• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2007.11a
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• pp.118-119
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• 2007

Phase stability and morphological investigation on the $Si/SiO_2/HfO_2$ and $Si/SiO_2/ZrO_2$ stack are presented. Thermal stability of $HfO_2$ and $ZrO_2$ determines the quality of interface and subsequently the performance of device. The stacks have been fabricated and annealed at $1000^{\circ}C$ for various time. In evolution of crystalline phase and morphology (electrical and geometrical) of high-k materials, annealing time and process are observed to be crucial factors. The crystallization of some phase has been observed in the case of $Si/SiO_2/HfO_2$. The chemical environment around Zr and Hf in respective samples is observed to be different.

• Polymer Science and Technology
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• v.25 no.3
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• pp.194-200
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• 2014

• Journal of Welding and Joining
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• v.21 no.4
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• pp.39-45
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• 2003

Nano-TiO$_2$ photocatalytic coatings were deposited on the stainless steel 304(50$\times$70$\times$3mm) by the APS(Atmospheric Plasma Spraying). Photocatlytic reaction was tested in MB(methylene blue) aqueous solution. For applying nano-TiO$_2$ powders by thermal spray, the starting nano-TiO$_2$ powder with 100% anatase crystalline was agglomerated by spray drying. Plasma second gas(H$_2$) flow rate and spraying distance were used as principal process parameters which are known to control heat enthalpy(heat input). The relationship between process parameters and the characteristics of microstructure such as the anatase phase fraction and grain size of the TiO$_2$ coatings were investigated. The photo-decomposition efficiency of TiO$_2$ coatings was evaluated by the kinetics of MB aqueous solution decomposition. It was found that the TiO$_2$ coating with a lower heat input condition had a higher anatase fraction, smaller anatase grain size and a better photo-decomposition efficiency.

• Korean Journal of Materials Research
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• v.15 no.3
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• pp.172-176
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• 2005

Formation of aluminum hydroxide by a hydrolytic reaction of nano aluminum powder synthesized by a pulsed wire evaporation (PWE) method has been studied. The type and morphology of the hydroxides were investigated with various initial temperatures and pHs. The nano fibrous boehmite (AlOOH) was formed predominantly over $40^{\circ}C$ of the hydrolytic temperature in acid solution, while the bayerite $(Al(OH)_3)$ was formed predominantly below $30^{\circ}C$ in alkali solution with a faceted crystalline structure. As a result the boehmite showed a much larger specific surface area (SSA) than that of bayerite. The highest SSA of the boehmite was about $409\;m^2/g$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.1
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• pp.58-61
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• 2012

In our report a relatively simple process for fast nano-texturing of p-type(100) CZ- silicon surface using silver catalyzed wet chemical etching in aqueous hydrofluoric acid (HF) and hydrogen peroxide solution($H_2O_2$) at room temperature. The wafers were saw-damaged by NaOH(6 wt%) at $60^{\circ}C$ for 150s. To obtain a nano-structured black surface, a thin layer of silver with thickness of 1 - 10 nm was deposited on the surfaces by evaporation system. After this process the samples were etched in HF : $H_2O_2$ : $H_2O$ = 1:5:10 at room temperature for 80s - 220s. Due to the local catalytic of the Ag clusters, this treatment results in the nano-scale texturing on the surface. This resulted in average reflectance values less than 9% after the silver on the surface of the wafers were removed.

• Journal of Powder Materials
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• v.14 no.5
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• pp.303-308
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• 2007

The oxidation of $Fe_{73}Si_{16}B_7Nb_3Cu_1$ nanocrystalline powder has been conducted to investigate its influence on the electromagnetic wave absorption characteristics of the soft magnetic material. Oxidation occurred primarily on the surface of nanocrystals. Oxidation reduced the real part of complex permeability due to the reduction of the relative volume of the powder, which otherwise contributes to the permeability. Oxidation reduced the absorption efficiency of the sheet at frequencies over 1GHz, indicating that the relative contribution of skin depth increments to the absorption was not significant. The pulverization and milling process lowered the optimum crystallization temperature of the material by $40{\sim}50^{\circ}C$ because of the internal energy accumulated during the fragmentation and powder thinning processes.

• Journal of the Korean Ceramic Society
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• v.45 no.6
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• pp.320-323
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• 2008

The preparation of $Zn_xMn_{1-x}Fe_2O_4$ nanoparticles in an Igepal CO-520-cyclohexane water reverse micelle solution has been studied. The transmission electron microscopy and X-ray diffraction pattern analyses revealed the resulting particles to be $Zn_xMn_{1-x}Fe_2O_4$. The average size and distribution of the synthesized particles calcined at $500^{\circ}C$ for 5 h were in the range of 10 to 20 nm and broad, respectively. The phase of the synthesized particles was crystalline, the magnetic behavior of the synthesized particles was ferromagnetic. The effect of the synthesis parameters, such as the molar ratio of water to surfactant and calcination temperature, is discussed.

• Korean Journal of Materials Research
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• v.18 no.6
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• pp.298-301
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• 2008

A preparation of $Ni_xMn_{1-x}Fe_2O_4$ nanoparticles produced via the reduction of Nickel nitrate hexahydrate, Manganese (II) nitrate hexahydrate and Iron nitrate nonahydrate with hydrazine in Igepal CO-520/cyclohexane reverse micelle solutions was investigated. Transmission Electron Microscope (TEM), X-ray Diffraction (XRD) and Vibration Sample Magnetometer (VSM) analyses showed that the resultant nanoparticles increased the molar ration of water to Igepal CO-520 as the concentrations of Nickel nitrate hexahyrate, Manganese (II) nitrate hexahydrate and Iron nitrate nonahydrate increased. The average size of the synthesized particles calcined at $600^{\circ}C$ for 2hrs was in the range of 20 nm to 30 nm, and the particle distribution was broadened. The phase of the synthesized particles was crystalline, and the magnetic behavior of the synthesized particles was superparamagnetism. The effect of the synthesis parameters of the molar ratio of water to surfactant and the calcination temperature was discussed.

• Composites Research
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• v.32 no.3
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• pp.141-147
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• 2019

In this study, micro-sized and nano-sized pure aluminum (Al) powders were compressed by unidirectional pressure at room temperature. Although neither type of Al bulk was heated, they had a high relative density and improved mechanical properties. The microstructural analysis showed a difference in the process of densification according to particle size, and the mechanical properties were measured by the Vickers hardness test and the nano indentation test. The Vickers hardness of micro Al and nano Al fabricated in this study was five to eight times that of ordinary Al. The grain refinement effect was considered to be one of the strengthening factors, and the Hall-Petch equation was introduced to analyze the improved hardness caused by grain size reduction. In addition, the effect of particle size and dispersion of aluminum oxide in the bulk were additionally considered. Based on these results, the present study facilitates the examination of the effect of particle size on the mechanical properties of compacted bulk fabricated by the powder metallurgy method and suggests the possible way to improve the mechanical properties of nano-crystalline powders.

• Journal of the Korean Electrochemical Society
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• v.14 no.4
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• pp.196-200
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• 2011

The formation of niobium oxide microcones on niobium substrates was investigated in NaF to the HF electrolytes. This condition builds on the uniqueness of the microstructures niobium oxide. The dimensions and integrity of the bulk microstructures were found to be strongly dependent on potential, temperature, electrolyte composition, and anodization time. The anodic oxide was initially amorphous at all temperatures, but crystalline oxide nucleated during anodization. From XRD patterns of the anodized specimens, the microcones consisted of crystalline $Nb_2O_5$. We demonstrated niobium oxide microcone structures with nanorods. The anodized niobium oxide microcone texture revealed nanorod bundles. The surface of $Nb_2O_5$ microcones is very regular and has a nano-scale. The surface morphologies of the nanorods were examined using FE-SEM. EDS analyses show that the anodically prepared niobium oxide consists of $Nb_2O_5$. The aim of this study is to find the condition of forming the favorable nanorods by anodization method.