• 한국진공학회:학술대회논문집
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.60-60
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• 2015

Nanosheets of graphene and related 2D materials have attracted much attention due to excellent physical, chemical and mechanical properties. Single-layer graphene (SLG) was first synthesized by Blakely et al in 1974 [1]. Following his achievements, we initiated the growth and characterization of graphene and h-BN on metal substrates using surface segregation and precipitation in 1980s [2,3]. There are three important steps for nanosheet growth; surface segregation of dopants, surface reaction for monolayer phase, and subsequent 3-D growth (surface precipitation). Surface phase transition was clearly demonstrated on C-doped Ni(111) by in situ XPS at elevated temperatures [4]. The growth mode was clarified by inelastic background analysis [5]. The surface segregation approach has been applied to C-doped Pt(111) and Pd(111), and controllable growth of SLG has been demonstrated successfully [6]. Recently we proposed a promising method for producing SLG fully covering an entire substrate using Ni films deposited on graphite substrates [7]. A universal method for layer counting has been proposed [8]. In this paper, we will focus on the effect of competitive surface-site occupation between carbon and other surface-active impurities on the graphene growth. It is known that S is a typical impurity of metals and the most surface-active element. The surface sites shall be occupied by S through surface segregation. In the case of Ni(110), it is confirmed by AES and STM that the available surface sites is nearly occupied by S with a centered $2{\times}2$ arrangement. When Ni(110) is doped with C, surface segregation of C may be interfered by surface active elements like S. In this case, nanoscopic characterization has discovered a preferred directional growth of SLG, exhibiting a square-like shape (Fig. 1). Also the detailed characterization methodologies for graphene and h-BN nanosheets, including AFM, STM, KPFM, AES, HIM and XPS shall be discussed.

• 한국전기전자재료학회논문지
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• 제23권3호
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• pp.240-244
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• 2010

The surface segregation and surface order near the order-disorder phase transition of FeCo alloy was studied through Monte Carlo simulation of an Ising type model Hamiltonian. The results showed that the proper choice of Hamiltonian parameters could reproduce the recent observation of surface order above the transition temperature and that the field term played dominant role.

• 한국진공학회지
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• 제5권1호
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• pp.39-47
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• 1996

The segregation of S in electrotransport-purified polycrystaline $\alpha$-Ti and Ti-aluminide alloys has been studied by Auger electron spectroscopy(AES), Ion scattering spectroscopy(ISS) and Secondary ion mass spectrometry(SIMS) in the temperature range extending from 20 to $1000^{\circ}C$. The chemisorbed oxygen and carbon on Ti were observed to disappear at T>$400^{\circ}C$ after which the S signal increased to levels approaching 0.5 monolayer. At lower temperatures the presence of the surface oxygen and carbon appeared to inhibit the segregation, presumably because there were no available surfaces sites for the S emerging from the bulk. The activation energy for the S segregation in pure polycrystaline Ti was determined to be 16.7 kcal/mol, which, when compared to S segretation from single-crystal Ti, is quite small and suggests grain boundary or defect diffusion segregation kinetics. In the Ti-aluminide alloys, the presence of Al appeared to enhance the retention of surface oxygen which, in turn, substantially reduced the S segretation. The $\gamma$ alloy, with its high Al content, exhibited the greatest retention of surface oxygen and the smallest quantity of the S segregation(T$\simeq1000^{\circ}C$).

• 한국도로학회논문집
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• 제20권4호
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• pp.1-6
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• 2018

PURPOSES : The objective of this study is to evaluate of the effect of thermal segregation reduction in asphalt paving using material transfer vehicles (MTVs). METHODS : Asphalt paving using MTVs was carried out, and the paved surface temperature was measured using an infrared camera. The amount of thermal segregation was estimated from temperature variations. RESULTS : The transportation of hot mix asphalt (HMA) using dump trucks caused temperature segregation that persisted in the paving surface if an MTV was not used. The average temperature variation was 8.58% in paved surfaces where an MTV was not used. However, the temperature variation was 3.10%, 2.86%, and 4.53% for the base layer, inter-layer, and surface layer, respectively, when an MTV was used. CONCLUSIONS : The use of an MTV in asphalt paving reduces thermal segregation approximately 2.3 times in an asphalt mat via a remixing process and also allows for a smoother work process because the paver never needs to stop to receive HMA. However, MTV equipment without pre-heating devices requires careful temperature control during the warm up process at the MTV during construction in the winter.

• Korean Chemical Engineering Research
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• 제55권2호
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• pp.275-278
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• 2017

Heterogeneous semiconductor composites have been widely used to establish high-performance microelectronic or optoelectronic devices. During a deposition of silicon atoms on silicon/germanium compound surfaces, germanium (Ge) atoms are segregated from the substrate to the surface and are mixed in incoming a silicon layer. To suppress Ge segregation to obtain the interface sharpness between silicon layers and silicon/germanium composite layers, approaches have used silicon hydride gas species. The hydrogen atoms can play a role of inhibitors of silicon/germanium exchange. However, there are few kinetic models to explain the hydrogen effects. We propose using segregation probability which is affected by hydrogen atoms covering substrate surfaces. We derived the model to predict the segregation probability as well as the profile of Ge fraction through layers by using chemical reactions during silicon deposition.

• 한국진공학회지
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• 제22권6호
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• pp.285-290
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• 2013

금속 기판 위에 성장한 그래핀은 원자구조와 전자구조 연구에 우수한 기반이 된다. 그래핀은 금소 기판에서 탄소의 surface segregation 이나 chemical vapor deposition으로 성장할 수 있는데, 이 두 방법의 성장 양상에 대한 비교 연구는 아직까지 없었다. 본 연구에서는 surface segregation, 흡착된 에틸렌의 post-annealing, 에틸렌의 high-temperature dose 등 3 방법으로 성장한 그래핀의 성장구조를 주사형 터널링 현미경으로 연구했다. 처음 2종류의 방법에서는 $100nm^2$ 수준의 작은 그래핀 영역이 나타났고, 3 번째 방법에서는 $10^4nm^2$ 보다 큰 그래핀이 육각형 무아레 무늬와 함께 타나났다. 본 연구에서는 에틸렌의 high-temperature dose 방법이 추가적인 분자성장 등에 필요한 넓은 그래핀을 성장하기에 가장 좋은 방법임을 보였다.

• 레미콘
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• 7호통권68호
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• pp.9-16
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• 2001

Execution of exposed concrete has some problems such as segregation, surface honey comb and insufficient surface flossing due to unsuitable mix proportion and unfavorable construction in our field. Therefore, in this paper, field application of exposed concrete at training center building of Chongju university in Daecheon are carried out based on the mixing data obtained from laboratory test. Base concrete are made in accordance with mixing data. Segregation reducing type superplasticizer developed are applied in order to flow the vase concrete with out segregation of materials. According to test results, air content shows to be reduced after flowing. Compressive strength of flowing concrete is higher than that of base concrete about 7%. Surface glossing is reducing as the age goes on. It is improved about 10% compared to that of vase concrete.

• Journal of Magnetics
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• 제4권1호
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• pp.5-9
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• 1999

Effect of sulfur segregation on tertiary recrystallization and magnetic induction during final annealing was investigated in a 3% Si-Fe electrical strip containing 6 ppm(LS) and 15 ppm(HS) sulfur. During final annealing, Auger peak height of segregated sulfur on the surface of the strips reached a maximum, and then decreased to low level with increasing annealing time, which is attributed to sulfur segregation and evaporation. The magnetic induction of the thin-gauged 3% Si strip was inversely proportional to the Auger peak height of segregated sulfur on the surface. The overall profile for surface segregation of sulfur and B10 was observed, irrespective of sulfur content in Si-Fe strips, but the peaks of LS strips appeared earlier than those of HS strips. The grain growth rate of the LS strips during final annealing was faster than that of the HS strips, which may be attributed to the pinning effects of segregated sulfur. With increasing final annealing temperature, B10 value increased rapidly and the saturation level in B10 increased.

• 한국도로학회논문집
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• 제20권1호
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• pp.69-76
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• 2018

PURPOSES : This study determined the optimal usage rate of RAP (reclaimed asphalt pavement) using cold central-plant recycling (CCPR) on a road-surface layer. In addition, a mixture-aggregate gradation design and a curing method based on the proposed rate for the surface-layer mix design were proposed. METHODS : First, current research trends were investigated by analyzing the optimum moisture content, mix design, and quality standards for surface layers in Korea and abroad. To analyze the aggregate characteristics of the RAP, its aggregate-size characteristics were analyzed through the combustion asphalt content test and the aggregate sieve analysis test. Moreover, aggregate-segregation experiments were performed to examine the possibility of RAP aggregate segregation from field compaction and vehicle traffic. After confirming the RAP quality standards, coarse aggregate and fine aggregate, aggregate-gradation design and quality tests were conducted for mixtures with 40% and 50% RAP usage. The optimum moisture content of the surface-layer mixture containing RAP was tested, as was the evapotranspiration effect on the surface-layer mixture of the optimum moisture content. RESULTS : After analyzing the RAP recycled aggregate size and extraction aggregate size, 13-8mm aggregate was found to be mostly 8mm aggregate after combustion. After using surface-chipping and mixing methods to examine the possibility of RAP aggregate segregation, it was found that the mixing method contributed very little for 3.32%, and because the surface-chipping method applied compaction energy directly as the maximum assumption the separation ratio was 15.46%. However, the composite aggregate gradation did not change. Using a 40% RAP aggregate rate on the surface-layer mixture for cold central-plant recycling satisfied the Abroad quality standard. The optimum moisture content of the surface-layer mixture was found to be 7.9% using the modified Marshall compaction test. It was found that the mixture was over 90% cured after curing at $60^{\circ}C$ for two days. CONCLUSIONS : To use the cold central-plant recycling mixture on a road-surface layer, a mixture-aggregate gradation design was proposed as the RAP recycled aggregate size without considering aggregate segregation, and the RAP optimal usage rate was 40%. In addition, the modified Marshall compaction test was used to determine the optimum moisture content as a mix-design parameter, and the curing method was adapted using the method recommended by Asphalt Recycling & Reclaiming Association (ARRA).

• 한국분말재료학회지
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• 제18권6호
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• pp.538-545
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• 2011

This study shows that catalytic activity of bimetallic RhPt nanoparticle arrays under CO oxidation can be tuned by varying the size and composition of nanoparticles. The tuning of size of RhPt nanoparticles was achieved by changing concentration of rhodium and platinum precursors in one-step polyol synthesis. Two-dimensional RhPt bimetallic nanoparticle arrays in different size and composition were prepared through Langmuir-Blodgett thin film technique. CO oxidation was carried out on these two-dimensional nanoparticle arrays, revealing higher activity on the smaller nanoparticles compared to the bigger nanoparticles. X-ray photoelectron spectroscopy (XPS) results indicate the preferential surface segregation of Rh compared to Pt on the smaller nanoparticles, which is consistent with the thermodynamic analysis. Because the catalytic activity is associated with differences in the rates of $O_2$ dissociative adsorption between Pt and Rh, this paper suppose that the surface segregation of Rh on the smaller bimetallic nanoparticles is responsible for the higher catalytic activity in CO oxidation. This result suggests a control mechanism of catalytic activity via synthetic approaches of colloid nanoparticles, with possible application in rational design of nanocatalysts.