• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.240-240
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• 2016

반도체 양자점은 불연속적인 에너지준위의 특성 때문에 고전적인 빛과는 다른 단일광자를 방출하여 양자정보 처리과정에 기본 요소로써 사용 될 수 있다. III-Nitride (III-N) 반도체 물질은 III족 원소의 구성비를 조절하였을 때 밴드갭 에너지차이가 크므로 깊은 양자 우물을 만들 수 있으며 최근에는 기존에 연구되던 III-Arsenide 기반의 반도체 양자점과 다르게 상온 (300 K) 동작 가능한 단일광자 방출원이 개발되었다.[1] 또한 약한 split-off 에너지 때문에 양자점 모양에 작은 비대칭성만 존재해도 큰 선형편광도를 가질 수 있다. 하지만 III-N 반도체 양자점의 이러한 특성에도 불구하고 이종기판과의 격자상수 불일치에 따른 많은 threading dislocation, 압전효과에 의한 큰 내부전기장에 의해 발광 효율이 떨어지는 등의 문제가 있다. 이를 해결하기 위해 반도체 양자점을 3차원 구조체와 결합하여 threading dislocation 및 내부전기장을 줄이는 연구들이 진행되고 있다.[2] 본 연구에서는 선택적 영역 성장 방식을 통해 마이크로미터 크기를 가지는 피라미드 형태의 3차원 구조체를 이용, 피라미드의 꼭지점에 형성된 InGaN/GaN 양자점의 광학적 특성에 대해 분석하였다. 저온(9 K)에서 마이크로 photoluminescence 측정을 통해 양자점의 발광파장이 피라미드의 옆면의 파장과는 다름을 확인하였다. 여기광의 세기에 따른 양자점의 발광 세기 측정하여 여기광에 선형 비례함을 보이고, 양자점의 편광도를 측정하여 선형 편광임을 확인하였다. 마지막으로, 광량에 대해 시간에 따른 상관관계를 측정함으로써 양자점이 양자 발광체의 특성을 보이는 지 확인하였다.

• Journal of Korea Foundry Society
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• v.15 no.5
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• pp.514-522
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• 1995

The microstructural evolution with isothermal stirring during semi-solid state processing of hypoeutectic Al-6.2wt%Si alloy was studied. Substructure of the individual primary solid particle in the slurry was investigated through transmission electron microscopy(TEM). Formation of subgrain boundaries on the rheocast Al-6.2wt%Si alloy is observed and the misorientation between the grains is shown typically under 2 degrees by analyzing selected area diffraction (SAD) and convergent beam electron diffraction (CBED) patterns. The existence of high angle grain boundaries are also observed in the alloy. Based upon these observations, mechanisms for the primary particles fragmentation are considered. With isothermal stirring, the dislocation density increases, and the evolution of dislocation cell structure takes place, which is interpreted as a process of achieving uniform deformation by dynamic recovery under applied shear stress.

• Journal of Yeungnam Medical Science
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• v.9 no.2
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• pp.302-311
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• 1992

Talus is a important structure of the ankle joint and its function is critical for ambulation and weight bearing. The talus fracture is rare, but the complications of fracture and dislocation are serious and resulting in avascular necrosis, osteoarthritis. So its treatment is carefully considered at initial status. Authors reviewed 11 cases of fracture and dislocation of the talus treated at Yeungnam university hospital from 1984 to 1991. The longest follow up was 8 years and shortest, 1 year. The results were as follows. 1. There were all males, the average age was 30 years old. 2. The most common cause was fall down(8 cases), and next traffic accident(2cases), sports injury(1 case). 3. According to Marti-Weber classification, 1 cases was type I, 1 in type II, 4 in type III and 5 in type IV. 4. The method of treatment were open reduction and internal fixation in 6 cases, the others were closed reduction in 5 cases. 5. Final results(by Hawkins grading system) were as follows, 3 cases were excellent, 4 cases were good, 1 case was fair and 3 cases were poor. 6. Complications were AVN in 2 cases, degenerative arthritis in 8 cases, malunion in 1 case. 7. The range of motion of the ankle joint was relatively preserved(74%), but in the subtalar joint it was decreased(43%).

• Korean Journal of Materials Research
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• v.30 no.2
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• pp.57-60
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• 2020

Titanium aluminides have attracted special interest as light-weight/high-temperature materials for structural applications. The major problem limiting practical use of these compounds is their poor ductility and formability. The powder metallurgy processing route has been an attractive alternative for such materials. A mixture of Ti and Al elemental powders was fabricated to a mechanical alloying process. The processed powder was hot pressed in a vacuum, and a fully densified compact with ultra-fine grain structure consisting of Ti₃Al intermetallic compound was obtained. During the compressive deformation of the compact at 1173 K, typical dynamic recrystallization (DR), which introduces a certain extent of grain refinement, was observed. The compact had high density and consisted of an ultra-fine equiaxial grain structure. Average grain diameter was 1.5 ㎛. Typical TEM micrographs depicting the internal structure of the specimen deformed to 0.09 true strain are provided, in which it can be seen that many small recrystallized grains having no apparent dislocation structure are generated at grain boundaries where well-developed dislocations with high density are observed in the neighboring grains. The compact showed a large m-value such as 0.44 at 1173 K. Moreover, the grain structure remained equiaxed during deformation at this temperature. Therefore, the compressive deformation of the compact was presumed to progress by superplastic flow, primarily controlled by DR.

• Journal of the Korean Vacuum Society
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• v.6 no.S1
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• pp.80-88
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• 1997

The attempt to enhance the strength of materials has been an important subject for materials engineering and scientists. The strength of materials is termed as the ability to support high load without excessive deformation and without breaking catastrophically. The control of dislocation densities and barriers to the movement of dislocations have been considered to be the important methods for the strengthening materials. One of the approaches is mechanical blocking of dislocations by alternately depositing material layers. The typical structure of materials is multilayered and laminated composites. The thickness of each layer is typically in the range of nanometer. Ton avoid confusion with other terminology they may be defined as microlaminate composite materials. The manufacturing process of multilayered laminate structure will be introduced. And the current theoretical theories will be reviewed in view of strengthening of microlaminte composite materials.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1995.03a
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• pp.252-263
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• 1995

It is visualized that dislocations move straightly in polycrystalline structure and the trans-grain dislocation moving occur from yield point to ultimate tensile stress. Some fracturemodes in uniaxial tensile test are ilustrated in order to explain that after the ultimate point the grains deforms by twins and the rotations of grains make cracks at the grain-boundaries by the incompatibility . The luders banks. which propagates along the axis of the specimen, are twin bands whcih are formed by rearrangement of the atoms within the structure of three-dimensional crystallizing $\pi$-bondings. The fatigue limit can be found through the atom's rolling back motion during elastic deformation inthe uniaxial tensile test by the change of the gradient.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.1
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• pp.131-140
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• 1993

The activation energy for high temperature creep is associated with stresses, temperatures, straians And the creep strain appears to be a function of a temperature, compensated time, namely $te^{-}$.DELTA.H/RT/, and the stress. In fact this functional relation appears to be isomorphic to material structure by x-ray analyses. Applying this functional relation, the dependance of activation energy for A17075 creep was investigated. The activation energy for creep is insensitive to stress, temperature, structure, and strain. And phenomenological model agrees with experimental creep data.

• Journal of the Korean Society for Heat Treatment
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• v.6 no.1
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• pp.26-36
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• 1993

In this study, the ausformed martensite and marformed martensite obtained from austenite with various deformation degrees in Fe-31% Ni-0.2%C alloy were transformed to revesed austenite at $510^{\circ}C$ by cyclic reverse martensite transformation. The effect of prior deformation, the rapid heating rate of reversion and number of cyclic transformation on the microstructure, mechanical properties of reversed austenite were investigated. The reverse austenite transformation is accomplised by the mechanism of shear type transformation. The structure of reversed austenite formed from ausformed martensite and marformed martensite with high deformation degrees is a fine structure of nearly equiaed grain containg a high density of dislocation tangles and was largely affected by the prior deformation applied before reversal transformation. The strength of reversed austenite is more increased with of cyclic transformation especially it is strength at the first cyclic transformation. The yield stress of revesed austenite of ausformed martensite is lower than that of marformed martensite.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.126-127
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• 2006

In this study, nano grain W is fabricated by Severe Plastic Deformation-Powder Metallurgy (SPD-PM) process. W powder and W-Re powder mixtures are processed by SPD-PM process, a Mechanical Milling (MM) process. As results, a nano grain structure, whose grain size is approximately 20nm, is obtained in W powder after MM for 360ks. A nano grain W compact, whose grain size 630nm, has excellent deformability above 1273K. A nano grain W-10Re compact is composed of equiaxed grain, a grain growth is restrained and has low dislocation density after the large deformation; therefore it is considered that W-Re compact shows superplasticity.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2000.04a
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• pp.51-56
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• 2000

Demand for new nondestructive evaluations is growing to detect tensile crack growth behavior to predict long term performance of materials and structure in aggressive environments, especially when they are in non-visible area. Acoustic emission technique is well suited to these problems and has drawn a keen interests because of its dynamic detection ability, extreme sensitivity and location of growing defects. In this study, we analysed acoustic emission signals obtained in tensile test of high strength fire resistance steel for frame structure with time frequency analysis methods. The results obtained are summaries as follows ; In the T and TN specimen consisting of ferrite and pearlite grains, most of acoustic emission events were produced near yield point, mainly due to the dislocation activities during the deformation. However, B specimen under $600^{\circ}C$ - 10min had a two peak which was attribute to the presence of martensite phase. The first peak is before yield point the second is after yield point. The sources of second acoustic emission peak were the debonding of martensite-martensite interface and the micro-cracking of brittle martensite phase. In $600^{\circ}C$-30min to $700^{\circ}C$-60min specimens, many signals were observed from area before yield point and counts were decreased after yield point.