• 한국결정성장학회지
• /
• 제30권2호
• /
• pp.41-46
• /
• 2020

본 연구에서는 HVPE 성장법으로 GaN 성장 시 GaN 내에 잔류하는 stress로 인한 crack 현상을 감소시키고자 기판 종류 및 V/III 비를 조절하여 잔류 stress 특성을 알아보고자 하였다. Sapphire, GaN template 위에 각각 V/III 비 5, 10, 15의 조건으로 GaN을 성장시켜 형성된 hexagonal pit의 분포 및 깊이를 분석하였다. 이를 통해 GaN on GaN template 성장에서 V/III 비가 높을수록 hexagonal pit의 분포 영역 및 깊이가 증가하는 것을 확인하였다. Raman 측정을 통해 hexagonal pit 영역 및 깊이가 컸던 GaN on GaN template 성장에서 V/III 비가 높을수록 stress가 감소하는 것을 확인하였다. 이를 통해 hexagonal pit의 분포 및 깊이가 증가할수록 잔류 stress가 낮아짐을 확인할 수 있었으며, 향후 후막 GaN 성장 시 stress 감소 가능성에 대해 확인하였다.

• 한국해양공학회:학술대회논문집
• /
• 한국해양공학회 2002년도 추계학술대회 논문집
• /
• pp.267-272
• /
• 2002

Pitting corrosion is a very common occurrence in marine structures. Therefore, the 3-D finite element analysis is carried out to determine the stress intensity factors at the pit depth and also at the surface of the pit. The pits are modeled as a part of sphere, based on the pit depth and the pit diameter as specified by the Ship Structural Committee. The pit depth and pit diameter are function of the percentage of pitting that the plate is subjected to. A dog-bone shaped specimen is subjected to different intensities of pitting and the stress intensity factors are determined under axial tensile loads.

• Current Applied Physics
• /
• 제18권12호
• /
• pp.1558-1563
• /
• 2018

We demonstrate improved surface pit and phase separation in thick InGaN grown on a GaN/Si (111) substrate, using plasma-assisted molecular beam epitaxy with an indium modulation technique. The formation of surface pit and compositional inhomogeneity in the InGaN epilayer are investigated using atomic force microscopy, scanning electron microscopy and temperature-dependent photoluminescence. Indium elemental mapping directly reveals that poor compositional homogeneity occurs near the pits. The indium-modulation epitaxy of InGaN minimizes the surface indium segregation, leading to the reduction in pit density and size. The phase separation in InGaN with a higher pit density is significantly suppressed, suggesting that the pit formation and the phase separation are correlated. We propose an indium migration model for the correlation between surface pit and phase separation in InGaN.

• 한국패류학회지
• /
• 제27권2호
• /
• pp.91-97
• /
• 2011

This study examines the morphological features of larval and postlarval shells of the paedomorphic bivalve Crenella decussata Montagu, 1808 from the Sea of Japan. During the early morphogenesis of the shell of C. decussata the following characteristics appear: prodissoconch I -the anterior and posterior provincular teeth, a broad primary ligament pit located on the chondrophore; nepioconch - the anterior and posterior juvenile teeth,primary lateral teeth, fine commarginal and radial sculpture. Larvae of C. decussata distinctly differ from other mytilid larvae by a D-shaped shell, absence of umbo, astraight hinge margin, and homogeneous fine-grained sculpture without co-marginal lines of growth. These shell characters indicate lecithotrophic development of this species. Some morphostructures are revealed which might be used in crenellin taxonomy.

• 한국응용과학기술학회지
• /
• 제29권3호
• /
• pp.486-494
• /
• 2012

다양한 화장품에 응용을 위하여 제주산 유채오일 추출물을 대상으로 PIT유화시스템을 이용한 나노에멀젼을 제조하였다. 천연 유채오일 추출물은 n-헥산을 용매로 사용하여 추출하였다. 천연유채오일 추출물은 엷은 노란색의 점성을 가진 액체이었고, 수율은 $43{\pm}2.5%$이었다. 산가는 $2.76{\pm}0.5$이었고, 비중은 $0.89{\pm}0.05$ 이었다. 20wt%의 유채오일을 사용한 PIT-Yuche-NE의 입자크기는 50-120nm (평균입자크기: $82{\pm}5.8nm$)이었고, 제타 포텐셜은 -29.5mV 이었다. 이것은 $(PEG)_{5-30}$ 지방산 에테르를 사용하기 때문에 열역학적으로 안정하였다. 특징적인 결과로부터 얻은 몇 개의 결론을 다음과 같이 나열하였다. 첫째, DPPH (1,1-diphenyl-2-picrylhydrazyl radical)방법을 이용한 자유 라디칼 소거력을 측정하였다. PIT-Yuche-NE의 항산화력은 $37.2{\pm}6.7%$이었고, 비교군인 10 mg/mL의 PIT-Toco-NE(토코페롤 20wt% 나노에멀젼)은 $28.8{\pm}6.5%$, 10 mg/mL의 PIT-Nokcha-NE (녹차추출물 20wt% 나노에멀젼)은 $29.6{\pm}7.2%$이었다. 둘째, PIT-Yuche-NE의 콜라겐합성율은 $148{\pm}15.2%$ 이었고, 동일 농도에서 비교군인 PIT-Toco-NE은 $121{\pm}13.5%$, PIT-Nokcha-NE은 $95{\pm}12.7%$이었다. 셋째, 6시간 후, Aramo-TS를 사용한 Yuche-CRM의 피부보습효과는 $47{\pm}3.9%$ (*p-value￡0.05, n=7)이었다. 반면, Toco-CRM은 $30{\pm}5.2%$(*p-value￡0.05, n=7)이었고, Nokcha-CRM은 $35{\pm}4.5%$이었다. 따라서 Yuche-CRM은 다른 두 크림보다 높은 보습효과를 보였다. 최종적으로 본 연구는 화장품 산업 및 제약산업에서도 폭넓게 응용될 것으로 기대한다.

• Restorative Dentistry and Endodontics
• /
• 제46권1호
• /
• pp.6.1-6.10
• /
• 2021

Objectives: The aim of this study was to evaluate the corrosion resistance of heat-treated (Reciproc and WaveOne) and non-heat-treated (ProTaper and Mtwo) superelastic nickel-titanium endodontic files when immersed in a 5.25% sodium hypochlorite solution. Materials and Methods: Anodic polarization curves were obtained with potential sweeps that began at the open circuit potential or corrosion potential (E_corr). The pitting potential (E_pit) was identified on the anodic polarization curve as the potential at which a sudden increase in current was observed. The micromorphology of the 28 tested files was analyzed before and after the electrochemical assay using scanning electron microscope (SEM). The data were analyzed using 1-way analysis of variance with the post hoc Bonferroni test (for E_corr) and the Student t-test for independent samples (for E_pit). Results: The mean E_corr values were 0.506 V for ProTaper, 0.348 V for Mtwo, 0.542 V for Reciproc, and 0.321 V for WaveOne files. Only WaveOne and Protaper files exhibited pitting corrosion, with E_pit values of 0.879 V and 0.904 V, respectively. On the SEM images of the ProTaper and WaveOne files, cavities suggestive of pitting corrosion were detected. Conclusions: Signs of corrosion were observed in both heat-treated and non-heat-treated files. Of the evaluated files, WaveOne (a heat-treated file) and ProTaper (a non-heat-treated file) exhibited the lowest corrosion resistance.

• 치위생과학회지
• /
• 제10권5호
• /
• pp.373-378
• /
• 2010

불소도포와 치면열구전색은 치아우식을 예방하기 위한 목적으로 임상에서 널리 병용하여 사용되고 있지만, 불소가 치면열구전색제의 표면 구조를 변화시켜 미생물이 서식할 조건을 마련하여 수복물의 수명을 단축시키는 원인이 될 수 있다. 이에 본 연구에서는 현재 치과 임상에서 많이 사용되고 있는 레진계 실란트 Concise와 Eco-S를 사용하였고, 대표적인 불소도포제재 1.23% APF gel과 5% NaF Fluoride Varnish가 치면열구전색제의 표면 구조에 미치는 영향을 평가하기 위해 제작된 치면열구전색제시편을 각각 5군으로 불소제재를 처리하지 않은 I군, APF gel 1분간 처리한 II군, APF gel 4분간 처리한 III군, Fluoride Varnish 1분간 처리한 IV군, Fluoride Varnish 4분간 처리한 V군으로 분류하여 마모실험에 의한 무게변화를 측정하였고, 광학현미경을 이용하여 표면구조를 관찰하여 다음과 같은 결론을 얻었다. 1. 치면열구전색제 Concise를 이용한 마모실험에서 불소제재를 처리하지 않은 I군에 비하여 APF gel 4분간 처리한 III군에 무게 감소가 증가하였으며, Fluoride Varnish 4분간 처리한 V군에서 무게 감소가 적으며(p<0.05), Eco-S를 이용한 마모실험 결과 또한 같았다(p<0.05). 2. 광학현미경으로 표면의 변화를 관찰한 결과 APF gel을 도포한 경우 기질의 소실로 필러가 두드러진 양상을 보였으며, 각 군 별로는 APF gel 4분간 처리한 III군, APF gel 1분간 처리한 II군, 불소제재를 처리하지 않은 I군, Fluoride Varnish 1분간 처리한 IV군, Fluoride Varnish 4분간 처리한 Ⅴ군의 순으로 표면 거칠기가 감소되는 결과를 보였다. 결론적으로, 치면열구전색과 불소도포를 당일 시행하는 경우, 불소도포제를 1.23% APF gel 사용 시 4분 보다 1분 도포하며, 1.23% APF gel보다는 5% NaF Fluoride Varnish 도포하는 것이 치면열구전색제의 표면 구조에 영향을 줄일 수 있다고 사료된다.

• Corrosion Science and Technology
• /
• 제3권3호
• /
• pp.102-106
• /
• 2004

Al foil used was 99.9 and 99.99 %. Test solution used was NaCl solution. The noise was determined using controlled potential electrolysis at -200 and -700 mV vs. NHE. The current fluctuation was caused by breakdown and repaired process of aluminum oxide film. The current fluctuation value of noise was proportion to degree of growth. The number of noise was proportion to the number of pit. The examining of current flutulation value and number of noise could be evaluated corrosion. A 99.99 % Al foil was the mostly crystal of {100} plane, and showed three-dimensional, as azimuth pit with along the direction of this place piled up. A 99.9 % Al foil was polycrystal, and in order of (311) >(222) >(200) >(111) plane. The azimuth pit did not occurred as the dissolution was occurred from each plane.

• 한국분말야금학회:학술대회논문집
• /
• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
• /
• pp.1211-1212
• /
• 2006

The electrophoretic deposition process of Ni nano-particles was employed for self-repairing of heat exchanger tubes. For electrophoretic deposition of Ni nano-particles on pitted Ni alloy specimen, a constant electric field of 100 V $cm^{-1}$ was applied to the specimen for 180 s in Ni-dispersed solution. It was found that as electrophoretic deposition proceeded, the size of the pit remarkably decreased due to the agglomeration of Ni nano-particles at the pit. This strongly suggests that the electrophoretic mobility of the charged particles is larger for the pit with a higher current value rather than outer surfaces with a lower current value.

• 한국재료학회지
• /
• 제25권1호
• /
• pp.1-8
• /
• 2015

This study suggested comprehensive structural characterization methods for the commercial blue light emitting diodes(LEDs). By using the Z-contrast intensity profile of Cs-corrected high-angle annular dark field scanning transmission electron microscope(HAADF-STEM) images from a commercial lateral GaN-based blue light emitting diode, we obtained important structural information on the epilayer structure of the LED, which would have been difficult to obtain by conventional analysis. This method was simple but very powerful to obtain structural and chemical information on epi-structures in a nanometer-scale resolution. One of the examples was that we could determine whether the barrier in the multi-quantum well(MQW) was GaN or InGaN. Plan-view TEM observations were performed from the commercial blue LED to characterize the threading dislocations(TDs) and the related V-pit defects. Each TD observed in the region with the total LED epilayer structure including the MQW showed V-pit defects for almost of TDs independent of the TD types: edge-, screw-, mixed TDs. The total TD density from the region with the total LED epilayer structure including the MQW was about $3.6{\times}10^8cm^{-2}$ with a relative ratio of Edge- : Screw- :Mixed-TD portion as 80%: 7%: 13%. However, in the mesa-etched region without the MQW total TD density was about $2.5{\times}10^8cm^{-2}$ with a relative ratio of Edge- : Screw- :Mixed-TD portion of 86%: 5%: 9 %. The higher TD density in the total LED epilayer structure implied new generation of TDs mostly from the MQW region.