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허진희,Youngmok Rhyim 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.9
In this study, we designed and fabricated a poly-Si-based solar cell device by using conventional Si processes. The electrical properties, such as the open-circuit voltage (V<sub>oc</sub>), the short-circuit current (I<sub>sc</sub>), the fill factor, the external quantum efficiency (EQE) and the efficiency of prepared solar cell devices, were characterized with a standardized measurement system. Also, the correlation between the photoinduced current and the variation of the defect density was then investigated for various locations by using a photoconductive atomic force microscopy (PC-AFM) system. We verified that in a high-defect-density region such as a grain boundary, a triple junction or a crack, photoinduced carriers easily recombined and induced a decrease in the diffusion length and a low level of photoinduced current. Moreover, we suggest a very effective method to reduce the contact resistance between the cantilever tip and the sample surface, which can disturb the flow of photoinduced current.
Microstructure and Wear-Resistance of Fe-Cr-B Base Metamorphic Alloys
Jin, H W,Rhyim, Y M,Park, C G,Kim, M C 대한금속재료학회(대한금속학회) 1997 METALS AND MATERIALS International Vol.3 No.1
Metamorphic (crystalline-to-amorphous) transition and consequent microstructural change were investigated in relation with the wear-resistance during the wear process of Fe-base metamorphic coating layer. The spray coating was accomplished using a detonation gun with various fuel gas conditions. The spray coated layer exhibited significantly improved wear resistance, which is about 45 times higher than that of the noncoated substrate. The significantly low friction coefficient and high hardness, resulting from the presence of amorphous surface film, seems to be the main cause of the improved wear-resistance. Electron microscopy on the cross-section of the coated layer exhibited intra-particle micro-segregations associated with rod-shape Cr and B rich particles and Fe-Cr solid solution phase. From the observations using TEM and EDS, Fe-Cr solid solution with supersaturated B and Si content seems to be the main phase contributing to the crystalline-to-amorphous transition during wear.
Characterization of zirconium hydrides in Zircaloy-4 cladding with respect to cooling rate
Kim, Sung-Dae,Rhyim, Youngmok,Kim, Ju-Seong,Yoon, Jonghun Elsevier 2015 Journal of nuclear materials Vol.465 No.-
<P><B>Abstract</B></P> <P>In order to characterize the habit planes and crystallographic relation between the α-matrix and various kinds of Zr hydrides, three different Zr hydrides including δ-hydride, γ-hydride, and surface hydride are produced by controlling the cooling rate from 0.5 to 300 °C/min. Analysis of SAED patterns and TEM images of the Zr hydrides demonstrates representative habit planes and crystallographic relation according to the hydride morphologies. The macroscopic δ-hydride has two kinds of habit planes such as <SUB> { 10 1 ¯ 7 } α </SUB> and <SUB> { 0002 } α </SUB> , while microscopic δ-hydride has the habit plane of <SUB> { 0002 } α </SUB> at the cooling rate of 0.5–10 °C/min. The microscopic γ-hydride has the major habit plane of <SUB> { 10 1 ¯ 7 } α </SUB> at the cooling rate of 300 °C/min in which the crystallographic relation between the γ-hydride and the α-Zr matrix as <SUB> ( 11 1 ¯ ) γ </SUB> ‖ <SUB> ( 01 1 ¯ 1 ) α </SUB> ; <SUB> ( 111 ) γ </SUB> ‖ <SUB> ( 0001 ) α </SUB> ; <SUB> [ 1 1 ¯ 0 ] γ </SUB> ‖ <SUB> [ 11 2 ¯ 0 ] α </SUB> .</P>
An Evaluation of Thermal Fatigue Cracking and Chemical Reaction in Die Casting Mould
Youn, Kuk Tae,Rhyim, Young Mok,Lee, Jong Hoon,Lee, Chan Gyu,Jung, Yun Chul Trans Tech Publications, Ltd. 2007 Key Engineering Materials Vol.345-346 No.-
<P>It is well known that the main failure mechanisms in die-casting mould are heat checking due to thermal fatigue and melt-out caused by chemical reaction between die and molten alloys. Thermal fatigue tests were carried out using the thermal cycle simulator to establish the proper method to estimate the thermal fatigue resistance of hot die steel. In this study, the thermal shock tester consisted of induction heating and water spray cooling unit was constructed to evaluate thermal crack propagation resistance and the sum of crack length per unit specimen length, Lm is proposed as the index representing the susceptibility to crack initiation and propagation. Also, new concept of measurement for the melt-out behavior was suggested. AISI H13 hot work tool steel was solution treated and tempered at various temperatures, to control the hardness and toughness that have effect on the behavior of thermal crack propagation. The result of thermal fatigue test showed that there is optimum value of hardness and impact energy to maximize the thermal crack propagation resistance. The influence of nitriding on melt-out resistance was also investigated. The dissolution rate due to melt-out phenomenon tended to be smaller for thicker compound layer. Furthermore, the resistance to melt-out was affected by the compound layer thickness rather than that of diffusion layer. The results of the both tests properly reflect the effect of materials properties on failure modes of die-casting mould and it means those test methods are suitable to evaluate the durability of hot work tool steel for die-casting.</P>
천소영,임영목,김두현,이재호,Chun, So-Young,Rhyim, Young-Mok,Kim, Doo-Hyun,Lee, Jae-Ho 한국마이크로전자및패키징학회 2010 마이크로전자 및 패키징학회지 Vol.17 No.1
다공성 탄소전극기지 위의 무전해 니켈도금에 관한 연구를 하였다. 다공성 탄소전극기지로는 다공도가 20 ${\mu}m$ 이상인 것과 16~20 ${\mu}m$ 인 것을 사용하였다. 소수성인 탄소 표면은 $60^{\circ}C$ 이상의 암모니아 용액에 침적함으로써 그 표면 성질이 친수성으로 변화 되었고, 40분 이상 침적 시 접촉각이 $20^{\circ}$ 이하까지 측정 되었다. 도금욕의 pH가 증가됨에 따라 탄소기지 위에 도금된 니켈 도금층의 인의 석출량은 감소하였으며 니켈 도금층이 결정질 구조를 갖는 현상이 관찰되었다. 도금층의 두께는 pH가 증가함에 따라 증가하였다. 활성화 처리를 위한 $PdCl_2$의 농도에 따른 도금층의 두께 변화는 없었으나, 도금에 필요한 $PdCl_2$의 최소농도는 5 ppm 이상인 것으로 나타났다. Electroless nickel plating on porous carbon substrate was investigated. The pore sizes of carbon substrates were 16-20 ${\mu}m$ and over 20 ${\mu}m$. The carbon surface was changed from hydrophobic to hydrophilic after immersing the substrate in an ammonia solution for 40 min at $60^{\circ}C$. The contact angle of water was decreased from $85^{\circ}$ to less than $20^{\circ}$ after ammonia pretreatment. The content of phosphorous in nickel deposit was decreased with increasing pH and then deposits became crystallized. The thickness of nickel deposit was increased with increasing pH. The minimum concentration of $PdCl_2$ for the electroless nickel plating was 5 ppm and the thickness of nickel was not significantly affected by the concentration of $PdCl_2$.
Enhanced polarization by the coherent heterophase interface between polar and non-polar phases
Kim, G. Y.,Sung, K. D.,Rhyim, Y.,Yoon, S. Y.,Kim, M. S.,Jeong, S. J.,Kim, K. H.,Ryu, J.,Kim, S. D.,Choi, S. Y. Royal Society of Chemistry 2016 Nanoscale Vol.8 No.14
<P>A piezoelectric composite containing the ferroelectric polar (Bi(Na0.8K0.2)(0.5)TiO3: f-BNKT) and the non-polar (0.94Bi(Na0.75K0.25)(0.5)TiO3-0.06BiAlO(3): BNKT-BA) phases exhibits synergetic properties which combine the beneficial aspects of each phase, i.e., the high saturated polarization (P-s) of the polar phase and the low coercive field (E-c) of the non-polar phase. To understand the origin of such a fruitful outcome from this type of polar/non-polar heterophase structure, comprehensive studies are conducted, including transmission electron microscopy (TEM) and finite element method (FEM) analyses. The TEM results show that the polar/non-polar composite has a core/shell structure in which the polar phase (core) is surrounded by a non-polar phase (shell). In situ electrical biasing TEM experiments visualize that the ferroelectric domains in the polar core are aligned even under an electric field of similar to 1 kV mm(-1), which is much lower than its intrinsic coercive field (similar to 3 kV mm(-1)). From the FEM analyses, we can find that the enhanced polarization of the polar phase is promoted by an additional internal field at the phase boundary which originates from the preferential polarization of the relaxor-like non-polar phase. From the present study, we conclude that the coherent interface between polar and non-polar phases is a key factor for understanding the enhanced piezoelectric properties of the composite.</P>
전제춘,이종수,임영목,정희돈 대한금속재료학회(대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.11
The crack closure phenomenon is important in the aspect of effecitve driving force for crack growth. Therefore, the precise measurement of crack closure load is an essential prerequisite for the determination of the effective driving force. In this study, the acoustic emission(AE) technique was employed as one of crack closure measurement methods and the results were compared with those of crack opening displacement method(CD), back face strain gage method(BFS) and surface strain gage method. Results have shown that the intrinsic fatigue Life curve(da/dN vs. ΔK_(eff)) obtained by use of the AE technique vvas best fit with the curve of high stress ratio (R=0.8) test, which implied that the AE technique could be considered as a reliable crack closure measurement method.