• Korean Journal of Metals and Materials
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• v.48 no.4
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• pp.347-352
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• 2010

This study reports a novel method off abricating highly sensitive hydrogen gas sensors based on PdO thin films. The PdO thin films with a thickness of 40 nm were deposited on Si substrates under Ar and $O_2$ ambient conditions using a reactive de magnetron sputtering system. Considerable changes in the resistance of the palladium oxide thin films were observed when they were initially exposed to hydrogen gas, as a result of the reduction process. The sensitivity of the PdO thin films was found to be as high as 90%. After the thin films were exposed to hydrogen gas, the nano-sized cracks were discovered to have formed on the surface of the PdO thin films. These types of nano-cracks that formed on the deoxidized PdO thin films are known to play a key role incausing a four-fold reduction of the response time of the absorption process. The results of this study demonstrate that deoxidized PdO thin films can be applied for use in the creation of high-sensitivity hydrogen sensors.

• Korean Journal of Metals and Materials
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• v.47 no.6
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• pp.372-377
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• 2009

We report on hysteresis behavior in the electrical resistance-hydrogen concentration of Pd thin films. The variation of the electrical resistance has been investigated during the process of absorption and desorption of hydrogen gas ($H_{2}$) as a function of thickness of Pd thin films. The hysteresis behavior in the electrical resistance with $H_{2}$ concentration was found for Pd thin films and consists of $\alpha$ phase, ${\alpha}+{\beta}$ phase, and $\beta$ phase regions. The sensitivity of Pd thin films with $H_{2}$ concentration was found to follow Sieverts' law in the $\alpha$ phase region. However, the sensitivity was observed to increase abruptly with $H_{2}$ concentration in the ${\alpha}+{\beta}$ phase co-exist region. This is because Pd-H interaction is stronger in the $\beta$ phase than in the $\alpha$ phase and needs a higher concentration gradient as a driving force to desorb. The formation of the $\beta$ phase also was observed to cause the structural change because of the lattice expansion during absorption. The hysteresis height and the trace of structural change were affected by the thickness of the Pd film. As the film becomes thinner, the hysteresis height becomes lower and the amount of delamination on the surface becomes smaller. For films thinner than 20 nm in thickness, the delamination was not found but electrical resistance hysteresis was still observed.

• Journal of Korean Society of Environmental Engineers
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• v.38 no.4
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• pp.193-200
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• 2016

Water flea is a widely used test species in the aquatic ecotoxicity test. In Korea, D. magna is currently used as a standard test species, however that do not inhabit in the Korean aquatic ecosystem. In this study, Daphnia galeata, which is a dominant species in the Korean aquatic ecosystem, was collected from domestic lake and investigated to suggest the D. galeata for ecotoxicity assessment in Korea. We investigated the characteristics, life span, and toxicity sensitivity compared with D. magna. The life span test of D. galeata was performed in this study, and then the results were compared to the sensitivity with D. magna to confirm the applicability for ecotoxicity assessment. The 48h-L(E)C50 values for seven heavy metals (As, Cd, Cr, Cu, Hg, Ni, and Zn) of D. galeata and D. magna were collected and analyzed. As a results, shorter lifetime, less reproduction, smaller body size of D. galeata were observed compared with D. magna. D. galeata was similar or more sensitive than D. magna for seven heavy metals. Therefore, we propose that D. galeata is a suitable test species for ecotoxicity testing in Korea.

• Journal of Sensor Science and Technology
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• v.26 no.6
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• pp.402-407
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• 2017

Characteristics of various material surface plasmon resonance (SPR) chips were investigated in angular interrogation mode and intensity interrogation mode. Among five metals, silver (Ag), gold (Au), copper (Cu), chromium (Cr) and titanium (Ti), three metals, Ag, Au and Cu were paid attention to since their characteristics can be easily analyzed in angular interrogation mode by investigating the change of their reflectance curves according to refractive index change from 1.331 to 1.335. Most of SPR chips with various configurations showed the similar property in angular interrogation mode. The application of the SPR chip made of Ag, Au and Cu or their combinations depends on their reflectance properties. In intensity interrogation mode, the operation range may be limited since the variation of the intensity was not linearly related to refractive index change ranging from 1.331 to 1.335. However, the SPR chip containing high ratio of Ag may be applicable to high sensitive detection due to their sharp reflectance curves in intensity interrogation mode.

• Korean Journal of Metals and Materials
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• v.46 no.10
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• pp.627-633
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• 2008

The austenitic Fe-Mn alloys have received considerable attention as a possible candidate for the automotive structural materials due to their high strength and high formability with high elongation. This research investigates the effect of alloying elements on the phase transformation, deformation behavior and mechanical properties in high Mn steels for the development of a high strength high ductility steel. The mechanical stability of austenitic phases is very important for high ductility and it depends largely on the composition of carbon, manganese and aluminum. The dominant deformation mode shifts from TRIP to TWIP mode as the amount of C, Mn and Al is increased. Especially, even a small amount of Al addition facilitates significantly TWIP deformation due to the increase of stacking fault energy in Fe-Mn alloys, this leads to increase the ductility and also decrease the crack sensitivity.

• Korean Journal of Metals and Materials
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• v.47 no.10
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• pp.644-651
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• 2009

The passivation (or deactivation) of a metal surface during oxide film formation has been quantitatively explored for a ferritic stainless steel by using dynamic electrochemical impedance spectroscopy (DEIS). For this purpose, the electrochemical impedance spectra were carefully examined as a function of applied potential in the active nose region of the potentiodynamic polarization curve, to separate the charge transfer resistance and oxide film resistance. From the discrepancy in the potential dependence between the experimental charge transfer resistance and the semi-empirically expected one, the degree of passivation could be quantitatively estimated. The sensitivity of passivation of the steel surface to anodic potential, which might be the measure of the quality of the oxide film formed under unit driving force or over-potential, decreased by 31% when 3.5 wt% NaCl was added to a 5 wt% $H_2SO_4$ solution.

• Environmental Analysis Health and Toxicology
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• v.22 no.2 s.57
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• pp.171-175
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• 2007

Indigenous species means a species that is likely, due to historical presence, to occur at a specified site for some portion of its life span. Therefore, indigenous species can be useful as an indicator to assess environmental risk caused by hazardous chemicals in a specific site. So far a few toxicity studies using freshwater species which are indigenous to Korea have been carried out. In this study, a freshwater shrimp (Neocardina denticulata) indigenous to Korea was used for acute toxicity test of heavy metals. Neocardina denticulata were exposed to cadmium chloride $(CdCl_2)$, copper chloride $(CuCl_2)$ and zinc chloride $(ZnCl_2)$ using automatic flow-through system for 96 hours. The 96h LC50s were calculated as 0.043 $(0.042{\sim}0.045)mg\;CdCl_2/L,\;0.104(0.098{\sim}0.113)mg\; CuCl_2/L\;and\;2.021\;(1.633{\sim}2.594)mg\;ZnCl_2/L$. When compaired with some international standard species such as medaka(Oryzias latipes), Neocardina denticulata had high sensitivity. Therefore, this study suggested that Neocardina denticulata have possibilities for a sensitive test species to test heavy metal toxicity in aqua-system.

• Journal of Korea Soil Environment Society
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• v.1 no.2
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• pp.43-50
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• 1996

The adsorption charateristics of lead(II) ions on Aspergillus niger and Rhizopus arrhizus were investigated. Adsorption amount of A. niger and R. arrhizus was about 95 mg/g and 25 mg/g, respectively. These biomass was approached to adsorption equilibrium within reaction time of 1hr because of their high reactivity. The uptake of lead ion by A. niger was less sensitivity than it by R. arrhizus on the inhibition effect of alkali metals and the decreasing ratio of uptake of lead ion of A. niger and R. arrhizus by inhibition effect of alkali metals was 37% and 50%, respectively. In pre-treatment on these biomass, NaOH treatment was contributed high adsorption capacity to these biomass. Then, adsorption amount of A. niger and R. allhizus was increased about 25 mg/g and 10 mg/g, respectively. In isotherm for the adsorption of lead ion based on Freundlich equation, 1/n value of A. niger and R. ar고izus was calculated the range of 0.28-0.56 and 0.44-0.67, respectively.

• Journal of Life Science
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• v.21 no.1
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• pp.159-164
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• 2011

Microbial whole-cell biosensors can be excellent analytical tools for monitoring environmental pollutants. They are constructed by fusing reporter genes (e.g., lux, gfp or lacZ) to inducible regulatory genes which are responsive to the relevant pollutants, such as aromatic hydrocarbons and heavy metals. A large spectrum of microbial biosensors has been developed using recombinant DNA technology and applied in fields as diverse as environmental monitoring, medicine, food processing, agriculture, and defense. Furthermore, their sensitivity and target range could be improved by modification of regulatory genes. Recently, microbial biosensor cells have been immobilized on chips, optic fibers, and other platforms of high-throughput cell arrays. This paper reviews recent advances and future trends of genetically modified microbial biosensors used for monitoring of specific environmental pollutants.

• Korean Journal of Optics and Photonics
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• v.1 no.1
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• pp.73-86
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• 1990

The technique of Spectroscopic Ellipsometry (SE) has been examined with emphasis on its inherent sensitivity to the existence of thin films or surface equivalents. A brief review of related theories like the Fresnel reflection coefficients, the effect of a multilayer upon reflectivities, together with the validity of the effective medium theory and the modelling procedure, is followed by a short description of the experimental setup of a rotating polarizer type SE as well as the necessful expressions which lead to tan and cos. Out of its numerous, successful applications, a few are exampled to convince a reader that SE can be applied to a variety of research fields related to surface, interface and thin films. Specifically, those are adsorption and/or desorption on metals or semiconductors, oxidation process, formation of passivation layers on an electrode, thickness determination, interface between semiconductor and its oxide, semiconductor heterojunctions, surface microroughness, void distribution of dielectric, optical thin films, depth profile of multilayered samples, in-situ or in-vitro characterization of a solid surface immersed in electrolyte during electrochemical, chemical, or biological treatments, and so on. It is expected that the potential capability of SE will be widely utilized in a very near future, taking advantage of its sensitivity to thin films or surface equivalents, and its nondestructive, nonperturbing characteristics.