• 한국진공학회:학술대회논문집
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.169.2-169.2
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• 2015

$VO_2$ is a well-known a metal-to-insulator-transition (MIT) material, accompanied with a first order structural phase transition near room temperature. Because of the structural phase transition and the MIT occur near a same temperature, there is an ongoing argument whether the MIT is induced by the structural phase transition. $VO_2$ exhibits a relatively weak anti-oxidization ability and can be oxidized to higher-valence oxides (e.g., $V_4$ $O_7$ or $V_2$ $O_5$) when annealed at a high temperature in an oxygen-rich atmosphere. We fabricated $VO_2$ films on $Al_2$ $O_3$ (0001) substrates using a DC magnetron sputtering deposition process with carefully control the $O_2$ percentage in an atmosphere. X-ray diffraction measurements from the films showed only (0l0) peaks with no extra peaks, indicating b-oriented films. The temperature-dependent local structural properties of $VO_2$ films were investigated by using in-situ X-ray absorption fine structure (XAFS) measurements at the V K edge. XAFS revealed that the structural phase transition was occurred nearly $70^{\circ}C$ for heating process and reproducible. Resistance measurements as a function of temperature (R-T) demonstrated that the resistance of $VO_2$ films was changed by a factor of 4 near $75^{\circ}C$ which was higher than $68^{\circ}C$ reported from a $VO_2$ bulk. We will discuss the MIT of $VO_2$ films, comparing with the local structural properties determined by XAFS measurements.

• Carbon letters
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• 제19권
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• pp.72-78
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• 2016

Spinnable pitches and carbon fibers were successfully prepared from petroleum or coal pyrolysis residues. After pyrolysis fuel oil (PFO), slurry oil, and coal tar were simply filtered to eliminate the solid impurities, the characteristics of the raw materials were evaluated by elemental analysis, ¹³C nuclear magnetic resonance spectrometer, matrix-assisted laser desorption/ionization time-of-flight mass spectrometer (MALDI-TOF-MS), and so on. Spinnable pitches were prepared for melt-spinning carbon fiber through a simple distillation under strong nitrogen flow, and further vacuum distillation to obtain a high softening point. Carbon fibers were produced from the above pitches by single-hole melt spinning and additional heat treatment, for oxidization and carbonization. Even though spinnable pitches and carbon fibers were processed under the same conditions, the melt-spinning and properties of the carbon fiber were different depending on the raw materials. A fine carbon fiber could not be prepared from slurry oil, and the different diameter carbon fibers were produced from the PFO and coal tar pitch. These results seem to be closely correlated with the initial characteristics of the raw materials, under this simple processing condition.

• 대한방사선기술학회지:방사선기술과학
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• 제2권1호
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• pp.71-83
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• 1979

Not only the insulating oil used for extra high voltage and high capacity transformer has a lot of possibilites of a corona discharge in oil, but the oil is easily degraded by a response of light oxidization. This study is either to classfy, with priority given to a transformer oil produced in Korea belonging to, the insulating oil No. 2, the sample irradiated the ultraviolet rays, treated a corona discharge in oil by a high voltage DC source and done nothing, or to measure the characteristics of breakdown, V-i, I-t and electrode material. The obtained results can be summarized as followings: (1) Unless the sample is contacted with the air, on the process to irradiate the ultraviolet rays, the sample less influence on the changes of the electric characteristics. At the same time, if the sample is contacted with the air and irradiated the ultraviolet rays, the sample shows a remarkable changes of the electric characteristics, and a declined breakdown strength. This tells us that the influence of the light irradiation must be considered as a primary factor of degrading the insulating oil. (2) In the oil treated by a corona discharge, breakdown voltage is declined more than in the oil not to be treated with it. This means that the degradation of the insulating oil is getting increased by a corona discharge in oil. (3) It shows that the increase of conducting current has little to do with breakdown voltage. (4) The conducting current depending on the electrode materials can be put in order by value as Al>Cu>Fe. This is due to the differences of the work function of each metals, and an chemical reaction with the insulating oil. These result can be a great help in verifying the degradation progress of the insulating oil and furnish a new technical information to the manufacturers of the insulating oil and electrical equipment designers and operators. Besides, this study would be helpful to improve the electrical characteristics of the insulating oil produced in Korea.

• 한국기계가공학회지
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• 제12권3호
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• pp.1-6
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• 2013

This study has focused on transparency recovering of the polycarbonate by polishing its surface for recycling. The polycarbonate has many properties such as excellent mechanical strength, electrical insulating, superior heat resistance to other plastic material and especially good transparency. It has been used as barrier for the traffic noise at the roadside and the greenhouse for the palm house. But the polycarbonate has changed slightly as time goes by 10 years because of exposure to the strong sunlight and oxidization in the atmosphere, as result has lost its transparency. Magnetic assisted polishing has been utilized as an effective polishing method to recover the transparency of polycarbonate. The polycarbonate which has been used for 10 years was adopted as the sample. The first surface roughness of the sample was 1$1.23{\mu}mRa$, $7.5{\mu}mRz(DIN)$ respectively. In the experimental results, it showed that the surface roughness of the polished sample improved $0.013{\mu}mRa$, $0.08{\mu}mRz(DIN)$ from the first surface roughness respectively. The surface roughness get almost back again by magnetic assisted polishing. These results also showed that the magnetic assisted polishing was efficient machining method to reuse the polycarbonate material.

• Advances in nano research
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• 제5권3호
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• pp.193-201
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• 2017

ZnO, ZnO: Cu, Ga, and ZnO: Cu, Ga, Ag thin films were obtained by oxidization of ZnS and ZnS: Cu, Ga films deposited onto glass substrates by electron-beam evaporation from ZnS and ZnS: Cu, Ga targets and from ZnS: Cu, Ga film additionally doped with Ag by the closed space sublimation technique at atmospheric pressure. The film thickness was about $1{\mu}m$. The oxidation was carried out at $600-650^{\circ}C$ in air or in an atmosphere containing water vapor. Structural characteristics were investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM). Photoluminescence (PL) spectra of the films were measured at 30-300 K using the excitation wavelengths of 337, 405 and 457.9 nm. As-deposited ZnS and ZnS: Cu, Ga films had cubic structure. The oxidation of the doped films in air or in water vapors led to complete ZnO phase transition. XRD and AFM studies showed that the grain sizes of oxidized films at wet annealing were larger than of the films after dry annealing. As-deposited doped and undoped ZnS thin films did not emit PL. Shape and intensity of the PL emission depended on doping and oxidation conditions. Emission intensity of the films annealed in water vapors was higher than of the films annealed in the air. PL of ZnO: Cu, Ga films excited by 337 nm wavelength exhibits UV (380 nm) and green emission (500 nm). PL spectra at 300 and 30 K excited by 457.9 and 405 nm wavelengths consisted of two bands - the green band at 500 nm and the red band at 650 nm. Location and intensities ratio depended on the preparation conditions.

• 한국자기학회지
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• 제13권2호
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• pp.47-52
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• 2003

DC 마그네트론 스파터법과 RLSA(Radial Line Slot Antenna)을 이용한 마이크로파 여기 프라즈마를 이용하여 Ta/Cu/Ta/NiFe/Cu/Mn$_{75}$Ir$_{25}$/ $Co_{70}$Fe$_{30}$/Al-oxide 구조의 접합을 제조한 후, contact-mode AM(Atomic Force Microscope)을 이용하여 Al 산화막의 국소전도 특성의 평가를 수행하였다. AFM 동시전류측정으로부터, 얻어지는 표면상과 전류상은 대응하지 않는다. 국소 전류-전압(I-V)의 측정 결과, 전류상은 절연층의 barrier height의 분포를 나타내고 있다는 것을 알았다.다.다.

• 한국환경과학회지
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• 제14권2호
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• pp.231-240
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• 2005

The number of cases exceeding environmental standards of atmospheric ozone in the major cities in Korea has steadily increased during the past decades. In order to understand and analyze the atmospheric reactions in the atmosphere, especially the secondary photochemical reactions, smog chambers studies have been performed very actively by many research groups worldwide. However, these studies have focused on the mechanism of photochemical reactions in high concentration conditions, not at the ambient levels. Therefore, in-depth studies in these conditions are essentially needed to realize exact mechanism in the atmosphere near the earth surface, especially at Korean atmospheric conditions. In this experiment, the mechanism of photochemical smog was examined through a comparative experiment of smog chambers under sun light and black light conditions. The results of our study indicated that concentrations of ozone, aldehyde, and PAN increased as the radiation of light source increases. Photochemical reaction patterns can be considered quite similar for both black light and sun light experiments. Based on our experiments using toluene as a reactant which is present at significant high levels in ambient air relative to other VOCs, it was found that toluene could contribute notably to oxidize NO to $NO_2$, this reaction can eventually generate some other photochemical oxidants such as ozone, aldehyde, and PAN. The results of simulation and experiments generally showed a good agreement quite well except for the case of $O_3$. The restriction of oxidization of NO to $NO_2$ seems to cause this difference, which is mainly from the reaction of peroxy radical itself and other reactants in the real gas.

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1996년도 The 9th KACG Technical Annual Meeting and the 3rd Korea-Japan EMGS (Electronic Materials Growth Symposium)
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• pp.508-508
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• 1996

;The growth of films have considerable interest in the field of superlattice structured multi-layer epitaxy led to realization of new devices concepts. Molecular beam epitaxy (MBE) with in situ observation by reflection high-energy electron diffraction (RHEED) is a key technology for controlled layered growth on the atomic scale in oxide crystal thin films. Also, the combination of radical oxygen source and MBE will certainly accelerate the progress of applications of oxides. In this study, the growth process of single crystal films using by MBE method is discussed taking the oxide materials of Bi-Sr-Ca-Cu family. Oxidation was provided by a flux density of activated oxygen (oxygen radicals) from an rf-excited discharge. Generation of oxygen radicals is obtained in a specially designed radical sources with different types (coil and electrode types). Molecular oxygen was introduced into a quartz tube through a variable leak valve with mass flowmeter. Corresponding to the oxygen flow rate, the pressure of the system ranged from $1{\;}{\times}{\;}10^{-6}{\;}Torr{\;}to{\;}5{\;}{\times}{\;}10^{-5}$ Torr. The base pressure was $1{\;}{\times}{\;}10^{-10}$ Torr. The growth of Bi-oxides was achieved by coevaporation of metal elements and oxygen. In this way a Bi-oxide multilayer structure was prepared on a basal-plane MgO or $SrTiO_3$ substrate. The grown films compiled using RHEED patterns during and after the growth. Futher, the exact observation of oxygen radicals with MBE is an important technology for a approach of growth conditions on stoichiometry and perfection on the atomic scale in oxide. The oxidization degree, which is determined and controlled by the number of activated oxygen when using radical sources of two types, are utilized by voltage locked loop (VLL) method. Coil type is suitable for oxygen radical source than electrode type. The relationship between the flux of oxygen radical and the rf power or oxygen partial pressure estimated. The flux of radicals increases as the rf power increases, and indicates to the frequency change having the the value of about $2{\times}10^{14}{\;}atoms{\;}{\cdots}{\;}cm^{-2}{\;}{\cdots}{\;}S^{-I}$ when the oxygen flow rate of 2.0 seem and rf power 150 W.150 W.

• 한국지역사회생활과학회지
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• 제24권2호
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• pp.251-258
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• 2013

Korean oil and honey Yukwa has been paid attention as formal cake for traditional national seasons' holiday and religious service. Quality of Yukwa, however, has been maintained arbitrarily by each Yukwa manufacturer. Since even same Yukwa had severe differences in size, weight, and pattern, it has given the negative effect to the consumer. Yukwa industries need to setup the quantitative quality specifications instead of qualitative ones to maintain the uniformity of Yukwa quality. Efficient and economical inspection and process control system should be developed. In developing quality standards of Yukwa, features which can measure quality quantitatively in real time should be properly chosen. Existing quality features such as acidity, oxidization, hardness, viscosity, and texture were measured by the chemical or physical base destructive methods. Many research and developments have been performed in investigating and analyzing chemical transition states of those quality features as environment or storage condition changes. Most methods, however, require either off-line or complex treatment or time consuming process of analysis in evaluating quality features. Consumer, however, selects products mostly based on the external features such as shape, size, and color. Therefore, critical visual quality features should be chosen and the efficient real time measurement system must be developed. In this paper, computer image acquisition and processing system were developed and software modules were developed to extract the quantitative data of those features in real-time. Computer image processing system will promote in maintaining uniform quality of Yukwa and establishing quality standards of Yukwa.

• Composites Research
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• 제32권6호
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• pp.342-348
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• 2019

고분자 재료의 사용이 늘어남에 따라 난연성 고분자 재료에 대한 연구가 더욱 활발히 진행되고 있다. 고분자 재료의 난연성 향상을 위한 방법으로 제조된 섬유의 후처리 또는 섬유내 난연제의 도입에 관한 연구가 진행되고 있다. 많은 고분자들 중 탄소섬유 전구체인 폴리아크릴로니트릴(PAN)은 의류용으로도 많이 사용되고 있어서 낮은 난연성을 지닌 PAN으로 이루어진 소재의 난연성 향상이 절실히 요구되고 있다. 본 총설 논문에서는 PAN 섬유의 후처리(안정화 또는 화학반응)을 통한 난연성 PAN 섬유와, 유/무기 소재(실리카, 2차원 소재, 탄소나노튜브)과 함께 혼합하여 섬유로 제조하는 난연성 PAN 복합소재의 제조에 대한 연구를 소개하고자 한다.