• 한국세라믹학회지
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• 제33권10호
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• pp.1101-1108
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• 1996

No-doped PZT thin films have been fabricated on Pt/Ti/SiO2/Si substrate using Sol-Gel technique. A fast annealing metho (three times of intermediate and final annealing) was used for the preparation of multi-coated 1800$\AA$ thick Nb-doped PZT thin films. As Nb doping percent was increased leakage current was lowered approximately 2 order but dielectic properties were degraded due to the appearance of pyrochlore phase and domain pinning. Futhermore the increase of the final annealing temperature up to 74$0^{\circ}C$lowered the pyrochlore phase content resulting in enhancing the dielectric properties of the Nb doped films. The 3%-Nb doped PZT thin films with 5% excess Pb showed a capacitance density of 24.04 fF/${\mu}{\textrm}{m}$2 a dielectric loss of 0.13 a switchable polarization of 15.84 $\mu$C/cm2 and a coercive field of 32.7 kV/cm respectively. The leakage current density of the film was as low as 1.47$\times$10-7 A/cm2 at the applied voltage of 1.5 V.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2013년도 임시총회 및 하계학술연구발표회
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• pp.15-16
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• 2013

Magnetization behavior of ultra thin $Fe_xCo_{1-x}$ alloy (where x varies from 0 to 100) has been investigated as functions of composition on Cr (100) substrate by using in situ surface magneto optical Kerr effect (SMOKE). It's always show in plane uniaxial magnetic anisotropy at room temperature (RT) & Low temperature (LT). It is observed that composition dependent coercive force maximum at about 30 at % Co and 70 at % Co atomic ratio and minimum near equiatomic site. The relative magnetic moments as composition variation also show magnetization collapse near equiatomic site. The magnetization behaviors of Fe-Co alloy on Cr (100) due to composition varies are supported the order-disordering as well as structural stability bcc (ferromagnetic)/fcc (anti-ferromagnetic) phase stability magnetism.

• 대한전자공학회논문지TC
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• 제38권1호
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• pp.34-42
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• 2001

편파기 특성을 갖는 새로운 주파수 선택반사기의 새로운 주기적 배열 구조를 제시하였다. 배열 구조는 평면 유전체 슬랩의 양면에 도체 다이폴을 주기적으로 배열하고 윗면의 다이폴과 아래면의 다이폴은 서로 대략 $90^{\circ}$ 정도로 직교되며 유전체 두께는 유전율을 고려한 주파수 파장의 1/8정도이다. 산란 해석으로는 파수 영역 이미턴스방법과 모멘트 방법이 사용되었다. 제시한 새로운 주파수 선택반사기의 편파 변환 기능을 확인하기 위해 설계/제작하여 반사 손실과 투과 손실을 측정하였다. 측정 결과는 이론치와 매우 일치되었으며 반사시 선형 편파인 입사파가 원형 편파로 변환됨을 확인하였다.

• Transactions on Electrical and Electronic Materials
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• 제7권3호
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• pp.129-133
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• 2006

Ferroelectric PZT heterolayered thick films were fabricated by the alkoxide-based sol-gel method. PZT(20/80) and PZT(80/20) paste were made and alternately screen-printed on the alumina substrates. The coating and drying procedure was repeated 4 times to form the heterolayered thick films. The thickness of the PZT heterolayered thick films was approximately $60{\mu}m$. All PZT thick films showed the typical XRD patterns of a polycrystalline rhombohedral structure. And in the PZT thick films sintered at $1100^{\circ}C$, the pyrochlore phase was observed due to the evaporation of PbO. The relative dielectric constant and the dielectric loss of the PZT thick films sintered at $1050^{\circ}C$ were 445.2 and 1.90 % at 1 kHz, respectively. The remanent polarization and coercive field of the PZT thick films sintered at $1050^{\circ}C$ were $14.15{\mu}C/cm^2$ and 19.13 kV/cm, respectively.

• Corrosion Science and Technology
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• 제19권1호
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• pp.8-15
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• 2020

In this paper, the efficiency and the inhibition mechanisms of cobalt salts (cobalt nitrate and cobalt-exchange silica Co/Si) for the corrosion protection of AA2024 were investigated in a neutral aqueous solution by using the electrochemical impedance spectroscopy (EIS) and polarization curves. The experimental measurements suggest that cobalt cation plays a role as a cathodic inhibitor. The efficiency of cobalt cation was important at the concentration range from 0.001 to 0.01 M. The formation of precipitates of oxides/hydroxides of cobalt on the surface at low inhibitor concentration was confirmed by the Scanning Electron Microscopy/Energy Dispersive X-Ray Spectroscopy (SEM/EDS) analysis. EIS measurements were also conducted for the AA2024 surface covered by water-based epoxy coating comprising Co/Si salt. The results obtained from exposure in the electrolyte demonstrated the improvement of the barrier and inhibition properties of the coating exposed in the electrolyte solution for a lengthy time. The SEM/EDS analysis in artificial scribes of the coating after salt spray testing revealed the release of cobalt cations in the coating defect to induce the barrier layer on the exposed AA2024 substrate.

• 한국진공학회지
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• 제12권S1호
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• pp.113-115
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• 2003

We investigate transmission of light in nanoscale structures. We present spatial and temporal domain measurements of the dephasing of surface plasmon excitations in metal films with periodic nano-hole arrays. By probing coherent spatial SP propagation lengths of a few f1. $\mu$m and an ultrafast decay of the SP polarization on a 10 fs timescale, we demonstrate that the SP transmission peaks are homogeneously broadened by the SP radiative lifetime. The pronounced wavelength and hole size dependence of the dephasing rate shows that the microscopic origin of the conversion of SP into light is a Rayleigh-like scattering by the periodic hole array. We have experimentally studied the dephasing of surface plasmon excitations in metallic nano-hole arrays. By relating nanoscopic SP propagation, ultrafast light transmission and optical spectra, we demonstrate that the transmission spectra of these plasmonic bandgap structures are homogeneously broadened. The spectral line shape and dephasing time are dominated by Rayleigh scattering of SP into light and can varied over a wide range by controlling the resonance energy and/or hole radius. This opens the way towards designing SP nano-optic devices and spatially and spectrally tailoring light -matter interactions on nanometer length scales.

• Advances in nano research
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• 제13권5호
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• pp.475-485
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• 2022

Crystalline silicon photovoltaic cells have advantages of zero pollution, large scale and high reliability. A major challenge is that sunlight wavelength with photon energy lower than semiconductor band gap is converted into heat and increase its temperature and reduce its conversion efficiency. Traditional cooling PV method is using water flowing below the modules to cool down PV temperature. In this paper, the idea is proposed to reduce the temperature of the module and improve the energy conversion efficiency of the module through the modulation of the solar spectrum. A spectrally selective nanofilm reflector located directly on the surface of PV is designed, which can reflect sunlight wavelength with low photon energy, and even enhance absorption of sunlight wavelength with high photon energy. The results indicate that nanofilm reflector can reduce spectral reflectivity integral from 9.0% to 6.93% in 400~1100 nm wavelength range, and improve spectral reflectivity integral from 23.1% to 78.34% in long wavelength range. The nanofilm reflector can reduce temperature of PV by 4.51℃ and relatively improved energy conversion efficiency of PV by 1.25% when solar irradiance is 1000 W/m². Furthermore, the nanofilm reflector is insensitive in sunlight's angle and polarization state, and be suitable for high irradiance environment.

• 지질공학
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• 제6권3호
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• pp.137-153
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• 1996

본 연구는 이미 알려져 있는 공동 지역에서 1년 6개월에 걸친 고정점 관측 및 이동 관측망에 의한 실험을 통하여 지하 매질에 공동이 존재할 때에 나타나는 지진파의 이상 현상에 의하여 지하에 존재하는 공동을 탐지 및 식별할 수 있는 가능성을 찾는데 그 목적이 있다. 한양 대학교 지진 연구소에서는 경기도 화성군 봉담면에 위치한 삼보 광산에서 고정 지진 관측을 수행하였다. 이 자료의 대부분은 인근 골재 채취장에서의 화약류 발파에 의한 것이며 본 연구에서는 이 화약류 발파에 의한 자료를 이용하였다. 고정 관측소 관측의 경우 지상 관측과 삼보 광산의 갱도 안에서의 지하 관측을 수행하였다. 이 두 자료으 경우 종파의 초동 후 150 ~ 250 msec 후에 전환파(converted phase)의 출현에 의하여 편파 특성이 매우 급격하게 변하는 양상을 보여 준다. 전환파가 발생하는 깊이는 평균 약 190m 정도로서 삼보 광산의 갱도 깊이와 잘 일치되는 결과를 보여 준다. 또한 횡파 분열(Shear-wave Splitting) 현상이 관측되었다. 빠른 횡파(fS)와 느린횡파(sS)의 시간 차이는 약 30-60ms 정도의 차이(평균 42 ms)를 보인다. 이러한 결과는 다른 연구의 결과보다는 상당히 큰 값을 보여 주는데 이는 지하 공동에 의한 균열(Crack)이 상당히 발달해 있는 것을 나타내는 결과이다. 또한 화약 발파 실험에 의한 자료는 공동에 설칠한 지진계와 비공동 지역에 설피한 지진계를 비교 분석하였다. 공동 지역에서 설치한 지진계의 경우 고정 관측소의 경우와 같이 종파의 초동후에 편파 특성이 매우 급격하게 변하는 양상을 보이나 비공동 지역에 설치한 지진계의 경우는 편파 특성이 매우 안정적인 양상을 보인다. 또한 공동 지역을 지난 지진파의 특징은 현저한 고주파수 성분의 감쇄와 탁월한 저주파의 성질을 갖는 위상이 관측되었다.

• 한국세라믹학회지
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• 제48권6호
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• pp.487-492
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• 2011

The effect of the application of lanthanum strontrium manganite and yttria-stabilized zirconia (LSM-YSZ) nano-composite fabricated by pulsed laser deposition (PLD) as a cathode of solid oxide fuel cell (SOFC) is studied. A gradient-structure thin-film cathode composed of 1 micron-thick LSM-YSZ deposited at an ambient pressure ($P_{amb}$) of 200 mTorr; 2 micron-thick LSM-YSZ deposited at a $P_{amb}$ of 300 mTorr; and 2 micron-thick lanthanum strontium cobaltite (LSC) current collecting layer was fabricated on an anode-supported SOFC with an ~8 micron-thick YSZ electrolyte. In comparison with a 1 micron-thick nano-structure single-phase LSM cathode fabricated by PLD, it was obviously effective to increase triple phase boundaries (TPB) over the whole thickness of the cathode layer by employing the composite and increasing the physical thickness of the cathode. Both polarization and ohmic resistances of the cell were significantly reduced and the power output of the cell was improved by a factor of 1.6.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2001년도 추계학술발표회 초록집
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• pp.29-30
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• 2001

This paper presents some results of plasma nitriding on hard chromium deposit. The substrates were C45 steel and $30~50{\;}\mu\textrm{m}$ of chromium deposit by electroplating was formed. Plasma nitriding was carried out in a plasma nitriding system with $95NH_3{\;}+{\;}SCH_4$ atmosphere at the pressure about 600 Pa and different temperature from $450^{\circ}C{\;}to{\;}720^{\circ}C$ for various time. Optical microscopy and X-ray diffraction were used to evaluate the characteristics of surface nitride layer formed by nitrogen diffusion from plasma atmosphere inward iCr coating and interface carbide layer formed by carbon diffusion from substrate outward Cr coating. The microhardness was measured using microhareness tester at the load of 100 gf. Corrosion resistance was evaluated using the potentiodynamic measurement in 3.5% NaG solution. A saturated calomel electrode (SiCE) was used as the reference electrode. Fig.1 shows the typical microstructures of top surface and cross-section for nitrided and unnitrided samples. Aaer plasma nitriding a sandwich structure was formed consisting of surface nitride layer, center chromium layer and interface carbide layer. The thickness of nitride and carbide layers was increased with the increase of processing temperature and time. Hardness reached about 1000Hv after nitriding while 900Hv for unnitrided hard chromium deposit. X-ray diffraction indicated that surface nitrided layer was a mixture of $Cr_2N$ and CrN at low temperature and erN at high temperature (Fig.2). Anodic polarization curves showed that plasma nitriding can greatly improve the corrosion resistance of chromium e1ectrodeposit. After plasma nitriding, the corrosion potential moved to noble direction and passive current density was lower by 1 to 4 orders of magnitude compared with chromium deposit(Fig.3).