• 한국전기전자재료학회논문지
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• 제22권7호
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• pp.616-621
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• 2009

Reduction of optical losses in crystalline silicon solar cells by surface modification is one of the most important issues of silicon photovoltaics. Porous Si layers on the front surface of textured Si substrates have been investigated with the aim of improving the optical losses of the solar cells, because an anti-reflection coating(ARC) and a surface passivation can be obtained simultaneously in one process. We have demonstrated the feasibility of a very efficient porous Si ARC layer, prepared by a simple, cost effective, electrochemical etching method. Silicon p-type CZ (100) oriented wafers were textured by anisotropic etching in sodium carbonate solution. Then, the porous Si layers were formed by electrochemical etching in HF solutions. After that, the properties of porous Si in terms of morphology, structure and reflectance are summarized. The structure of porous Si layers was investigated with SEM. The formation of a nanoporous Si layer about 100nm thick on the textured silicon wafer result in a reflectance lower than 5% in the wavelength region from 500 to 900nm. Such a surface modification allows improving the Si solar cell characteristics. An efficiency of 13.4% is achieved on a monocrystalline silicon solar cell using the electrochemical technique.

• International Journal of Precision Engineering and Manufacturing
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• 제8권4호
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• pp.27-32
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• 2007

Gears, crucial components in modern precision machinery for power transmission mechanisms, are required to have low contacting noise with high torque transmission, which makes the use of gear-tooth profile modifications and gear-tooth surface crowning extremely efficient and valuable. Due to the shortcomings of current techniques, such as manual rectification, mechanical modification, and numerically controlled rectification, we propose a novel electrochemical gear-tooth profile modification method based on an artificial neural network control technique. The fundamentals of electrochemical tooth-profile modifications based on real-time control and a mathematical model of the process are discussed in detail. Due to the complex and uncertain relationships among the machining parameters of electrochemical tooth-profile modification processes, we used an artificial neural network to determine the required processing electric current as the tooth-profile modification requirements were supplied. The system was implemented and a practical example was used to demonstrate that this technology is feasible and has potential applications in the production of precision machinery.

• Journal of Microbiology and Biotechnology
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• 제16권3호
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• pp.399-407
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• 2006

In this study, an electrical conductive carbon fiber was used as a biofilter matrix to electrochemically improve the biofilter function. A bioreactor system was composed of carbon fiber (anode), titanium ring, porcelain ring, inorganic nutrient reservoir, and VOC reservoir. Electric DC power of 1.5 volt was charged to the carbon fiber anode (CFA) to induce the electrochemical oxidation potential on the biofilter matrix, but not to the carbon fiber (CF). We tested the effects of electrochemical oxidation potential charged to the CFA on the biofilm structure, the bacterial growth, and the activity for metabolic oxidation of VOCs to $CO_2$, According to the SEM image, the biofilm structure developed in the CFA appeared to be greatly different from that in the CF. The bacterial growth, VOCs degradation, and metabolic oxidation of VOCs to $CO_2$ in the CFA were more activated than those in the CF. On the basis of these results, we propose that the biofilm structure can be improved, and the bacterial growth and the bacterial oxidation activity of VOCs can be activated by the electrochemical oxidation potential charged to a biofilter matrix.

• 분석과학
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• 제18권1호
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• pp.89-95
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• 2005

Studies on the electrochemical reduction of 7-acetoxy-4-bromomethyl-coumarin (ABMC), 7-acetoxymethyl coumarin (AMC), and coumarin in 0.1 M tetraethyl ammonium perchlorate acetonitrile solution were carried out with direct current, differential pulse polarography, cyclic voltammetry, and controlled potential coulometry. The electrochemical reduction of ABMC was proceeded through three irreversible steps coupled with the chemical reactions. The solution color was changed to yellow when the carbonyl group was reduced during second step and the color change was independent with bromo group of ABMC. Fluorescent intensity was highest when the electrochemical reduction was controlled at near the overpotential of supporting electrolyte (-2.3 volts).

• 한국응용과학기술학회지
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• 제32권3호
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• pp.451-460
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• 2015

An enantioselective recognition of D- and L-tryptophan (Trp)-b-cyclodextrin (CD) inclusion complex was performed using electrochemical and FT-Raman spectroscopic analysis. From the electrochemical analysis, the selectivity coefficient ($K_{DL}$) of b-CD inclusion complexes was found higher than that of the D- and L-Trp in phosphate buffered saline (PBS, pH=7.0) solution. The percentage of enantioselectivity ($I_{%{ee}}$) for peak current of D-Trp-b-CD inclusion complexes was observed higher than that of L-Trp-b-CD inclusion complexes in PBS solution. From Raman spectroscopy, chemical shift difference (D, $cm^{-1}$) for the C=C stretch, ring vibration, and ring breathing of D-Try-b-CD inclusion complex were observed higher than that of L-Trp-b-CD inclusion complex. The electrochemical and Raman spectroscopic analyses were found very useful for chiral detection of racemic amino acid in the presence of b-CD.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 춘계학술발표대회
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• pp.40.2-40.2
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• 2011

As the old saying 'nothing is complete unless you put it in final shape', although nanosheets (NSs) are a promising functional building block for various electrochemical applications, their true value cannot be realized until they are well woven into electrical conducting materials. As an effort to determine their ideal shape, in this study, a unique manufacturing route to build a layer-by-layer (LBL) structure of two-dimensionally ordered, free-standing ${\beta}$-nickel hydroxide nanosheets (${\beta}$-NHNSs) that are fully electrically addressed with single-wall carbon nanotube fabrics was demonstrated, and its capabilities were verified through a comparative study on the differences between a simple bulky and LBL-structured electrochemical cathode, representing two extreme cases. The LBL-structured cathode showed a discharging current peak that was 25 times larger than the bulky structured one measured in cyclic voltammetry, which implies that the LBL structure is near an ideal electrode configuration for NS-based electrochemical applications.

• 전기화학회지
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• 제12권4호
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• pp.301-310
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• 2009

본 논문에서는 현재 많이 연구되고 있는 염료감응 태양전지에 대해 전기화학적 접근을 통해 설명한다. 특히, 기존 도핑 개념을 적용하는 반도체 태양전지와 다른 점을 비교 설명하고, 이론적으로 어떻게 태양전지가 형성될 수 있는지를 설명한다. 또한 염료감응 태양전지가 탄생되게 된 과정을 고찰해 본다. 이어서, 태양전지에서 많이 사용되는 전기화학적 분석법을 설명하고, 어떻게 적용될 수 있는지 임피던스 분석법을 통해 설명한다. 전기화학에서 많이 사용되는 임피던스와 순환전압전류법을 통해, 염료감응 태양전지를 이루는 주성분인 금속산화물과 염료, 전해질의 에너지준위 분석법에 대해서 간단히 소개한다.

• 한국전기전자재료학회논문지
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• 제15권11호
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• pp.958-962
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• 2002

This paper reports on the fabrication of free-standing microstructures by DRIE (deep reactive ion etching). SOI (Si-on-insulator) structures with buried cavities are fabricated by SDB (Si-wafer direct bonding) technology and electrochemical etch-stop. The cavity was formed the upper handling wafer by Si anisotropic etch technique. SDB process was performed to seal the formed cavity under vacuum condition at -760 mmHg. In the SDB process, captured air and moisture inside of the cavities were removed by making channels towards outside. After annealing (100$0^{\circ}C$, 60 min.), the SDB SOI structure with a accurate thickness and a good roughness was thinned by electrochemical etch-stop in TMAH solution. Finally, it was fabricated free-standing microstructures by DRIE. This result indicates that the fabrication technology of free-standing microstructures by combination SDB, electrochemical etch-stop and DRIE provides a powerful and versatile alternative process for high-performance bulk micromachining in MEMS fields.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 하계학술대회 논문집 Vol.5 No.2
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• pp.1226-1229
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• 2004

Supercapacitors, also known as electrochemical capacitors, are being extensively studied due to an increasing demand for energy-storage systems. These devices offer many advantages over conventional secondary batteries, which include the ability of fast charge propagation, long cycle-life and better storage efficiency. That is to say supercapacitor bridges the gap between conventional capacitors and batteries. A new type electric double layer capacitor (EDLC) also called supercapacitors. Recently, supercapacitors concerns about their high power density and energy density. So we experiment with EDLC by using carbon nanofibers (CNFs) and DAAQ(1,5-diaminoanthraquinone) electrode. The electrode for supercapacitor was prepared by synthesis of DAAQ covered CNFs. CNFs could be covered with very thin DAAQ oligomer from the results of CV, XRD, DSC, SEM images, and TEM images. Dissolved electrode active material in NMP solution has been drop-coated on carbon plate. Its electrochemical characteristics were investigated by cyclic voltammograms. And compared with different electrolyte of aqueous type. As a result, CNFs coated by DAAQ composite electrode showed relatively good electrochemical behaviors with respect to specific capacity and scan rate dependency.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 영호남학술대회 논문집
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• pp.7-12
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• 2000

This paper presents the electrochemical etch-stop characteristics of single-crystal silicon in a tetramethyl ammonium hydroxide(TMAH):isopropyl alcohol(IPA):pyrazine solution. Addition of pyrazine to a TMAH:IPA etchant increases the etch-rate of (100) silicon, thus the elapsed time for etch-stop was shortened. The current-voltage (I-V) characteristics of n- and p-type silicon in a TMAH:IPA:pyrazine solution were obtained, respectively. Open circuit potential(OCP) and passivation potential(PP) of n- and p-type silicon, respectively, were obtained and applied potential was selected between n- and p-type silicon PP. The electrochemical etch-stop is applied to the fabrication of 801 microdiaphragms having $20{\mu}m$ thickness on a 5-inch silicon wafer. The averge thicknesses of 801 microdiaphragms fabricated on the one wafer were $20.03{\mu}m$ and standard deviation was ${\pm}0.26{\mu}m$. The silicon surface of the etch-stopped microdiaphragm was extremely flat without noticeable taper or other nonuniformities. The benefits of the electrochemical etch-stop in a TMAH:IPA:pyrazine solution become apparent when reproducibility in the microdiaphragm thickness for mass production is considered. These results indicate that the electrochemical etch-stop in a TMAH:IPA:pyrazine solution provides a powerful and versatile alternative process for fabricating high-yield silicon microdiaphragms.