• Title/Summary/Keyword: V-pit

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Study on residual stress characteristics according to the substrate type and V/III ratio during GaN growth by HVPE (HVPE 법을 통한 GaN 성장 시 기판 종류 및 V/III 비에 따른 잔류 stress 특성 연구)

  • Lee, Joo Hyung;Lee, Seung Hoon;Lee, Hee Ae;Kang, Hyo Sang;Oh, Nuri;Yi, Sung Chul;Lee, Seong Kuk;Park, Jae Hwa
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.30 no.2
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    • pp.41-46
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    • 2020
  • The characteristics of the residual stress on the types of the substrate was investigated with adjusting the V/III ratio during GaN growth via the HVPE method. GaN single crystal layers were grown on a sapphire substrate and a GaN template under the conditions of V/III ratio 5, 10, and 15, respectively. During GaN growth, multiple hexagonal pits in GaN single crystal were differently revealed in accordance with growth condition and substrate type, and their distribution and depth were measured via optical microscopy(OM) and white light interferometry(WLI). As a result, it was confirmed that the distribution area and depth of hexagonal pit tended to increase as the V/III ratio increased. Moreover, it was found that the residual stress in GaN single crystal decreased as the distribution area and depth of the pit increased through measuring micro Raman spectrophotometer. In the case of GaN growth according to substrate type, the GaN on GaN template showed lower residual stress than the GaN grown on sapphire substrate.

Estimation of Stress Intensity Factors for 3-Dimensional Surface Defects under Axial Tensile Loads Using the Finite Element Method

  • Jeon, Byung-Young;Kumar, Y.V. Satish;Kang, Sung-Won
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • 2002.10a
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    • pp.267-272
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    • 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.

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Correlation between pit formation and phase separation in thick InGaN film on a Si substrate

  • Woo, Hyeonseok;Jo, Yongcheol;Kim, Jongmin;Cho, Sangeun;Roh, Cheong Hyun;Lee, Jun Ho;Kim, Hyungsang;Hahn, Cheol-Koo;Im, Hyunsik
    • Current Applied Physics
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    • v.18 no.12
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    • pp.1558-1563
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    • 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.

Early Stages in Morphogenesis of the Shell of Crenella decussata (Bivalvia: Mytilidae)

  • Kolotukhina, N.K.;Kulikova, V.A.;Evseev, G.A.
    • The Korean Journal of Malacology
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    • v.27 no.2
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    • pp.91-97
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    • 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.

Effectiveness and Preparation of Nano-emulsion of a Rapeseed Oil Extract Originated from Jeju with PIT Emulsifying System (PIT유화시스템을 이용한 제주산 유채씨앗 오일추출물의 나노에멀젼의 제조 및 효과)

  • Joo, Se-Jin;Kim, Hack-Soo;Lee, Jeong-Koo;Lee, Min-Hee;Kim, In-Young
    • Journal of the Korean Applied Science and Technology
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    • v.29 no.3
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    • pp.486-494
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    • 2012
  • Nano-emulsion with phase inversion temperature (PIT) emulsifying system was prepared to use rapeseed oil from originating Jeju in order to apply various cosmetic applications. Natural rape seed oil (NRSO) extraction was extracted using n-hexane as a solvent. NRSO extract showed a light yellowish color of viscous liquid as well as yield was $43{\pm}2.5%$. Acid value was $2.76{\pm}0.5$ and gravity was $0.89{\pm}0.05$. Droplet size of PIT-Yuche-NE with 20wt% of rapeseed oil was 50-120nm (average: $82{\pm}5.8nm$) and zeta potential was -29.5mV. It was thermodynamically good stable emulsion due to $(PEG)_{5-30}$fattyacidether. Some conclusions from the result of characteristic experiment were obtained as follows. First, the anti-oxidative activity was measured by free radical scavenging activity using DPPH (1,1-diphenyl-2-picrylhydrazyl radical). Anti-oxidative activity of PIT-Yuche-NE was $37.2{\pm}6.7%$ on 10mg/mL compared with PIT-Toco-NE (Natural tocopherol nano-emulsion, $28.8{\pm}6.5%$ on 10 mg/mL) and PIT-Nokcha-NE (Green tea extract nano-emulsion, $29.6{\pm}7.2%$ on 10mg/mL). Second, the collagen synthesis activity of PIT-Yuche-NE was $148{\pm}15.2%$ compared with PIT-Toco-NE (Natural tocopherol nano-emulsion, $121{\pm}13.5%$ on 10mg/mL) and PIT-Nokcha-NE (Green tea extract nano-emulsion, $95{\pm}12.7%$ on 10mg/mL). Third, the effectiveness of moisturizing activity of Yuche-CRM with Aramo-TS after 6 hours increase $47{\pm}3.9%$ (*p-value£0.05, n=7) whereas Both Toco-CRM was $30{\pm}5.2%$ (*p-value£0.05, n=7) and Nokcha-CRM was $35{\pm}4.5%$. Therefore, Yuche-CRM has higher moisturizing effect than other two creams. Finally, Nano-emulsion stabilizing rapeseed oil using PIT emulsifying system of this study can be used to apply cosmetics industry and pharmaceutical industry.

Corrosion resistance assessment of nickel-titanium endodontic files with and without heat treatment

  • Tatiana Dias Costa;Elison da Fonseca e Silva;Paula Liparini Caetano ;Marcio Jose da Silva Campos ;Leandro Marques Resende ;Andre Guimaraes Machado;Antonio Marcio Resende do, Carmo
    • Restorative Dentistry and Endodontics
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    • v.46 no.1
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    • pp.6.1-6.10
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    • 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 (Ecorr). The pitting potential (Epit) 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 Ecorr) and the Student t-test for independent samples (for Epit). Results: The mean Ecorr 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 Epit 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.

Experimental Research on the Surface Changes and the Abrasion Resistance of Pit and Fissure Sealant by Fluoride (불소도포제에 의한 치면열구전색제의 마모저항성과 표면 변화에 관한 실험연구)

  • Hwang, Su-Hyun;Yu, Ji-Su
    • Journal of dental hygiene science
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    • v.10 no.5
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    • pp.373-378
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    • 2010
  • To test the effects of representative fluoride vanishes-1.23% APF gel and 5% NaF Fluoride Varnish-on the surface structure of pit and fissure sealant, this study classified samples of pit and fissure sealant into five groups: Group I deposited in distilled water for ten minutes, Group II treated with APF gel for one minute, Group III treated with APF gel for four minutes, Group IV treated with Fluoride Varnish for one minute, and Group V treated with Fluoride Varnish for four minutes. An abrasion test was carried out to measure changes in weight, along with observation of the surface structure by using an optical microscope, consequently drawing the following conclusions. 1. The results of the abrasion test using pit and fissure sealant, Concise, showed that Group III had the reduction in weight more increased than Group I and that Group V had less reduction in weight (p<0.05); the results of the abrasion test using Eco-S showed Group III had the reduction in weight more increased than Group I and that Group V had less reduction in weight (p<0.05). 2. The results of observation using an optical microscope showed that application of APF gel made the filler remarkable due to loss of substrate and that Group III treated with APF gel for four minutes had the toughest surface, followed by Group II treated with APF gel for one minute, Group I deposited in distilled water for ten minutes, Group IV treated with Fluoride Varnish for one minute, and Group V treated with Fluoride Varnish for four minutes.

Elucidation of the Noise in Corrosion of Aluminum Foil

  • Chiba, Atsushi;Hattori, Atsushi;Wu, Weng-Chang
    • Corrosion Science and Technology
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    • v.3 no.3
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    • pp.102-106
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    • 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.

Electrophoretic Deposition of Ni Nano-particles for Self-repairing of Heat Exchanger Tubes

  • Lee, Gyoung-Ja;Pyun, Su-Il;Rhee, Chang-Kyu
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • 2006.09b
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    • pp.1211-1212
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    • 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.

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Comprehensive Structural Characterization of Commercial Blue Light Emitting Diode by Using High-Angle Annular Dark Filed Scanning Transmission Electron Microscopy and Transmission Electron Microscopy (고각 환형 암시야 주사투과전자현미경기법과 투과전자현미경기법을 이용한 상용 청색 발광다이오드의 종합적인 구조분석)

  • Kim, Dong-Yeob;Hong, Soon-Ku;Chung, Tae-Hoon;Lee, Sang Hern;Baek, Jong Hyeob
    • Korean Journal of Materials Research
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    • v.25 no.1
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    • pp.1-8
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    • 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.