Finite-Size Errect에 의한 강바성 Gd박막의 상전이온도 이동

이일수,이의완,이상윤,Rhee, Il-Su,Lee, Eui-Wan,Lee, Sang-Yun 한국재료학회 1993 한국재료학회지 Vol.3 No.1

Gd박막의 강자성-상자성 상전이 온도(Tc)이동을 조사했다. 강자성-상자성 상전이 온도에서 전기저항이 변화되는 변곡점을 관측하여 Tc를 결졍하였는데, 두께가 6600$\AA$인 Gd박막의 상전이 온도는 bulk상태의 Gd의 전이온도보다 4$\pm$0.$3^{\circ}C$정도 아래로 이동됨을 알았다. 이것은 강자성 Gd박막의 Tc이동에 대한 최초의 측정이며, 실험과 finite-sime scaling이론을 비교 분석했다. Abstract We report the result of measurement for the ferro-to paramagnetic phase transition temperature shift of a gadolinium film. The phase transition temperature has been determined by measuring the resistance changes of film as function of temperature. At the ferro-to paramagnetic transition temperature, we can observe the inflection point of resistance changes. The phase transition temperature of 6600$\AA$ gadolinium film is found to be shifted by 4 $\pm$ 0.$3^{\circ}C$ below the transition temperature of bulk gadolinium. This is the first measurement for the phase transition temperature shift of ferromagnetic gadolinium film. This and further results might give a milestone in resolving the differences between experiments and finite-size scaling theory.

Rheed 반점강도의 변화를 이용한 Si(111)-Ad 표면조사

곽호원,이의완,이상윤,Kwak, Ho-Weon,Lee, Eui-Wan,Lee, Sang-Yun 한국재료학회 1994 한국재료학회지 Vol.4 No.6

Si(111)표면위에 Au의 증착량과 기판온도에 따른 표면구조의 변화를 RHEED(Reflection High Energy Electron Diffraction)상(pattern)과 RHEED상의 회절반점(spot)강도변화를 이용하여 조사하였다. Si(111) $7\times7$구조를 Au 를 0.1ML-0.4ML증착후에 기판을 $350^{\circ}C$-$750^{\circ}C$로 수초간 가열하면 $7\times7$구조에서 $7\times7$ + $5\times2$의 혼합 구조로 변화하였으며 증착량 0.4ML-1.0ML에서는 RHEED상이 기판온도와 증착량에 따라 $5\times2,\alpha- \sqrt{3} \times \sqrt{3},\beta- \sqrt{3} \times \sqrt{3}$의 구조들이 관찰되었다. $6\times6$구조는 기판온도 $270^{\circ}C$-$370^{\circ}C$에서 증착량 0.8ML에서부터 형성되기 시작하여 1ML에서 완성되었다. AES(Auger Electron Spectroscopy)를 이용한 $\alpha- \sqrt{3} \times \sqrt{3},5 \times 2$구조에서의 Au원자의 이탈과정 조사에서 이탈 에너지는 각각 79kcal/mol, 82kcal/mol로 조사되었다. The Si(ll1) surface structures induced by deposition of Au atoms were investigated by RHEED system. When Au atoms were deposited on the Si(ll1) $7\times7$ surfade, the dependence of structures and phases on the substrate temperatures and coverages was drastic. For O.1ML to 0.4ML of coverage the $7\times7$ structure changes to $7\times7$ + $5\times2$ structure as temperature increases to $350^{\circ}C$-$750^{\circ}C$. Between 0.4M1 to 1.OML the phase changed to $5 \times 2,\alpha- \sqrt{3} \times \sqrt{3},\beta- \sqrt{3} \times \sqrt{3}$ structure according to the substrate temperature and coverages. When the coverages exceeds O.SML, the 6 x 6 structure appears at the substrate temperature range between $270^{\circ}C$-$370^{\circ}C$ and compeletely transforms to 6 x6 at 1,OML. The isothermal desorption of Au on Si(ll1) surface investigated by using AES in the $\alpha- \sqrt{3} \times \sqrt{3},5 \times 2$ structures shows that the desorption energys of $\alpha- \sqrt{3} \times \sqrt{3}$ and 5 x 2 were 79Kcal/mol and 82 Kcal/mol respectively.

RHEED회절점의 강도변화에 따른 In / Si(111)에 대한 연구

곽호원(Ho-Weon Kwak),이의완(Eui-wan Lee),박동수(Tong-Soo Park),이운환(Woon-Hwan Lee) 한국진공학회(ASCT) 1997 Applied Science and Convergence Technology Vol.6 No.2

Si(111) 7×7표면에 In을 증착시킬 때 기판용도와 증착량에 따른 표면구조의 변화를 RHEED(Reflection High Energy Electron Diffraction) 상 (pattern)과 RHEED상의 회절반점(spot)강도 변화를 관찰하여 조사하였다. Si(111) 기판온도를 400℃로 유지하면서 In을 증착시킬 때 증착량이 약 0.1, 0.3, 0.5 ML에서 각각 √3×√3, √31×√31, 4×1구조가 관찰되기 시작하였다. 기판온도 300°에서는 증착량이 약 0.2ML에서부터 4×1구조가 나타나고 0.8ML이상에서부터는 4×1+√3×√3 혼합구조가 관찰되기 시작하였다. Si(111)-√3×√3구조의 기판온도를 실온으로 유지하면서 In를 증착시킬 때 증착량이 0.25, 0.7ML에서 각각 2×2, √7×√3구조가 나타나기 시작하였다. RHEED 반점의 강도변화를 이용하여 Si(111)-√7×√3구조에서의 In원자의 이탈 과정을 조사한 결과 이탈 에너지는 2.84 eV로 조사되었다. The change of surface structures for the deposition of indium on clean Si(111) surface is investigated as a function of substrate temperature and surface coverage by RHEED. We find that at substrate temperature of 400℃, √3×√3, √31×√31 and 4×1 structures are formed at indium coverages of 0.2, 0.3 and 0.5 ML, respectively. We also find that for the substrate temperature of 300℃, 4×1 structure starts to be formed by 0.2 ML of indium, and the mixed structure of 4×1 and √3×√3is observed for more than 1.0ML. On the other hand, if the indium is deposited on the Si(111)-√3×√3 structure at room temperature, 2×2 and √7×√3 structures are found to form at 0.2 and 0.4 ML, respectively. From the desorption process, the desorption energy of indium in Si √7×√3 structure is observed to be 2.84 eV.

RHEED 반점의 강도변화를 이용한 Si(111) - Sn 표면조사

곽호원(Ho Weon Kwak),이의완(Eui-Wan Lee) 한국진공학회(ASCT) 1994 Applied Science and Convergence Technology Vol.3 No.2

Si(111)-7×7 표면에 Sn을 증착시킬 때 기판온도와 증착량에 따른 표면구조의 변화를 RHEED(Reflection High Energy Electron Diffraction)상(pattern)과 RHEED상의 회절반점(spot) 강도변화를 관찰하여 조사하였다. Si(111) 기판온도를 400℃로 유지하면서 Sn을 증착시킬 때 √3×√3 구조가 관찰되었으며 기판온도 200℃ 이하에서는 증착량에 따라 √3×√3×, 2√3×2√3 구조들이 관찰되었다. RHEED 반점의 강도변화를 이용하여 Si(111)-Sn √3×√3 구조에서의 Sn원자의 이탈 과정을 조사한 결과 이탈에너지는 3.3±0.1 eV로 조사되었다. On the Si(111)-7×7 surface, we investigated the surface structures according to the temperatures of the substrate and the thickness of Sn which is deposited on the Si(111) surface by using RHEED. When Sn was deposited on the Si(111)-7×7 surface at 400℃, √3×√3 structure was formed. On the Si(111)-7×7 surface at 200℃, according to the thickness of Sn which is deposited, √3×√3, 2√3×2√3 structures were formed respectively. By using the RHEED intensity oscillation of Si(111)-Sn √3×√3 spots, we investigated the desorption process of Sn on the √3×√3 structure and obtained the desorption energy. The desorption energy is 3.3±0.1 eV.

강자성 가돌리늄 박막의 큐리 온도의 이동

이일수(Ilsu Rhee),추교진(Gyojin Chu),이의완(Eui-Wan Lee),이상윤(Sang-Yun Lee),이종용(Chong-Yong Lee),김양수(Yaung-Soo Kim),김동락(Dong-Lak Kim),이형철(H. C. Ri) 한국진공학회(ASCT) 1994 Applied Science and Convergence Technology Vol.3 No.3

가돌리늄 박막의 큐리온도를 자기화의 온도에 따른 변화를 측정함으로써 결정하였다. 박막의 큐리온도는 bulk계의 큐리온도보다 낮아지며 이 박막에서의 큐리온도의 이동은 두께가 얇아질수록 커진다는 것이 관측되었다. 이 실험결과를 유한축적 이론의 관점에서 분석한 결과 전이온도의 이동에 관련된 지수 λ는 0.82±0.13로서 이론적인 값의 1.48과 상치한다는 사실이 발견되었다. 이러한 유한계의 실험치와 유한축척이론과 차이는 여러 유한계에서 관측되었다. We determine the Curie temperature of thin gadolinium films by the measurement of magnetizations as a function of temperature. From this measurement, we observe the systematic shift of Curie temperatures for films, that is, the larger the shift is, the thinner the film is. By analyzing the data in light of finite-size scaling theory, we determine the exponent λ to be 0.82±0.13, not equal to the theoretical prediction of 1.48, which is already seen in other experimental works.

강편 빌레트의 건식 자분 탐상

이의완,김구화,임종수 韓國非破壞檢査學會 1996 한국비파괴검사학회지 Vol.16 No.3

본 연구는 강편 빌레트의 표면 결함을 검출하기 위한 건식 자분 탐상에 관한 것으로 자분 탐상능을 대상체에 흘리는 자화 전류, 대상체의 온도, 자분의 총 분사량 등에 대하여 평가하였다. 선재 제품의 등급에 따라 필요로 하는 몇까지 강종을 선택하여 강종별 자기적 특성을 평가하였으며, 이를 입력자료로 하여 유한 요소법에 의한 자기 해석을 행하였고, 그 결과를 직류 자화 전류에 의한 누설 자속 측정 결과와 비교 분석하였다. 교류 자화 전류에 의한 건식 자분 탐상능을 직류 자화 전류에 의한 탐상능과 비교하여 강종 및 자화 전류의 유형에 따른 자화 전류치를 결정하였다. 직류 자화 전류에 의한 자분 탐상 결과를 유한 요소법에 의한 계산과 비교하였고, 빌레트의 표면과 표면 결함 부위에서 측정한 누설 자속으로 비교 결과를 평가하였다. 각 강편재의 경우 직류 자화 전류에 의한 표면 자장은 그 형상에 의한 영향으로 코너 부위에서는 면 중앙의 표면 자장치에 비해 30% 정도였으며, 교류 자화 전류에 의해서는 그 비율이 70%정도였다. 교류 자화 전류는 코너로부터 면중앙으로 10mm 되는 영역을 제외하고는 전 면에서 균일한 표면 자장을 발생하엿다. 대상체의 온도에 따른 자분의 흡착은 대상체의 온도 150℃까지는 큰 변화가 없으나 자분의 고착에 있어서 60℃ 이상의 고온재에 대해서는 융착 용매로 메틸렌 크로라이드를 사용하는 것이 부적합하였다. 자분의 총분사량은 자분 탐상능에 상당히 큰 영향을 미침을 확인하였고 이에 대한 정량적 평가를 행하였다. Dry magnetic particle inspection(MPI) was performed to detect the surface defects of steel ingot cast billets. Magnetic properties of several materials were characterized by the measurement of the B-H hysteresis curve. The inspection results were evaluated in terms of the magnetizing current, temperature, and the amount of magnetic particles applied to billets. Magnetic flux leakage near the defect site of interest was measured and with the results of calculation by the finite element method in the case of direct magnetizing current. Direct and alternating magnetizing currents for materials were deduced by the comparison of the inspections. Results of the magnetic particle inspection by direct magnetizing current were compared with those of finite element method calculations, which were verified by measuring magnetic leakage flux above the surface and the surface defects of the material. For square rods, due to the geometrical effect, the magnetic flux density at the edges along the length of the rods was about 30% of that at the center of rod face for a sufficiently large direct magnetizing current, while it was about 70% for an alternating magnetizing current. Thus, an alternating magnetizing current generates rather uniform magnetic flux density over the rods, except for the region on the face across about 10 mm from the edge. The attraction of the magnetic particle by the magnetic leakage field was nearly independent of the surface temperature of the billets up to 150℃. However, the temperature should have been limited below 60℃ for an effective fixing of gathered magnetic particles to the billet surface using methylene chloride. We also found that the amount of applied magnetic particles tremendously affected the detection capability.

Li이 吸着된 실리콘 表面의 超構造變化와 離脫 에너지 測定

李義完 慶北大學校 1989 論文集 Vol.48 No.-

At the surfaces there are many important phenomena such as oxidation, adsorption, desorption, corrosion, and friction because it is the place where the materials interact with the environment at first. The semiconductor surfaces generally make reconstructions to minimize the total energy of the system. Among many semiconductors the Si(111) surface has been known as it posesses various kinds of reconstructed surface structures and phases. When the metal atoms are adsorbed on Si(111) surface, the reconstructed superstructure phase transition is drastical according to the both substrate temperature and the thickness of adsorbed metal films. These adsorbed systems are almost solved by recent decade studies. Alkali-metal adsorption of solid surfaces has been the intense objects. In this paper Li desorption processes on Si surface and superstructure change according to the alkali-metal deposition were investigated by using RHEED-AES system.

평가기준표에 의한 물리 실험 평가 방안

이의완,곽호원,이상우 경북대학교 과학교육연구소 1994 科學敎育硏究誌 Vol.18 No.-

We selected 17 kinds required experimental subjects according to analysis of content of the experiment in the 7 sorts of physics textbook being used at the high school, and made the assessment's standard table of the group and the individual. And we used those subjects as the method of assessment in order to increase reasonably the accomplishment of learning goal. As the result of that, experimenting behaviors turned into more active and the role of individual was made concrete. Therefore students had more interest in the experiment. Consequentely, students understood better not only the learning of the experiment but also the contents of the textbooks through the comprehension of the learning of the experiment and the improvement of ability of research.

液晶의 Cholesteric Blue Phase에 관한 光學的 硏究

李義完 慶北大學校 1985 論文集 Vol.39 No.-

The blue phases B_1 and B_2 in the mixture of cholesteric and nematic materials have been studied using optical Bragg reflection. It is found that in a TM59/E5(95 : 5) mixture two phases coexist in the B_2 phase. A critical choleteric pitch at which the crossover from discontinuous to continuous behavior of the lattice parameter(B_1-B_2 transition) takes place has been found at 400㎚. Above this critical value, the shorter B_2 phase lattice vanishes.

Zr계 Vitreloy 박막의 특성에 대한 조사

이경민,이병준,김병훈,이의완,박동수 慶北大學校 師範大學 科學敎育硏究所 1999 科學敎育硏究誌 Vol.23 No.-

We have grown Zr based vitreloy alloy thin films by thermal deposition methode and ion beam sputtering method and compared them with Zr-Ti-Cu-Ni-Be bulk metallic glass bulk. Thermal analysis caused Zr-Ti-Cu-Ni-Be bulk metallic glass to recrystallize in the two region. The onset point temperature of the first region was 414.12℃ and the peak temperature was 410.02℃. The onset point temperature of the second region was 445.21℃ and the peak point temperature was 454.45℃. The X-ray diffraction measurement and thermal analysis as a function of temperature showed that the bulk metallic glass thin films recrystallize in the same temperature region. As a result, Zr based vitreloy alloy was the same as phase transition of bulk metallic glass bulk and bulk metallic glass thin film.