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저온 분자선에피탁시 방법으로 성장시킨 GaMnAs의 planar Hall 효과
김경현,박종훈,김병두,김도진,김효진,임영언,김창수,Kim, Gyeong-Hyeon,Park, Jong-Hun,Kim, Byeong-Du,Kim, Do-Jin,Kim, Hyo-Jin,Im, Yeong-Eon,Kim, Chang-Su 한국재료학회 2002 한국재료학회지 Vol.12 No.3
Planar Hall effect of ferromagnetic GaMnAs thin films was investigated for the first time. The films were grown in an optimized growth condition via molecular beam epitaxy at low temperatures. For the optimization of the growth conditions, we used reflection high-energy electron diffraction, electrical conductivity, double crystal x-ray diffraction, and superconducting quantum interference device measurements techniques. We observed that the difference between the longitudinal resistance and the transverse resistance matches the planar Hall resistance. The ratio of the planar Hall resistance at saturation magnetic field to that at zero reached above 500%.
암모니아를 이용하여 분자선에피탁시 방법으로 AIN/Si 기판에 성장시킨 GaN의 구조적,광학적 특성
김경현,홍성의,강석준,이상현,김창수,김도진,한기평,백문철,Kim, Gyeong-Hyeon,Hong, Seong-Ui,Gang, Seok-Jun,Lee, Sang-Hyeon,Kim, Chang-Su,Kim, Do-Jin,Han, Gi-Pyeong,Baek, Mun-Cheol 한국재료학회 2002 한국재료학회지 Vol.12 No.5
A new approach of using double buffer layers of AlN and GaN for growth of GaN films on Si has been undertaken via molecular beam epitaxy using ammonia. The first buffers layer of AlN was grown using $N_2$plasma and the second of GaN was grown using ammonia. The surface roughness of the grown films was investigated by atomic force microscope and was compared with the normally grown films on sapphire. Double crystal x-ray rocking curve and low temperature photoluminescence techniques were employed for structural and optical properties examination. Donor bound exciton peak at 3.481 eV with full width half maximum of 41 meV was observed at 13K.
Al-Cu-Mu 주조합금의 피로성질에 미치는 Sn 첨가의 영향
김경현,김정대,김인배,Kim, Kyung-Hyun,Kim, Jeung-Dae,Kim, In-Bae 한국재료학회 2002 한국재료학회지 Vol.12 No.4
Effect of Sn addition on the fatigue properties of Al-Cu-Mn cast alloy was investigated by low and high cycle fatigue tests. Fatigue life showed the maximum value of 5450cycles in the Al-Cu-Mn alloy containing 0.10%Sn, but decreased rapidly beyond 0.20% of Sn additions. It was found that the fatigue strength was 132MPa and fatigue ratio was 0.31 in the alloy containing 0.10%Sn. Metallographic observation revealed that the fatigue crack initiated at the surface and propagated along the grain boundary. This propagation path was attributed to the presence of PFZ along the grain boundary. The tensile strength increased from 330MPa in 7he Sn-free Al-Cu-Mn cast alloy to 429MPa in the alloy containing 0.10%Sn. But above 0.20%Sn additions, tensile strength was decreased by the segregation of Sn.
김경현,홍성의,백문철,조경익,최상식,양전욱,심규환,Kim, Kyung-Hyun,Hong, Sung-Ui,Paek, Moon-Cheol,Cho, Kyung-Ik,Choi, Sang-Sik,Yang, Jeon-Wook,Shim, Kyu-Hwan 한국전기전자재료학회 2006 전기전자재료학회논문지 Vol.19 No.7
We have investigated $Al_{0.25}Ga_{0.75}As/In_{0.2}Ga_{0.8}As$ structures for pseudomorphic high electron mobility transistor(pHEMT), which were grown by molecular beam epitaxy(MBE) and consequently annealed by rapid thermal anneal(RTA), using Hall measurement, photoluminescence, and transmission electron microscopy (TEM). According to intensity and full-width at half maximum maintained stable at the same energy level, the quantized energy level in $Al_{0.25}Ga_{0.75}As/In_{0.2}Ga_{0.8}As$ quantum wells was independent of the RTA conditions. However, the Hall mobility was decreased from $6,326cm^2/V.s\;to\;2,790cm^2/V.s\;and\;2,078cm^2/V.s$ after heat treatment respectively at $500^{\circ}C\;and\;600^{\circ}C$. The heat treatment which is indispensable during the fabrication procedure would cause catastrophic degradation in electrical transport properties. TEM observation revealed atomically non-uniform interfaces, but no dislocations were generated or propagated. From theoretical consideration about the mobility changes owing to inter-diffusion, the degraded mobility could be directly correlated to the interface scattering as long as samples were annealed below $600^{\circ}C$ lot 1 min.
반성적 성찰활동에 기반한 사이버 학습상담이 초등학생의 학습동기 및 학습습관에 미치는 효과
김경현,도은경,Kim, Kyung-Hyun,Do, En-Kyeong 한국정보교육학회 2009 정보교육학회논문지 Vol.13 No.2
This study examines the effects of cyber learning counseling based on self-reflective activities on learning motivation and habits of elementary students. From the above processes, following findings could be drawn: First, the cyber learning counseling based on self-reflective activities turned out to have positive effects on promoting the motivation of elementary students for learning. Positive impacts were found in 4 sub-factors of motivation for learning, that are, attention, relevance, conviction and satisfaction that were enhanced after cyber counseling for learning was given. Second, the cyber learning counseling based on self-reflective activities were found to have positive effects on changing elementary students' habit of learning. After cyber learning counseling was carried out, Positive impacts were visible in sub-factors of learning habit which are the behavioral indexes of applying learning skill and student-initiated behavior.
웹 기반 문제중심학습 프로그램 개발과 학업성취에 미치는 효과 분석
김경현,정미경,최운필,Kim, Kyung-Hyun,Jung, Mi-Kyong,Choi, Un-Phil 한국정보교육학회 2005 정보교육학회논문지 Vol.9 No.1
Establishing problem-based leaning(PBL) that is one type of constitutional learning models is meaningful not only for finding the diversity of WBI types but also for being the specific example of constitutional usage of WBI. This paper shows the development of web-based and problem-based learning program for 6th grade students of elementary school and finds its effect on their studies achievement. There were two classes of traditional lessons and one class of web-based and problem-based lessons. It performed a test with the classes for science lesson. It was found that web-based and problem-based learning is more effective on the improvement of studies achievement. There was meaningful difference in studies achievement according to ICT utilization ability. Web-based and problem-based learning statistically had a meaningful effect on the improvement of ICT utilization ability.
Al-10%Si-0.3%Mg 합금에서 Sr 첨가가 미세조직 및 기계적 성질에 미치는 영향
김경현,이정무,정신검 ( Kyung Hyun Kim,Jung Moo Lee,Shin Kum Jung ) 한국주조공학회 1993 한국주조공학회지 Vol.13 No.1
N/A The effects of strontium content as modifier on microstructure and mechanical properties were studied in Al-10%Si-0.3%Mg cast alloys. There were not big differences in the form of eutectic Si particle and its morphology depending on adding amount of strontium, but the alloy modified by 0.012%Sr had shown the higher values than the alloy modified 0.038%Sr in strength, elongation and impact value.