• Journal of the Korean institute of surface engineering
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• v.47 no.6
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• pp.293-296
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• 2014

Fe-Ni has been of great interest because it is known as one of low thermal expansion alloys as various application areas. This alloy was fabricated by electroforming process, and effect of heat treatment on thermal expansion and hardness was investigated. Nano-crystalline structure of 13.3 - 63.5 nm in size was observed in the as-deposited alloy. To investigate the effect of heat treatment on grain growth and mechanical/thermal properties, we conducted hardness and coefficient of thermal expansion (CTE). From this, we confirmed these properties were varied by heat treatment. In this nano-crystalline alloy, we could observe abnormal behavior in thermal expansion between $350-400^{\circ}C$. Additionally, an abrupt change in hardness has also been observed. However, once the grains grow up to micro-sized the mechanical and thermal properties mentioned above were stabilized similar to those of bulk alloys due to heat treatment.

• Journal of the Korean Ceramic Society
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• v.56 no.3
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• pp.256-268
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• 2019

In this research, some mechanical properties of Al₂O₃-based composites containing nanoSiC and nanoMgO additives, including elasticity modulus, hardness, and fracture toughness, have been evaluated. Micron-sized Al₂O₃ powders containing 0.08 wt.% nanoMgO particles have been mixed with different volume fractions of nanoSiC particles (2.5 to 15 vol.%). Untreated samples have been sintered by using hot-press technique at temperatures of 1600 to 1750℃. The results show significant increases in the mechanical characteristics with increases in the sintering temperature and amount of nanoSiC particles, with the result that the elasticity modulus, hardness, and fracture toughness were obtained as 426 GPa, 21 GPa, and 4.5 MPa.m^1/2, respectively.

• Journal of the Korean Ceramic Society
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• v.37 no.1
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• pp.96-101
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• 2000

Comparative studies on microstructure, and mechanical and anti-oxidation properties between TiN and Ti-Si-N films were performed. The Ti-Si-N films were deposited on high-speed steel and silicon wafer substrates by plasma-assisted chemcial vapor deposition(PACVD) technique. The Si addition to TiN film caused to change the microstructure such as grain size refinement, randomly multi-oriented microstructure, and nano-sized codeposition of silicon nitride in the TiN matrix. The Ti-Si-N film, contains Si content of ∼7 at.%, showed the micro-hardness value of ∼3400 HK, which was higher than the pure TiN film whose hardness was ∼1500HK. The Ti-Si(7 at.%)-N film also showed much improved anti-oxidation properties compared with those of the pure TiN film. These properties were also related to the microstructure of Ti-Si(7 at.%)-N film was formed and retarded further oxidation of the nitridelayer. These properties were also related to the microstructure of Ti-Si(7 at.%)-N film which was characterized by nano-sized precipitates of silicon nitride phase in the TiN matrix and randomly oriented grains.

• Journal of the Korean Ceramic Society
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• v.40 no.1
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• pp.31-36
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• 2003

In this study, nano-sized NiCuZn-ferrites for the multi-layered chip inductor application were prepared by a coprecipitation method and its electromagnetic properties were analyzed. Also, the property of low temperature sintering were studied with the initial heat treatment of powder.$(Ni_{0.4-x}Cu_xZn_{0.60})_{1+w}(Fe_2O_4)_{1-w}$ (x=0.2, w=0.03) were calcined at $300^{circ}C~750^{circ}C.$ The sintered NiCuZn-ferrites at $900^{\circ}C$ showed good apparent density $4.90g/cm^3,$ and magnetic properties of initial permeability 164 and quality factor 72. As the calcination temperature increase, the grain size of NiCuZn-ferrite increased with irregular grain distribution and its magnetic properties were deteriorated.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.154-155
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• 2012

The promise of nano-crystalites (nc) as a technological material, for applications including display backplane, and solar cells, may ultimately depend on tailoring their behavior through doping and crystallinity. Impurities can strongly modify electronic and optical properties of bulk and nc semiconductors. Highly doped dopant also effect structural properties (both grain size, crystal fraction) of nc-Si thin film. As discussed in several literatures, P atoms or radicals have the tendency to reside on the surface of nc. The P-radical segregation on the nano-grain surfaces that called self-purification may reduce the possibility of new nucleation because of the five-coordination of P. In addition, the P doping levels of ${\sim}2{\times}10^{21}\;at/cm^3$ is the solubility limitation of P in Si; the solubility of nc thin film should be smaller. Therefore, the non-activated P tends to segregate on the grain boundaries and the surface of nc. These mechanisms could prevent new nucleation on the existing grain surface. Therefore, most researches shown that highly doped nc-thin film by using conventional PECVD deposition system tended to have low crystallinity, where the formation energy of nucleation should be higher than the nc surface in the intrinsic materials. If the deposition technology that can make highly doped and simultaneously highly crystallized nc at low temperature, it can lead processes of next generation flexible devices. Recently, we are developing a novel CVD technology with a neutral particle beam (NPB) source, named as neutral beam assisted CVD (NBaCVD), which controls the energy of incident neutral particles in the range of 1~300eV in order to enhance the atomic activation and crystalline of thin films at low temperatures. During the formation of the nc-/pm-Si thin films by the NBaCVD with various process conditions, NPB energy directly controlled by the reflector bias and effectively increased crystal fraction (~80%) by uniformly distributed nc grains with 3~10 nm size. In the case of phosphorous doped Si thin films, the doping efficiency also increased as increasing the reflector bias (i.e. increasing NPB energy). At 330V of reflector bias, activation energy of the doped nc-Si thin film reduced as low as 0.001 eV. This means dopants are fully occupied as substitutional site, even though the Si thin film has nano-sized grain structure. And activated dopant concentration is recorded as high as up to 1020 #/$cm^3$ at very low process temperature (＜ $80^{\circ}C$) process without any post annealing. Theoretical solubility for the higher dopant concentration in Si thin film for order of 1020 #/$cm^3$ can be done only high temperature process or post annealing over $650^{\circ}C$. In general, as decreasing the grain size, the dopant binding energy increases as ratio of 1 of diameter of grain and the dopant hardly be activated. The highly doped nc-Si thin film by low-temperature NBaCVD process had smaller average grain size under 10 nm (measured by GIWAXS, GISAXS and TEM analysis), but achieved very higher activation of phosphorous dopant; NB energy sufficiently transports its energy to doping and crystallization even though without supplying additional thermal energy. TEM image shows that incubation layer does not formed between nc-Si film and SiO2 under later and highly crystallized nc-Si film is constructed with uniformly distributed nano-grains in polymorphous tissues. The nucleation should be start at the first layer on the SiO2 later, but it hardly growth to be cone-shaped micro-size grains. The nc-grain evenly embedded pm-Si thin film can be formatted by competition of the nucleation and the crystal growing, which depend on the NPB energies. In the evaluation of the light soaking degradation of photoconductivity, while conventional intrinsic and n-type doped a-Si thin films appeared typical degradation of photoconductivity, all of the nc-Si thin films processed by the NBaCVD show only a few % of degradation of it. From FTIR and RAMAN spectra, the energetic hydrogen NB atoms passivate nano-grain boundaries during the NBaCVD process because of the high diffusivity and chemical potential of hydrogen atoms.

• Proceedings of the IEEK Conference
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• 1998.10a
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• pp.601-604
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• 1998

NOX detecting gas sensors using TiO2 doped tungsten oxide semiconductor were prepared and their electrical and sensing characteristics have been investigated. In normal air condition, the sensors of WO3, TiO2 doped WO3 show grain boundary heights of 0.34 eV, 0.25 eV, respectively. The grain boundary barrier energy variation was increased by doping TiO2 into large variation of resistance to NOX gases. And doping the TiO2 4 wt.%, the particle size of WO3 polycrystal films showed higher sensitivity and better sorption characteristics to NOX gas than the pure WO3 films material in air at operating temperature of $350^{\circ}C.$ The TiO2 doped WO3 semiconductor gas sensor shows nano-sized particle size and good sensitivity to sub-ppm concentration of NOX.

• Journal of Powder Materials
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• v.9 no.3
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• pp.182-188
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• 2002

Conventional Fe-Co alloys are important soft magnetic materials that have been widely used in industry. Compared to its polycrystalline counterpart, the nanostructured materials have showed superior magnetic properties, such as higher permeability and lower coercivity due to the single domain configuration. However, magnetic properties of nanostructured materials are affected in complicated manner by their microstructure such as grain size, internal strain and crystal structure. Thus, studies on synthesis of nanostructured materials with controlled microstructure are necessary for a significant improvement in magnetic properties. In the present work, starting with two powder mixtures of Fe and Co produced by mechanical alloying (MA) and hydrogen reduction process (HRP), differences in the preparation process and in the resulting microstructural characteristics will be described for the nano-sized Fe-Co alloy particles. Moreover, we discuss the effect of the microstructure such as crystal structure and grain size of Fe-Co alloys on the magnetic properties.

• Journal of the Korean institute of surface engineering
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• v.43 no.6
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• pp.255-259
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• 2010

In this work, Ni-Co composites incorporated with nano-sized SiC particles in the range of 45-55 nm are prepared by electroplating. The effects of plating duration on the chemical composition, surface morphology, crystalline structures and hardness have been studied. The maximum hardness of Ni-Co-SiC composite coating is approximately 633 Hv at plating duration of 1 h. The hardness is gradually decreased with increasing plating duration, which can be attributed to the growth of crystalline size and the agglomerates of SiC nano-particles. It is therefore explained that the grain refinement of Ni-Co matrix and stable dispersion of SiC particles play an important role for strengthening, which indicate Hall-Petch relation and Orowan model were dominant for hardening of Ni-Co-SiC composite coatings.

• 연구논문집
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• s.26
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• pp.103-112
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• 1996

$Al_2O_3/SiC$ Hybrid-Composite has been fabricated by conventional powder process. The addition of $\alpha-Al_2O_3$ as seed particles in the transformation of $\gamma-Al_2O_3 to $\alpha-Al_2O_3$ provided a homogeneity of the microstructure, resulting in increase of mechanical properties. The grain growth of $Al_2O_3$ are significantly surpressed by the addition of nano-sized. SiC particles, increasing in fracture strength. The addition of SiC plates to $Al_2O_3$ nano-composite decreased the fracture strength, but increased the fracture toughness. Coated SiC plates with nitrides such as BN and /SiC$Si_3N_4$ enhanced fracture toughness much more than uncoated SiC plates by inducing crack deflection.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.13 no.6
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• pp.309-314
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• 2003

A spark plasma sintering technique has been used for the fabrication of $Al_2O_3$-SiC nanocomposites at the low temperature of $1100^{\circ}C$∼$1500^{\circ}C$. The sintered $Al_2O_3$-SiC composites shows very homogeneous microstructure without any particular abnormal grain growth, indicating that the addition of nano-sized SiC particles is very effective to control grain growth and to induce the residual stress in the $Al_2O_3$ matrix, resulting in the intragranular fracture. These SiC particles are present in the grain boundaries and also intragrain, depending on the sintering condition, and improve remarkably the mechanical properties of $Al_2O_3$-SiC composite through the mechanisms of strengthening and toughening induced by crack diffraction and crack bridging.