• Journal of Microbiology and Biotechnology
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• v.30 no.1
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• pp.118-126
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• 2020

Silicon and phosphorus are elements that are beneficial for plant growth. Despite the abundant availability of silicate and phosphate in the Earth's crust, crop nutritional requirements for silicon and phosphorus are normally met through the application of fertilizer. However, fertilizers are one of the major causes of heavy metal pollution. In our study, we aimed to assess silicate and phosphate solubilization by the bacteria Enterobacter ludwigii GAK2, in the presence and absence of phosphate [Ca₃(PO₄)₂] or silicate (Mg₂O₈Si₃), to counteract cadmium stress in rice (Oryza sativa L). Our results showed that the GAK2-treated rice plants, grown in soil amended with phosphate [Ca₃(PO₄)₂] or silicate (Mg₂O₈Si₃), had significantly reduced cadmium content, and enhanced plant growth promoting characteristics including fresh shoot and root weight, plant height, and chlorophyll content. These plants showed significant downregulation of the cadmium transporter gene, OsHMA2, and upregulation of the silicon carrier gene, OsLsi1. Moreover, jasmonic acid levels were significantly reduced in the GAK2-inoculated plants, and this was further supported by the downregulation of the jasmonic acid related gene, OsJAZ1. These results indicate that Enterobacter ludwigii GAK2 can be used as a silicon and phosphorus bio-fertilizer, which solubilizes insoluble silicate and phosphate, and mitigates heavy metal toxicity in crops.

• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.2
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• pp.270-287
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• 2015

According to the increase of the operating cost and material cost of a ship due to the change of international oil price, a demand for the lightening of the ship weight is being made from various parties such as shipping companies, ship owners, and shipyards. To satisfy such demand, many studies for a light ship are being made. As one of them, an optimal design method of an existing hull structure, that is, a method for lightening the ship weight based on the optimization technique was proposed in this study. For this, we selected a hatch cover of a bulk carrier as an optimization target and formulated an optimization problem in order to determine optimal principal dimensions of the hatch cover for lightening the bulk carrier. Some dimensions representing the shape of the hatch cover were selected as design variables and some design considerations related to the maximum stress, maximum deflection, and geometry of the hatch cover were selected as constraints. In addition, the minimization of the weight of the hatch cover was selected as an objective function. To solve this optimization problem, we developed an optimization program based on the Sequential Quadratic Programming (SQP) using C++ programming language. To evaluate the applicability of the developed program, it was applied to a problem for finding optimal principal dimensions of the hatch cover of a deadweight 180,000 ton bulk carrier. The result shows that the developed program can decrease the hatch cover's weight by about 8.5%. Thus, this study will be able to contribute to make energy saving and environment-friendly ship in shipyard.

• Korean Chemical Engineering Research
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• v.50 no.4
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• pp.690-695
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• 2012

Gas hydrate is an inclusion compound consisting of water and low molecular weight gases, which are incorporated into the lattice structure of water. Owing to its promising aspect to application technologies, gas hydrate has been widely studied recently, especially $CO_2$ hydrate for the CCS (Carbon Capture and Storage) issue. The key point of $CO_2$ hydrate technology for the CCS is how to produce gas hydrate in an efficient and economic way. In this study, we have tried to study the characteristic of gas hydrate formation using micro-sized ice through an ultrasonic nozzle which generate 2.4 MHz frequency wave. $CO_2$ as a carrier gas brings micro-sized mist into low-temperature reactor, where the mist and carrier gas forms $CO_2$ hydrate under $-55^{\circ}C$ and atmospheric pressure condition and some part of the mist also remains unreacted micro-sized ice. Formed gas hydrate was average 10.7 of diameter at average. The starting ice particle was set to constant pressure to form $CO_2$ hydrate and the consumed amount of $CO_2$ gas was simultaneously measured to calculate the conversion of ice into gas hydrate. Results showed that the gas hydrate formation was highly suitable because of its extremely high gas-solid contact area, and the formation rate was also very high. Self-preservation effect of $CO_2$ hydrate was confirmed by the measurement of $CO_2$ hydrate powder at normal and at pressed state, which resulted that this kind of gas storage and transport could be feasible using $CO_2$ hydrate formation.

• Korean Journal of Materials Research
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• v.31 no.11
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• pp.619-625
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• 2021

Cu₂ZnSn(S,Se)₄ (CZTSSe) based thin-film solar cells have attracted growing attention because of their earth-abundant and non-toxic elements. However, because of their large open-circuit voltage (V_oc)-deficit, CZTSSe solar cells exhibit poor device performance compared to well-established Cu(In,Ga)(S,Se)₂ (CIGS) and CdTe based solar cells. One of the main causes of this large V_oc-deficit is poor absorber properties for example, high band tailing properties, defects, secondary phases, carrier recombination, etc. In particular, the fabrication of absorbers using physical methods results in poor surface morphology, such as pin-holes and voids. To overcome this problem and form large and homogeneous CZTSSe grains, CZTSSe based absorber layers are prepared by a sputtering technique with different RTA conditions. The temperature is varied from 510 ℃ to 540 ℃ during the rapid thermal annealing (RTA) process. Further, CZTSSe thin films are examined with X-ray diffraction, X-ray fluorescence, Raman spectroscopy, IPCE, Energy dispersive spectroscopy and Scanning electron microscopy techniques. The present work shows that Cu-based secondary phase formation can be suppressed in the CZTSSe absorber layer at an optimum RTA condition.

• Korean Journal of Materials Research
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• v.20 no.12
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• pp.676-680
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• 2010

Most TCOs such as ITO, AZO(Al-doped ZnO), FTO(F-doped $SnO_2$) etc., which have been widely used in LCD, touch panel, solar cell, and organic LEDs etc. as transparent electrode material reveal n-type conductivity. But in order to realize transparent circuit, transparent p-n junction, and introduction of transparent p-type materials are prerequisite. Additional prerequisite condition is optical transparency in visible spectral region. Oxide based materials usually have a wide optical bandgap more than ~3.0 eV. In this study, single-phase transparent semiconductor of $SrCu_2O_2$, which shows p-type conductivity, have been synthesized by 2-step solid state reaction at $950^{\circ}C$ under $N_2$ atmosphere, and single-phase $SrCu_2O_2$ thin films of p-type TCOs have been deposited by RF magnetron sputtering on alkali-free glass substrate from single-phase target at $500^{\circ}C$, 1% $H_2$/(Ar + $H_2$) atmosphere. 3% $H_2$/(Ar + $H_2$) resulted in formation of second phases. Hall measurements confirmed the p-type nature of the fabricated $SrCu_2O_2$ thin films. The electrical conductivity, mobility of carrier and carrier density $5.27{\times}10^{-2}S/cm$, $2.2cm^2$/Vs, $1.53{\times}10^{17}/cm^3$ a room temperature, respectively. Transmittance and optical band-gap of the $SrCu_2O_2$ thin films revealed 62% at 550 nm and 3.28 eV. The electrical and optical properties of the obtained $SrCu_2O_2$ thin films deposited by RF magnetron sputtering were compared with those deposited by PLD and e-beam.

• Journal of the Korean Ceramic Society
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• v.41 no.11
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• pp.858-863
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• 2004

The thermoelectric power, dc conductivity and magnetic properties of the cubic L $a_{2}$ 3/Ti $O_{2.84}$ were investigated. The thermoelectric power was negative below 350 K. The measured thermoelectric power of L $a_{2}$ 3/Ti $O_{2.84}$ increased linearly with temperature, in agreement with model proposed by Emin and Wood, and was represented by A+BT. Temperature dependence indicates that the charge carrier in this material is a small polaron. L $a_{2}$ 3/Ti $O_{2.84}$ exhibited a cross over from variable range hopping to small polaron hopping conduction at a characteristic temperature well below room temperature. The low temperature do conduction mechanism in L $a_{2}$ 3/Ti $O_{2.84}$ was analyzed using Mott's approach. Mott parameter analysis gave values for the density of state at Fermi level [N( $E_{F}$)] = 3.18${\times}$10$^{20}$ c $m^{-3}$ e $V^{-1}$ . The disorder energy ( $W_{d}$) was found to be 0.93 eV, However, it was noted that the value of the disorder energy was much higher than the high temperature activation energy. The exist linear relation between log($\sigma$T)와 1/T in the range of 200 to 300 K, the activation energy for small polaron hopping was 0.15 eV.

• Korean Journal of Materials Research
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• v.17 no.8
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• pp.414-419
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• 2007

We report the electrical conductivity of the mixed alkali silicate glasses in the system (60-x)$SiO_2-40Na_2O-xCaO(x=0\sim15wt%)$ in the temperature range from $150^{\circ}C$ to $620^{\circ}C$. In the range from $150^{\circ}C$ to glass transition temperature$(T_g)$, the electrical conductivities of glass samples had a tendency to be proportion with temperature. The glasses of containing over 7.5wt% CaO showed lower conductivities than the glasses of containing 0 and 5wt% CaO because two kinds of alkali ions$(Na^+,\;Ca^{2+})$ were obstructed each other. On the other hand, in the range from $T_g$ to $620^{\circ}C$, the electrical conductivity of glasses($7.5{\leq}x{\leq}12.5$) was unstable and decreased in some region. From XRD results, the $Na_4Ca(SiO_3)_3$ phase were observed in these glasses. This means the alkali ions didn't behave as carrier, it seems that this caused the conductivities decrease. In case of glass of containing 15wt% CaO, any crystal phase were not observed. This means the alkali ions behaved as carrier, it consequently seems the conductivity increased.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.158-158
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• 2016

최근 화석연료의 고갈과 환경 보전 및 에너지 절약에 대한 관심이 높아짐에 따라 화석연료의 소비를 최소화하고 실내조건을 쾌적하게 유지하려는 연구가 진행되고 있다. 국내의 경우 전체 에너지 소비의 30%이상을 차지하고 있는 건물부문에서의 에너지 소비를 줄이기 위한 활발한 연구가 진행되고 있으며 이에 따른 에너지절약 소재개발이 활발하게 진행되고 있다. 1975년 이후 여러 차례에 걸친 단열강화 조치를 통해 건물에서의 에너지 소모를 줄이고 있었으나 건물의 외벽에 대한 사항으로 한정되어있었고, 또한 건물의 창 면적이 증가함에 따라 창을 통한 열손실량과 열획득량이 더욱 증가하게 되었다. 이러한 문제를 해결하기 위해 열반사유리에 대한 많은 연구가 진행되고 있다. 열반사유리는 근적외선(열선)영역의 빛을 반사시켜 실내의 열손실량 및 외부에서의 열획득량을 감소시켜 에너지의 소비를 줄일 수 있는 유리을 말한다. 이러한 열반사유리은 fresnel 방정식을 통해 빛의 파장대에 따른 반사율 및 투과도를 예측할 수 있는데, 다층박막구조인 Oxide-Metal-Oxide(OMO)구조는 Oxide의 높은 굴절률과 Metal의 낮은 굴절률을 통해 가시광영역대의 높은 투과도와 근적외선 영역의 높은 반사율을 얻을 수 있다. 또한 Metal층을 삽입함으로서 flexible한 코팅이 가능하고, 높은 carrier density와 mobility로 표면 플라즈몬 공명을 통해 특정 파장대의 반사율을 높일 수 있으므로 많은 연구가 진행되고 있다. $TiO_2$는 고굴절률 및 낮은 광흡수성의 특성을 가지는 산화물반도체로 기존의 $In_2O_3$계 산화물에 비해 값이 싸고 높은 안정성과 광촉매특성을 보이므로 외부에 노출된 환경에 적합한 재료이다. Ag는 저굴절률과 낮은 광흡수성을 가지는 재료로 금속층에 적합하다. 본 연구에서는 fresnel 방정식을 통해 반사도 및 투과도를 예측하고 마그네트론 스퍼터링법으로 다층박막을 열선인 적외선 영역에서의 반사율 및 반사 효율을 평가하였다. Index-matching 시뮬레이션을 통해 $TiO_2/Ag/TiO_2$ 다층박막의 투과도와 반사도를 이론적으로 검토하였다. 시뮬레이션 프로그램은 Macleod프로그램을 이용하였고 재료 각각의 굴절률은 Ellipsometry를 이용하여 측정하였다. 두께 40 nm 와 8 ~ 16 nm를 가지는 $TiO_2$층과 Ag층을 각각 RF/DC 마그네트론 스퍼터링법을 이용하여 Glass기판 위에 증착하였다. 직경 3 in 의 $TiO_2$, Ag 소결체 타깃을 이용하였고 스퍼터링 파워는 각각 200 W, 50 W로 설정하였고, 스퍼터링 가스는 Ar가스의 유량을 20 sccm으로 설정하였다. 작업압력은 모두 1 Pa로 설정하였고 타깃 표면의 불순물 및 이물질 제거를 위해 Pre-sputtering을 10분 진행하였다. 박막의 두께는 reflectometer와 Alphastep을 이용하여 측정하였고 Hall effect measurement를 이용하여 비저항, carrier density, mobility등 전기적 특성을 측정하였다. 또한 UV-VIS spectrometer와 USPM-RU-W NIR Micro-Spectrophotometer를 통해 광학적 특성을 측정하였고 계산 값과 비교분석하였다. 또한 열반사 특성을 평가하기 위해 직접 set-up한 장비를 이용하였다. 단열 박스에 샘플을 장착해 적외선 램프를 조사하였을 때의 열 반사효율을 평가하였고, IR Camera를 이용하여 단열 박스 내부의 온도 변화를 관찰하였다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.32 no.6
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• pp.496-500
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• 2019

In this study, we investigate the effect of an Sb-deficiency on the thermoelectric properties of double-filled n-type skutterudite ($In_{0.05}Yb_{0.15}Co_4Sb_{12-x}$). Samples were prepared by encapsulated induction melting, consecutive long-time annealing, and finally spark plasma sintering processes. The Sb-deficient sample contained a $CoSb_2$ secondary phase. Both the double-filled n-type skutterudite pristine and Sb-deficient samples showed metallic behavior in electrical conductivity with increasing temperature. The carrier concentration of the Sb-deficient sample decreased compared with that of the pristine sample. Due to a decrease in carrier concentration, the Sb deficient sample showed decreased electrical conductivity and an increased Seebeck coefficient compared with the conductivity and coefficient of the pristine sample. Furthermore, the Sb deficient sample showed an increase in the power factor (${\sigma}{\cdot}S^2$); the power factor maximum shifted to athe lower temperature side than ones of the pristine sample. As a result, the Sb-deficient sample represents an improved average figure of merit (ZT) and a $ZT_{max}$ temperature lower than that of the pristine sample. Therefore, we propose that Sb-deficient double-filled n-type skutterudite thermoelectric material ($In_{0.05}Yb_{0.15}Co_4Sb_{12-x}$) be used in the 573~673 K temperature range.

• Korean Journal of Optics and Photonics
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• v.13 no.5
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• pp.455-459
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• 2002

The transport and optical properties of $In_2O_3$:Zn(IZO) thin films grown by DC magnetron sputtering deposition have been studied. The deposition temperatures ($T_s$) were varied from room temperature to $400^{\circ}C$ in $50^{\circ}C$ steps. The IZO films are an amorphous phase for $T_s$<$300^{\circ}C$ and polycrystalline phase for $350^{\circ}C$＜$T_s$. In contrast to ordinary films, amorphous IZO films have lower resistivity and higher optical transmittance than polycrystalline IZO films. The resistivity of amorphous IZO was in the range of 0.29~0.4 m$\Omega$cm and that of polycrystalline IZO was in the range of 1~4 m$\Omega$cm. The carrier type for IZO film was found to be n-type, and the carrier density, was $3~5{\times}10^{20}/cm^3$. The Hall mobility, $({\mu}_H)$, was 20~$50\textrm{cm}^2$/V.sec. The predominant scattering mechanisms in both amorphous and polycrystalline IZO films were believed to be ionized impurity scattering and lattice scattering. The visible transmittance of the IZO films, which decreases with an increase of TS, was above 80%.