• Bulletin of the Korean Chemical Society
• /
• v.4 no.4
• /
• pp.176-180
• /
• 1983

A series of new liquid crystalline compounds having two identical mesogenic terminal units, the 4-(p-nitrobenzoyloxy)phenoxy group, attached to both ends of a central polymethylene spacer of various lengths was prepared. The mesomorphic properties of the compounds were investigated by differential scanning calorimetry (DSC) and by polarizing microscopy. Almost all of the compounds formed monotropic nematic mesophases. The trimethylene spacer compound was found to be non-liquid crystalline, while the one with the hexamethylene central spacer was enantiotropic. A thermodynamic analysis was performed for the phase transitions of the compounds and the results are discussed in relation to their liquid crystal properties.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2022.05a
• /
• pp.98-98
• /
• 2022

도수는 사류가 상류로 천이되며 흐름이 불연속적으로 변하는 현상이다. 도수는 롤러와 벽 제트와 같은 흐름이 발생하는 영역으로 구분되며 큰 에너지 손실을 발생시키므로, 보나 댐과 같은 수리시설물에서는 에너지 소산을 위한 목적으로 도수를 발생시킬 수 있다. 도수구간 중 롤러 영역에서는 공기가 유입되어 복잡한 3차원 2상 흐름을 발생시키므로 공기방울의 거동에 대한 정밀한 모의는 매우 중요한 것으로 평가된다. 그러나 현실적으로 롤러 영역에서의 작은 공기방울까지 재현하는 것은 어려운 일이다. 본 연구에서는 k-ω SST 난류모형을 이용하여 수문 아래에서 발생하는 자유도수를 수치모의하고 연행된 공기량에 대한 특성을 검토하였다. 롤러 영역에서 격자의 해상도를 다르게 하여 도수구간 내 공기의 체적비와 공기방울의 크기 및 공기방울의 거동을 분석하였다. 실내 실험자료에 난류모형을 적용하고 그 결과와 비교하여 모의 결과의 적정성을 확인하였다. 또한 도수구간에서 공기방울 거동의 정밀한 모의가 평균흐름 및 난류량의 종방향 변화에 미치는 영향을 검토하였다.

• Journal of Surface Science and Engineering
• /
• v.42 no.6
• /
• pp.267-271
• /
• 2009

Multicomponent transparent conducting oxide films were deposited on glass substrates at 150 by dual magnetron sputtering of AZO and ITO targets. In the case of mixing a limited amount of ITO (10W), resistivity of TCO films was significantly increased compared to the AZO film; from $3.5{\times}10^{-3}$ to $9.7{\times}10^{-3}{\Omega}{\cdot}cm$. Deterioration of the electrical conductivity is attributed to the decreases in carrier concentration and Hall mobility. Improvement of the conductivity could be obtained for the films prepared with ITO powers larger than 40 W. The lowest resistivity ($\rho$) of $7.3{\times}10^{-4}{\Omega}{\cdot}cm$ was achieved when ITO power was 100 W. Effects of $H_2$ incorporation on the electrical and optical properties of AZO-ITO films were investigated in this work. Addition of small amount of hydrogen resulted in the increase of carrier concentration and the improvement of electrical conductivity. It is apparent that the roughness of AZO-ITO films decreases dramatically after the transition of microstructure from polycrystalline to amorphous phase, which gives practical advantages such as an excellent uniformity of surface and a high etching rate. AZO-ITO films grown at sputtering ambient with hydrogen gas are expected to be applicable to optoelectronic devices such as organic light emitting diodes and flexible displays due to their sufficient electrical and structural properties.

• Journal of the Korean Society for Heat Treatment
• /
• v.26 no.2
• /
• pp.55-58
• /
• 2013

ITO thin films deposited on glass substrate with RF magnetron sputtering were vacuum annealed at 100, 200 and $300^{\circ}C$ for 30 minutes and then effect of annealing temperature on the structural, electrical and optical properties of ITO films were investigated. The structural properties are strongly related to annealing temperature. The annealed films above $100^{\circ}C$ are grown as a hexagonal wurtzite phase and the largest grain size is observed in the films annealed at $300^{\circ}C$. The electrical resistivity also decreases as low as $4.65{\times}10^{-4}{\Omega}cm$ with a increase in annealing temperature and ITO film annealed at $300^{\circ}C$ shows the lowest sheet resistance of $43.6{\Omega}/{\Box}$. The optical transmittance in a visible wavelength region also depends on the annealing temperature. The films annealed at $300^{\circ}C$ show higher transmittance of 80.6% than those of the films prepared in this study.

• Journal of the Korean Ceramic Society
• /
• v.34 no.3
• /
• pp.241-248
• /
• 1997

RuO2 thin films were deposited on SiO2(1000$\AA$)/Si and MgO(100) single crystal substrates at low tem-peratures by hot-wall metalorganic chemical vapor deposition(MOCVD), and effects of deposition paramet-ers on the properties of the thin films were investigated. RuO2 single phase was obtained at lower de-position temperature of 25$0^{\circ}C$. RuO2 thin films deposited onto SiO2(1000$\AA$)/Si substrates showed a random orientation, and RuO2 films onto MgO(100) single crystals showed the (hk0) orientation. The crystallinity and resistivity of RuO2 thin films increased and decreased with increasing deposition temperature, respec-tively. The resistivity of RuO2 thin films decreased with decreasing the flow rate. The resistivity of the 2600$\AA$-thick RuO2 thin films deposited with O2 flow rate of 50 sccm at 35$0^{\circ}C$ was 52.7$\mu$$\Omega$-cm, and they could be applicable to bottom electrodes of high dielectric materals.

• Korean Journal of Materials Research
• /
• v.2 no.1
• /
• pp.43-51
• /
• 1992

Thin films of )$Pb(Zr, \;TiO_3$ are fabricated by MOCVD using ultrasonic spraying. The films having perovskite structure are made at low deposition temperature, $300-450^{\circ}C$. The phase and composition of the films vary with the composition of the starting solution and the deposition temperature. Dielectric constant of the films is 187 at 1MHz. Ferroelectric hysterysis loop measurements indicate a remanant polarization of $5.5{\mu}C/cm^2$, and coercive field of 65kV/cm. Resistivity of thin films is about $10^{11}{\Omega}cm$ and the breakdown electric field abort 35kV/cm.

• Journal of the Korean Applied Science and Technology
• /
• v.19 no.3
• /
• pp.222-244
• /
• 2002

A mixture of methyl ester derivatives of fatty acids from the oils of pine nuts was well resolved to five fractions differing by degree of unsaturation by silver ion solid-phase extraction column chromatography ($Ag^{+}$-SEC). Polyunsaturated fatty acid with non-methylene interrupted conjugated double bond (NMiDB) radical held more strongly to silver ions in the column than methylene interrupted conjugated double bond (MiDB) one when they had the same number of double bonds. Although both the picolinyl ester and DMOX derivative provided clear mass ion species powerful enough to elucidate the structure of the polyunsaturated fatty acid (PUFA) with NMiDB and/or methylene interrupted conjugated double bond (MiDB) radical in the oils, the picolinyl ester of PUFA with NMiDB radical did not provide a cluster of mass ions neighboring diagnostic mass ions induced by the double bond in the proximal to the carboxyl group. However, the DMOX derivative of PUFA with NMiDB group as well as MiDB showed abundant mass ion species differing by gaps of 12 amu, which made it possible with greater ease to locate the double bonds in the molecule. The oil contained $C_{18:2{\omega}6}$ (46.2 %) and $C_{18:1{\omega}9}$ (25.4 %) as main components, and considerable amounts of PUFAs with NMiDB radical such as ${\Delta}^{5.\;9.\;12}-C_{18:3}$ (16.0 %), ${\Delta}^{5.\;9}-C_{18:2}$ (2.3 %) and ${\Delta}^{5.\;11.\;14}-C_{20:3}$ (0.8 %).

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.43 no.10 s.352
• /
• pp.90-96
• /
• 2006

A novel ${\Sigma}{\Delta}$ fractional-N PLL architecture for fast locking and fractional spur suppressing is proposed based on the capacitance scaling scheme. It changes the effective capacitance of loop filter (LF) by increasing and decreasing current to the capacitor via different paths with multiple charge pumps. The effective capacitance of loop filter (LF) can be scaled up/down depending on operating status while keeping LF capacitors small enough to be integrated into a single PLL chip. Fractional spurs suppressing have been achieved by reducing the magnitude of charge pump current when the PLL is in-lock without degrading fast locking characteristic. It has been simulated by HSPICE in a CMOS $0.35{\mu}m$ process, and shows flat locking time is less than $8{\mu}s$ with the small size of LF capacitors, 200pF and 17pF, and $2.8k{\Omega}$ resistor.

• Journal of IKEEE
• /
• v.22 no.2
• /
• pp.427-431
• /
• 2018

This research was worked about $Ga_2O_3$ Epi wafer that was one of the mose wide band gap semiconductors to be used power semiconductor industry. This wafer was grown $5.3{\mu}m$ thickness on Sn doped $Ga_2O_3$ Substrate by HVPE(Hydride Vapor Phase Epitaxy). Generally, we can fabricate 600V class power semiconductor devices when the thickness of compoound power semiconductor is $5{\mu}m$. but in case of $Ga_2O_3$ Epi wafer, we can obtain over 1000V class. As a result of J-V measurment of the grown $Ga_2O_3$ Epi wafer, we obtain $2.9-7.7m{\Omega}{\cdot}cm^2$ on resistance. Specially, in case of reverse, we comfirmed a little leakage current when the reverse voltage is over 200V.

• Journal of the Korean Institute of Telematics and Electronics
• /
• v.27 no.10
• /
• pp.113-123
• /
• 1990

Tungsten film was deposited on the single crystal silicon wafer in a low pressure chemical vapor deposition reactor from silane and tungsten hexafluoride in the temperature range of $250-400^{\circ}C$ Deposition rate was found to be determined by the mass transfer rate of reactants from the gas phase to the safter surface. It was found out that tungsten films deposited contained about 3 atomic $\%$ of silicon and that the crystallinity and the grain size increased as the deposition temperature was increased. The resistivity of the film was measured to be in the range of $7~25{\mu}{\Omega}-cm$ and decreased with increasing deposition temperature. The adhesion of the tungsten film on a silicon surface was measured by the tape peel off test and it was improved with increasing deposition temperature. From the analysis of the gas composition, the reaction pathway to form $SiF_{4}$ and $H_{2}$ was found to be more favorable than HF formation.