Leakage Current Behavior of PZT Ferroelectric Thin Films on Annealed LaNiO₃ Bottom Electrodes

Heesan Kim,Jai-Hyun Kim,Woong Kil Choo 한국자기학회 2003 한국자기학회 학술연구발표회 논문개요집 Vol.13 No.2

Preparation of conductive LaNiO3 thin films by reactive RF magnetron sputtering using La and Ni metals

Heesan Kim,Jai-Hyun Kim,Woong Kil Choo 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.43 No.51

Conductive LaNiO3 (LNO) thin lms were successfully prepared on SiO2/Si (100) substrates by using the reactive RF magnetron sputtering method. Instead of a LNO ceramic target, La metal chips and a Ni metal target were used to deposit the LNO lms. The atomic ratio of La to Ni gradually increased as the number of La chip increased, and the change of the ratio was measured using an energy dispersive spectrometer (EDS). The sputtering was conducted for 6 La chips. The ratio of Ni to La decreased with increasing sputtering temperature, to 1 at 400 C after which it increased. The LNO lms on SiO2/Si (100) usually had a (100) orientation for the deposition temperatures characterized by X-ray diraction (XRD) analysis. The preferred orientation of LNO was (100) for deposition temperatures between 300 C and 500 C. Below 300 C, the peaks from the (100) orientation had very low intensities. The resistivity of sputtered LNO lm was measured using a DC four-point probe after a 600 C- annealing for 30 min, and the LNO lm sputtered at 200 C showed the lowest resistivity, 280 cm. The surface morphology of the LNO deposited at room temperature was very smooth. With increasing substrate temperature, the grain size gradually increased.

Selective Catalytic Reduction (SCR) 환경에서 18% 크롬 스테인리스강의 부식 거동

김희산 ( Heesan Kim ) 한국부식방식학회 2023 Corrosion Science and Technology Vol.22 No.3

Effects of high-temperature environment and low-temperature environment on corrosion behaviours of 18Cr stainless steels (type 304L, type 441) in simulated selective catalytic reduction (SCR) environments were studied using weight loss test in each environment and rust analysis. With time to exposure to the hightemperature environment, type 441 was more resistant to corrosion than type 304L due to both higher diffusivity of Cr and lower thermal expansion coefficient in α-iron. The former provides a stable protective Cr₂O₃ layer. The latter leaded to low residual stress between scale and steel, reducing the spallation of the scale. With time to exposure to the low-temperature environment, on the other hand, type 304L was more resistant to corrosion than type 441. The lower resistance of type 441 was caused by Cr-depleted zone with less than 11% formed during the pre-exposure to a high-temperature environment, unlike type 304L. It was confirmed by results from the crevice corrosion test of sensitised 11Cr steel. Hence, to achieve higher corrosion resistance in simulated SCR environments, ferritic stainless steels having lower thermal expansion coefficient and higher diffusivity of Cr but containing more than 18% Cr are recommended.

의료 데이터의 자기지도학습 적용을 위한 pretext task 분석

공희산(Heesan Kong),박재훈(Jaehun Park),김광수(Kwangsu Kim) 한국정보통신학회 2021 한국정보통신학회 종합학술대회 논문집 Vol.25 No.1

의료 데이터 분야는 레코드 수는 많지만 응답 값이 없기 때문에 인공지능을 적극적으로 활용하지 못하고 있다. 이러한 문제점을 해결하기 위해 자기지도학습(Self-Supervised learning)을 의료 분야에 적용하는 연구가 등장하고 있다. 자기지도학습은 model이 레이블링이 없는 데이터의 semantic 표현을 이해할 수 있도록 pretext task와 supervision을 학습한다. 그러나, 자기지도학습의 성능은 pretext task로 학습한 표현에 의존하므로 데이터의 특성에 적합한 pretext task를 정의할 필요가 있다. 따라서 본 논문에서는 의학 데이터 중 활용도가 높은 x-ray 이미지에 적용할 수 있는 pretext task를 실험적으로 탐색하고 그 결과를 분석한다. Medical domain has a massive number of data records without the response value. Self-supervised learning is a suitable method for medical data since it learns pretext-task and supervision, which the model can understand the semantic representation of data without response values. However, since self-supervised learning performance depends on the expression learned by the pretext-task, it is necessary to define an appropriate Pretext-task with data feature consideration. In this paper, to actively exploit the unlabeled medical data into artificial intelligence research, experimentally find pretext-tasks that suitable for the medical data and analyze the result. We use the x-ray image dataset which is effectively utilizable for the medical domain.

다중 레이블 분류 작업에서의 Coarse-to-Fine Curriculum Learning 메카니즘 적용 방안

공희산(Heesan Kong),박재훈(Jaehun Park),김광수(Kwangsu Kim) 한국컴퓨터정보학회 2022 한국컴퓨터정보학회 학술발표논문집 Vol.30 No.2

Control of the Preferred Orientation of Polycrystalline Mo and Cu(InGa)Se₂ Thin Films by Inserting Graphene Layers

Ryu, Heesan,Park, Do Hyun,Jung, Younghun,Kim, Jihyun,Kim, Woo Kyoung American Scientific Publishers 2018 Science Of Advanced Materials Vol.10 No.4

<P>To demonstrate the effect of graphene (Gr) layer on subsequently deposited Mo and Cu(InGa)Se-2 (CIGS) crystal orientation, graphene sheets grown on Cu foil by chemical vapor deposition were transferred to low-alkali glass substrates by a simple wet-based graphene transfer process. Mo was sputter-deposited on glass and glass/Gr substrates, and CIGS was formed by selenization of the co-sputtered CuGaIn precursors. The Mo thin films on the graphene coated glass substrates (glass/Gr) had a more preferred (110) orientation than the bare glass substrate, showing a lower sheet resistance. Subsequently, glass/Gr/Mo/CIGS revealed the (220) preferred CIGS orientation, which is potentially beneficial to the CIGS cell efficiency but difficult to obtain by selenization of the metal precursors.</P>

고 크롬 페라이트계 강의 인성 및 내식성에 미치는 티타늄의 영향

金熙山 홍익대학교 산업기술연구소 2002 産業技術 Vol.12 No.-

Lower toughness and intergranular corrosion resistance of ferritic stainless steels(SSs) than austenitic SSs limited the applications of ferritic SSs. The effects of Ti on toughness and corrosion were studied as a series of basic studies for optimizing the concentrations of minor alloying elements. Toughness was closely related to the formation of an angular shaped inclusion(TiN) rather than the concentration of Ti. It is due to that the edge of TiN acts as a stress concentrator. In addition, TiN on surface induces surface defect during mechanical deformation, providing a site for corrosion. It seems to be contradictory to the fact that titanium removes sulfur in steels and improves corrosion resistance. However, electrochemical noise(EN) tests showed that titanium added as much as not forming large angular TiN did not deteriorate corrosion resistance. Hence, the addition of Ti is expected to improve corrosion resistance without degrading toughness if titanium is added under the controls to prevent TiN from forming.

Effects of Chloride and Crevice on Corrosion Resistance of Stainless Steels Buried in Soil within Seoul Metropolitan

현영민,Heesan Kim,김영호 대한금속·재료학회 2014 METALS AND MATERIALS International Vol.20 No.2

Field and laboratory tests were conducted to find the factors affecting corrosion of stainless steels in soil. During one-year exposure, corrosion occurred within a joint and on the surface of type 304 pipe with thejoint, which was buried at the site with a high chloride concentration of about 3680 ppm; however, corrosionwas not observed at any of the other sites independent of the stainless steel grade and the presence of joints. At some sites, a seasonal fluctuation of corrosion potential was observed in the soil though corrosion didnot occur. This observation may be due to the activity of sulfate reducing bacteria because a decrease ofcorrosion potential with the inoculated bacteria did not cause corrosion of stainless steels. These resultsindicate that both the level of chloride and the presence of crevices are the main factors affecting corrosionof stainless steels in soil but that the activity of bacteria is not. From measurements of pitting potential, aguideline for stainless steel use in soil is drawn as follows: Corrosion of stainless steels in soil occurs when thepitting potential of stainless steel under crevices in synthetic ground water that contains the same chlorideconcentration as the soil is less than the saddle potential. Finally, the guideline for stainless steels applicationswas provided in this paper according to this criterion.

페라이트계 강의 인성 및 내식성에 미치는 알루미늄과 칼슘의 영향

金熙山 홍익대학교 산업기술연구소 2003 産業技術 Vol.13 No.-

The effects of aluminum and calcium on toughness and corrosion were studied as a series of basic studies for optimizing the concentrations of minor alloying elements. Toughness was closely related to the concentration of oxide and dissolved oxygen, depending on aluminum and calcium as an alloying element, in ferritic steels not containing titanium. However, the toughness of Ti added steels were independent of the addition of aluminum and/or calcium playing a role of reducing the concentrations of oxide and dissolved oxygen. It indicates the presence of Ti-containing secondary phase formation more susceptible to toughness that oxide inclusion. The corrosion resistance was degraded by the addition of aluminum and calcium but their causes were different. The formation of calcium sulfide chemically unstable provided a site for crevice corrosion and pitting corrosion. The micro-crevice formed at matrix-alumina interface give a site for pitting corrosion but not for crevice corrosion.

고 크롬 페라이트계 강의 인성 및 내식성에 미치는 안정화 원소 및 알루미늄의 영향

김희산 대한금속재료학회 2003 대한금속·재료학회지 Vol.41 No.4

Effects of stabilizing elements such as titanium and niobium, and aluminium on toughness and corrosion of ferritic stainless steels were studied as a series of basic studies for optimizing the concentrations of minor alloying elements. Aluminum reduced the concentration of total oxygen and the size of oxides to improve toughness. Niobium, one of stabilizing elements used in this study improved toughness as well as corrosion resistance. It is due to the fact that niobium retards the formation of chromium-carbonnitride known as a site for crack initiation and as resulting in chromium depleted zone. Unexpectedly, titanium, the other of stabilizing elements did not improve toughness as effective as niobium. The cause in a angular shaped TiN formed at the temperature around the solidus line of the alloy. It was proved by inclusion analysis, measurements of DBTT, and the calculation on phase equilibrium. In addition, the reducement of pitting corrosion resistance by titamium seems to be contradictory to the previous known fact that titanium removes sulfur in steels and improves corrosion resistance. The discrepancy was solved by observation of the angular TiN on the surface causing micro cracks to provide a site for pitting.