A STUDY ON IMPACT CHARACTERISTICS OF THE STACKING SEQUENCES IN CFRP COMPOSITES SUBJECTED TO FALLING-WEIGHT IMPACT LOADING

K.-H. IM,N.-S. PARK,Y.-N. KIM,L.-Y. YANG 한국자동차공학회 2003 International journal of automotive technology Vol.4 No.4

Electrical conductivity enhancement of epitaxially grown TiN thin films

Khim Yeong Gwang,Park Beomjin,Heo Jin Eun,Khim Young Hun,Khim Young Rok,Gu Minseon,Rhee Tae Gyu,Chang Seo Hyoung,Han Moonsup,Chang Young Jun 한국물리학회 2023 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.82 No.5

Titanium nitride (TiN) presents superior electrical conductivity with mechanical and chemical stability and compatibility with the semiconductor fabrication process. Here, we fabricated epitaxial and polycrystalline TiN (111) thin flms on MgO (111), sapphire (001), and mica substrates at 640℃ and room temperature by using a DC sputtering, respectively. The epitaxial flms show less amount of surface oxidation than the polycrystalline ones grown at room temperature. The epitaxial flms show drastically reduced resistivity (~ 30 micro-ohm-cm), much smaller than the polycrystalline flms. Temperature-dependent resistivity measurements show a nearly monotonic temperature slope down to low temperature. These results demonstrate that high-temperature growth of TiN thin flms leads to signifcant enhancement of electrical conductivity, promising for durable and scalable electrode applications.

Control of Threshold Voltage for Top-Gated Ambipolar Field-Effect Transistor by Gate Buffer Layer

Khim, Dongyoon,Shin, Eul-Yong,Xu, Yong,Park, Won-Tae,Jin, Sung-Ho,Noh, Yong-Young American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.27

<P>The threshold voltage and onset voltage for p-channel and n-channel regimes of solution-processed ambipolar organic transistors with top-gate/bottom-contact (TG/BC) geometry were effectively tuned by gate buffer layers in between the gate electrode and the dielectric. The work function of a pristine Al gate electrode (-4.1 eV) was modified by cesium carbonate and vanadium oxide to 2.1 and 5.1 eV, respectively, which could control the flat -band voltage, leading to a remarkable shift of transfer curves in both negative and positive gate voltage directions without any side effects. One important feature is that the mobility of transistors is not very sensitive to the gate buffer layer. This method is simple but useful for electronic devices where the threshold voltage should be precisely controlled, such as ambipolar circuits, memory devices, and light -emitting device applications.</P>

High Performance and Stable N-Channel Organic Field-Effect Transistors by Patterned Solvent-Vapor Annealing

Khim, Dongyoon,Baeg, Kang-Jun,Kim, Juhwan,Kang, Minji,Lee, Seung-Hoon,Chen, Zhihua,Facchetti, Antonio,Kim, Dong-Yu,Noh, Yong-Young American Chemical Society 2013 ACS APPLIED MATERIALS & INTERFACES Vol.5 No.21

<P>We report the fabrication of high-performance, printed, <I>n</I>-channel organic field-effect transistors (OFETs) based on an <I>N</I>,<I>N</I>-dialkyl-substituted-(1,7&1,6)-dicyanoperylene-3,4:9,10-bis(dicarboximide) derivative, PDI-RCN2, optimized by the solvent-vapor annealing (SVA) process. We performed a systematic study on the influence of solubility and the chemical structure of a solvent used for the SVA process on the ordering and orientation of PDI-RCN2 molecules in the thin film. The PDI-RCN2 film showed improved crystallinity under vapor annealing with the aliphatic 1,2-dichloroethane (DCE) as a marginal solvent. The <I>n</I>-type OFETs with DCE-vapor-annealed PDI-RCN2 show highly improved charge-carrier mobility of ∼0.5 cm<SUP>2</SUP> V<SUP>–1</SUP> s<SUP>–1</SUP> and higher stability under gate bias stress than the pristine OFETs. This large performance improvement was mainly attributed to increased crystallinity of the semiconductor thin film, enhancing π–π stacking. We also introduced a new method to pattern crystallinity of a certain region in the semiconducting film by selective exposure to the solvent vapor using a shadow mask. The crystal-patterned PDI-RCN2 OFETs exhibit decreased off-currents by ∼10× and improved gate bias stability by minimizing crosstalk, reducing leakage current between devices, and reducing the density of charge trap states of the organic semiconductor.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2013/aamick.2013.5.issue-21/am4029075/production/images/medium/am-2013-029075_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am4029075'>ACS Electronic Supporting Info</A></P>

Oxygen Isotope Profile and Age Determination of venus Clam Mercenaria stimpsoni (Bivalvia: Veneridae) from the East Sea

Khim, Boo-Keun,Je Jong-Geel,Han, Sang-Joon,Woo, Kyung-Sik,Park, Yong-ahn 江原大學校 附設 環境硏究所 1999 環境硏究 Vol.16 No.-

동해 연안에서 채취된 뷔나스백합(Mercenaria stimpsoni)의 연령과 성장률을 이매패의 표면에서 확인된 연륜과 이매패 각질에서 분석된 산소동위원소비의 성장에 따른 변화를 이용하여 비교 하였다. 뷔닉스백합의 산소동위원소상은 일련의 주기적인 변화를 뚜렷하게 보여주며 이러한 변화 진폭은 이매패가 성장한 해수의 온도변화에 일차적으로 제어된다. 산소동위원소상의 주기와 연륜의 관계로부터 뷔나스백합의 연륜이 해마다 여름철에 형성됨을 보여준다. 해수 온도의 계절적 변화와 · 산소 동위원소비에서 얻어진 예측 온도와의 비교로부터, 뷔나스백합은 겨울철에 성장이 멈추는 것으로 사료된다. 또한 산소동위원소비는 뷔나스백합의 성장에 따른 전형적인 노화현상을 보여준다. 따라서 이매패가 성장하는 해수의 물리화학적 조건에 의해 제어되는 산소동위원소비는 뷔나스백합의 경우 연령과 성장률을 측정하는 독립적인 시간 척도가 될 수 있다.

Chronostratigraphy and paleoceanography of a piston core (EBP-3) from the South Korea Plateau in the East Sea (Japan Sea)

Khim, B.K.,Bahk, J.J. Pergamon Press 2014 Quaternary international Vol.344 No.-

A piston core (EBP-3) collected from the South Korea Plateau in the East Sea (Japan Sea) preserved typical alternations of thick, dark laminated mud layers and bioturbated hemipelagic mud layers, but included several intercalated volcanic lapilli layers. The age estimate of core EBP-3 was aided by correlation of biostratigraphic radiolarian data, the abundance of microfossils (warm-water radiolarians), and geochemical properties (CaCO<SUB>3</SUB>) with the proxies of the well-dated core MD01-2407 obtained from the Oki Ridge. A part from the Marine Isotope Stage (MIS) 11 to MIS 9 in the middle of core EBP-3 was missing, presumably because of erosion following the abrupt deposition of a volcanic lapilli layer. Despite some uncertainty, the age estimate of core EBP-3 revealed that the lower part of core EBP-3 represents MIS 13, as was also evident from a comparison with the oxygen isotope stratigraphy. Downcore biogenic opal and CaCO<SUB>3</SUB> variations in core EBP-3 exhibited less distinct orbital-scale cyclic changes than cores from other areas in the East Sea (Japan Sea). However, differences in features were discernible between MIS 2 and MIS 12 in terms of their lithology and CaCO<SUB>3</SUB> constituent, although both periods were characterized by relatively high levels of CaCO<SUB>3</SUB> (about 30% for MIS 2 and about 50% for MIS 12). MIS 2 preserved a typical thick, dark laminated mud layer, whereas MIS 12 preserved a distinctly light mud layer with thin parallel laminations. This difference of the lithologic facies between MIS 2 and MIS 12 highlighted a discrepancy among the major constituents, indicating that planktonic foraminifera were dominant in MIS 2, whereas coccolithophores were dominant in MIS 12. Our results suggest that the thinly-laminated light mud layer, which is characterized by a high CaCO<SUB>3</SUB> content primarily composed of coccolithophores in MIS 12, can be used as a reliable time marker for the establishment of chronostratigraphy in the East Sea.

A Vacuum-Compatible Air Bearing: Design Analysis and Optimization

Khim, G.H.,Park, Chun Hong,Lee, H.S.,Kim, S.W. Trans Tech Publications, Ltd. 2007 Key Engineering Materials Vol.339 No.-

<P>This paper describes the vacuum-compatible air bearing designed with a cascaded exhaust scheme to minimize the leakage of air in a vacuum environment. The design of the air bearing, including the differential exhaust system, required great care because several design parameters, such as the number of exhaust stages, diameter and length of the exhaust tube, pumping speed and ultimate pressure of the vacuum pump, and seal length and gap greatly influenced the leakage of air and thus the degree of vacuum. A leakage analysis was performed to estimate the chamber pressure and an optimization method based on the genetic algorithm was proposed under several constraint conditions. The results showed that the degree of vacuum improved dramatically compared to the initial design, and that the distribution of the spatial design parameters and technical limit of the pumping speed were well achieved.</P>

Different nature of glacial CaCO₃ constituents between MIS 2 and MIS 12 in the East Sea/Japan Sea and its paleoceanographic implication

Khim, B.K.,Tada, R.,Itaki, T. Pergamon Press 2014 QUATERNARY INTERNATIONAL Vol.333 No.-

Two piston cores (PC-05 and PC-08) were collected on the Yamato Rise in the East Sea/Japan Sea during the KR07-12 cruise. Both cores showed typical alternations of light (high L*) and dark (low L*) layers, which are characteristic in the hemi-pelagic sediment deposited in the deep part of the East Sea/Japan Sea. A composite core was achieved with the successful replacement of almost half of the upper part of core PC-05 by the entirety of core PC-08 based on the co-equivalence of L* values and the dark layers, because an interval (170 cm-410 cm) of core PC-05 was considerably disturbed due to fluidization during the core execution. Chronostratigraphy of the composite core was constructed by the direct comparison of L* values to the well-dated core MD01-2407 that was obtained in the Oki Ridge. The lower-bottom of the composite core extended to Marine Isotope Stage (MIS) 14, based on the age estimate by LR04 stacks. Downcore opal variation of the composite core exhibited the distinct orbital-scale cyclic changes; high during the interglacial and low during the glacial periods. However, downcore CaCO<SUB>3</SUB> variation showed no corresponding orbital-scale cyclic change between glacial and interglacial periods. Some intervals of both periods were high in CaCO<SUB>3</SUB> content. Frequent and large fluctuations in CaCO<SUB>3</SUB> content seemed to be more related to the presence of dark layers containing thin lamination (TL) within the glacial and interglacial intervals. It is worthy to note that MIS 2 and MIS 12 are characterized by distinctly high CaCO<SUB>3</SUB> content, showing up to 18% and 73%, respectively, among the glacial periods. Furthermore, in terms of lithology, MIS 2 was characterized by a thick dark layer (low L* values) with TL, whereas MIS 12 preserved the distinctly light layer (high L* values) with parallel laminations. Another remarkable dissimilarity between MIS 2 and MIS 12 was the nature of their CaCO<SUB>3</SUB> constituent; the CaCO<SUB>3</SUB> constituent of MIS 2 consisted of mostly planktonic foraminifera, whereas that of MIS 12 was mostly dump of coccolithophorids, regardless the presence of planktonic foraminifera. The distinctness of the CaCO<SUB>3</SUB> constituents between MIS 2 and MIS 12 indicates that the preservation of CaCO<SUB>3</SUB> contents was different temporarily during the glacial periods in the East Sea/Japan Sea. Enhanced CaCO<SUB>3</SUB> preservation in MIS 2 is attributed primarily to less dissolution during the sinking through the water column or at the seafloor, but increased CaCO<SUB>3</SUB> preservation in MIS 12 is mainly due to the high primary production in the surface water. With respect to the different function of the biological pump which controls CO<SUB>2</SUB> cycles, the East Sea/Japan Sea clearly experienced carbonate-ocean-like state during MIS 12, despite normally silica-ocean-like state.

Orbital Variations of Biogenic CaCO3 and Opal Abundance in the Western and Central Equatorial Pacific Ocean During the Late Quaternary

Khim, Boo-Keun,Kim, Hyung Jeek,Cho, Young Seuk,Chi, Sang Bum,Yoo, Chan Min Chinese Geoscience Union 2012 TAO Vol.23 No.1

A Three-axis Translation Stage Using Opposing Wedges with Error Compensation

Khim, Gyung-Ho,Ro, Seung-Kook,Park, Jong-Kweon,Ehmann, Kornel 한국정밀공학회 2012 International Journal of Precision Engineering and Vol.13 No.3

We describe the development of a three-axis translation stage using wedges and its motion error compensation. The three-axis stage uses three wedges and is capable of translation in the vertical and longitudinal directions by controlling the horizontal separation of two opposing wedges. An independent linear translation stage is used to achieve displacement along the third axis. Compensation for straightness and positioning errors is achieved using the combined motion of the two opposing wedges and the motion of an independent linear stage. The straightness error in the vertical and horizontal directions through the longitudinal axis was 0.83 ${\mu}m$ and 1.65 ${\mu}m$, respectively, before compensation and 0.22 ${\mu}m$ and 0.29 ${\mu}m$ with error compensation. The positioning error through the longitudinal axis was reduced from 8.96 ${\mu}m$ to 0.85 ${\mu}m$.