• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.77-77
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• 1999

박막시료의 분석에는 RBS, XPS, SIMS, AES 등이 주로 이용되고 있으며, 특히 RBS는 비교체가 필요없고 정량성이 좋다는 장점 때문에 중요하다. 그러나 RBS는 원리적으로 경원소에 대한 감도가 낮아 기판원소보다 무거운 질량을 갖는 원소의 분석에만 이용되는 것이 보통이다. 이러한 단점을 보완하기 위해 본 연구에서는 수년전부터 RBS와 비슷한 원리를 갖고 같은 장비를 이용하여 수행이 가능한 경원소 분석법인 TOF-ERDA(Time of Flight Elastic Recoil detection)을 개발하여 실용화 하였다. 본 연구실에서 보유하고 있는 미국 NEC사의 5SDH 가속기는 최대 가속전압이 1.7MV로 Cl5+ 이온을 사용하는 경우 10 MeV가 최대 가속에너지가 된다. 이런 정도의 에너지 범위에서는 TOF spectrometer의 시간분해능이 아주 높을 필요가 없고 비교적 작은 가속기로도 분석이 가능하며, 수소의 검출효율이 우수하다는 점 등 많은 장점이 있다. 그러나 한편으로는 분석가능한 깊이가 수천 $\AA$ 정도로 제한되고 질량 분해능도 수십 MeV 내지 100MeV 이상의 고에너지 이온빔을 이용하는 경우에 비해 떨어진다는 단점이 있다. 또한 묵운 원소의 분석이 불가능하기 때문에 경원소의 분석에 국한하여 적용하고 무거운 원소에 대해서는 RBS를 병용하게 된다. 본 연구에서는 일본 이화학연구소의 선형가속기인 RILAC으로부터 얻은 40MeV Ar 이온 및 138 MeV Xe 이온을 이용하여 TOF-ERDA 시스템을 제작하였다. 그러기 위해서 고에너지 이온의 비행시간을 측정하는 목적으로 높은 시간 분해능을 갖는 시간 검출기를 설계, 제작하였다. 또한 표적함 밑에는 회전원판이 있어 시간검출기 및 에너지 검출기가 중앙의 시료홀더를 중심으로 회전이 가능하도록 되었다. 회전은 표적함 밖에서 원격조정 가능하다. 이렇게 함으로써 검출각을 임의로 바꾸면서 측정이 가능하도록 하였다. 제작된 분석시스템의 성능을 확인하기 위해 YBaCuO 초전도 박막을 측정하였으며 그 결과를 그림에 나타낸다. 저 에너지 ERDA에서는 나타나기 힘든 Ba, Y, Cu 등의 무거운 원소의 피크들이 분명히 나타남을 확인할 수 있다.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.382.2-382.2
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• 2014

We explain a method to fabricate multi-layered transparent conductive films (TCF) using graphene oxide (GO), copper powder and polyurethane (PU) solution. The flexible graphene nanosheets (GNSs) serve as nanoscale connection between conductive copper nanoparticles (CuNps) and PU nanofibers, resulting in a highly flexible TCF. To fabricate conductive films with high transmittance, polyurethane (PU) nanofibers were used for a conductive network consisting of CuNps and GNSs (CuNps-GNSs). In this experiment, copper powder and graphene oxides were mixed in deionized water with the ultrasonication for 2 h. NaBH4 solution is used as a reduction agents of CuNps and GNSs (CuNps-GNSs) under a nitrogen atmosphere in the oil bath at 100% for 24 h to mixed. The purified and dispersed CuNp-GNS were obtained in deionized water, and diluted to a 10wt.% based on the contents of GNSs. Polyurethane (PU) nanofibers on a PET substrate were formed by electrospinning method. PET slides coated with the PU nanofibers were immersed into CuNp-GNS solution for several second, rinsed briefly in deionized water, and dried to obtain self-assembled CuNp-GNS/PU films. The morphology of the multi-layered films were characterized with a field emission scanning electron microscope (FE-SEM, Hitachi S-4700) and atomic force microscope (AFM, PSIA XE-100). The electrical property was analysed by the I-V measurement system and the optical property was measured by the UV/VIS spectroscopy.

• Korean Journal of Clinical Laboratory Science
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• v.36 no.1
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• pp.43-48
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• 2004

Cerebral vasoreactivity is an index of autoregulation of cerebral perfusion, and can be measured using functional images such as Xe CT, SPECT and PET in reponse to hypercapneic stimulus. In order to measure cerebral $CO_2$ vasoreactivity in routine TCD study conveniently and reliably, we devised a method of rebreathing into closed volume of reservoir bag as a hypercapneic stimulus, and applied it to 44 healthy volunteers. As a hypercapneic stimulus, we applied fitting mask connected with closed reservoir bag for about 90 seconds, and mean blood flow velocity(MBFV) and pulsatility index(PI) were evaluated at proximal middle cerebral arteries(MCA) of 50-55 mm depth, before and after the hypercapneic stimulus. Age affected the MFV and PI value showed significant and the MFV was 56.45(SD=9.75)cm/sec, while PI was 0.406(SD=0.089). As age increases the flow velocity decreased significantly whereas PI value increased(P<0.05). The vasoreactvity significantly decreased with age(P<0.05). The decrease of cerebral blood flow quantity and cerebral blood flow velocity is not only because of increase of diameter of cerebrovascular resulting from aging, but the resistance increase of small blood vessel resulting from the increase of PI & RI value is regarded. We suppose that the rebreathing method is a reliable and convenient technique as a hypercapneic stimulus in determining cerebral $CO_2$ vasoreactivity. The rebreathing method could be non-invasive and useful methods in estimation of the cerebrovascular reactivity and could be applied to the basal and follow-up evaluation of the cerebrovascular reserve of the ischemic stroke patients.

• Journal of Hydrogen and New Energy
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• v.18 no.2
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• pp.109-115
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• 2007

Solar energy conversion to hydrogen was carried out via a two-step thermochemical water splitting using metal oxide redox pair. To simulate the solar radiation, a 7 kW short arc Xe-lamp was used. Partially reduced iron oxide and cerium oxide have the water splitting ability, respectively. So, $Fe_3O_4$ supported on $CeO_2$ was selected as the active material. $Fe_3O_4/CeO_2$(20 wt/80 wt%) was prepared by impregnation method, then the active material was washcoated on the ceramic honeycomb monolith made of mullite and cordierite. Oxygen was released at the reduction step($1673{\sim}1823\;K$) and hydrogen was produced from water at lower temperature($873{\sim}1273\;K$). The result demonstrate the possibility of the 2-step thermochemical water splitting hydrogen production by the active material washcoated monolith. And hydrogen and oxygen was produced separately without any separation process in a monolith installed reactor. But the SEM and EDX analysis results revealed that the support used in this experiment is not suitable due to the thermal instability and coating material migration.

• Journal of the Korean Ceramic Society
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• v.45 no.6
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• pp.331-335
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• 2008

The purpose of this study is to characterize the photo-catalytic efficiency of $TiO_2$ nanotube with respect to the distribution of anatase phase which can be changed by the annealing temperature of $TiO_2$ nanotube. $TiO_2$ nanotube was fabricated by the anodization method in the 0.5 wt% HF electrolyte. And then the $TiO_2$ nanotube was annealed at temperatures ranging from $380^{\circ}C$ to $780^{\circ}C$ in dry oxygen ambient for 2 h. For the photo-catalytic water-splitting tests, the photocurrent density was measured as a function of applied potential with a potentiostat using a Ag/AgCl reference, Pt counter electrode, and 1 M KOH electrolyte under illumination of UV by a Xe arc lamp of 1 KW. According to the UV photo-catalytic water-splitting tests, the nanotube annealed at $560^{\circ}C$ was found to show the highest photocurrent density.

• Proceedings of the Korean Nuclear Society Conference
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• 1995.05a
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• pp.707-712
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• 1995

Grain boundary diffusion plays significant role in the fission gas release, which is one of the crucial processes dominating nuclear fuel performance. Gaseous fission products such as Xe and Kr generated inside fuel pellet have to diffuse in the lattice and in the grain boundary before they reach open space in the fuel rod. In the mean time, the grains in the fuel pellet grow and shrink according to grain growth kinetics, especially at elevated temperature at which nuclear reactors are operating. Thus the boundary movement ascribed to the grain growth greatly influences the fission gas release rate by lengthening or shortening the lattice diffusion distance, which is the rate limiting step. Sweeping fission gases by the moving boundary contributes to the increment of the fission gas release as well. Lattice and grain boundary diffusion processes in the fission gas release can be studied by 'tracer diffusion' technique, by which grain boundary diffusion can be estimated and used directly for low burn-up fission gas release analysis. However, even for tracer diffusion analysis, taking both the intragranular grain growth and the diffusion processes simultaneously into consideration is not easy. Only a few models accounting for the both processes are available and mostly handle them numerically. Numerical solutions are limited in the practical use. Here in this paper, an approximate analytical solution of the lattice and stationary grain boundary diffusion in a polycrystalline solid is developed for the tracer diffusion techniques. This short closed-form solution is compared to available exact and numerical solutions and turns out to be acceptably accurate. It can be applied to the theoretical modeling and the experimental analysis, especially PIE (post irradiation examination), of low burn up fission. gas release.

• Korean Journal of Optics and Photonics
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• v.10 no.2
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• pp.152-156
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• 1999

We have developed the pulse-width variable Quenched Dye Laser (QDL). QDL consisted of the dye cell of 5 mm length containing a $2.5{\times}10^{-3}$[mol/l] solution of Rhodamine 6G and the cylindrical lens focal length of 150 mm and quenching mirror. QDL system was pumped by s XeCl excimer laser with 150 mJ pulse energy in a 20 ns pulse at 1 Hz repetition rate. Pulse-width of QDL was measured by a noncollinear intensity autocorrelator. The focused thckness was measured by changing the position of the focusing cylindrical lens. Pulse-width of QDL as a function of the focused thickness (273.0${\mu}{\textrm}{m}$~845.0${\mu}{\textrm}{m}$) varied continuously from 86 ps to 201 ps.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.444-444
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• 2011

Recently, patterned magnetic films and elements attract a wide interest due to their technological potentials in ultrahigh-density magnetic recording and spintronic devices. Among those patterned magnetic structures, magnetic anti-dot patterning induces a strong shape anisotropy in the film, which can control the magnetic properties such as coercivity, permeability, magnetization reversal process, and magneto-resistance. While majority of the previous works have been concentrated on anti-dot arrays with a single magnetic layer, there has been little work on multilayered anti-dot arrays. In this work, we report on study of the magnetic properties of bilayered anti-dot system consisting of upper perforated Co layer of 40 nm and lower continuous Ni layer of 5 nm thick, fabricated by photolithography and wet-etching processes. The magnetic hysteresis (M-H) loops were measured with a superconducting-quantum-interference-device (SQUID) magnetometer (Quantum Design: MPMS). For comparison, investigations on continuous Co thin film and single-layer Co anti-dot arrays were also performed. The magnetic-domain configuration has been measured by using a magnetic force microscope (PSIA: XE-100) equipped with magnetic tips (Nanosensors). An external electromagnet was employed while obtaining the MFM images. The MFM images revealed well-defined periodic domain networks which arise owing to the anisotropies such as magnetic uniaxial anisotropy, configurational anisotropy, etc. The inclusion of holes in a uniform magnetic film and the insertion of a uniform thin Ni layer, drastically affected the coercivity as compared with single Co anti-dot array, without severely affecting the saturation magnetization ($M_s$). The observed changes in the magnetic properties are closely related to the patterning that hinders the domain-wall motion as well as to the magneto-anisotropic bilayer structure.

• Nuclear Engineering and Technology
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• v.46 no.2
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• pp.147-158
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• 2014

In order to investigate how the microstructure of fuel/matrix-interaction (FMI) layers change during irradiation, different U-7Mo dispersion fuel plates have been irradiated to high fission density and then characterized using scanning electron microscopy (SEM). Specifially, samples from irradiated U-7Mo dispersion fuel elements with pure Al, Al-2Si and AA4043 (~4.5 wt.%Si) matrices were SEM characterized using polished samples and samples that were prepared with a focused ion beam (FIB). Features not observable for the polished samples could be captured in SEM images taken of the FIB samples. For the Al matrix sample, a relatively large FMI layer develops, with enrichment of Xe at the FMI layer/Al matrix interface and evidence of debonding. Overall, a significant penetration of Si from the FMI layer into the U-7Mo fuel was observed for samples with Si in the Al matrix, which resulted in a change of the size (larger) and shape (round) of the fission gas bubbles. Additionally, solid fission product phases were observed to nucleate and grow within these bubbles. These changes in the localized regions of the microstructure of the U-7Mo may contribute to changes observed in the macroscopic swelling of fuel plates with Al-Si matrices.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.630-630
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• 2013

Recently, atomically smooth hexagonal boron nitride(h-BN) known as a white graphene has drawn great attention since the discovery of graphene. h-BN is a III-V compound and has a honeycomb structure very similar to graphene with smaller lattice mismatch. Because of strong covalent sp2bonds like graphene, h-BN provides a high thermal conductivity and mechanical strength as well as chemical stability of h-BN superior to graphene. While graphene has a high electrical conductivity, h-BN has a highly dielectric property as an insulator with optical band gap up to 6eV. Similar to the graphene, h-BN can be applied to a variety of field, such as gate dielectric layers/substrate, ultraviolet emitter, transparent membrane, and protective coatings. However, up until recently, obtaining and controlling good quality monolayer h-BN layers have been too difficult and challenging. In this work, we investigate the controlled synthesis of h-BN layers according to the growth condition, time, temperature, and gas partial pressure. h-BN is obtained by using chemical vapor deposition on Cu foil with ammonia borane (BH3NH3) as a source for h-BN. Scanning Transmission Electron Microscopy (STEM, JEOL-JEM-ARM200F) is used for imaging and structural analysis of h-BN layer. Sample's surface morphology is characterized by Field emission scanning electron microscopy (SEM, JEOL JSM-7100F). h-BN is analyzed by Raman spectroscopy (HORIBA, ARAMIS) and its topographic variations by Atomic force microscopy (AFM, Park Systems XE-100).