permeability of theprotective layer increases rapidly with the release of stress, thendecreases gradually with the recovery of the geostress. However,matrix shrinkage and decreased pore pressure caused by CO2 desorptionfrom coal seams also cannot be ignored when considering thefactors that affect the permeability. Thus, it is necessary to appropriatelyconfigure the cross-measure boreholes in advance to drainthe stress-relief gas during remote protective layer mining. StressreliefCO2 gas extraction presents multiple consecutive peaks. TheNo. 2 coal seam has different trap pressure systems as CO2 migratesinto the coal seam. The protected seam experiences different effectivestresses during protective layer mining, and the permeabilitiesappear to periodically increase due to differences in the originalpermeability. The various permeability and diffusion coefficientsfor CO2 and CH4 in coal induce CO2 and CH4 fractionation in theroof and floor of the No. 2 coal seam.
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