• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.441-441
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• 2012

Franz Keldysh Oscillation (FKO)은 p-n 접합 구조의 Photoreflectance (PR) spectra에서 표면 및 계면의 전기장(electric field) 특성을 반영한다. InAs/GaAs 양자점 태양전지(Quantum Dot Solar Cell, QDSC) 구조에서 InAs 양자점 층 전후에 AlGaAs 층을 삽입하여 퍼텐셜 장벽(potential barrier) 두께에 따른 PR spectra 및 GaAs-matrix에서 FKO 주파수 특성을 비교 분석하였다. InAs/GaAs 양자점 태양전지는 p-i-n 구조의 i-GaAs에 2.0 monolayer (ML), 8주기의 InAs 양자점 층을 삽입하여 Molecular Beam Epitaxy (MBE) 방법으로 성장하였다. 각 양자점 층 전후에 두께가 각각 0.0, 1.6, 2.8, 6.0 nm인 AlGaAs 층을 삽입하여 퍼텐셜 장벽 두께에 따른 FKO 주파수 변화를 관측하였다. 또한 태양전지 구조의 전기장 분포를 좀 더 용이하게 관측하기 위해 여기 광의 세기(power intensity)를 충분히 낮추어 Photovoltaic effect에 의한 내부 전기장의 변화를 최소화하여 비교 분석하였다. InAs/GaAs 양자점 태양전지 구조에서 AlGaAs 장벽층이 없는 경우, PR spectra의 Fast Fourier Transform 결과에 반영되는 FKO 주파수 특성은 p-i-n 구조 계면에서 공핍층(depletion region)의 space charge field보다 양자점 층의 내부 전기장에 의한 FKO 주파수가 더 큰 진폭(amplitude)을 보였다. 반면에, AlGaAs 장벽층이 삽입되면 두께가 커짐에 따라 p-i-n 구조 계면의 space charge field에 의해 더 큰 진폭의 FKO 주파수가 관측되었다. 이는 AlGaAs 장벽층이 삽입됨으로써 양자점 층 내 양자 상태 수 및 여기광에 의한 캐리어의 수와 관련이 있음을 확인하였으며, 결과적으로 GaAs-matrix에서 p-i-n 구조 계면의 space charge field에 영향을 미치게 됨을 알 수 있다. 이러한 PR 특성 결과들을 InAs/GaAs 양자점 태양전지의 설계 및 제조에 반영함으로써 양자효율 증대에 기여할 것으로 기대된다.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.423-423
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• 2013

3~5 족 반도체 물질인 phosphorus 화합물 중 대표적인 InAlP 삼종화합물은 작은 굴절률, 큰 밴드갭, GaAs와 lattice 일치 때문에 큰 주목을 받고 있고, p-type high electron mobility transistors(p-HEMT), laser diodes 등의 고속 전자소자 및 광전 소자에 응용이 가능한 매우 중요한 물질이다. 최적의 소자 응용기술을 위해서는, 정확한 광물성 연구가 수행되어야 하지만 InxAl1-xP 화합물에 대한 유전율 함수 및 전자전이점 등의 연구는 미흡한 실정이다. 이에 본 연구에서는 1.5~6.0 eV 에너지 영역에서 각기 다른 In 조성비를 갖는 InxAl1-xP 화합물의 가유전율 함수 ${\varepsilon}={\varepsilon}_1+i{\varepsilon}_2$와 전자전이점 데이터를 보고한다. GaAs 기판 위에 molecular beam epitaxy (MBE)를 이용하여 InxAl1-xP (x=0.000, 0.186, 0.310, 0.475, 0.715, 0.831, 1.000) 박막을 성장하였고 타원편광분석기를 이용하여 유전율 함수를 측정하였다. 또한 실시간 화학적 에칭을 통하여 시료 표면에 자연산화막을 제거함으로써 순수한 InAlP의 유전율 함수를 측정할 수 있었고, 측정된 유전율 함수를 이차미분하여 In 조성비에 따른 전자전이점을 얻을 수 있었다. 얻어진 전자전이점 값을 이용하여 linear augmented Slater-type orbital method (LASTO) 를 통해 이론적 전자 밴드 구조 계산을 하였고, 이를 바탕으로 $E_0$, $E_1$, $E_2$ 전이점 지역의 여러 전자전이점($E_1$, $E_1+{\Delta}_1$, $E_0'$, $E_0'+{\Delta}_0'$, $E_2$, $E_2'$)의 특성을 정의할 수 있었고, $E_0'$과 $E_2$ 전이점의 에너지 값이 In 조성비가 증가함에 따라 서로 교차함을 발견할 수 있었다. 타원 편광 분석법을 이용한 유전율 함수 및 전자전이점 연구는 InAlP의 광학적 데이터베이스를 확보하는 성과와 더불어 새로운 디바이스 기술 및 광통신 산업에도 유용한 정보가 될 것이다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.4
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• pp.1301-1308
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• 1996

In order to save the energy and protect the environment, it were studied about ecomaterials with the developed countries as central figure. In the Metal Matrix Composites(MMCs), this trends appeared the development of the MMCs which had excellent mechanical properties in spite of the low volume fraction of reinforcement. Therefore, in this study, fatigue crack growth test, tensile and hardness test were conducted in order to investigate the mechanical and fatigue properties of 5 %, and 10 % $SiC_{p}$/Al composites. As the results, in the tensile and hardness test, tensile strength and hardness increased but fatigue crack growth rate decreased with $SiC_{p}$/Al volume fraction. And in the view of fatigue failured surface through the SEM, fatigue crack initiated around the SiC particle and in low $\Delta{K}$ regions, fatigue creck detoured the SiC particle but crack propagated through the SiC particle in the high $\DeltaK$ regions.

• Journal of Korean Society for Atmospheric Environment
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• v.13 no.4
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• pp.249-256
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• 1997

To identify the long-term influence of acid rain treatment on tree growth, acid rain of various composition (pH 2.0, pH 4.0 and pH 5.6 as control) was applied to several landscape trees for five months (April through August, 1991). Tree height, pH values and $Al^{3+}$ concentration in soil were investigated. Acid rain treatments seemed to promote height growth in the first year (1991), but have become an inhibiting factor over five years. All of coniferous species and most broad-leaved species, except Acer ginnala, showed opposite trends in height responses to acid rain treatments between the first (1991) and last (1996) year. In contrast, Acer ginnala showed similar trends to acid rain treatments in the height growth between 1991 and 1996. This result suggested that Acer ginnala has a characteristic adapability to acid rain stress. pH values of surface soil were lower than those of 30 cm soil depth. This fact suggested that acid rain treatments made surface soil acidic condition. In addition, physiological characteristics (photosynthesis, stomatal condition and biomass) have to be investigated to identify the relationship between long-term effects of $AL^{3+}$ concentration and growth.

• Composites Research
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• v.13 no.6
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• pp.23-29
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• 2000

The internal residual stresses within the multilayered structure with sharp interface induced by the difference in thermal expansion coefficient between the materials of adjacent layers often provide the source of failure such as delamination of interfaces etc. Recent development of the multilayered structure with functionally graded interface would be the solution to prevent this kind of failure. However a systematic thermo-mechanical analysis is needed for the customized structural design of multilayered structure. In this study, theoretical model for the thermo-mechanical analysis is developed for multilayered structures of the $Al-SiC_p$ functionally graded composite for electronic packaging. The evolution of curvature and internal stresses in response to temperature variations is presented for the different combinations of geometry. The resultant analytical solutions are used for the optimal design of the multilayered structures with functionally graded interface as well as with sharp interface.

• Journal of the Korean Ceramic Society
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• v.30 no.12
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• pp.1045-1053
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• 1993

Alumina hydrates were prepared by the neutralization of AlCl3.6H2O solution with NH3 gas diluted with N2 gas. The values of pH in reaction solution influenced the formation of alumina hydrates minerals. Amorphous alumina hydrates, for example, were formed at ${\gamma}$-Al2O3longrightarrow$\delta$-Al2O3longrightarrow$\theta$-Al2O3longrightarrow$\alpha$-Al2O3. (2) Bayeritelongrightarrowamorphouslongrightarrow${\gamma}$-Al2O3longrightarrow$\delta$-Al2O3longrightarrowη-Al2O3longrightarrow$\theta$-Al2O3longrightarrow$\alpha$-Al2O3. On the other hand, the shape of alumina hydrates whichw ere prepared by the reacton of Al2(SO4)3.16H2O solution and NH3 gas was spherical, the progress of its phase transformation with increasing temperature was amorphouslongrightarrow${\gamma}$-Al2O3longrightarrow$\alpha$Al2O3 in sequence.

• Journal of the Korean Ceramic Society
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• v.26 no.1
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• pp.100-108
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• 1989

Aluminum hydroxides were prepared by the alkoxide hydrolysis method using Al-isopropoxide as a starting material and NH4OH as a catalytic agent. When Al-isopropoxide was hydrolyzed in a H2O-NH3 system, only Al(OH)3 was obtained over all pH values. However, AlOOH was formed besides Al(OH)3 when Al-isopropoxide was hydrolyzed in a H2O-NH3-isopropyl alcohol system. The AlOOH/Al(OH)3 ratio was increased as the isopropyl alcohol content was increased. The hydroxides, Al(OH)3 and AlOOH, obtained in this study and the commerical products, $\alpha$-Al2O3 and AlOOH were subjected to the carbothermal reduction and nitridation reaction to product AlN powder, using carbon black as a reducing agent under N2 atmosphere at various temperatures. AlN was synthesized from the obtained Al(OH)3 and the commercial AlOOH at 145$0^{\circ}C$, however, synthesized from the obtained AlOOH and the commercial alpha-alumina at 135$0^{\circ}C$. The temperature difference is assumed to be attributed to the reactivity of those powders. AlN powder prepared from the Al-isopropoxide was observed to have the narrower particle size distribution than that prepared from the commercial $\alpha$-Al2O3 or AlOOH.

• Journal of the Mineralogical Society of Korea
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• v.9 no.2
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• pp.71-81
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• 1996

Dissolution experiments were conducted to understand chemical nature of weathering of anorthosite from the Hadong area. Anorthosite and plagioclase from it were reacted with HCl or KOH solutions under various conditions concerning such as grain size, initial pH of solutions, and shaking Average composition of plagioclase used in the experiment was Na0.32Ca0.71Al1.71Si2.28O8.Under acidic conditions, solution pH increases rapidly in the initial stage and then gradually to reach palteau. Shaking agitates the reaction rate in the initial stage but does not affect after the system reached steady state. Ca and si concentrations show rapid increase and then gradual increase. Al concentration increases rapidly in the early stage and then decreases. Later decrease was interpreted as the precipitation of an Al-bearing material. Different dissolution rates of different constituents of plagioclase together the with precipitation of al-bearing material might be responsible for the non-stoichiometric dissolution of plagioclase.X-ray diffraction analyses on anorthosite before and after dissolution experiment show dissolution rates differ with different lattice planes of plagioclase. It suggests the crystallographic control on dissolution reaction. X-ray photoelectron spectroscopic result shows that the average composition of plagioclase surface reacted with HCL of initial pH 1.97 for 2000 hours is Na0.20Ca0.26Al1.7Si2.3O8. It means that Na- and Ca-depleted H-feldspar is developed without Al-depleted layer on the surface of plagioclase by reaction with HCl and that dissolution reaction takes place sparsely on the surface of plagioclase. Al and Si are dissolved preferentially over Ca from anorthosite powder in KHO solution. Reaction of acid-reacted anorthosite with KOH solution shows the same Si dissolution behavior as in the fresh anorthosite. This indicates that the Al-depleted and Si-enriched layer does not build up on the acid-reacted surface.

• Journal of environmental and Sanitary engineering
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• v.16 no.3
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• pp.80-86
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• 2001

This research was carried out to investigate the effect of microscopic silica matrix coagulation on heavy metals and anion removal in mining wastewater. pH and alkalinity played an important role to coagulate heavy metals such as Al, and Fe and an anion such as ${SO_4}^{2-}$ with silica matrix as well as NaOH. However, the efficiency to form coagulates was much greater in silica matrix-treated wastewater than NaOH-treated one. Fe in wastewater formed coagulation with both silica matrix and NaOH treatments resulting in lowering Fe content in wastewater at above pH 9. For Al removal in wastewater, silica matrix-treated wastewater at above pH 12.3 formed stable coagulate with Al, while NaOH-treated one did not. Alkalinities of 89 and 220 mg/L were required to stabilize silica matrix treated coagulate with Fe and Al, respectively. Reaction time of ten minute was required to provide enough reaction for coagulation between heavy metals and silica matrix. Heavy metals and anion leachates were much lower in coagulate with silica matrix than that with NaOH, which indicates that silica matrix could be used to remove heavy metals efficiently.

• Clean Technology
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• v.18 no.4
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• pp.366-372
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• 2012

Three acrylic copolymers containing tris(8-hydroxyquinoline) aluminum (AlQ3) pendant group (25 wt%), acrylateco-HEMA-$AlQ_3$ (25 wt%), were successfully synthesized by free radical polymerization from acrylates [methyl methacrylate (MMA), acrylonitrile (AN) or 2-hydroxyethyl methacrylate (HEMA)] with HEMA functionalized with AlQ3 pendant groups (HEMA-p-$AlQ_3$). The glass transition temperatures ($T_g$) of MMA-co-HEMA-p-$AlQ_3$ (copolymer 1), AN-co-HEMA-p-$AlQ_3$ (copolymer 2) and HEMA-co-HEMA-p-$AlQ_3$ (copolymer 3) were found to be 158, 150 and $126^{\circ}C$, respectively. They have good thermal stability: a very desirable feature for the stability of OLEDs. Their solubility, thermal properties, UV-visible absorption and photoluminescence behaviors were investigated. They were found to be soluble in various organic solvents such as tetrahydrofuran (THF), dimethylformamide (DMF), toluene and chloroform. It was also found that the UV-visible absorption and photoluminescence behaviors of these copolymers were similar to those of pristine $AlQ_3$. Green organic light-emitting diodes (OLEDs) have also been fabricated using these copolymers as light emission/electron transport components obtained easily by spin coating, and their current density voltage (J-V) curves were compared. The OLED device of the copolymer 3 had the lowest turn-on voltage of about 2 V compared to other copolymer types devices.