• The Transactions of the Korean Institute of Electrical Engineers C
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• v.55 no.10
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• pp.461-466
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• 2006

In the present work, we investigated the photodissolution and photodiffusion effect on the interface of Ag/chalcogenide $As_{40}Ge_{10}Se_{15}S_{35}$ thin film by measuring the absorption coefficient, the optical density, the resistance change of Ag layer. It was found that the photodissolutioniphotodiffution ratio depends on the magnitude of photon energy absorbed in the chalcogenide thin film and the depth of photodiffution was proportional to the square root of the exposed time. Also, we have investigated the holographic grating formation with P-polarization states on chalcogenide $As_{40}Ge_{10}Se_{15}S_{35}$ thin film and $As_{40}Ge_{10}Se_{15}S_{35}/Ag$ double layer structure thin film. Holographic gratings have been formed using He-Ne laser (632.8 nm) which have a smaller energy than the optical energy gap, $E_g\;_{opt}$ of the film, i. e., an exposure of sub-bandgap light $(h{\upsilon} under P-polarization. As the results, we found that the diffraction efficiency on $As_{40}Ge_{10}Se_{15}S_{35}/Ag$ double layer structure thin film was more higher than that on single $As_{40}Ge_{10}Se_{15}S_{35}$ thin film. Also, we obtained that the maximum diffraction efficiency was 0.27 %, 1,000 sec on $As_{40}Ge_{10}Se_{15}S_{35}\;(1{\mu}m)/Ag$ (10 nm) double layer structure thin film by (P: P) polarized recording beam. It will offer lots of information for the photodoping mechanism and the analyses of chalcogenide thin films.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.167-168
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• 2007

$CdIn_2S_4$ (110) films were grown on semi-insulating GaAs (100) by a hot wall epitaxy method. Using photocurrent (PC) measurement, the PC spectra in the temperature range of 30 and 10 K appeared as three peaks in the short wavelength region. It was found that three peaks, A-, B-, and C-excitons, correspond to the intrinsic transition from the valence band states of ${\Gamma}_4(z),\;{\Gamma}_5(x),\;and\;{\Gamma}_5(y)$ to the exciton below the conduction band state of ${\Gamma}_1(s)$, respectively. The 0.122 eV crystal field splitting and the 0.017 eV spin orbit splitting were obtained. Thus, the temperature dependence of the optical band gap obtained from the PC measurement was well described by $E_g$(T)=2.7116eV - $(7.65{\times}10^{-4}\;eV/K)T^2$/(425+T). But, the behavior of the PC was different from that generally observed in other semiconductors. The PC intensities decreased with decreasing temperature. This phenomenon had ever been reported at a PC experiment on the bulk crystals grown by the Bridgman method. From the relation of log $J_{ph}$ vs 1/T, where $J_{ph}$ is the PC density, two dominant levels were observed, one at high temperatures and the other at low temperatures. Consequently, the trapping centers due to native defects in the $CdIn_2S_4$ film were suggested to be the causes of the decrease in the PC signal with decreasing temperature.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.193.2-193.2
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• 2016

We evaluate the change in defects in the oxidized SiO2 grown on 4H-SiC (0001) by plasma assisted oxidation, by comparing with that of conventional thermal oxide. In order to investigate the changes in the electronic structure and electrical characteristics of the interfacial reaction between the thin SiO2 and SiC, x-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), DFT calculation and electrical measurements were carried out. We observed that the direct plasma oxide grown at the room temperature and rapid processing time (300 s) has enhanced electrical characteristics (frequency dispersion, hysteresis and interface trap density) than conventional thermal oxide and suppressed interfacial defect state. The decrease in defect state in conduction band edge and stress-induced leakage current (SILC) clearly indicate that plasma oxidation process improves SiO2 quality due to the reduced transition layer and energetically most stable interfacial state between SiO2/SiC controlled by the interstitial C.

• Journal of the Korean Chemical Society
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• v.45 no.1
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• pp.76-82
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• 2001

In this study, the effects of grouping method (homogeneous/ heterogeneous) considering students' teamwork skills on their conceptual understanding, perceptions of science learning environments, communication anxiety, communication ability, and perceptions toward small group discussions were compared. Students were taught concerning changes of states, density, and dissolution for 9 class periods. The ANCOVA results indicated that there was no significant difference in the conceptions test scores. In the subcategory of 'students' negotiation' of the perceptions of science learning environments test, high teamwork skill students perceived more positively in the heterogeneous group, but low teamwork skill students in the homogeneous group. No significant differences were found in the communication anxiety. More students in the heterogeneous group perceived unequal participation as a disadvantage of the small group discussions than those in the homogeneous group.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.11
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• pp.29-34
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• 2004

This paper reports the RF dispersion and linearity characteristics of unpassivated AlGaN/InGaN/GaN high electron-mobility transistors (HEMTs) grown by molecular beam epitaxy (MBE). The devices with a 0.5 ${\mu}{\textrm}{m}$ gate-length exhibited relatively good DC characteristics with a maximum drain current of 730 mA/mm and a peak g$_{m}$ of 156 mS/mm. Highly linear characteristic was observed by relatively flat DC transconductance (g$_{m}$) and good inter-modulation distortion characteristics, which indicates tight channel carrier confinement of the InGaN channel. Little current collapse in pulse I-V and load-pull measurements was observed at elevated temperatures and a relatively high power density of 1.8 W/mm was obtained at 2 GHz. These results indicate that current collapse related with surface states will not be a power limiting factor for the AlGaN/InGaN HEMTs.

• Journal of the Korean Geotechnical Society
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• v.21 no.9
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• pp.53-64
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• 2005

For geotechnical design in practice, soils are, in general, assumed to behave as a linear elastic or perfect plastic material. More realistic geotechnical design, however, should take into account various factors that affect soil behavior in the field, such as non-linearity of stress-strain response, stress history, and water content. In this study, a series of laboratory tests including triaxial and resonant column tests were peformed with sands of various silt contents, relative densities, stress states, OCR and water contents. This aims at investigating effects of various factors that affect strength and stiffness of sands. From the results in this study, it is found that the effect of OCR is significant for the intermediate stress-strain range from the initial to failure, while it may be ignored for the initial stiffness and peak strength. For the effect of water content, it is observed that the initial elastic modulus decreases with increasing water content at lower confining stress and relative density At higher confining stresses, the effect of water content Is found to become small.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.10
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• pp.2073-2081
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• 2002

In product design and manufacturing, axiomatic design provides a systematic approach for the decision-making process. Two axioms have been defined such as the Independence Axiom and the Information Axiom. The Information Axiom states that the best design among those that satisfy the independence axiom is the one with the least information content. In other words, the best design is the one that has the highest probability of success. On the other hand, the Taguchi robust design is used in the two-step process; one is "reduce variability," and the other is "adjust the mean on the target." The two-step can be interpreted as a problem that has two FRs (functional requirements). Therefore, the Taguchi method should be used based on the satisfaction of the Independence Axiom. Common aspects exist between the Taguchi method and Axiomatic Design in that a robust design is induced. However, different characteristics are found as well. The Taguchi method does not have the design range, and the probability of success may not be enough to express robustness. Our purpose is to find the one that has the highest probability of success and the smallest variation. A new index is proposed to satisfy these conditions. The index is defined by multiplication of the robustness weight function and the probability density function. The robustness weight function has the maximum at the target value and zero at the boundary of the design range. The validity of the index is proved through various examples.gh various examples.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.5B
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• pp.797-808
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• 2000

This paper presents the bit error rate(BER) upper bounds for trellis coded asymmetric 8PSK(TC-A8PSK) system using the Ka-band satellite in the rain fading environment. The probability density function(PDF) for the rain fading random variable can be theoretically derived by assuming that the rain attenuation can be approximated to a long-normal distribution and the rain fading parameters are calculated by using the rain precipitation data from the Crane global model. Furthermore, we analyze the BER upper bounds of TC-A8PSK system according to the number of states in the trellis diagram and the availability of channel state information(CSI). In the past, Divsalar and Simon[9] has analyzed the BER upper bounds of 2-state TCM system in Rician fading channels however this paper is the first to analyze the BER upper bounds of TCM system in the rain fading channels. Finally, we summarize the dominant six factors which are closely related to the BER upper bounds of TC-A8PSK satellite system in the rain fading channel as follows: 1) frequency band, 2) rain intensity, 3) elevation angle, 4) signal to noise ratio, 5) asymmetric angle, and 6) availability of CSI.

• Journal of the Korean Institute of Landscape Architecture
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• v.30 no.2
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• pp.88-94
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• 2002

This study was conducted to select suitable turfarasses for use at 2002 world cup soccer fields in Korea. A 1/1000 scale Inchon worldcup soccer dome was constructed for this research. Species and seeding rates of cool-season grasses used inside and outside the dome were Kentuck bleugrass 10g/$m^2$ (KB), Kentucky bleugrass 10g/$m^2$+ perennial ryegrass 10g/$m^2$ mixture (KB+PR) and Kentucky bleugrass 6g/$m^2$+tall fescue 14g/$m^2$+ perennial ryegrass 4g/$m^2$ mixture (KB+TF+PR). Warm-season grasses also used in this study were Zoysia japonica 'Anyangjungzii' (ZA) and Zoysia japonica 'Zenith'(ZZ) which were layed as sod. So, total 5 types of grasses were used inside and outside the dome. The rootzone was constructed by the multi-layer method(United States Golf Association method). The plots were designed by randomized block design. Cool-season grasses(KB, KB+PR, KB+TF+PR) were found to be better performers for visual rating and visual color than the zoysiagrasses(ZA, ZZ). There were no significant differences in turf performance within cool-season grasses, while ZA showed better turf performances than ZZ within zoysiagrasses. The green color was maintained for about 10 months in the col-season grasses(KB, KB+PR, KB+TF+PR) compared to about 5~6 months in the zoysiagrasses. Root length and density data revealed higher values for KB, KB+PR and KB+TF+PR compared to ZA and ZZ. Root performance of 22 was better than ZA within zoysiagrasses which was the opposite result of turf performances. There was also no significant difference between U performance inside and outside the dome. However, the decreasing tendency of turf quality inside the dome at the end of the study showed that more proper maintenance technology was needed inside the d[me. It could be concluded by this study that cool-season grasses(KB, KB+PR, KB+TF+PR) were more suitable turfgrasses than waits-season zoysiagrasses(ZA, ZZ) for use at 2002 world cup soccer fields in Korea.

• Journal of the Korean Magnetics Society
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• v.18 no.6
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• pp.201-205
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• 2008

In order to investigate the origin of the band gap in the half-metallic Heusler alloy, $Co_2MnSi$, through the electronic structure calculation, we have calculated the electronic structures for the compounds consisted of parts of Heusler structures, i.e. zinc-blende CoMn, half-Heusler CoMnSi, and artificial $Co_2Mn$, using the full-potential first-principles band calculation method. By investigating the band hybridization and energy gap for the calculated density of states for these compounds, we found that the the origin of the band gap is not consistent with the explanation discussed by Galanakis et al. We have also discussed the magnetism for these compounds by the calculated number of majority- and minority-spin electrons.