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K.-H. IM,N.-S. PARK,Y.-N. KIM,L.-Y. YANG 한국자동차공학회 2003 International journal of automotive technology Vol.4 No.4
This paper describes a method for a falling weight impact test to estimate the impact energy absorbing characteristics and impact strength of CFRP (Carbon-fiber reinforced plastics) laminate plates based on considerations of stress wave propagation theory, which were converted to measurements of load and displacement verses time. The delamination area of impacted specimens for the different ply orientations was measured with an ultrasonic C-scanner to determine the correlation between impact energy and delamination area. The energy absorbed by a quasi-isotropic specimen having four interfaces was higher than that of orthotropic laminates with two interfaces. The more interfaces, the greater the energy absorbed. The absorbed energy of a hybrid specimen embedding GFRP (Glass-fiber reinforced plastics) layer was higher than that of normal specimens. Also, a falling weight impact tester was built to evaluate the characteristics and impact strength of CFRPs.
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.
Khim, Dongyoon,Han, Hyun,Baeg, Kang‐,Jun,Kim, Juhwan,Kwak, Sun‐,Woo,Kim, Dong‐,Yu,Noh, Yong‐,Young WILEY‐VCH Verlag 2013 ADVANCED MATERIALS Vol.25 No.31
<P><B>Large‐area polymer FET arrays and integrated circuits (ICs)</B> are successfully demonstrated via a simple wire‐bar–coating process. Both a highly crystalline conjugated polymer layer and very smooth insulating polymer layer are formed by a consecutive wire‐bar–coating process on a 4‐inch plastic substrate with a short processing time for application as the active and dielectric layers of OFET arrays and ICs.</P>
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>
Khim, Dongyoon,Baeg, Kang-Jun,Kim, Juhwan,Yeo, Jun-Seok,Kang, Minji,Amegadzea, Paul S. K.,Kim, Mu-Gyeom,Cho, Joonhyuk,Lee, Jung Hun,Kim, Dong-Yu,Noh, Yong-Young The Royal Society of Chemistry 2012 Journal of materials chemistry Vol.22 No.33
<P>Here we report the effects of a Cs-salt based charge injection interlayer on the characteristics of top-gate/bottom-contact (TG/BC) ambipolar polymer OFETs with poly(thienylenevinylene-co-phthalimide)s functionalized at the imide nitrogen with dodecyl (PTVPhI-C12). P-channel dominant PTVPhI-C12 ambipolar OFETs showed both an improved electron injection and blocked hole injection properties by insertion of a thermally deposited thin CsF interlayer between Au source/drain electrodes and the organic semiconductor. X-ray and UV photoelectron spectroscopy results exhibited that the work-function of the Au electrode progressively changed from −4.5 eV to −3.9 eV and the Fermi levels of PTVPhI-C12 concomitantly moved towards the LUMO level of the conjugated polymer with an increase of CsF thickness from 0 nm to 1.5 nm, respectively. Both the shifting of Au work-function and the molecular doping of PTVPhI-C12 by insertion of CsF provide an order of magnitude improved n-channel properties in p-channel dominant ambipolar PTVPhI-C12 OFETs. In the end, the characteristics of the PTVPhI-C12 complementary inverter were improved (gain > 23) by a selective deposition and optimization of the CsF interlayer thickness on the n-channel region of ambipolar CMOS inverters.</P> <P>Graphic Abstract</P><P>Here we report the effects of a Cs-salt based charge injection interlayer on the characteristics of top-gate/bottom-contact ambipolar polymer OFETs. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2jm32721j'> </P>
Khim, T.-Y.,Shin, M.,Park, B.-G.,Lee, H.,Park, J.-H. American Institute of Physics 2014 JOURNAL OF APPLIED PHYSICS - Vol.115 No.23
We acquired direct measurements for in-plane and perpendicular-to-plane magnetic moments of Fe films using an x-ray magnetic circular dichroism technique with increase of the Fe thickness (up to 40 angstrom) on the Ag(001) surface. Epitaxial Fe/Ag(001) films were grown in situ with the thickness varying from 2 angstrom to 40 angstrom, and the magnetic anisotropy was carefully investigated as a function of the film thickness. We found re-entrance of the in-plane magnetic anisotropy of the Fe film in ultrathin region. The results manifest that the epitaxial Fe/Ag(001) film undergoes two distinct spin reorientation transitions from in-plane to out-of-plane at the film thickness t approximate to 9 angstrom and back to in-plane at t approximate to 18 angstrom as t increases. (C) 2014 AIP Publishing LLC.
Khim, Jong Seong,Park, Jinsoon,Song, Sung Joon,Yoon, Seo Joon,Noh, Junsung,Hong, Seongjin,Kwon, Bong-Oh,Ryu, Jongseong,Zhang, Xiaowei,Wang, Tieyu,Lu, Yonglong,Giesy, John P. Elsevier 2018 The Science of the total environment Vol.645 No.-
<P><B>Abstract</B></P> <P>To investigate benthic ecological quality associated with coastal pollution in the Bohai Sea and northern Yellow Sea, a sediment quality triad (SQT) approach was applied. Chemical (six groups of persistent toxic substances (PTSs) and 8 metals and metalloids), toxicological (AhR-mediated potency), and ecological (bacterial and meiofaunal communities) elements were selected and used in an integrated sediment assessment. The benthic meiofaunal community was newly analyzed and used as an additional component of the infaunal community during the SQT. Concentrations of chemicals and potential toxicity in sediments both indicated moderate to severe pollution in the study area, characterized by site-specific and land-uses. In particular, As, DDTs, and bioassay-derived dioxin equivalents exceeded corresponding sediment quality guidelines at nearly all locations. Limited occurrences of meiofaunal taxa (mean = 5.2) and relatively low species diversity, mainly comprised of nematodes (75.3%) and copepods (14.6%), among locations was generally consistent with pollution. The benthic community was consistent with compound-specific responses to gradients of contamination, particularly for As. Densities of two taxa, Nematoda and Nemertea exhibited strong negative correlations with concentrations of As. Compound-, site-, and taxa-specific variability of pollution of sediments was further supported by results of cluster analysis (CA) and nonmetric multidimensional scaling (NMDS). Finally, assessment integrating five benthic quality elements, including: 1) PTSs; 2) metals and metalloids; 3) sediment toxicity; 4) sediment microbiome; and 5) benthic meiofaunal community, explained contamination of sediments associated with land-uses, locality, or habitat. Status of the benthic community could not be explained by single component and their associations were not quantitative. Results of the integrated assessment, considering multiple benthic quality elements were useful to address overall quality of sediment, and were consistent with chemical-, species-, or site-dependent pollution of sediments in the Bohai and Yellow Seas.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Extended-sediment quality triad was applied to enhance typical benthic assessment. </LI> <LI> Sediment toxicity might be over- or under-estimate chemical pollution and benthic health. </LI> <LI> Meiofaunal abundance would be a good ecological indicator of pollution by arsenic. </LI> <LI> Moderate to severe pollution evidenced in over half of the sampling locations. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Analysis of 5-DOF Motion Errors Influenced by the Guide Rails of an Aerostatic Linear Motion Stage
Khim, Gyungho,Oh, Jeong Seok,Park, Chun Hong 한국정밀공학회 2014 International Journal of Precision Engineering and Vol.15 No.2
This paper presents an estimation method for five-degrees-of-freedom (5-DOF) motion errors, which are influenced by the profiles of guide rails of an aerostatic linear motion stage. The transfer function, which is the relationship between the magnitude of the rail form error and the reaction force of a bearing pad, was introduced to simplify and systematize the estimation of the motion errors. The motion errors were calculated from the equilibrium conditions for the forces and moments of the stage using the geometrical relationships between the bearing pads, the transfer function, and rail form errors. Experimental verification of the rail form error was carried out using a porous aerostatic linear motion stage and the mixed sequential two-probe method. The aerostatic feed table of the experimental stage, on which sensors were mounted, was also used as the feed unit for measuring the rail profiles. The 5-DOF motion errors were estimated from the measured rail form errors using the transfer function method. The estimated results were in good agreement with the experiments.