• Journal of the Korean Crystal Growth and Crystal Technology
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• v.31 no.6
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• pp.282-286
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• 2021

Penetration depth and compressive residual stress of laser-carburized TiZrN coating by thickness of carbon paste were investigated in terms of carbon potential. The carbon paste was covered with a thickness of 1.1 mm using screen printing, and applied to a thickness of 0.4 mm using spin coating, and laser carburization was performed under the same conditions. As the thickness of carbon paste increased, the diffraction pattern of the laser-carburized TiZrN coating shifted to a lower angle, indicating solid solution strengthening and lattice distortion. For microstructure analysis using TEM, the defects and carbon concentration of the laser-carburized TiZrN coating increased as the carbon paste was thicker. It indicated that the variation of the carbon potential corresponds to the change in the paste thickness. In XPS depth profile analysis, high concentration of carbon and formation of carbide were observed in laser-carburized TiZrN coating with thick carbon paste. It revealed that the carbon concentration on the surface and carbon potential were changed by the thickness control of carbon paste. The compressive residual stress increased from 3.67 GPa to 4.58 GPa by the variation of carbon concentration.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.6
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• pp.239-245
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• 2022

Reduced graphene oxide (rGO) has attracted many attention and applications due to its excellent electrochemical ability. Therefore, standardization of rGO through structural and thermal analysis facilitates quality improvement and management, enabling users to increase efficiency and reduce relevant costs. For rGO and graphene-related materials, it is very important to determine the number of layers and define the resulting difference in physical properties. In this study, 3~4 layers of rGO-1 and 9~10 layers of rGO-2 were obtained from graphene oxide (GO) through a hydrazine reduction process. For the prepared rGOs, X-ray diffraction (XRD) pattern obtained a diffraction peak at 2θ≈25° related to (002) reflection was used to calculate the layer numbers by determining interlayer distance and FWHM value. To reduce the angular uncertainty, XRD data analysis was performed with angle correction using standard reference materials for X-ray powder diffraction analysis. Precise interlayer distance and number of layers were determined using OriginLab and open-source XRD diffraction analysis programs using the angle-corrected diffraction data. TG-DSC thermal analysis was performed to further standardize the physical properties of rGO samples.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.4
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• pp.151-158
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• 2022

In this study, the waste concrete sample obtained as various particle size (0~2.36 mm) was carried out the basic measurements and carbonation for analyzing the possibility of its carbonation. It was then investigated some analysis such as crystallization (XRD pattern), microstructure (SEM), and the production of CaCO₃ through the ignition loss (TG-DTA). The content of CaCO₃ in the waste concrete sample before carbonation was found in 14.51 % and 28.52 % after carbonation in 24 hours. Moreover, the content of CaCO₃ carbonated in 24 hours with fine grinded waste concrete sample was 32.73 %. The carbonation of the waste concrete sample was rapidly performed up to 6 hours, but gradually increased from 12 to 24 hours. Especially, the amount of CaCO₃ between 12 and 24 hours was only produced 2.32 %. The calcite-shaped CaCO₃ crystals after carbonation of the waste concrete sample were found in microstructure and their peaks were strongly detected on XRD pattern.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.34 no.5
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• pp.187-193
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• 2024

Lanthanide-doped upconversion nanoparticles (UCNPs) are capable of converting low energy near-infrared photons into relatively high energy visible and ultraviolet photon. Their unique optical properties have a broad range of applications such as volumetric display, security labelling and deep-tissue imaging. Herein, the optically active hexagonal phased NaYF₄:Nd³⁺, Yb³⁺@NaYF₄:Yb³⁺, Tm³⁺ core-shell nanoparticles were synthesized via facile co-precipitation method which can show upconversion luminescence upon 745 nm laser excitation. This is accomplished by taking advantages of the large absorption cross-section of Nd³⁺ ions between 720 to 760 nm plus efficient spatial energy transfer and migration which starts from Nd³⁺ ions to Yb³⁺ ions and Tm³⁺ ions. Also, the formation of inert NaYF₄ shell significantly enhance the upconversion efficiency. The core-shell-shell UCNPs were characterized with X-ray diffraction (XRD) patterns, scanning electron microscope (SEM), transmission electron microscope (TEM), absorbance, and photoluminescence spectra.

• Journal of Food Hygiene and Safety
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• v.26 no.1
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• pp.25-30
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• 2011

In this study, predictive mathematical models were developed to predict the kinetics of Listeria monocytogenes growth in the mixed fresh-cut vegetables, which is the most popular ready-to-eat food in the world, as a function of temperature (4, 10, 20 and $30^{\circ}C$). At the specified storage temperatures, the primary growth curve fit well ($r^2$=0.916~0.981) with a Gompertz and Baranyi equation to determine the specific growth rate (SGR). The Polynomial model for natural logarithm transformation of the SGR as a function of temperature was obtained by nonlinear regression (Prism, version 4.0, GraphPad Software). As the storage temperature decreased from $30^{\circ}C$ to $4^{\circ}C$, the SGR decreased, respectively. Polynomial model was identified as appropriate secondary model for SGR on the basis of most statistical indices such as mean square error (MSE=0.002718 by Gompertz, 0.055186 by Baranyi), bias factor (Bf=1.050084 by Gompertz, 1.931472 by Baranyi) and accuracy factor (Af=1.160767 by Gompertz, 2.137181 by Baranyi). Results indicate L. monocytogenes growth was affected by temperature mainly, and equation was developed by Gompertz model (-0.1606+$0.0574^*Temp$+$0.0009^*Temp^*Temp$) was more effective than equation was developed by Baranyi model (0.3502-$0.0496^*Temp$+$0.0022^*Temp^*Temp$) for specific growth rate prediction of L.monocytogenes in the mixed fresh-cut vegetables.

• Journal of Energy Engineering
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• v.23 no.4
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• pp.61-72
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• 2014

This paper analyzed transition pathways toward a low carbon society in Korea to meet global $2^{\circ}C$ climate target. Lower economic growth, industrial structure change, enhance of energy demand management, decarbonization of power sector, and replacement of low carbon fuel could reduce greenhouse gas (GHG) emission from fuel combustion in 2050 by 67% against in 2011, or by 74% against in BAU (Business-As-Usual). Lower economic growth contributes to 13% of cumulative emission reduction relative to BAU, industrial structure change 9%, enhance of energy demand management 72%, decarbonization of power sector 5% and replacement of low carbon fuel 1% respectively. Final energy consumption in 2050 needs to be reduced to 50% relative to 2011, or to 41% relative to BAU. Nuclear, coal and renewable energy represent 31%, 40%, 2% respectively among electricity generation in 2011, but 38%, 2%, 32% in 2050. CCS represents 23% of total generation in 2050. Emission intensity of electricity in 2050 was decreased to 19% relative to 2011, or to 24% relative to BAU. Primary energy in 2050 was decreased to 64% compared to 2011, or to 44% compared to BAU. Final energy consumption, primary energy supply and GHG emission from fuel combustion from 1990 to 2011 increased by 176%, 197%, 146%. Radical change from historical trend is required to transit toward a low carbon society by 2050. Appropriate economic growth, structural change to non-energy intensive industries, energy technology research, development and deployment (RD&D) in terms of enhancement of energy efficiency and low carbon energy supply technologies, and fuel change to electricity and renewable energy are key instruments.

• Journal of the Korean Vacuum Society
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• v.16 no.5
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• pp.322-329
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• 2007

The interaction of oxygen with the ordered $Ni_3Al(111)$ alloy surface at 800 K and 1000 K has been investigated using LEED, STM, HREELS, UPS, and PAX. The clean $Ni_3Al(111)$ surface exhibits a "$2{\times}2$" LEED pattern corresponding to the ordered bulk-like terminated surface structure. For an adsorption of oxygen at 800 K, LEED shows an unrelated oxygen induced superstructure with a lattice spacing of $2.93\;{\AA}$ in addition to the ($1{\times}1$) substrate spots. The combined HREELS and the UPS data point to an oxygen chemisorption on threefold aluminum sites while PAX confirms an islands growth of the overlayer. Since such sites are not available on the $Ni_3Al(111)$ surface, we conclude the buildup of an oxygen covered aluminum overlayer. During oxygen exposure at 1000 K, however, we observe the growth of ${\gamma}'-Al_2O_3$ structure on the reordered $Ni_3Al(111)$ substrate surface. This structure has been identified by means of HREELS and STM. The HREELS data will show that at 800 K the oxidation shows a very characteristic behavior that cannot be described by the formation of an $Al_2O_3$ overlayer. Moreover, the STM image shows a "Strawberry" structure due to the oxide islands formation at 1000 K. Conclusively, from the oxygen interaction with $Ni_3Al(111)$ alloy surface at 800 K and 1000 K an islands growth of the aluminum oxide overlayer has been found.

• Korean Journal of Culture and Social Issue
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• v.16 no.3
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• pp.355-383
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• 2010

In this study, the effects of skill-utilization based underemployment on self-esteem and mental health were examined. Also the moderating effects of employment commitment and social support were verified. Data obtained by a longitudinally designed survey with the reemployed (N=153) after job loss were used. The skill-utilization based underemployment was measured in two ways. One is measured in the way that use objective data, the ratio of education - 'educational requirement for the current job' divided by 'individual educational attainment.' The other is measured in the way that use psychological and self-reported measure, two factors of overqualification - the absence of opportunity for growth (no-growth) and the occupational mismatch in educational attainment, skills and experiences (mismatch). The main effect revealed that the no-growth made self-esteem lower and mental health (GHQ-social maladjustment) worse. The significant interaction of the ratio of education and employment commitment indicates that the negative effects of underemployment measured by the ratio of education on mental health (GHQ-social maladjustment, GHQ-depression/anxiety) were greater for those perceiving low employment commitment than for those perceiving high employment commitment. The significant interaction of the ratio of education and social support indicates that the negative effects of underemployment measured by the ratio of education on mental health (GHQ-depression/anxiety) were greater for those perceiving low social support than for those perceiving high social support. The two moderators also interacted with the two factors of perceived overqualification. Employment commitment had significant interaction effects with the no-growth and the mismatch on self-esteem and mental health (GHQ-depression/anxiety), whereas social support had a significant interaction only with the no-growth on mental health (GHQ-depression/anxiety). The significant interactions show that employment commitment and social support function as buffers in reducing the negative effects of skill-utilization based underemployment on self-esteem and mental health.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.375.2-375.2
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• 2016

그래핀(Graphene)은 원자 한 층 두께의 얇은 특성에 기인하여 우수한 투과도(~97.3%)를 나타내며, 높은 전자 이동도($200,000cm^2V^{-1}s^{-1}$)로 인하여 전기 전도도가 우수한 2차원 전자소재이다. 또한 유연하고 우수한 기계적 물성을 가지고 있어 실제로 다양한 소자에서 활용되고 있다. 그래핀을 이용하여 다양한 소자로 응용하기 위한 과정 중 하나인 포토리소그래피 공정(Photolithography process)은 원하는 패턴을 만들기 위해 제작하고자 하는 기판 위에 포토레지스트(Photoresist)를 코팅하는 과정을 거치게 된다. 하지만 이러한 과정은 소자 제작에 있어서 포토레지스트 잔여물을 남기게 된다. 그래핀 위에 남은 포토레지스트 잔여물은 그래핀의 우수한 전기적 특성을 저하시켜 소자특성에 불이익을 주게 된다. 본 연구에서는 수소 플라즈마를 이용하여 그래핀 위에 남은 중합체(Polymer) 잔여물을 제거한다. 사용한 그래핀은 화학 기상 증착법(Chemical vapor deposition)을 이용하여 성장시켰으며, PMMA(Poly(methyl methacrylate))를 이용하여 이산화규소(silicon dioxide) 기판에 전사하였다. 그래핀의 손상 없이 중합체 잔여물을 제거하기 위해 플라즈마 처리시간을 15초부터 1분까지 늘려가며 연구를 진행하였으며, 플라즈마 처리 시간에 따른 중합체 잔여물의 제거 정도와 그래핀의 보존 여부를 확인하기 위해 라만 분광법(Raman spectroscopy)과 원자간력현미경(Atomic force microscopy)을 사용하였다. 본 연구 결과를 통해 간단한 플라즈마 처리로 보다 나은 특성의 그래핀 소자를 얻게 됨으로써, 향상된 특성을 가진 그래핀 소자로 산업적 응용 가능성을 높일 수 있을 것이라 생각된다.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.262-262
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• 2016

최근 고해상도 디스플레이가 주목받으면서 기존 비정질 실리콘(a-Si)을 대체할 수 있는 재료에 관한 연구가 활발히 진행되고 있다. a-Si의 경우 간단한 공정 과정, 적은 생산비용, 대면적화가 가능하다는 장점이 있지만 전자 이동도가 매우 낮은 단점이 있다. 반면, 산화물 반도체는 비정질 상태에서 전자 이동도가 높으며 큰 밴드갭을 가지고 있어 투명한 특성을 나타낼 뿐만 아니라, 저온공정이 가능하여 기판의 제한이 없는 장점을 가지고 있다. 대표적으로 가장 널리 연구되고 있는 산화물 반도체는 a-IGZO(amorphous indium-gallium-zinc oxide)이다. 그러나 InZnO(IZO) 기반의 산화물 반도체에서 carrier suppressor 역할을 하는 Ga(gallium)은 수요에 대한 공급이 원활하지 못하여 비싸다는 단점이 있다. 그러므로 경제적이면서 a-IGZO와 유사한 전기적 특성을 나타낼 수 있는 suppressor 물질이 필요하다. 따라서 본 연구에서는 IZO 기반의 산화물 반도체에서 Ga을 Hf(hafnium), Zr(zirconium), Si(silicon)으로 대체하여 용액증착(solution-deposition) 공정으로 각각의 채널층을 형성한 back-gate type의 박막 트랜지스터(thin-film transistor, TFT) 소자를 제작하였다. 용액증착 공정은 물질의 비율을 자유롭게 조절할 수 있고, 대기압의 조건에서도 공정이 가능하기 때문에 짧은 공정시간과 저비용의 장점이 있다. 제작된 소자는 p-type Si 위에 게이트 절연막으로 100 nm의 열산화막이 성장된 기판을 사용하였다. 표준 RCA 클리닝 후에 각 solution 물질을 spin coating 방식으로 증착하였다. 이후, photolithography, develop, wet etching의 과정을 거쳐 채널층 패턴을 형성하였다. 또한, 산화물 반도체의 전기적 특성을 향상시키기 위해서 후속 열처리 과정(post deposition annealing, PDA)은 필수적이다. CTA 방식은 높은 열처리 온도와 긴 열처리 시간의 단점이 있다. 따라서, 본 연구에서는 $100^{\circ}C$ 이하의 낮은 온도와 짧은 열처리 시간의 장점을 가지는 MWI (microwave irradiation)를 후속 열처리로 진행하였다. 그 결과, 각 물질로 구현된 소자들은 기존 a-IGZO와 비교하여 적은 양의 carrier suppressor로도 우수한 전기적 특성 및 안정성을 얻을 수 있었다. 따라서, Si, Hf, Zr 기반의 산화물 반도체는 기존의 Ga을 대체하여 저비용으로 디스플레이를 구현할 수 있는 IZO 기반 재료로 기대된다.