• Journal of Magnetics
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• v.13 no.4
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• pp.163-166
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• 2008

Multiferroic $CoCr_2O_4$ film was deposited on MgO and $MgAl_2O_4$ substrates by the rf-sputtering process. The films were prepared at an RF-magnetron sputtering power of 50 W and a pressure of 10 mtorr (20 sccm in Ar), and at substrate temperatures of $550^{\circ}C$. The crystal structure was determined to be a spinel (Fd-3m) structure by means of X-ray diffraction (XRD) with Cu $K{\yen}{\acute{a}}$ radiation. The thickness and morphology of the films were measured by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The magnetic properties were measured using a Superconducting Quantum Interference Device (SQIUD) magnetometer. While the ferrimagnetic transitions were observed at about 93 K, which was determined as the Neel temperature, the magnetic properties all show different behaviors. The differences between the magnetic properties can be explained by the stress effects between $CoCr_2O_4$ and the substrates of MgO and $MgAl_2O_4$.

• Journal of the Korean Ceramic Society
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• v.32 no.7
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• pp.769-776
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• 1995

Infrared radiators of a cordierite system [cordierite (2MgO.2Al2O3.5SiO2)＋30wt% clay＋X wt% MnO2 (X=0, 0.1, 0.25, 0.5, 1.0, 1.5, 2.0, 2.5)] were manufactured by a slurry casting method. Thermal and physical properties of these infrared radiators were studied by the measurement of spectra emissivity, thermal expansion coefficient and apparent density, SEM and EPMA analyses were also carried out. The thermal expansion coefficient and apparent density were decreased with increasing amouonts of MnO2 additives. On the other hand, the spectral emissivity was increased in the wavelength below 4.5${\mu}{\textrm}{m}$. Also, infrared radiators of the cordierite system, of which the spectral emisivity was 0.8, could be attainable in the wavelength above 4.5${\mu}{\textrm}{m}$. The infrared radiator of the cordierite system with 2.0wt% MnO2, of which the spectral emissivity was approximately 1.0, could be attainable in the wavelength between 4.5${\mu}{\textrm}{m}$ and 8${\mu}{\textrm}{m}$. The spectral emissivity of the specimen containing 2.0wt% MnO2 was higher than others in the wavelength between 8${\mu}{\textrm}{m}$ and 14${\mu}{\textrm}{m}$.

• Journal of the Korean Ceramic Society
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• v.33 no.1
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• pp.119-125
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• 1996

Magnetic properties through controlled nucleation and crystallization wer studied for ferrimagnetic 40Fe2O3-20CaO-40SiO2 glass useful as thermoseeds for hyperthermia of tumor therapy. The maximum nucleation and crystal growth temperature are $700^{\circ}C$ and 100$0^{\circ}C$ respectively. The glass showed the maximum saturation magnetization of 168.4 emu/cm3 when nucleated $700^{\circ}C$ for 60 min and crystal grown at 100$0^{\circ}C$ for 4hrs. The maximum coercive force was 390 Oe when uncleated $700^{\circ}C$ for 60 min and crystal grown at 975$^{\circ}C$ for 2 hrs. The variation of the saturation magnetization could be well quantitatively interpreted in terms of the volume fraction of the magnetite whereas that of the coercive forces could be explained only qual.itatively in terms of the particle size of the magnetite. Hysteresis losses showed the maximum value of 0.18W/cm3 when heat treated at 100$0^{\circ}C$ for 4 hrs pre-necleated at $700^{\circ}C$ for 60 min and temperature increase of 7K under AC magnetic field of 10 kOe and 10kHz.

• Journal of the Korean Magnetics Society
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• v.5 no.1
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• pp.21-26
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• 1995

The systematic variation of complex permeability and complex permittivity and their relationship with micro-wave absorbing properties are investigated in sintered Ni-Zn ferrites of non-stoichiometric composition. The specirrens of ${(Ni_{0.5}Zn_{0.5}O)}_{1-x}(Fe_{2}O_{3})_{1+x}$ spinels were prepared by a conventional ceramic processing technique. In the present study. complex permeability and permittivity can be controlled by the variation of ${\alpha}-Fe_{2}O_{3}$ contents in the spinel lattice. The primary effect of the excess ${\alpha}-Fe_{2}O_{3}$ is to increase the dielectric constant. while the notable decrease of magnetic loss is observed in the iron-deficient ferrites. The results suggest that the matching fre-queocyand matching thickness could be controlled by the variation of ${\alpha}-Fe_{2}O_{3}$ contents in the Ni-Zn ferrite.

• Journal of Korean Society on Water Environment
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• v.31 no.4
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• pp.360-366
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• 2015

In this study $TiO_2$ nanotube was grown on Ti by anodic oxidation to be used as a photocatalyst. The growth and formation of $TiO_2$ nanotube was monitored during anodization in ethylene glycol electrolyte by changing voltage and composition of electrolyte. Commercially available titanium plate (purity>99.8%, thickness:1mm) Applied voltage and concentration of $NH_4F$ and $H_2O$ were varied to find the optimum condition. Applied voltage is important to make $TiO_2$ nanotube and the electrolyte containing ethylene glycol, 0.2 wt% $NH_4F$ and 2 vol% $H_2O$ was confirmed to be the optimum conditions for the formation and growth of $TiO_2$ nanotubes.

• Proceedings of the KIEE Conference
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• 2006.10a
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• pp.48-49
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• 2006

Highly conductive and transparent films of Ga-doped ZnO have been prepared by pulsed laser deposition using a ZnO target with 3 wt% ${Ga_2}{O_3}$ dopant. Films with the resistivity as low as $3.3{\times}10^{-4}{\Omega}cm$ and the transmittance above 80 % at the wavelength of 400 to 800 nm can be fabricated on glass substrate at room temperature. It is shown that a stable resistivity for the use in oxidation ambient at high temperature can be obtained for the films. Heat treatments were performed to examine the thermal stability of ZnO and GZO films at ptemperature range from $100^{\circ}C$ to $400^{\circ}C$ in $O_2$ ambient for 30 minutes. The resistivity of ZnO film annealed at $400^{\circ}C$ increased by two orders of magnitude, in case of GZO film was relatively stable up to at $400^{\circ}C$. For practical applications at high temperatures the thermal stability of resistivity of GZO thin films might become an advantage for transparent electrodes.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.4
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• pp.279-285
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• 2000

High quality crystals of $YMnO_3$, which is interested in non-volatile memory device application, were grown by the floating zone method. Optimum condition for powder synthesis was established to be $1200^{\circ}C$ for 10 hrs and optimum condition for sintering of $YMnO_3$feed-rod was established to be $1500^{\circ}C$ for 10hrs respectively. It was found from non-seeded growth experiment that $YMnO_3$crystal was grown preferentially to the [1010] orientation. The $YMnO_3$single crystal, which was grown to the direction of perpendicular to C-axis, was typically 5mm in diameter, 50 mm in length and showed dark-blue color.

• Environmental Engineering Research
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• v.13 no.3
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• pp.136-140
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• 2008

$TiO_2$ photocatalyst has been known to exhibit a notable disinfecting activity against a broad spectrum of microorganisms. A lot of commercial $TiO_2$ photocatalyst products have been developed for antimicrobial purposes. However, a standard method has not yet been proposed for use in testing antimicrobial activity. In this study, we developed a $TiO_2$ photocatalytic adhesion test method with film as the standard testing method for the evaluation of antimicrobial activity. This method was devised by modifying the previous antimicrobial products test method, which has been widely used, and considering the characteristics of $TiO_2$ photocatalytic reaction. The apparatus for testing the antimicrobial activity was composed of a Black Light Blue (BLB) lamp as UV-A light source, a Petri dish as the cover material, and a polypropylene film as the adhesion film. The standard $TiO_2$ photocatalyst sample, Degussa P25 $TiO_2$ - coated glass, could only be used once. The optimal initial concentration of the microorganism, proper light intensity, and light irradiation time were determined to be $10^6$ CFU/mL, 1.0 mW/$cm^2$, and 3 hr, respectively, for testing and evaluating antimicrobial activity on the $TiO_2$ surface.

• Journal of Environmental Science International
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• v.14 no.4
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• pp.389-395
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• 2005

The changes of O-J-I-P transients were investigated using leaves of four subtropical plant species (Crinum asiaticum var. japonicum, Osmanthus insularis, Chloranthus glaber and Asplenium antiquum) under the natural conditions in winter, in order to select the stress indicators for diagnosing physiological states of plants under low temperature. In the O-J-I-P transients of these species, the fluorescence intensity was found to be higher in O-step and lower in P-step in winter than in summer. Particularly, the fluorescence intensity of the P-step in Crinum asiaticum var. japonicum was lower than those of other three plant species, indicating that Crinum asiaticum var. japonicum is the most sensitive to low temperature. Of the chlorophyll fluorescence parameters derived from O-J-I-P transients of four subtropical plants, Fm, Fv/Fo, ABS/CS, TRo/CS, $\phi_{po}$ and $\phi_{po}/(1-\phi_{po})$ decreased significantly with the increase of Fo, Sm, N, EToICS, ETo/RC and $\psi_o/(1-\psi_o)$ depending on temperature drop in winter. Therefore, these parameters could be used as indicators for estimating low temperature stress and diagnosing physiological states of plants under the natural conditions in winter.

• Journal of the Korean institute of surface engineering
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• v.52 no.3
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• pp.145-149
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• 2019

Transparent and conductive ZnO/Ag/SnO2 (ZAS) tri-layer films were deposited onto glass substrates at room temperature by using radio frequency (RF) and direct current (DC) magnetron sputtering. The thickness values of the ZnO and $SnO_2$ thin films were kept constant at 50 nm and the value for Ag interlayer was varied as 5, 10, 15, and 20 nm. In the XRD pattern the diffraction peaks were identified as the (002) and (103) planes of ZnO, while the (111), (200), (220), and (311) planes could be attributed to the Ag interlayer. The optical transmittance and electrical resistivity were dependent on the thickness of the Ag interlayer. The ZAS films with a 10 nm thick Ag interlayer exhibited a higher figure of merit than the other ZAS films prepared in this study. From the observed results, a ZAS film with a 10 nm thick Ag interlayer was believed to be an alternative transparent electrode candidate for various opto-electrical devices.