• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.86-86
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• 2012

The new approaches for silicon solar cell of new concept have been actively conducted. Especially, solar cells with wire array structured radial p-n junctions has attracted considerable attention due to the unique advantages of orthogonalizing the direction of light absorption and charge separation while allowing for improved light scattering and trapping. One-dimenstional semiconductor nano/micro structures should be fabricated for radial p-n junction solar cell. Most of silicon wire and/or pillar arrays have been fabricated by vapour-liquid-solid (VLS) growth because of its simple and cheap process. In the case of the VLS method has some weak points, that is, the incorporation of heavy metal catalysts into the growing silicon wire, the high temperature procedure. We have tried new approaches; one is electrochemical etching, the other is noble metal catalytic etching method to overcome those problems. In this talk, the silicon pillar formation will be characterized by investigating the parameters of the electrochemical etching process such as HF concentration ratio of electrolyte, current density, back contact material, temperature of the solution, and large pre-pattern size and pitch. In the noble metal catalytic etching processes, the effect of solution composition and thickness of metal catalyst on the etching rate and morphologies of silicon was investigated. Finally, radial p-n junction wire arrays were fabricated by spin on doping (phosphor), starting from chemical etched p-Si wire arrays. In/Ga eutectic metal was used for contact metal. The energy conversion efficiency of radial p-n junction solar cell is discussed.

• 한국신재생에너지학회:학술대회논문집
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• 2005.06a
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• pp.192-195
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• 2005

The silicon thin film solar cells were fabricated by 13.56 MHz PECVD (Plasma-Enhanced Chemical-Vapor Deposition) and 60 MHz VHF PECVD (Very High-Frequency Plasma-Enhanced Chemical-Vapor Deposition). We focus on textured ZnO:Al films prepared by RF sputtering and post deposition wet chemical etching and studied the surface morphology and optical properties. These films were optimized the light scattering properties of the textured ZnO:Al after wet chemical etching. Finally, the textured ZnO:Al films were successfully applied as substrates for silicon thin films solar cells. The efficiency of tandem solar cells with $0.25 cm^2$ area was $11.8\%$ under $100mW/cm^2$ light intensity. The electrical properties of tandem solar cells were measured with solar simulator (AM 1.5, $100 mW/cm^2)$ and spectral response measurements.

• Textile Coloration and Finishing
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• v.8 no.2
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• pp.1-7
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• 1996

Thermotropic liquid-crystalline polyurethanes were synthesized by the polyaddition reaction of such para-substiuted diisocyanate monomer as 1,4-phenylene diisocyanate(1,4-PDI) and 2,5-tolylene diisocyanate(2,5-TDI), with 4,4'-bis($\omega$-hydroxyalkoxy)biphenyls(BPm: $HOC_{m}OC_{6}H_{4}C_{6}H_{4}OC_{m}H_{2m}OH$; m is the carbon number of the hydroxyalkoxy group). These polyurethanes have mesogenic biphenyl units in the main chain. Properties of polymers were studied by differential scanning calorimetry, wide-angle X-ray scattering, thermogravimetic analysis, polarizing microscopy, and infraed spectroscopy. DSC thermograms for these polymers exhibited two endothermic peaks corresponding to phase transitions of melting and isotropization. Mesomorphic behavior of the polyurethanes were also observed under the polarizing microscope. For example, polyurethane 2,5-YDI/BP5 with [$\theta$]=0.44 prepared from 2,5-TDI and BP5 exhibited a liquid crystalline phase from 194 to 205$^{\circ}C$. Infrared spectrum study indicated that the hydrogen bonding between urethane linkages affected the mesomorphism. The thermostabilities of polyurethanes 2,5-TDI/BP5 and 1,4-PDI/BP5 were measured at a heating rate of 1$0^{\circ}C$/min in air. The temperatures of 5% weight loss for 2,5-TDI/BP5 and 1,4-PDI/BP5 were 297 and 334$^{\circ}C$, respectively.

• Journal of Astronomy and Space Sciences
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• v.24 no.4
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• pp.309-314
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• 2007

Originating from the Oort cloud, some comets disappear to impact against the Sun or to split up by strong gravitational force. Then they don't go back to the Oort cloud. They are called sungrazing comets. The comets are detected by sublimation of ices and ejection of gas and dust through solar heat close to the Sun. There exists the charge transfer from heavy ions in the solar wind to neutral atoms in the cometary atmosphere by interaction with the solar wind. Cometary atoms would be excited to high electronic levels and their do-excitation would result in X-ray emission, or it would be scattering of solar X-ray emission by very small cometary grains. We calculated the X-ray emission applying the model suggested by Mendis & Flammer (1984) and Cravens (1997). In our estimation, the sungrazing comet whose nucleus size is about 1 km in radius might be detectable within a distance of 3 solar radius from the sun on soft X-ray solar camera.

• Journal of the Korean Vacuum Society
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• v.7 no.3
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• pp.176-186
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• 1998

Pure Pt, Co and their alloy thin films with three different compositions (Pt66-Co34, Pt40-Co60 and Pt18-Co82) were deposited on Si(100) wafers and proposed as a set of certified reference materials (CRM) for the quantification and standardization of surface compositional analysis. The compositions of the binary alloy thin films were controlled by in-situ XPS analyses and the certified compositions of the films have been determined by ICP-AES and RBS analyses after thin film growth. Through comparison of the compositions determined by in-situ XPS with those by ICP, relatively accurate compositions could be obtained with a matrix effect correction. Standard deviations of XPS and AES round robin tests with the Pt-Co alloy thin films were large up to about 4%. On the other hand, the average compositions of the Pt-Co alloy thin films by two methods were in a good agreement within 1%. The formation of a Pt rich surface layer by ion beam sputtering indicates that the surface modification by preferential sputtering must be understood for a better compositional analysis.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.38 no.3
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• pp.197-201
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• 2002

The object of this study was to find out the probability of the abundance estimation by geographical parameters of fish school during the acoustic survey using scanning sonar. The acoustic survey was carried out in Funka Bay, off southern Hokkaido, Japan in December 1998. The 180-degree scanning sonar and the echo sounder were used simultaneously. The relationship was examined between geographical parameters (fish school area and volume) measured by sonar and area back scattering coefficient by the echo sounder. The obtained result showed positive correlation. Therefore, the use of geographical parameters of fish school is a useful method in estimating fish school abundance in the acoustic survey using sonar.

• Journal of Biomedical Engineering Research
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• v.28 no.4
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• pp.520-529
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• 2007

An efficient method for implementing image reconstruction algorithms for Compton cameras is presented. Since Compton scattering formula establishes a cone surface from which the incident photon must have originated, it is crucial to implement a computationally efficient cone-surface integration method for image reconstruction. In this paper we assume that a cone is made up of a series of ellipses (or circles) stacked up one on top of the other. In order to reduce computational burden for tracing ellipses formed by the intersection of a cone and an image plane, we propose a new method using a series of imaginary planes perpendicular to the cone axis so that each plane contains a circle, not an ellipse. In this case the cone surface integral can be performed by simply accumulating the circles along the cone axis. To reduce the computational cost of tracing circles, only one of the circles in the cone is traced and the rest are determined by using simple trigonometric ratios. For our experiments, we used the three different schemes for tracing ellipses; (i) using the samples generated by the ellipse equation, (ii) using the fixed number of samples along a circle on the imaginary plane, and (iii) using the fixed sampling interval along a circle on the imaginary plane. We then compared performance of the above three methods by applying them to the two reconstruction algorithms - the simple back-projection method and the expectation-maximization algorithm. The experimental results demonstrate that our proposed methods (ii) and (iii) using imaginary planes significantly improve reconstruction accuracy as well as computational efficiency.

• The Journal of the Acoustical Society of Korea
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• v.24 no.2
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• pp.97-102
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• 2005

Acoustic experiments were performed with Zostera marina to study the characteristics of backscattering of seagrass living in the bottom interface. Field experiments were conducted in the Dongdae man, Namhae for day and night to consider the effects of air-bubble from photosynthesis of seagrass. The multi-frequency (30$\~$120 kHz) responses were measured and the distributions of back scattering strength due to the movement of seagrass were Presented by PDF (probability density function) at 120 120 kHz. The results were shown both the frequency dependence and diurnal variation of the backscattering strength between day and night. This diurnal variation may be caused by the amount of oxygen in dissolved bubbles formed by Photosynthesis of seagrass.

• Journal of Korea Foundry Society
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• v.32 no.2
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• pp.104-108
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• 2012

The effect of heat treatment on mechanical properties of 0.4C-2.3Si(wt%) steel with bainitic ferrite matrix were investigated. This steel has been synthesized intergrating concepts from TRIP(Transformation Induced Plasticity) steel & Austempered Ductile Cast Iron(ADI) technology. The low alloy medium carbon (0.4 %C) steel with high silicon (2.3 %Si) was initially annealed for 60 min at $800^{\circ}C$, $820^{\circ}C$ and $840^{\circ}C$ respectively in the intercritical region and then subsequently austempered at various temperatures at $260^{\circ}C$, $320^{\circ}C$ and $380^{\circ}C$ for 30 min in a salt bath. The mechanical properties were measured by using a tensile test. A detailed study of the microstructure of this steel after heat treatment was carried out by means of electron back scattering diffraction (EBSD) technic. In this study, a new low alloy steel with high strength (780~1,050MPa) and exceptionally high ductility (20~40%) was obtained.

• Journal of Korea Foundry Society
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• v.32 no.3
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• pp.138-143
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• 2012

This steel has been synthesized integrating concepts from Austempering Ductile Cast Iron (ADI) technology. While ADI has excellent mechanical and physical properties, the Young's modules of ADI is approximately 20% lower than steel. In addition, the presence of graphite nodules in ADI can be sites of crack initiation, where fracture takes place at graphite matrix interface. Because of this limitations of ADI, there has been a growing interest in austempered steels as structural materials in resent years. In this investigation, a new steel with microstructure composed of ferrite and austenite and with simultaneous high tensile strength (1,150 MPa) and high ductility (33%) was developed. The goal of this investigation is to obtain a better understanding of deformation and transformation behaviour in high carbon retained austenite(${\gamma}_{HC}$) and over-saturated ferrite(${\alpha}$) during the plastic deformation. A detailed study of the microstructure of this steel was carried out by means of X-ray diffraction (XRD) and electron back scattering diffraction (EBSD) technic. In this way it was shown that BCC phase (BCC) took up the larger part of the nominal strain whereas the a part of retained austenite responded to the mechanincal load by partial martensite transformation, and misorientation change in the retained austenite after plastic strain could be attributed to the large elongation.