Interfacial Reactions in Gold and Nickel Thin Films in (111) Silicon Single Crystals

윤기현 대한금속재료학회(대한금속학회) 1976 대한금속·재료학회지 Vol.14 No.1

Pure nickel and gold thin film were vacuum-deposited on (111) silicon single crystals. When Au/Ni/Si or Ni/Au/Si samples were heated to about 550℃ in situ, hexagonal or deformed hexagonal shaped crystallites were formed on silicon substrates. The formation mechanism and composition of these crystallites were determined by using X-ray diffraction, scanning electron microscopy and scanning Auger micro-probe methods. The crystallites were identified as NiSi₂. The crystallites on the (111) silicon plane parallel to the surface appeared as regular hexagons while the inclined crystallites resembled trapezia. The results of Auger spectra and in-depth composition profiles for Ni. Au and Si showed that the NiSi₂crystallites are islands in a matrix of Au-Si eutectic.

RICKETTISA TSUTSUGAMUSHI에 의한 폐렴 1예

윤기현,유지홍,강홍모 한국의학사 1991 診斷과治療 Vol.11 No.2

인산형 연료전지용 SiC-SiC Whisker 전해질 매트릭스의 특성

윤기현,이현임,이근행,김창수 한국세라믹학회 1992 한국세라믹학회지 Vol.29 No.8

Sheets of SiC-SiC whisker maxed matrix were prepared from the mixed slurry of SiC whisker and SiC matrix by the rolling method. With the increase of SiC whisker, the pore size, the porosity and the phosphoric acid absorbency of the matrix were increased, while the bubble pressure was decreased. The activation energy for the transfer of H+ ion was decreased with the increase of mixing ratio of SiC whisker to the SiC matrix from the measurement of hydrogen ion conductivity. The activation energy was evaluated as 0.25 eV when the mixing ratio of SiC whisker to the SiC matrix was 1 : 2 and the activation energy was 0.16 eV for the 2 : 1 matrix. It means that SiC whisker matrix contributes to attain a better microstructure for the diffusion of hydrogen ion. From the measurement of single cell performance of matrix with various mixing ratio, it is concluded that if SiC-SiC whisker maxed matrix has a sufficient bubble pressure to prevent the crossover of H2 gas, the current density of a fuel cell is increased with the increase of acid absorbency of the matrix. Current density was improved from 140 mA/$\textrm{cm}^2$ for 0.25 mm thickness of matrix to 170 mA/$\textrm{cm}^2$ for the 0.20 mm one at 700 mV.

고주파용 회로기판을 위한 PTFE(Polytetrafluoroethylene) 복합체의 제조 및 유전 특성

윤기현,정도환,양병덕,장재혁,김종희 한국세라믹학회 2003 한국세라믹학회지 Vol.40 No.8

The PTFE composites for the microwave printed circuit board were prepared using woven glass fiber. The dielectric constant of the PTFE composites with oven glass fiber tended to decrease with an increase of immersion time, and was saturated at 3 times immersion. It resulted from the fact that fine powders of PTFE filled up at the pore and bend of woven glass fiber sufficiently. As the immersion time increased, the propagation velocity increased due to the reduction of dielectric constant. 고주파용 회로기판으로 사용하는 PTFE 복합체를 woven glass fiber를 사용하여 제조하였다. 유전상수는 PTFE 분산액에 woven glass fiber를 함침하는 횟수 증가에 따라 감소하는 특성을 나타내었으며, 3회 함침 횟수부터는 변화율이 감소하였는데, 이것은 PTFE 미세분말이 woven glass fiber의 기공과 굴곡 사이를 충분히 채우기 때문이다. 또한 함침 횟수 증가에 따라 PTFE의 비율이 증가하면서 유전 상수가 감소하여 회로 기판의 전파 전송속도는 증가하였다.

Li₂O-TiO₂-P₂O₅계 유리의 구조와 전기적 성질

윤기현,곽만석,이용근 한국세라믹학회 2003 한국세라믹학회지 Vol.40 No.2

50Li$_2$O-xTiO$_2$-(50-x)P$_2$O$_{5}$의 조성을 가진 유리에서 중간산화물인 TiO$_2$의 치환량을 증가시키면서 유리를 제조하여 전기 전도도의 변화를 고찰하였다 TG-DTA를 이용하여 열적 특성을 관찰하였으며, FT-IR을 이용하여 유리의 구조변화를 관찰하였다. TiO$_2$의 양이 증가함에 따라 밀도와 유리 전이온도는 증가하였다. 이는 유리 내에서 P-O-Ti 교차결합이 형성되면서 결합 강화가 발생하기 때문이다. 전기 전도도는 TiO$_2$치환량과 함께 증가하여 x=20에서 1.27$\times$$10^{-6}$ S/cm(상온)의 최대값을 나타내었다. 전기 전도도는 유리의 지배적 구조가 pyrophosphate unit으로 변화하면서 크게 증가하는 것을 관찰할 수 있었으며, 이는 비가교 산소의 증가로 인한 Li+ 이동도의 증가 때문이다. Electrical conductivity of$50Li_2O-xTiO_2-(50-x)P_2O_5$ glasses has been studied with an increase of the intermediate$TiO_2$content. Thermal properties were observed from TG-DTA measurement and the variation of glass structure was investigated by FT-IR. The density and glass transition temperature increased with an increase of the $TiO_2$ content. These results were attributed to the fact that bond strengthening was occurred because of the formation of P-O-Ti cross linkages in the glass. The ionic conductivity increased with $TiO_2$ content and a maximum value, $1.2{imes}10^{-6}$S/cm showed at x=20. The ionic conductivity showed a large increasement as a result that the pyrophosphate group become the predominant structural unit. This result can explain that Li ions mobility increased as a number of non-bridging oxygen on phosphate units increased.

장래 인구변화에 따른 초․중등학교 과밀학급 전망 분석

윤기현,엄태영 한국교육정치학회 2023 한국교육정치학회 학술대회논문집 Vol.2023 No.-

학급은 교육주체인 교원과 학생이 함께 학습활동이 이루어지는 공간적인 개념뿐만 아니라 교원의 전문적인 교육활동을 위한 기본 여건인 만큼 과밀학급에 대한 분석과 이에 대한 정책 방향 수립은 중요하다. 이에 본 연구는 초․중등학교의 학령인구 변동과 과밀학급의 현황을 살펴보고 초․중등학교에 대한 장래 과밀학급을 전망하여 향후 과밀학급과 관련된 정책 방향 및 시사점을 제시하고자 하였다. 이를 위해 통계청와 행정안전부에서 제공하는 학령인구 관련 기초자료를 활용하여 코호트요인법으로 분석하고 과밀학급이 발생하고 있는 주요 학군지를 대상으로 실제 지역 내 인구 변동과 비교하였다. 분석 결과 학령인구 감소에 따라 장래 학생 수 및 장래 학급 수는 점차 감소될 것으로 전망되고 과밀학급은 이러한 추세에 따라 2025년을 제외하고 2036년까지 지속적으로 감소하는 가운데 2037년부터 반등하지만 다시 감소하여 2040년의 과밀학급은 2023년 대비 65.2% 감소할 것으로 전망되었으며, 소위 명문 학군지와 같은 특정 지역의 과밀학급의 경우 같은 지역 내 인구변동 구조와는 다른 양상이 나타나고 있었다. 이러한 결과를 바탕으로 과밀학급과 관련된 향후 정책적 제언을 제시하였다.

비휘발성 용매(NMP)를 사용한 인산형 연료전지(PAFC)용 전해질 매트릭스 제조 및 특성

윤기현,양병덕 한국세라믹학회 2000 한국세라믹학회지 Vol.37 No.1

Preparation and characteristics of a matrix retaining electrolyte using SiC whisker, PES binder, and NMP(n-methyl-2-pyrrolidone) as a non-volatile solvent for a phosphoric acid fuel cell were investigated. The conditions of binder and plasticizer, and the effects of substituting a volatile solvent by a non-volatile solvent were also studied. The minimum amount of the binder was about 17 wt% for the proper bubble pressure and surrounding SiC whiskers. And the maximum amount of the plasticizer was about 10wt% to be fitted into the polymer chain of the binder. The matrix prepared by using a non-volatile solvent needed longer time to dry, and its pore size was smaller compared with that of the matrix prepared by using volatile solvent. The small pore size resulted in decrease of the overall pore volume. The ionic conductivity in the condition of the same thickness was decreased due to decrease of phosphoric acid absorbancy. As the internal resistance of the electrolyte increased, the fuel cell performance slightly decreased.

TiO2 세라믹 전극의 광전기 화학 변환에 미치는 결정립 크기와 첨가제 ZnO의 영향

윤기현,장병규,김태희 한국세라믹학회 1989 한국세라믹학회지 Vol.26 No.2

The effects of grain size and dopant ZnO on the photoelectrochemical conversion in TiO2 ceramic electrodes have been investigated. The photocurrent increases with increasing grain size in the undoped TiO2 ceramic electrode. In ZnO-doped TiO2 electrodes, the photocurrent decreases with increasing ZnO up to 0.4 wt% due to decrease of donor concentration, and then with further addition of ZnO, photocurrent increases according to the formation of second phase. However, the photoresponse appears at wavelength of 420nm, which is very close to the energy band gap of TiO2, regardless of grain size and amount of ZnO.

n-형 $TiO_2$ 세라믹 전극의 광 활동도

윤기현,김종선 한국세라믹학회 1985 한국세라믹학회지 Vol.22 No.4

The quantum efficiency vs. wavelength curves with different reducing treatments for the 99.99% and 98.5% $TiO_2$ ceramic electrodes have been analyzed according to the Schottky barrier model of the semiconductor-elect-rolyte interface, The model allows the main physical parameters governing the photoelectrochemical properties of the semicon-ductor to be determined. According to these data the impurity ions as three valence state ($Fe^{3+})$ in the $TiO_2$ raw materials have great influence on the photoresponse and the $TiO_2$ ceramic electrodes show much lower quantum efficiency than the $TiO_2$ single crystal due to existence of the recombination centers.

$TiO_2$의 유전성에 미치는 ZnO의 영향

윤기현,송효일,김창수 한국세라믹학회 1980 한국세라믹학회지 Vol.17 No.3

The effect of the additive on the dielectric property of TiO2 containing 0-2.5 wt. % ZnO was investigated as a function of frequency $5$\times$10^4$ to $6.3$\times$10^7$ cps and temperature from 25 to 375$^{\circ}C$. The dielectric constant decreased due to increasing density and grain size effect with increasing ZnO concentration.