• Journal of the Korean Vacuum Society
• /
• v.17 no.1
• /
• pp.67-72
• /
• 2008

We have studied the effect of heat treatment of multi-walled carbon nanotubes (MWNTs) as a counter electrode on the electro-chemical properties of dye-snsitized solar cells. MWNTs on the p-type Si substrate were synthesized by thermal chemical vapor deposition (CVD) using Fe catalysts. We prepared the two types of MWNTs samples with the different diameters. The rapid thermal annealing (RTA) treatment for the MWNTs was carried out at the growth temperature ($900^{\circ}C$) for 1 minute with $N_2$ gas atmosphere. The structural, electrical and electrochemical properties of MWNTs were investigated by field-emission scanning electron microscopy (FE-SEM), Raman spectroscopy, 2-point probe station and electrochemical impedance spectroscopy (EIS). The I(D)/I(G) ratio of heat-treated MWNTs in Raman spectra was considerably decreased. It was also found that the heat-treated MWNTs showed better redox reaction of iodide at the interface between MWNTs surface and electrolyte than that of as-grown MWNTs. The redox resistance value of heat-treated electrodes was measured to be much lower than that of as-grown electrode at the interface. As a result, the counter electrode using the heat-treated MWNTs showed better electrochemical properties.

• Journal of the Korean Vacuum Society
• /
• v.17 no.2
• /
• pp.160-164
• /
• 2008

The Characterization of $MgB_2$ Thin Film by Slow Positron Annihilation Spectroscopy Enhance signal-to-noise ratio, slow positron coincidence Doppler Broadening method has been applied to study of characteristics of $MgB_2$ superconductor film, which were performed at 30 K and 50 K sample temperature near Tc of it. In this investigation the numerical analysis of the Doppler spectra was employed to the determination of the shape parameter, S, defined as the ratio between the amount of counts in a central portion of the spectrum and the total counts of whole spectrum. The S-parameter values were increased then decreased while the positron implantation energies were increasing, that indicated the diffusion into the samples. The S-parameters of the anisotropic 1 ${\mu}m$ $MgB_2$ thin film which were implanted by positrons at 10 keV are 0.567 at 30 K and 0.570 at 50 K. It is believed that the positrons annihilate with normal-electrons instead of super-electrons in the $MgB_2$ superconductor.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2014.02a
• /
• pp.150.1-150.1
• /
• 2014

Showerhead is used as a main part in the semiconductor equipment. The face plate flatness should remain constant and the cleaning performance must be gained to keep the uniformity level of etching or deposition in chemical vapor deposition process. High operating temperature or long period of thermal loading could lead the showerhead to be deformed thermally. In some case, the thermal deformation appears very sensitive to showerhead performance. This paper describes the methods for robust design using computational fluid dynamics. To reveal the influence of the post distribution on flow pattern in the showerhead cavity, numerical simulation was performed for several post distributions. The flow structure appears similar to an impinging flow near a centered baffle in showerhead cavity. We took the structure as an index to estimate diffusion path. A robust design to reduce the thermal deformation of showerhead can be achieved using post number increase without ill effect on flow. To prevent the showerhead deformation by heat loading, its face plate thickness was determined additionally using numerical simulation. The face plate has thousands of impinging holes. The design key is to keep pressure drop distribution on the showerhead face plate with the holes. This study reads the methodology to apply to a showerhead hole design. A Hagen-Poiseuille equation gives the pressure drop in a fluid flowing through such hole. The assumptions of the equation are the fluid is viscous-incompressible and the flow is laminar fully developed in a through hole. An equation can be expressed with radius R and length L related to the volume flow rate Q from the Hagen-Poiseuille equation, $Q={\pi}R4{\Delta}p/8{\mu}L$, where ${\mu}$ is the viscosity and ${\Delta}p$ is the pressure drop. In present case, each hole has steps at both the inlet and the outlet, and the fluid appears compressible. So we simplify the equation as $Q=C(R,L){\Delta}p$. A series of performance curves for a through hole with geometric parameters were obtained using two-dimensional numerical simulation. We obtained a relation between the hole diameter and hole length from the test cases to determine hole diameter at fixed hole length. A numerical simulation has been performed as a tool for enhancing showerhead robust design from flow structure. Geometric parameters for the design were post distribution and face plate thickness. The reinforced showerhead has been installed and its effective deposition profile is being shown in factory.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2014.02a
• /
• pp.454-454
• /
• 2014

Silicon microwire array is one of the promising platforms as a means for developing highly efficient solar cells thanks to the enhanced light trapping efficiency. Among the various fabrication methods of microstructures, deep reactive ion etching (DRIE) process has been extensively used in fabrication of high aspect ratio microwire arrays. In this presentation, we show precisely controlled Si microwire arrays by tuning the DRIE process conditions. A periodic microdisk arrays were patterned on 4-inch Si wafer (p-type, $1{\sim}10{\Omega}cm$) using photolithography. After developing the pattern, 150-nm-thick Al was deposited and lifted-off to leave Al microdisk arrays on the starting Si wafer. Periodic Al microdisk arrays (diameter of $2{\mu}m$ and periodic distance of $2{\mu}m$) were used as an etch mask. A DRIE process (Tegal 200) is used for anisotropic deep silicon etching at room temperature. During the process, $SF_6$ and $C_4F_8$ gases were used for the etching and surface passivation, respectively. The length and shape of microwire arrays were controlled by etching time and $SF_6/C_4F_8$ ratio. By adjusting $SF_6/C_4F_8$ gas ratio, the shape of Si microwire can be controlled, resulting in the formation of tapered or vertical microwires. After DRIE process, the residual polymer and etching damage on the surface of the microwires were removed using piranha solution ($H_2SO_4:H_2O_2=4:1$) followed by thermal oxidation ($900^{\circ}C$, 40 min). The oxide layer formed through the thermal oxidation was etched by diluted hydrofluoric acid (1 wt% HF). The surface morphology of a Si microwire arrays was characterized by field-emission scanning electron microscopy (FE-SEM, Hitachi S-4800). Optical reflection measurements were performed over 300~1100 nm wavelengths using a UV-Vis/NIR spectrophotometer (Cary 5000, Agilent) in which a 60 mm integrating sphere (Labsphere) is equipped to account for total light (diffuse and specular) reflected from the samples. The total reflection by the microwire arrays sample was reduced from 20 % to 10 % of the incident light over the visible region when the length of the microwire was increased from $10{\mu}m$ to $30{\mu}m$.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2014.02a
• /
• pp.490.2-490.2
• /
• 2014

Since the general solar cells accept sun light at the front side, excluding the electrode area, electrons move from the emitter to the front electrode and start to collect at the grid edge. Thus the edge of gridline can be important for electrical properties of screen-printed silicon solar cells. In this study, the improvement of electrical properties in screen-printed crystalline silicon solar cells by contact treatment of grid edge was investigated. The samples with $60{\Omega}/{\square}$ and $70{\Omega}/{\square}$ emitter were prepared. After front side of samples was deposited by SiNx commercial Ag paste and Al paste were printed at front side and rear side respectively. Each sample was co-fired between $670^{\circ}C$ and $780^{\circ}C$ in the rapid thermal processing (RTP). After the firing process, the cells were dipped in 2.5% hydrofluoric acid (HF) at room temperature for various times under 60 seconds and then rinsed in deionized water. (This is called "contact treatment") After dipping in HF for a certain period, the samples from each firing condition were compared by measurement. Cell performances were measured by Suns-Voc, solar simulator, the transfer length method and a field emission scanning electron microscope. According to HF treatment, once the thin glass layer at the grid edge was etched, the current transport was changed from tunneling via Ag colloids in the glass layer to direct transport via Ag colloids between the Ag bulk and the emitter. Thus, the transfer length as well as the specific contact resistance decreased. For more details a model of the current path was proposed to explain the effect of HF treatment at the edge of the Ag grid. It is expected that HF treatment may help to improve the contact of high sheet-resistance emitter as well as the contact of a high specific contact resistance.

• Journal of the Korean Vacuum Society
• /
• v.17 no.2
• /
• pp.130-137
• /
• 2008

$La_{0.7}Sr_{0.3}MnO_3$ films were deposited on $SiO_2$/Si and Si substrates annealed at $350^{\circ}C$ by rf magnetron sputtering. The oxygen gas flow rates were varied as 0, 40, and 80 sccm. Without post annealing process, $La_{0.7}Sr_{0.3}MnO_3$ thin films on $SiO_2$/Si and Si substrates were polycrystalline with (100), (110), and (200) growth planes. The grain size of $La_{0.7}Sr_{0.3}MnO_3$ thin films was increased with increasing oxygen gas flow rate. The sheet resistance of $La_{0.7}Sr_{0.3}MnO_3$ thin films was decreased with oxygen flow rate due to the increased grain size which induced a reduction of grain boundary. TCR (temperature coefficient of resistance) values of $La_{0.7}Sr_{0.3}MnO_3$ thin films were obtained from -2.0% to -2.2%.

• Journal of Wetlands Research
• /
• v.14 no.4
• /
• pp.537-545
• /
• 2012

Decay rate and nutrient dynamics during leaf litter decomposition of deciduous Quercus acutissima were compared between Gongju and Jinju for 33 months from December 2008 through March 2011. Percent remaining weight of Q. acutissima leaf litter after 33 months elapsed in Gongju and in Jinju was $41.2{\pm}0.4%$ and $28.3{\pm}0.6%$, and decay constant (k) was 0.39 and 0.61, respectively. Decomposition in Jinju was significantly faster than that in Gongju. This seemed to be related to higher temperature and precipitation in Jinju than those in Gongju during the experimental period. Initial C/N and C/P ratio of Q. acutissima leaf litter was 46.8 and 270.9, respectively. After 33 months elapsed, C/N and C/P ratios in Gongju decreased to 22.0 and 106.8, and those in Jinju decreased to 19.2 and 170.2, respectively. Initial concentration of N, P, K, Ca and Mg in Q. acutissima leaf litter was 8.31, 0.44, 4.18, 9.38, 1.37 mg/g, respectively. After 33 month elapsed, remaining N, P, K, Ca and Mg were 91.0, 85.4, 30.2, 47.9, 11.7% in Gongju, and 67.0, 54.2, 19.9, 30.0, 40.8% in Jinju, respectively. Except for Mg, remaining nutrients of decomposing leaf litter in Jinju were lower than those in Gongju. In case of N and P, initial immobilization was observed, however, only mineralization was observed in K, Ca and Mg during the whole experimental period.

• The Korean Journal of Mycology
• /
• v.26 no.4 s.87
• /
• pp.531-537
• /
• 1998

Forest green mold incidence rate, extent of damage according to the inoculation periods, and its cultural characteristics were observed in the automatic cultural system of the winter mushroom, Flammulina velutipes. The incidence rate of the forest green mold was 7.7% in early cultivation stage and slowly increased to 14.9% in harvest stage. When the forest green mold was inoculated at cultural period, the rate was recorded at 100%, but the extent of the damage increased up to 40% (+++). There was also 100% incidence rate at early pinheading time, whereas the yield of mushroom decreased to ++ $(10{\sim}39%)$. The rate of forest green mold was greatly decreased to 34.4% at 10 days after pinheading, and its damage extent was also below 10%. A pathogen to infect the winter mushroom was identified as Trichoderma pseudokoningii. It's optimum temperature for mycelial growth is $25^{\circ}C$, and it grew 2.6 times faster than that of F. velutipes. The mycelial color of T. pseudokoningii was pale yellow or olivaceous in shades on PDA medium. Phialospore was one celled, and ellipsodal or obovoid, smooth walled, and measured $1.3{\sim}3.0{\times}1.0{\sim}2.5\;{\mu}m$. It aggregated in small heads at the tips of the phialides. The phialides were $3.2{\sim}9.2{\times}2.0{\sim}5.5\;{\mu}m$ and were of bowling pin type, solitary and alternate or more irregularly disposed at the conidiophore apex, T. pseudokoningii depressed the F. velutipes growth at the crossing cultivation when they were simultaneously. FV 4-1 (F. velutipes) cultivar was less depressed by T. pseudokoningii, but had a lower cross growth rate than the other four cultivars.

• The Korean Journal of Mycology
• /
• v.24 no.4 s.79
• /
• pp.293-304
• /
• 1996

A bacterial strain, KSl, possessing strong antifungal activity was isolated from soil samples of ginseng fields and identified as Bacillus subtilis. In greenhouse test, the culture filtrate of B. subtilis KS1 showed strong protective effect against several fungal diseases of agricultural plants such as cucumber gray mold and wheat leaf rust. In addition, the crude butanol fraction of the culture filtrate exhibited antagonistic effect against several fungi including plant or human pathogens, such as Botrytis maydis, Chytridium lagenarium and Candida albicans. The antifungal compound, SW1, produced by B. subtilis KS1 was purified through consecutive chromatographic separations on a pep-RPC column and a ${\mu}$ Bondapak $C_{18}$ reverse phase column. Temperature and pH showed little effect on the stability of the compound in the ranges $-20-121^{\circ}C$ and pH 4.0-10.0, respectively. The composition and structural characteristics of SW1 were analysed by HPLC and by $^1H-,\;^1H-^1H-COSY$, NOESY, COSY-NOESY and HOHAHA NMR spectroscopy, respectively, which revealed that the compound belongs to iturin A, a typical cyclic antifungal compound produced by B. subtilis. In contrast to the previously reported iturin A compounds which have one or no $-CH_3$ side chain in the hydrophobic hydrocarbon chain of ${\beta}-amino$ acids, SW1 was shown to have a ${\beta}-amino$ acid containing 12-carbon skeleton with two $-CH_3$ side chains.

• The Korean Journal of Mycology
• /
• v.22 no.4
• /
• pp.378-385
• /
• 1994

Interspecific somatic hybrids were obtained by protoplast fusion between Pleurotus ostreatus and Pleurotus sajor-caju. The fusion products between incompatible strains did not form clamp connections. Fruiting body of the clampless fusants was induced by light-dark cycle on saw-dust-rice bran substrate in glass bottles. Out of them, seven somatic hybrids produced fruiting bodies of intermediate morphology of the two species. Light and low temperature were the initiating factors for the development of clamped hyphae from the clampless mycelial colonies. All of these basidiocarps had clamp connections. Eight fusants from the six crosses were analysed with the segregation of genetic characters by random spore isolates. In the three combinations, unexpected alleles were shown. Somatic hybrid between P188 (P. ostreatus 2-1 + P. sajor-caju 2-53) and P. florida 2-3 by triple cross produced fruiting bodies similar to those of fusant between P. ostreatus and P. florida. All the genetic charaters from the three strains were shown to segregate and recombine.