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991.
Park S Kim KS Roh JY Jang GB Ahn SH Lee CS 《Journal of nanoscience and nanotechnology》2012,12(4):3376-3379
High mechanical properties of a tungsten carbide micro-end-mill tool was achieved by extending its tool life by electroplating nano-sized SiC particles (< 100 nm) that had a hardness similar to diamond in a nickel-based material. The co-electroplating method on the surface of the micro-end-mill tool was applied using SiC particles and Ni particles. Organic additives (saccharin and ammonium chloride) were added in a Watts bath to improve the nickel matrix density in the electroplating bath and to smooth the surface of the co-electroplating. The morphology of the coated nano-sized SiC particles and the composition were measured using Scanning Electron Microscope and Energy Dispersive Spectrometer. As the Ni/SiC co-electroplating layer was applied, the hardness and friction coefficient improved by 50%. Nano-sized SiC particles with 7 wt% were deposited on the surface of the micro-end mill while the Ni matrix was smoothed by adding organic additives. The tool life of the Ni/SiC co-electroplating coating on the micro-end mill was at least 25% longer than that of the existing micro-end mills without Ni/SiC co-electroplating. Thus, nano-sized SiC/Ni coating by electroplating significantly improves the mechanical properties of tungsten carbide micro-end mills. 相似文献
992.
Kim YH Kim KS Lee JW Kim MS Choi JO Ahn SH Lee CS 《Journal of nanoscience and nanotechnology》2012,12(4):3478-3482
TiO2 layers were fabricated using a nano-particle deposition system (NPDS) on transparent conductive oxide (TCO) glass for dye sensitized solar cells (DSSCs). Conventionally, TiO2 paste for working electrodes has been fabricated using paste type methods. The fabricated paste composed of a mixture of nano-sized TiO2 powders, binders and solutions is then painted on TCO glass. After drying, the TiO2 layer on TCO glass is sintered to make a path for electron transfer. TiO2 layers formed by this paste type method require numerous steps, which can be time consuming. In this study, TiO2 powders were sprayed directly on TCO glass using NPDS in order to simplify the fabrication steps. To improve porosity and produce scattering layers, commercial nanocrystalline TiO, powders with different sizes were alternately deposited. Moreover, powders with different sizes were mixed and deposited on the TCO glass. The results indicate that the DSSCs with a TiO2 layer composed of different particle sizes had better cell performance than the cells assembled with single-sized TiO2 particles. Therefore, this study shows that a dry TiO2 coating process is possible for DSSC fabrication to improve its cell efficiencies, and this method can easily be applied on flexible substrates since NPDS is a room-temperature deposition process. 相似文献
993.
Shah AA Kang H Kohlstedt KL Ahn KH Glotzer SC Monroe CW Solomon MJ 《Small (Weinheim an der Bergstrasse, Germany)》2012,8(10):1551-1562
DC electric fields are used to produce colloidal assemblies with orientational and layered positional order from a dilute suspension of spheroidal particles. These 3D assemblies, which can be visualized in situ by confocal microscopy, are achieved in short time spans (t < 1 h) by the application of a constant voltage across the capacitor-like device. This method yields denser and more ordered assemblies than had been previously reported with other assembly methods. Structures with a high degree of orientational order as well as layered positional order normal to the electrode surface are observed. These colloidal structures are explained as a consequence of electrophoretic deposition and field-assisted assembly. The interplay between the deposition rate and the rotational Brownian motion is found to be critical for the optimal ordering, which occurs when these rates, as quantified by the Peclet number, are of order one. The results suggest that the mechanism leading to ordering is equilibrium self-assembly but with kinetics dramatically accelerated by the application of the DC electric field. Finally, the crystalline symmetry of the densest structure formed is determined and compared with previously studied spheroidal assemblies. 相似文献
994.
Yoon SW Seo JH Chae KH Park JK Song JH Jayaram V Lee KB Seong TY Hoon-Kwon Ahn JP 《Journal of nanoscience and nanotechnology》2012,12(2):1476-1479
AIN/CrN multilayer hard coatings with various bilayer thicknesses were fabricated by a reactive sputtering process. The microstructural and mechanical characterizations of multilayer coatings were investigated through transmission electron microscope (TEM) observations and the hardness measurements by nano indentation. In particular, the variation of chemical bonding states of the bilayer nitrides was elucidated by near edge X-ray absorption fine structure (NEXAFS) spectroscopy. Many broken nitrogen bonds were formed by decreasing the bilayer thickness of AIN/CrN multilayer coatings. Existence of optimum AIN/CrN multilayer coatings thickness for maximum hardness could be explained by the competition of softening by the formation of broken nitrogen bonds and strengthening induced by decreasing bilayer thickness. 相似文献
995.
An SY Park JH Kim JH Choi CJ Kim H Ahn KS 《Journal of nanoscience and nanotechnology》2012,12(4):3398-3401
Mesoporous TiO2 films modified via sol-gel necking were fabricated by dispersing Ti tetra-isopropoxide (TTIP; 8 to 16 wt% over TiO2) with TiO2 nanoparticles in isopropyl alcohol. The dye-sensitized solar cells (DSSCs) with 13 wt% TTIP-modified TiO2 film exhibited significantly improved overall energy conversion efficiency, despite having less adsorbed dye when compared with DSSCs with untreated and TiCl4 post-treated TiO2 films. The improvement can be attributed to the sol-gel necking (or interconnection) between the nanoparticles which leads to a much faster electron transport and a suppression of the recombination (or back electron transfer) between the TiO2 and electrolyte. 相似文献
996.
997.
Yoon-Hwan Cho Yong-Hun Cho Ju Wan Lim Hee-Young Park Namgee Jung Minjeh Ahn Heeman Choe Yung-Eun Sung 《International Journal of Hydrogen Energy》2012
Pd-based nanoparticles, such as 40 wt.% carbon-supported Pd50Pt50, Pd75Pt25, Pd90Pt10 and Pd95Pt5, for anode electrocatalyst on polymer electrolyte membrane fuel cells (PEMFCs) were synthesized by the borohydride reduction method. PdPt metal particles with a narrow size distribution were dispersed uniformly on a carbon support. The membrane electrode assembly (MEA) with Pd95Pt5/C as the anode catalyst exhibited comparable single-cell performance to that of commercial Pt/C at 0.7 V. Although the Pt loading of the anode with Pd95Pt5/C was as low as 0.02 mg cm−2, the specific power (power to mass of Pt in the MEA) of Pd95Pt5/C was higher than that of Pt/C at 0.7 V. Furthermore, the single-cell performance with Pd50Pt50/C and Pd75Pt25/C as the anode catalyst at 0.4 V was approximately 95% that of the MEA with the Pt/C catalyst. This indicated that a Pd-based catalyst that has an extremely small amount of Pt (only 5 or 50 at.%) can be replaced as an anode electrocatalyst in PEMFC. 相似文献
998.
Choi D Jeong BS Ahn B Chung DS Lim K Kim SH Park SU Ree M Ko J Park CE 《ACS applied materials & interfaces》2012,4(2):702-706
A polymeric semiconductor, poly(3,6-dihexyl-[2,2']bi[thieno[3,2-b]thiophene]) (PDHTT), was synthesized and tested as an active layer in organic thin film transistors (OTFTs). This semiconductor showed considerable potential for use in commercial electronic devices because of its superior characteristics, particularly its good stability. PDHTT-based OTFTs exhibited high stability in air, retaining their initial performance after exposure to 70% relative humidity for 50 days; they were also stable under repeated electrical stress and even after exposure to temperatures as high as 250 °C. We attribute the remarkable stability of PDHTT OTFTs to the relatively low highest occupied molecular orbital (5.1 eV) level of the polymer and its highly interdigitated structure in the thin film state. 相似文献
999.
A nanocomposite of CoO and a mesoporous carbon (CMK-3) has been studied as a cathode catalyst for lithium-oxygen batteries
in alkyl carbonate electrolytes. The morphology and structure of the as-prepared nanocomposite were characterized by field
emission scanning electron microscopy, transmission electron microscopy and high resolution transmission electron microscopy.
The electrochemical properties of the mesoporous CoO/CMK-3 nanocomposite as a cathode catalyst in lithium-oxygen batteries
were studied using galvanostatic charge-discharge methods. The reaction products on the cathode were analyzed by Fourier transform
infrared spectroscopy. The CoO/CMK-3 nanocomposite exhibited better capacity retention than bare mesoporous CMK-3 carbon,
Super-P carbon or CoO/Super-P nanocomposite. The synergistic effects arising from the combination of CoO nanoparticles and
the mesoporous carbon nanoarchitecture may be responsible for the optimum catalytic performance in lithium-oxygen batteries.
相似文献
1000.
A glucosyltransferase cDNA, RF5, was cloned from Oryza sativa using an RT-PCR strategy and expressed in Escherichia coli. Several flavonoids were tested for their ability to serve as substrates for RF5. RF5 effectively glucosylated kaempferol and quercetin to produce their 3-O-glucosides. Thus, RF5 could be defined as a flavonol 3-O-glucosyltransferase. E. coli cells expressing RF5 effectively converted 100 microM of kaempferol and quercetin into their corresponding glucosides. 相似文献