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Effect of ammonia gas etching on growth of vertically aligned carbon nanotubes/nanofibers

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Transactions of Nonferrous Metals Society of China 2011年第A1期21卷 130-134页

作者： Sang-Gook KIM Sooh-Yung KIM hyung-woo lee Department of Mechanical Engineering Massachusetts Institute of Technology 77 Massachusetts Ave Cambridge MA 02139 USA National Core Research Center for Hybrid Materials Solution Pusan National University

The etching effect of ammonia （NH3） on the growth of vertically aligned nanotubes/nanofibers （CNTs） was investigated by direct-current plasma enhanced chemical vapor deposition （DC-PECVD）. NH3 gas etches Ni catalyst layer to form nanoscale islands while NH3 plasma etches the deposited amorphous carbon. Based on the etching effect of NH3 gas on Ni catalyst, the differences of growing bundles of CNTs and single strand CNTs were discussed; specifically, the amount of optimal NH3 gas etching is different between bundles of CNTs and single strand CNTs. In contrast to the CNT carpet growth, the single strand CNT growth requires shorter etching time （5 min） than large catalytic patterns （10 rain） since nano dots already form catalyst islands for CNT growth. Through removing the plasma pretreatment process, the damage from being exposed at high temperature substrate occurring during the plasma generation time is minimized. High resolution transmission electron microscopy （HTEM） shows fishbone structure of CNTs grown by PECVD.

关键词： carbon nanotube ammonia etching nickel catalyst plasma enhanced chemical vapor deposition (PECVD)

Effective parameters on diameter of carbon nanotubes by plasma enhanced chemical vapor deposition

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中国有色金属学会会刊：英文版 2012年第S3期22卷 712-716页

作者： Kang Young JEONG Hyun Kyung JUNG hyung woo lee National Core Research Center for Hybrid Materials Solution Hybrid Graduate SchoolPusan National University Department of Diagnostic Radiology Inje University College of MedicineHaeundae Paik Hospital

The effective parameters on the diameter of carbon nanotubes (CNTs) by plasma enhanced chemical vapor deposition (PECVD) were *** lots of influential parameters,the effects of the catalytic film thickness and the pretreatment plasma power on the growth of CNTs were *** results show that the size of catalytic islands increases by increasing the thickness of catalytic layer,but the density of CNTs *** pretreatment duration time of 30 s is the optimal condition for growing CNTs with about 50 nm in *** increasing the pretreatment plasma power,the diameter of CNTs decreases ***,the diameter of CNTs does not change drastically from 80 to 120 *** uniformly grown CNTs with the diameter of 50 nm are obtained at the pretreatment plasma power of 100 W.

关键词： carbon nanotubes catalytic film thickness pretreatment plasma power plasma enhanced chemical vapor deposition

Highly efficient and stable solid-state fiber dye-sensitized solar cells with Ag-decorated SiO_(2) nanoparticles

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Nano Research 2021年第8期14卷 2728-2734页

作者： Jae Ho Kim Seok-Ju Yoo Daseul lee Jin woo Choi Sang-Cheol Han Tae In Ryu hyung woo lee Myunghun Shin Myungkwan Song Materials Center for Energy Convergence Korea Institute of Materials Science(KIMS)797Changwon-daeroSungsan-guChangwonGyeongsangnam-do51508Republic of Korea CEN Nano.Co.Ltd. Nano Convergence CenterMuan-roBuduk-myeonMiryang-siGyeongsangnam-do50404Republic of Korea Accident Coordination and Training Division National Institute of Chemical Safety(NICS)90Gajeongbuk-roYuseong-guDaejeon34114Republic of Korea Department of Nanoenergy Engineering and Research Center of Energy Convergence Technology Pusan National UniversityBusandaehak-ro 63-2Geumjeong-guBusan 46241Republic of Korea School of Electronics and Information Engineering Korea Aerospace University Goyang-cityGyeonggi-do10540Republic of Korea

Fiber-shaped dye-sensitized solar cells(FDSSCs)represent promising futuristic flexible or wearable power sources,owing to their simple fabrication process,light weight,weavability,and *** with strategies on changing the properties of semiconductor materials,the effects of incorporating silver-embedded SiO_(2) nanoparticles(Ag@SiO_(2)NPs)on the photoanodes of solid-state FDSSCs(SS-FDSSCs)are *** power conversion efficiency(PCE)of SS-FDSSCs with Ag@SiO_(2) NPs reaches 5.38%,which is comparable to the reference(3.98%).The PCEs remain at 95%between-16.9 and 91.7℃,indicating the operational stability of SS-FDSSCs within this temperature *** fabricated SS-FDSSCs,whose radii were 2 mm,maintains more than 90%of their efficiency over 500 bending cycles and 10 washing cycles.

关键词： dye-sensitized solar cells fiber-shaped solar cells SiO_(2)nanoparticles plasmonic effect solid-state electrolyte

Distribution of electric field for carbon nanotube assembly: Experiments (II)

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Transactions of Nonferrous Metals Society of China 2011年第A1期21卷 121-125页

作者： Soongeun KWON Soo-Hyun KIM Kwang-ho KIM Myung-chang KANG hyung-woo lee Department of Mechanical Engineering Korea Advanced Institute of Science and Technology (KAIST) Daejeon 305-701 Korea National Core Research Center for Hybrid Materials Solution Pusan National University

The distribution effect of electric field on the alignment and attachment of carbon nanotubes （CNTs） were investigated. The experimental results were compared with the simulation results according to three different shaped electrodes. In previous simulation, the round shaped electrodes were expected to be more effective for aligning and attaching a single CNT between two electrodes than conical or rectangular shaped electrodes. To verify the simulation results, three different shaped electrodes were introduced and a single multi-walled carbon nanotube （MWNT） was attached. The optimal conditions for aligning and attaching MWNTs such as the frequency, applied voltage and concentration of MWNTs solution were investigated. Through repeated experiments, frequency of 100 kHz-10 MHz, applied voltage of 0.3-1.3 V^s/~m, concentration of 5 ktg/mL in MWNTs solution were obtained as a possible condition range to attach MWNTs. Under these conditions, the yield of MWNTs attachment between two electrodes was up to 70%. In previous simulation, furthermore, it was verified that the size of the stable or quasi-stable region made CNTs aligned and attached on different shaped electrodes from the comparison of the experimental and simulation results. Most single MWNT attachment was accomplished on the round shaped electrodes.

关键词： carbon nanotubes dielectrophoresis round shaped electrode simulation

Dielectrophoretic assembly of semiconducting single-walled carbon nanotube transistor

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Transactions of Nonferrous Metals Society of China 2011年第A1期21卷 126-129页

作者： Se-Hun KWON Young-Keun JEONG Soongeun KWON Myung-Chang KANG hyung-woo lee National Core Research Center for Hybrid Materials Solution Pusan National University Department of Mechanical Engineering Korea Advanced Institute of Science and Technology (KAIST) Daejeon 305-701 Korea

A novel burning technique for making a semiconducting single-walled carbon nanotubes （SWNTs） transistor assembled by the dielectrophoretic force was suggested. The fabrication process consisted of two steps. First, to align and attach a bundle of SWNTs between the source and drain, the alternating （AC） voltage was applied to the electrodes. When a bundle of SWNTs was connected between two electrodes, some of metallic nanotubes and semi-conducing nanotubes existed together. The second step is to burn the metallic SWNTS by applying the voltage between two electrodes. With increasing the voltage, more current flowed through the metallic SWNTs, thus, the metallic SWNTs burnt earlier than the semiconducting one. This technique enables to obtain only semi-conducting SWNTs connection in the transistor. Through the 1--V characteristic graph, the moment of metallic SWNTs burning and the characteristic of semi-conducing nanotubes were verified.

关键词： single-walled carbon nanotube (SWNT) semi-conducting carbon nanotube burning technique dielectrophoresis

Characteristic evaluation of Al_2O_3/CNTs hybrid materials for micro-electrical discharge machining

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Transactions of Nonferrous Metals Society of China 2011年第A1期21卷 28-32页

作者： Hyun-Seok TAK Chang-Seung HA Ho-Jun lee hyung-woo lee Young-Keun JEONG Myung-Chang KANG National Core Research Center for Hybrid Materials Solution Pusan National University Department of Electrical Engineering Pusan National University

The characteristic evaluation of aluminum oxide （A1203）/carbon nanotubes （CNTs） hybrid composites for micro-electrical discharge machining （EDM） was described. Alumina matrix composites reinforced with CNTs were fabricated by a catalytic chemical vapor deposition method. A1203 composites with different CNT concentrations were synthesized. The electrical characteristic of A1203/CNTs composites was examined. These composites were machined by the EDM process according to the various EDM parameters, and the characteristics of machining were analyzed using field emission scanning electron microscope （FESEM）. The electrical conductivity has a increasing tendency as the CNTs content is increased and has a critical point at 5% A1203 （volume fraction）. In the machining accuracy, many tangles of CNT in A1203/CNTs composites cause violent spark. Thus, it causes the poor dimensional accuracy and circularity. The results show that conductivity of the materials and homogeneous distribution of CNTs in the matrix are important factors for micro-EDM of A1203/CNTs hybrid composites.

关键词： A1203/CNTs hybrid materials micro-electrical discharge machining micro-hole electrical conductivity

Distribution of electric field for carbon nanotube assembly: Simulation (I)

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Transactions of Nonferrous Metals Society of China 2011年第A1期21卷 117-120页

作者： Soon-Geun KWON Soo-Hyun KIM Kwang-Ho KIM Myung-Chang KANG hyung-woo lee Department of Mechanical Engineering Korea Advanced Institute of Science and Technology (KAIST) Daejeon 305-701 Korea National Core Research Center for Hybrid Materials Solution Pusan National University

The distribution of electric field for the alignment and attachment of carbon nanotubes (CNTs) was simulated. To be attached at the desired place, the aligned and attracted CNTs should be stayed in the desired area called the stable region or the quasi-stable region for an instant where the change of electric field is minimized. Since the conical electrode has the very narrow sized quasi-stable region, few CNTs can be attached. The rectangular electrodes have a wide stable region, so lots of CNTs can be attached. The results indicate that the round electrode which has a proper sized quasi-stable region is more effective for aligning and attaching a single CNT than the conical or rectangular shaped electrodes.

关键词： carbon nanotubes (CNTs) dielectrophoresis (DEP) round shaped electrode simulation

Effects of honing treatment on AIP-TiN and TiAlN coated end-mill for high speed machining

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Transactions of Nonferrous Metals Society of China 2011年第A1期21卷 83-87页

作者： Jae-Young HEO Sung-Hak CHO Tae-Jin JE Kwang-Ho KIM hyung-woo lee Myung-Chang KANG National Core Research Center for Hybrid Materials Solution Pusan National University Nano Machining Laboratory Korea Institute of Machinery and Material (KIMM) 171 Jang-dong Yuseong-Gu Daejeon 305-343 Korea

The objective of this work is to compare the tool performance of TiN and TiA1N coated carbides end-mills deposited by an arc ion plating （ALP） method, using honing treatment to polish the cutting edge surface sleekly. The curve of surface roughness versus honing time showed a rapid improvement initially and thereafter became steady, manifesting a saturation effect. The optimal honing time related to surface roughness was determined to be approximately 20 s. As the surface roughness increased, the critical loads reduced. At an average surface roughness （Ra） of 0.028 p.m, the highest critical loads of TiN and TiAlN coating layers were 98 and 114 N, respectively. Tool performances of uncoated and coated tools were conducted under high speed machining （HSM） of AISI D2 cold-worked die steel （62 HRC）. Consequently, the TiAlN coated end-mill using honing treatment showed excellent tool life under HSM conditions.

关键词： TiA1N arc ion plating honing treatment high speed machining tool life

Global Genomic Variations of Pathogenic Bacteria <i>Salmonella</i>Reading

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Computational Molecular Bioscience 2021年第3期11卷 57-68页

作者： woo hyung lee Yein Jeon Jonathan S. Chung woo Jun Shim Min Jae Shin Seok Gyu Han Seunghan Baek James Kim Jaewoo Kim Paul S. Chung Biotechnology School of Sciences Hong Kong University of Science of Technology Hong Kong China Fuzbien Technology Institute Rockville USA Ernest Mario School of Pharmacy Rutgers University New Brunswick USA College of Letters & Sciences University of California Los Angeles USA Biology Bachelor of Science California Institute of Technology Pasadena USA School of Arts & Sciences Johns Hopkins University Baltimore USA School of Arts & Sciences University of Michigan Ann Arbor USA Youth with Talents Fairfax USA

US Centers for Disease Control and Prevention (CDC) estimates food-borne pathogenic Salmonella bacteria cause about 1.35 million infections, 26,500 hospitalizations, and 420 deaths in the U.S. every year. Outbreaks of multidrug-resistant Salmonella Reading linked mainly to raw turkey products and alfalfa sprouts have accounted for human illness including mortality. Therefore, we downloaded and compared genome sequences of 897 Salmonella Reading isolated from 27 resources in 11 countries at 21 year-points from the National Center for Biotechnology Information database. Isolates were clustered into 10 clades which consisted of 3 major and 7 minor or single node clades. Although 3 major clades included both Europe and American isolates, one clade consisted of 605 North American isolates out of 614 isolates. Evolutionary distance is more related to the continent than the source of isolation. The host source, continent (North America and Europe) and phylogenetic clade were related to the prevalence of isolates encoding Antimicrobial Resistance Genes (ARGs). Prevalence of prophages was greater in bovine and swine isolates than poultry and human isolates and the least prevalence was found in human isolates. Between continents, the prevalence of phage was greater in North Ame- rican isolates than European. The diversity of virulence factors in swine isolates differed from poultry isolate while no difference was found among continents. In conclusion, evolutionary distance is related to isolation host source rather than the continent, and genome features were distinguished by host and cluster. Our genomic analysis implies that Salmonella Reading evolved independently to environments within its lineages.

关键词： Salmonella Serovar Reading Genome Antimicrobial Resistance Genes Virulence Factors Phylogenomic Tree