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Kim, Sunbo,Jung, Junhee,Kim, YoungKuk,Le, Anh Huy Tuan,Ahn, Shihyun,Park, Jinjoo,Kim, Yongjun,Dao, Vinh Ai,Lee, Jaehyeong,Lee, Youn-Jung American Scientific Publishers 2017 Journal of Nanoscience and Nanotechnology Vol.17 No.5
<P>This study investigates the effect of hydrogen gas ratio [H-2/H-2+Ar] had on the structural, optical and electrical properties of ITO films for use in amorphous/crystalline silicon hetero-junction solar cells. The pulsed DC magnetron sputtered ITO films showed a higher optical transmittance for a hydrogen gas ratio of 3.2%. The lowest sheet resistance (43.12 Omega/square) and resistivity (3.25x10(-4) Omega.cm) were observed for ITO films where the hydrogen gas ratio was in the range from 1.31 to 3.22%. The Hall mobility of the ITO films decreased from 55.3 to 42.5 cm(2)/V.s with an increase in the hydrogen gas ratio from 1.31 to 3.2%. The surface morphology and crystallinity of films improved for the low hydrogen gas ratio while the characteristics of the ITO films deteriorated when the hydrogen ratio was higher than 3.2%. Then, we fabricated amorphous/crystalline silicon hetero-junction solar cells using ITO films for the front anti-reflection layer, and a hydrogen gas ratio of 3.22% resulted in a short circuit current density (J(sc)) of 38.17 mA/cm(2) and an efficiency of 19.02%.</P>
Atomic-scale mechanism of grain boundary motion in graphene
Kim, Dongwook,Kim, Youngkuk,Ihm, Jisoon,Yoon, Euijoon,Lee, Gun-Do Elsevier 2015 Carbon Vol.84 No.-
<P><B>Abstract</B></P> <P>Grain boundaries (GBs) in graphene can migrate when irradiated by electron beams from a transmission electron microscope (TEM). Here, we present an <I>ab initio</I> study on the atomic scale-mechanism for motion of GB with misorientation angle of ∼30° in graphene. From total energy calculations and energy barrier calculations, we find that a Stone–Wales (SW)-type transformation can occur more easily near GBs than in pristine graphene due to a reduced energy barrier of 7.23eV; thus, this transformation is responsible for the motion of GBs. More interestingly, we find that a mismatch in the crystalline orientation at GBs can drive the evaporation of a carbon dimer by greatly reducing the corresponding overall energy barrier to 11.38eV. After evaporation of the carbon dimer, the GBs can be stabilized through a series of SW-type transformations that result in GB motion. The GB motion induced by evaporation of the dimer is in excellent agreement with recent TEM experiments. Our findings elucidate the mechanism for the dynamics of GBs during TEM experiments and enhance the controllability of GBs in graphene.</P>
Youngkuk Kim 한양대학교 세라믹연구소 2012 Journal of Ceramic Processing Research Vol.13 No.S1
Wide band gap p-type hydrogenated amorphous silicon oxide (a-SiO:H) buffer layer has been used at the interface of transparent conductive oxide (TCO) and hydrogenated amorphous silicon (a-Si:H) p-type layer of a p-i-n type a-Si:H solar cell. Introduction of 5 nm thick buffer layer improves in blue response of the cell along with 0.5% enhancement of photovoltaic conversion efficiency (η). The cells with buffer layer show higher open circuit voltage (Voc), fill factor (FF), short circuit current density (Jsc) and improved blue response with respect to the cell without buffer layer.
모멘트 하중을 고려한 볼베어링의 하중분배, 접촉 및 피로수명 해석
김영국(Youngkuk Kim),문석만(Seokman Moon),김태완(Taewan Kim),조용주(Yongjoo Cho) 한국트라이볼로지학회 2011 한국트라이볼로지학회지 (Tribol. Lubr.) Vol.27 No.3
This study is aimed to predict the fatigue life for bearings under combined radial, thrust and moment load. In order to do this, a series of simulation such as bearing load distribution, initial surface stress, subsurface stress and fatigue analysis is needed. And using the bearing’s material fatigue property we can predict fatigue life for ball bearing.