• 에너지공학
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• 제24권3호
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• pp.89-95
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• 2015

레독스흐름전지의 전극으로 사용하기 위해 (주)CNF에서 제조한 탄소펠트를 여러 가지 온도에서 열처리하여 실험하였다. 열처리 조건에 따른 탄소펠트의 물성특성을 파악하기 위하여 BET(비표면적)와 무게감소를 측정하였고 표면특성을 살펴보기 위하여 주사전자현미경(SEM)과 XPS 분석을 실시하였다. 또한 전기저항, CV(cyclic voltammetry), RFB 충방전 성능 통해 열처리 조건에 따른 전극특성에 미치는 영향을 살펴보았다. SEM, BET분석을 통하여 탄소펠트 표면의 물성 변화를 확인하였고, XPS 분석을 통해 $550^{\circ}C$에서 1시간 열처리한 탄소펠트의 표면에 산소 관능기가 가장 많이 부가된 것을 확인하였다. CV 실험을 수행한 결과 $550^{\circ}C$ 열처리 전극의 활성면적이 가장 컸다. $400^{\circ}C$, $500^{\circ}C$, $550^{\circ}C$에서 열처리한 탄소펠트를 이용하여 바나듐 레독스흐름전지를 구성하고 충-방전 실험을 실시한 결과 충-방전 에너지효율이 $400^{\circ}C$ 열처리 전극의 경우 72.9%, $500^{\circ}C$ 열처리 전극의 경우 79.8%, $550^{\circ}C$ 열처리 전극의 경우 79.8%로 $550^{\circ}C$ 열처리 전극이 가장 우수하였다.

• Macromolecular Research
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• 제9권2호
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• pp.107-115
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• 2001

Poly(L-lactide-co-glycolide)(PLGA) was blended with poly[$\omega$-methacryloyloxyethyl phospho-rylcholine-co-ethylhexylmethacrylate (PMEH)] (PLGA/PMEH) to endow with new functionality i.e., to improve the cell-, tissue- and blood-compatibility. The characteristics of surface properties were investigated by measurement of contact angle goniometer, Fourier-transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR) and electron spectroscopy for chemical analysis (ESCA). NIH/3T3 fibroblast and bovine aortic endothelial cell were cultured on control and PLGA/PMEH surfaces for the evaluation of ceil attachment and proliferation in terms of surface functionality such as the concentration of phosphoryl-choline. Also, the behavior of platelet adhesion on PLGA/PMEH was observed in terms of the surface functionality. The contact angles on control and PLGA/PMEH surfaces decreased with increasing PMEH content from 75$^{\circ}$ to about 43$^{\circ}$. It was observed from the FTIR-ATR spectra that phosphorylcholine groups are gradually increased with increasing blended amount of MPC. The experimental P percent values from ESCA analysis were more 3.28∼7.4 times than that of the theoretical P percent for each blend films. These results clearly indicated that the MPC units were concentrated on the surface of PLGA/PMEH blend. The control and PLGA/PMEH films with 0.5 to 10.0 wt% concentration of PMEH were used to evaluate cell adhesion and growth in terms of phosphorylcholine functionality and wettability. Cell adhesion and growth on PLGA/PMEH surfaces were less active than those of control and both cell number decreased with increasing PMEH contents without the effect of surface wettability. It can be explained that the fibronectin adsorption decreased with an increase in the surface density of phosphorylcholine functional group. One can conclude the amount of the protein adsorption and the adhesion number of cells can be controlled and nonspecifically reduced by the introduction with phosphorylcholine group. Morphology of the adhered platelets on the PLGA/PMEH surface showed lower activating than control and the number of adhered platelets on the PLGA/PMEH sample decreased with increasing the phosphorylcholine contents. The amount of fibrinogen adsorbed on the PLGA/PMEH surface demonstrated that the phospholipid polar group played an important role in reducing protein adsorption on the surface. In conclusion, this surface modification technique might be effectively used PLGA film and scaffolds for controlling the adhesion and growth of cell and tissue, furthermore, blood compatibility of the PLGA was improved by blending of the MPC polymer for the application of tissue engineering fields.

• 신재생에너지
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• 제2권2호
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• pp.4-8
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• 2006

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 and a surface passivation can be obtained simultaneously in one process. We have demonstrated the feasibility of a very efficient porous Si AR 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 layer 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 surface morphology of porous Si layers were investigated using SEM. The formation of a porous Si layer about $0.1{\mu}m$ thick on the textured silicon wafer result in an effective reflectance coefficient Reff lower than 5% in the wavelength region from 400 to 1000nm. Such a surface modification allows improving the Si solar cell characteristics.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2006년도 춘계학술대회
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• pp.183-186
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• 2006

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 and a surface passivation can be obtained simultaneously in one process. We have demonstrated the feasibility of a very efficient porous Si AR 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 layer 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 surface morphology of porous Si layers were investigated using SEM. The formation of a porous Si layer about $0.1{\mu}m$ thick on the textured silicon wafer result in an effective reflectance coefficient $R_{eff}$ lower than 5% in the wavelength region from 400 to 1000nm. Such a surface modification allows improving the Si solar cell characteristics.

• Macromolecular Research
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• 제17권11호
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• pp.856-862
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• 2009

This study examined the effects of liquid and solid additives on the morphological, mechanical and thermal insulating properties of rigid polyurethane foams (PUFs). The PUFs synthesized with tetramethylsilane (TEMS) as a liquid-type additive showed a smaller average cell size and lower thermal conductivity than those with the aerosil 200 and clay 30B as solid-type additives. When TEMS was added, the average cell size of the PUF became more uniform and finer due to the reduced surface tension of the polymer solution, which increased the nucleation rate and number of bubbles produced and reduced cell size. The PUFs with TEMS showed the highest closed cell contents among the PUFs prepared using TEMS, aerosil 200 and clay 30B. This suggests that the insulation properties of PUF can be determined by both the size of the cell structure and the amount of closed cell contents in the system. The compression and flexural strengths of the PUF increased slightly when the aerosil 200, clay 30B and TEMS were added compared those of the neat PUF. The reaction profiles of the PUFs showed a similar gel and tack tree time with the reaction time among the PUFs synthesized with three different additives and neat PUF. This suggests that the nucleating additives used in this study do not affect the bubble growth of the chemical reaction, and the additives may act as nucleating agents during the formation of PUF. From the above results of the cell size, thermal conductivity, closed cell contents and reaction profile of the PUFs, liquid-type nucleating agent, such as TEMS, is more effective in decreasing the thermal conductivity of the PUF than solid-type nucleating agent, such as aerosil 200 and clay 30B.

• International Journal of Oral Biology
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• 제37권1호
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• pp.9-16
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• 2012

The aim of this study was to evaluate surface characteristics and biological properties of the dentin -derived hydroxyapatite (HA) coating on titanium substrate. Dentinderived HA was obtained from extracted human teeth using a calcination method at $850^{\circ}C$. The commercially pure titanium (cp-Ti, ASTM Grade II) was used as a metallic substrate and a radio frequency magnetron sputtering method was employed as a coating method. Scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) were utilized to investigate the coating aspects and composition. Atomic forced microscopy (AFM) and a surface profiler were used to assess the surface morphology and roughness. Corrosion tests were performed in phosphate-buffered saline at a $36.5{\pm}1^{\circ}C$ in order to determine the corrosion behavior of the uncoated and coated specimens. The biocompatibility of dentin-derived HA coated specimens with fetal rat calvarial cells and human gingival fibroblasts was assessed by SEM and cell proliferation analysis. The results showed that the dentin-derived HA coatings appeared to cover thinly and homogeneously the surfaces without changing of the titanium substrate. The EDX analysis of this the coating surface indicated the presence of Ca and P elements. The mean surface roughness of cp-Ti and dentin-derived coating specimens was $0.27{\mu}m$ and, $1.7{\mu}m$, respectively. Corrosion tests indicated a stable passive film of the dentin-derived HA coating specimens. SEM observations of fetal rat calvarial cells and human fibroblast cells on coated surfaces showed that the cells proliferated and developed a network of dense interconnections. The cells on all specimens proliferated actively within the culture period, showing good cell viability. At day 1 and 3, dentin-derived coating specimens showed 89% and 93% cell viability, respectively, when normalized to cp-Ti specimens. These results suggest that dentin-derived HA coating using the RF magnetron sputtering method has good surface characteristics and biocompatibility.

• 전기학회논문지
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• 제58권6호
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• pp.1146-1150
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• 2009

Cadmium telluride (CdTe) is one of the most attractive photovoltaic materials due to its low cost, high efficiency and stable performance in physical, optical and electronic properties. Few researches on the influences of uniform surface on the photovoltaic characteristics in large-area CdTe solar cell were not reported. As the preceding study of the effects of thickness-uniformity on the photovoltaic characteristics for the large-area CdTe thin film solar cell, chemical mechanical polishing (CMP) process was investigated for an enhancement of thickness-uniformity. Removal rate of CdTe thin film was 3160 nm/min of the maximum value at the 200 $gf/cm^2$ of down force (pressure) and 60 rpm of table speed (velocity). The removal rate of CdTe thin film was more affected by the down force than the table speed which is the two main factors directly influencing on the removal rate in CMP process. RMS roughness and peak-to-valley roughness of CdTe thin film after CMP process were improved to 96.68% and 85.55%, respectively. The optimum process condition was estimated by 100 $gf/cm^2$ of down force and 60 rpm of table speed with the consideration of good removal uniformity about 5.0% as well as excellent surface roughness for the large-area CdTe solar cell.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2017년도 춘계학술대회 논문집
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• pp.155-155
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• 2017

Surface modifications are commonly utilized to adjust the properties of the titanium and its alloy surface to the specific needs of the medical applications, but there are disadvantages such as poor osteoconductive properties and low adhesion of bone cell to implant surface. In order to improve these disadvantages, changes in surface properties have an important effect on osseointegration during implantation. In this paper we applied new technological method for improving a unique surface modification using the characteristic of an electrolytic Solution. Thus, in the electrolyte containing NaF in Na2SO4, TiO2 nanoporous was uniformly formed, and HAp nanoparticles were electrodeposited around the TiO2 nanopores, but in the electrolyte containing NH4F in (NH4)H2PO4, the coarse protrusions including HAp nano particles were regularly deposited onto the TiO2 barrier layer. The surface characteristics and the distributed elements and have been investigated by EDS analysis, and ultra-fine structure of surface are carried out using FE-SEM. To investigate the behavior of the anion, the analysis of chemical states was performed by XPS, and the narrow spectrums for Ti2P, Ca 2p, and P 2p seems to be almost similar depending on the characteristics of the electrolyte solution respectively. In addition, Ca 2p spectrum could be resolved into two peaks for Ca 2p3/2 and 2p1/2 at 347.4 and 351.3 eV, which are related to hydroxyapatite. And, the P peak can also be deconvoluted into two peaks for P1/2 and P3/2 levels with binding energy 134.2 and 133.4 eV, respectively. From the result of soaking test, the apatite morphologys were well-formed onto the modified surface according to the different conditions.

• 한국표면공학회지
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• 제49권3호
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• pp.301-306
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• 2016

The effects of nanotexturing and post-etching on the reflection and quantum efficiency properties of diamond wire sawn (DWS) multicrystalline silicon (mc-Si) solar cell have been investigated. The chemical solutions, which are acidic etching solution (HF-$HNO_3$), metal assisted chemical etching (MAC etch) solutions ($AgNO_3$-HF-DI, HF-$H_2O_2$-DI) and post-etching solution (diluted KOH at $80^{\circ}C$), were used for micro- and nano-texturing at the surface of diamond wire sawn (DWS) mc-Si wafer. Experiments were performed with various post-etching time conditions in order to determine the optimized etching condition for solar cell. The reflectance of mc-Si wafer texturing with acidic etching solution showed a very high reflectance value of about 30% (w/o anti-reflection coating), which indicates the insufficient light absorption for solar cell. The formation of nano-texture on the surface of mc-Si contributed to the enhancement of light absorption. Also, post-etching time condition of 240 s was found adequate to the nano-texturing of mc-Si due to its high external quantum efficiency of about 30% at short wavelengths and high short circuit current density ($J_{sc}$) of $35.4mA/cm^2$.

• 한국축산식품학회지
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• 제21권2호
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• pp.133-141
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• 2001

Adherence of probiotic bacteria to intestinal epithelium is found to be the most principal characteristics among the various physiological functionality. This study was conducted to investigate the effect of bifidobacterial growth properties and condition on the Caco-2 cell adherence and to construct a basic data on adherence-related research. Among 20 strains of bifidobacteris tested, when measured by cell surface hydrophobicity(CSH) and cell agglutination(CA), Bifidobacterium bifidum ATCC29521, Bif. adolescentis K8, and Bif. infantis K9 were selected. Using these strains, variations of Caso-2 cell adherence depending upon experimental condition were analyzed. The results obtained are as follows : Even though Bif. bifidum ATCC29521, Bif. adolescentis K8, and Bif. infantis K9 reached more 85% cell surface hydrophobicity there was no significant difference in cell agglutination, when reached 31.54$\pm$0.54mg/ml. By direct count method for adherence, viable cell count of M3, K1, K2, K8, K9 and K10 reached more 100 counts per 100 Caco-2 cells. When Bif. bifidum ATCC29521, Bif. adolescentistis K8, and Bif. infantis K9 were used to compare the adherence depending upon viable cell counts, reaction time, and growth phase, the more viable cell count, and the more adhered cell counts, the less adherence percentage. In addition, there was no difference in adherence percentage of bifidobacteria when bifidobacteria was incubated from 1 to 8 hrs after Caco-2 cells already formed monolayer. Considering of the effect of growth phase of bifidobacteria on adherence variation, all strains showed the highest adherence during the early stage of stationary phase. In conclusion, adherence of bifidobacteria was affected by strain specificity, viable cell count, and growth activity.