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분광타원해석법을 이용한 Ge₂Sb₂Te5의 복소굴절율 결정
김상준(S.J. Kim),김상열(S.Y. Kim),서훈(H. Seo),박정우(J.W. Park),정태희(T.H. Chung) 한국광학회 1997 한국광학회지 Vol.8 No.6
비정질상과 결정상으로 가역변화하는 특성을 이용하여, 기존의 읽기전용 기록매체인 Compact Disk (CD)를 대체할 차세대 광기록매체로 주목받고 있는 Ge₂Sb₂Te_5 (GST)의 상태변화에 따른 굴절율과 소광계수, 박막의 두께와 밀도등 박막상수들을 구하였다. DC 스퍼터링방법으로 제작한 두꺼운 GST의 복소굴절율을 양자역학적 분산식을 이용한 모델링방법으로 구하고, 한편으로는 표면미시거칠기를 AFM (Atomic Force Microscopy)으로 결정한 다음, 타원해석 스펙트럼들을 수치해석적 역방계산하여 구한 복소굴절율과 비교하였다. 결정상과 비정질상일 때의 GST의 복소굴절율을 각각 구하고 이로부터 계산된 반사율을 측정된 반사율과 비교함으로써 수치해석적인 방법이 실제 GST의 복소굴절율과 더 일치하는 값을 가지게 됨을 확인하였다. 이렇게 구한 GST의 복소굴절율을 기준데이터로 사용하여 실제 설계두께를 가지는 GST박막의 두께 및 표면거칠기층을 정량적으로 구하였다. The complex refractive indices of Ge₂Se₂Te_5 which show reversible phase change between the crystalline phase and an amorphous one depending upon the annealing process have been determined in the spectral range of 0.7-4.5 eV. The Ge₂Se₂Te_5 films were DC sputter deposited on the crystalline silicon substrate. The spectro-ellipsometry data of a thick film were analyzed following the modelling procedure where the quantum mechanical dispersion relation were used for the complex refractive indices of both the cryastalline phase Ge₂Se₂Te_5 and an amorphous phase Ge₂Se₂Te_5, respectively. On the other hand, with the surface micro-roughness layer whose effective thickness was determined from AFM analysis, the spectro-ellipsometry data were numerically inverted to yield the complex refractive index of Ge₂Se₂Te_5 at each wavelength. With these set of complex refractive indices, the reflectance spectra were calculated and those spectra obtained from the numerical inversion showed better agreement with the experimental reflection spectra for both the cryastalline phase and an amorphous phase. Finally, the thin Ge₂Se₂Te_5 film which has the optimum thickness of 26 ㎚ as the medium for optical recording was also analyzed and the quantitative result of the film thickness and the surface microroughness has been reported.
권용철(Y. C. Kwon),김상열(S. H. Kim),김홍태(H. T. Kim),문호근(H. K. Moon),이세희(S. H. Lee),정상인(S. I. Jeong),양재규(K. G. Yang),김상식(S. S. Kim) 한국소성가공학회 2013 한국소성가공학회 학술대회 논문집 Vol.2013 No.5
Main Shaft is one of the key components to connect between Rotor hub and Gear box in wind turbine. The mechanical components for wind turbine is most being manufactured with hot open die forging. The purpose of this study is to develop the manufacture process of Hollow Main Shaft by open die forging. In case of the open die forging for large forged part, pass schedule of manufacture process is most important because it can affect final dimensions of product. In this paper, hot compression tests were carried out to obtain the flow stress of cast microstructure at different temperature and strain rates. The measured flow stress dates were used to simulate the upsetting, piercing, pipe forging and final flange upsetting process of cast ingot using the practical material properties. Also the mechanical properties after forging of Hollow Main Shaft were investigated from the experiment. From the results, the prototypes of Hollow Main Shaft were manufactured based on analyzed results, productivity was stable, mechanical properties was increased and product dimension was optimized with suggested process. With FE-Analysis and prototype, the advantages of new method (hollow type) such as material utilization, mechanical properties and production cost were verified.