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Kim, Sungjune,Hong, Seokpyo,Ahn, Kilsoo,Gong, Sungyong The Korean Society of Environmental Toxicology 2015 환경독성보건학회지 Vol.30 No.-
Objectives This study presents the indicators and proxy variables for the quantitative assessment of green chemistry technologies and evaluates the relative importance of each assessment element by consulting experts from the fields of ecology, chemistry, safety, and public health. Methods The results collected were subjected to an analytic hierarchy process to obtain the weights of the indicators and the proxy variables. Results These weights may prove useful in avoiding having to resort to qualitative means in absence of weights between indicators when integrating the results of quantitative assessment by indicator. Conclusions This study points to the limitations of current quantitative assessment techniques for green chemistry technologies and seeks to present the future direction for quantitative assessment of green chemistry technologies.
Analog Synaptic Behavior of a Silicon Nitride Memristor
Kim, Sungjun,Kim, Hyungjin,Hwang, Sungmin,Kim, Min-Hwi,Chang, Yao-Feng,Park, Byung-Gook American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.46
<P>In this paper, we present a synapse function using analog resistive-switching behaviors in a SiNx-based memristor with a complementary metal-oxide-semiconductor compatibility and expandability to three-dimensional crossbar array architecture. A progressive conductance change is attainable as a result of the gradual growth and dissolution of the conducting path, and the series resistance of the AlOy layer in the Ni/SiNx/AlOy/TiN memristor device enhances analog switching performance by reducing current overshoot. A continuous and smooth gradual reset switching transition can be observed with a compliance current limit (>100 mu A), and is highly suitable for demonstrating synaptic characteristics. Long-term potentiation and long-term depression are obtained by means of identical pulse responses. Moreover, symmetric and linear synaptic behaviors are significantly improved by optimizing pulse response conditions, which is verified by a neural network simulation. Finally, we display the spike-timing-dependent plasticity with the multipulse scheme. This work provides a possible way to mimic biological synapse function for energy-efficient neuromorphic systems by using a conventional passive SiNx layer as an active dielectric.</P>
Kim, Sungjun,Jang, Segeun,Kim, Sang Moon,Ahn, Chi-Yeong,Hwang, Wonchan,Cho, Yong-Hun,Sung, Yung-Eun,Choi, Mansoo Elsevier Sequoia 2017 Journal of Power Sources Vol. No.
<P><B>Abstract</B></P> <P>This work reports the successful reduction in methanol crossover by creating a thin cracked metal barrier at the interface between a Nafion<SUP>®</SUP> membrane and an electrode in direct methanol fuel cells (DMFCs). The cracks are generated by simple mechanical stretching of a metal deposited Nafion<SUP>®</SUP> membrane as a result of the elastic mismatch between the two attached surfaces. The cracked metal barriers with varying strains (∼0.5 and ∼1.0) are investigated and successfully incorporated into the DMFC. Remarkably, the membrane electrode assembly with the thin metal crack exhibits comparable ohmic resistance as well as reduction of methanol crossover, which enhanced the device performance.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A thin, cracked metal layer on PEM is fabricated by simple method. </LI> <LI> The cracked metal layer reduces fuel crossover without affecting PEM conductivity. </LI> <LI> A MEA with the layer shows superior performance compared to conventional one. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Kim, Min Jeong,Kim, Ok-Hee,Kim, Sungjun,Choi, Young-Woo,Cho, Yong-Hun,Sung, Yung-Eun Elsevier 2018 Journal of industrial and engineering chemistry Vol.61 No.-
<P><B>Abstract</B></P> <P>In this study, by treating not only the membrane but also the whole membrane electrode assembly (MEA) with KOH solution prior to incorporation in alkaline anion exchange membrane fuel cells, an ionic pathway for hydroxide conduction has optimized in the catalyst layer. This lowers the ohmic resistance of the KOH-treated MEA as detected by the polarization curve and impedance spectroscopy analysis. The process has greater advantage for non-platinum group metal (PGM) catalysts than PGM catalysts, because of the lower active site density and consequent high loading required for non-PGM catalysts.</P> <P><B>Highlights</B></P> <P> <UL> <LI> AEMFC is improved by immersing the whole MEA in KOH solution before cell operation. </LI> <LI> KOH treatment reduces the ionic resistance in the catalyst layer. </LI> <LI> AEFMC prepared using a non-PGM catalyst shows higher performance improvement than one prepared with a Pt/C catalyst after treatment of MEA. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Kim, Sungjun,Lin, Chih-Yang,Kim, Min-Hwi,Kim, Tae-Hyeon,Kim, Hyungjin,Chen, Ying-Chen,Chang, Yao-Feng,Park, Byung-Gook Springer US 2018 NANOSCALE RESEARCH LETTERS Vol.13 No.1
<P>This letter presents dual functions including selector and memory switching in a V/SiO<SUB><I>x</I></SUB>/AlO<SUB><I>y</I></SUB>/p<SUP>++</SUP>Si resistive memory device by simply controlling compliance current limit (CCL). Unidirectional threshold switching is observed after a positive forming with low CCL of 1 μA. The shifts to the V-electrode side of the oxygen form the VO<SUB><I>x</I></SUB> layer, where the threshold switching can be explained by the metal-insulation-transition phenomenon. For higher CCL (30 μA) applied to the device, a bipolar memory switching is obtained, which is attributed to formation and rupture of the conducting filament in SiO<SUB><I>y</I></SUB> layer. 1.5-nm-thick AlO<SUB><I>y</I></SUB> layer with high thermal conductivity plays an important role in lowering the off-current for memory and threshold switching. Through the temperature dependence, high-energy barrier (0.463 eV) in the LRS is confirmed, which can cause nonlinearity in a low-resistance state. The smaller the CCL, the higher the nonlinearity, which provides a larger array size in the cross-point array. The coexistence of memory and threshold switching in accordance with the CCL provides the flexibility to control the device for its intended use.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (10.1186/s11671-018-2660-9) contains supplementary material, which is available to authorized users.</P>
Kim, Tae Wu,Yang, Cheolhee,Kim, Youngmin,Kim, Jong Goo,Kim, Jeongho,Jung, Yang Ouk,Jun, Sunhong,Lee, Sang Jin,Park, Sungjun,Kosheleva, Irina,Henning, Robert,van Thor, Jasper J.,Ihee, Hyotcherl The Royal Society of Chemistry 2016 Physical chemistry chemical physics Vol.18 No.13
<P>Real-time probing of structural transitions of a photoactive protein is challenging owing to the lack of a universal time-resolved technique that can probe the changes in both global conformation and light-absorbing chromophores of the protein. In this work, we combine time-resolved X-ray solution scattering (TRXSS) and transient absorption (TA) spectroscopy to investigate how the global conformational changes involved in the photoinduced signal transduction of photoactive yellow protein (PYP) is temporally and spatially related to the local structural change around the light-absorbing chromophore. In particular, we examine the role of internal proton transfer in developing a signaling state of PYP by employing its E46Q mutant (E46Q-PYP), where the internal proton transfer is inhibited by the replacement of a proton donor. The comparison of TRXSS and TA spectroscopy data directly reveals that the global conformational change of the protein, which is probed by TRXSS, is temporally delayed by tens of microseconds from the local structural change of the chromophore, which is probed by TA spectroscopy. The molecular shape of the signaling state reconstructed from the TRXSS curves directly visualizes the three-dimensional conformations of protein intermediates and reveals that the smaller structural change in E46Q-PYP than in wild-type PYP suggested by previous studies is manifested in terms of much smaller protrusion, confirming that the signaling state of E46Q-PYP is only partially developed compared with that of wildtype PYP. This finding provides direct evidence of how the environmental change in the vicinity of the chromophore alters the conformational change of the entire protein matrix.</P>
Flexible metal-oxide devices made by room-temperature photochemical activation of sol??gel films
Kim, Yong-Hoon,Heo, Jae-Sang,Kim, Tae-Hyeong,Park, Sungjun,Yoon, Myung-Han,Kim, Jiwan,Oh, Min Suk,Yi, Gi-Ra,Noh, Yong-Young,Park, Sung Kyu Nature Publishing Group, a division of Macmillan P 2012 Nature Vol.489 No.7414
Amorphous metal-oxide semiconductors have emerged as potential replacements for organic and silicon materials in thin-film electronics. The high carrier mobility in the amorphous state, and excellent large-area uniformity, have extended their applications to active-matrix electronics, including displays, sensor arrays and X-ray detectors. Moreover, their solution processability and optical transparency have opened new horizons for low-cost printable and transparent electronics on plastic substrates. But metal-oxide formation by the sol??gel route requires an annealing step at relatively high temperature, which has prevented the incorporation of these materials with the polymer substrates used in high-performance flexible electronics. Here we report a general method for forming high-performance and operationally stable metal-oxide semiconductors at room temperature, by deep-ultraviolet photochemical activation of sol??gel films. Deep-ultraviolet irradiation induces efficient condensation and densification of oxide semiconducting films by photochemical activation at low temperature. This photochemical activation is applicable to numerous metal-oxide semiconductors, and the performance (in terms of transistor mobility and operational stability) of thin-film transistors fabricated by this route compares favourably with that of thin-film transistors based on thermally annealed materials. The field-effect mobilities of the photo-activated metal-oxide semiconductors are as high as 14 and 7??cm<SUP>2</SUP>??V<SUP>??1</SUP>??s<SUP>??1</SUP> (with an Al<SUB>2</SUB>O<SUB>3</SUB> gate insulator) on glass and polymer substrates, respectively; and seven-stage ring oscillators fabricated on polymer substrates operate with an oscillation frequency of more than 340??kHz, corresponding to a propagation delay of less than 210??nanoseconds per stage.