• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.235.2-235.2
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• 2015

The front transparent conductive oxide (TCO) films must exhibit good transparency, low resistivity and excellent light scattering properties for high efficiency amorphous silicon (a-Si) thin film solar cells. The light trapping phenomenon is limited due to non-uniform and low aspect ratio of the textured glass [1]. We present the low cost electrochemically deposited uniform zinc oxide (ZnO) nanorods with various aspect ratios for a-Si thin film solar cells. Since the major drawback of the electrochemically deposited ZnO nanorods was the high sheet resistance and low transmittance that was overcome by depositing the RF magnetron sputtered AZO films as a seed layer with various thicknesses [2]. The length and diameters of the ZnO nanorods was controlled by varying the deposition conditions. The length of ZnO nanorods were varied from 400 nm to $2{\mu}m$ while diameter was kept higher than 200 nm to obtain different aspect ratios. The uniform ZnO nanorods showed higher haze ratio as compared to the commercially available FTO films. We also observed that the scattering in the longer wavelength region was favored for the high aspect ratio of ZnO nanorods and much higher aspect ratios degraded the light scattering phenomenon. Therefore, we proposed our low cost and uniform ZnO nanorods for the high efficiency of thin film solar cells.

• Journal of Biomedical Engineering Research
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• v.30 no.1
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• pp.18-22
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• 2009

Laser has been widely used in various fields of medicine. Recently, noninvasive low-level laser therapeutic medical devices have been introduced in market. However, low-level laser cannot deliver enough photon density to expect positive therapeutic results in deep tissue layer due to the light scattering property in tissue. In order to overcome the limitation, this study was aimed to develop a negative pressure applied low-level laser probe to optimize laser transmission pattern and therefore, to improve photon density in soft tissue. In order to evaluate the possibility of clinical application of the developed laser probe, ex-vivo experiments were performed with porcine skin samples and laser transmissions were quantitatively measured as a function of tissue compression. The laser probe has an air suction hole to apply negative pressure to skin, a transparent plastic body to observe variations of tissue, and a small metallic optical fiber guide to support the optical fiber when negative pressure was applied. By applying negative pressure to the laser probe, the porcine skin under the metallic optical fiber guide is compressed down and, at the same time, low-level laser is emitted into the skin. Finally, the diffusion images of laser in the sample were acquired by a CCD camera and analyzed. Compared to the peak intensity without the compression, the peak intensity of laser increased about $2{\sim}2.5$ times and FWHM decreased about $1.67{\sim}2.85$ times. In addition, the laser peak intensity was positively and linearly increased as a function of compression. In conclusion, we verified that the developed low-level laser probe can control the photon density in tissue by applying compression, and therefore, its potential for clinical applications.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.11
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• pp.975-982
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• 2010

In this study, the laser sintering of inkjet-printed silver lines was evaluated. Silver-nanoparticle ink and a drop-ondemand (DOD) inkjet printer were used for printing on glass and polyethylene terephthalate (PET) substrates with various thicknesses. To sinter the printed silver nanoparticles, the silver layer printed on the transparent substrates was irradiated by focused CW laser beams that were incident normal to the substrates; the irradiation was carried out for various beam intensities and for various irradiation times. The electrical conductivity of the laser-sintered silver patterns was measured and compared with the conductivity of silver patterns sintered by using an oven. The increase in the temperature caused by laser irradiation was also calculated on the basis of the laser beam intensity, irradiation time, surface reflectivity, and thermophysical property of the substrate in order to estimate the increase in the electrical conductivity caused by laser sintering.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.572-572
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• 2013

본 연구에서는 Plasma damage-free 선형 대향 타겟 스퍼터(Linear Facing Target sputtering: LFTS) 시스템을 이용하여 성막시킨 GaN-LED의 투명전극용 Ga-doped ZnO (GZO) 박막의 특성을 연구하였다. LFTS 시스템을 이용한 GZO 성막 공정 중 LED소자의 플라즈마 노출에 의한 데미지를 최소화 하기 위해 일정한 타겟간 거리(Target-to-Target distance: 65 mm)에서 타겟과 기판간 거리(Target-to-Substrate distance)를 50 mm에서 120 mm로 변화시키며 GZO 투명 전극을 성막해 박막의 특성과 소자의 특성을 동시에 분석하였다. LFTS에서 플라즈마는 GZO 타겟 사이에 형성된 일방향의 자장에 의해 효과적으로 구속되기 때문에 기판과 타겟 거리를 최적화 할 경우 플라즈마 데미지를 최소화하며 GaN-LED의 제작이 가능하다. 기판과 타겟 사이의 거리가 120 mm에서 최적화된 200 nm 두께의 GZO 투명 전극은 DC 파워 250 W, 공정 압력 0.3 mTorr, Ar 20 sccm 실험 조건하에서 LED 소자 위해 성막되었으며, 이후 $600^{\circ}C$ 수소 분위기에서 1분간 급속 열처리하였고 면저항(37 Ohm/sq.)과 450 nm 파장에서의 투과도(83%)를 나타냄을 확인할 수 있었다. LED 소자와 타겟 사이의 거리가 50 mm에서 120 mm로 증가할수록 성막공정 중 LED 소자에 미치는 플라즈마 데미지의 감소로 인해 GaN-LED 소자의 turn on voltage가 8.2 V에서 3.4 V로 감소한 것을 확인하였으며, 또한 radiant intensity는 20 mA의 전류를 인가하였을 시 0.02 mW/sr에서 8 mW/sr로 400배 향상되었다. 이러한 소자 특성은 대향 타겟 스퍼터 시스템으로 성장시킨 GZO 투명전극이 LED 소자의 투명 전극 층(Transparent Conductive Layer: TCL)에 적용될 수 있음을 말해준다.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.473-473
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• 2013

전자종이, 입을 수 있는 디스플레이, 플렉서블 터치 스크린, 투과성 면 등과 같은 차세대 플렉서블 투명 전자소자는 기계적으로 유연하고 광학적으로 투명하며 무게가 가벼운 특성을 지녀야 할 것으로 예상된다. 현재까지는Indium tin oxide (ITO), zinc tin oxide (ZTO), carbon nano tube (CNT)와 polyimide 계열의 물질들이flexible, wearable, and transparent electronics (FWTEs) 소자의 electrode, active channel, dielectric layers로 제안되어 활발히 연구되었다. 최근에는 높은 이동도(~200,000 cm2/Vs) 및 유연성(fracture strain of 30%), 투명도 (97.5% for monolayer)와 같은 특성을 갖는 그래핀에 대한 연구가 활발히 진행되고 있다. 그러나 그래핀을 차세대 플렉서블 투명 전자소자 구현에 적용하기 위해서는 플렉서블하고 투명한 절연체의 확보 및 그래핀의 진성(intrinsic) 특성 유지 등과 같은 문제점들을 해결해야 한다. 따라서, 본 연구팀에서는 그래핀 기반 플렉서블 투명 전자소자의 게이트 절연층으로 적합한 poly-4-vinylphenol/poly (melamineco-formaldehyde) (PVP/PMF) 물질을 제시하고 이에 대한 전기적 재료적 분석을 수행하였다. 특히 다양한 PVP와 PMF의 비율 및 가열(annealing 혹은 curing) 온도에서 형성된 PVP/PMF 층의 화학 및 전기적 특성을 FT-IR, I-V, 그리고 C-V 측정을 통해 확인하였다. PVP/PMF는 유기절연 물질의 하나로서 높은 유연성과 투명도를 갖고 있을 뿐만 아니라 그래핀에 적용 시 그래핀의 진성 특성을 확보할 수 있다. 이는 PVP/PMF에 존재하는 hydroxyl (-OH) 그룹과 그래핀 상에서 정공(hole)을 공급하는 것으로 알려져 있는 -OH 그룹들간의 cross-linking 메커니즘에 의한 것으로 예상된다. 마지막으로 최적화된 PVP/PMF (낮은 hysteresis 전압)를 게이트 절연층에 적용하여 polyethylene terephthalate (PET) 기판 및 연구원의 손가락 위에 95.8%의 투명도 및 0에 가까운 Dirac point를 갖는 그래핀 기반 플렉서블 투명 전자소자를 성공적으로 집적하였다.

• Ocean and Polar Research
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• v.26 no.2
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• pp.219-230
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• 2004

The aims of this study are to construct database using geostatistics and Geographic Information System (GIS), and to derive the spatial relationships between manganese nodule abundance and each factor affecting nodule abundance, such as metal grade, slope, aspect, water depth, topography, and acoustic characteristics of the subbottom using the GIS and probability methods. The greater is the copper and nickel grade, the higher is the rating. The distribution pattern of nickel grade is similar to that of copper grade. The slopes are generally less than $3^{\circ}$, excluding seamounts and cliff areas. There is no increment in the rating with increasing slope. The rating is highest for slopes between 2.5 and $3.5^{\circ}$ in block B2 and between 3 and $6^{\circ}$ in block C1. The topography is classified into five groups: seamount, hill crest, hill slant, hill base or plain, and seafloor basin or valley. The ratings prove lowest for seamount and hill crest. The results of the study show a decrease in the rating with an increase in water depth in the study area. There was a poor relationship between manganese nodule abundance and the thickness of the upper transparent layer in block C1. Using GIS, it is possible to analyze a large amount of data efficiently, and to maximize the practical application, to increase specialization, and to enhance the accuracy of the analyses.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.240.2-240.2
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• 2011

그라파이트 산화물(graphite oxide;G.O)는 그라파이트와는 다르게 물에서의 분산 능력이 뛰어나고 다양한 기판상에 단일 G.O layer를 형성할 수 있는 특성을 가지고 있으며, 유연(flexible)하고 투명(transparent)하기 때문에 다양한 전 자기 디바이스에 적용 가능하다. 특히, 최근 자성산화물 나노입자(magnetic oxide nanoparticles)에 대한 연구가 집중되고 있는데, 이러한 자성 나노입자와 G.O와의 복합체에 대한 연구는 다양한 분야로의 적용성에 대한 새로운 길을 열어주고 있다. 본 연구에서는 화학적 처리법을 적용하여 자성 나노입자(Co 나노입자)와 G.O 복합체를 제조하였다. Natural Graphite powder (N.G)에 $H_2O_4$ (98%) 및 $(NH_4)_2SO_4$를 적정 몰비로 첨가하여 반응 시킨 후 공기 중에서 열처리 공정을 수행하여 expanded graphite (E.G)를 제조 하였다. 열처리된 E.G를 $1,050^{\circ}C$ 온도에서 15~30초 및 30~60초 동안 공기 중에서 열처리 하여 expanded graphite oxide (E.G.O)를 제조하였으며, E.G.O와 $Co(acac)_3$의 화학적 반응을 통하여 Co 자성나노입자-G.O 복합체를 제조하였다. N.G, E.G, E.G.O 및 E.G.O+Co입자의 결정구조 분석을 위하여 XRD 측정을 수행하였으며, FTIR을 이용하여 각 단계에서의 반응성에 대한 연구를 수행하였다. 각 단계에서 표면 및 내부 미세구조 특성 분석을 위하여 SEM, TEM, 및 EDX 분석을 수행하였으며, E.G.O+Co 복합체의 자기적 특성 평가를 위하여VSM (vibrating sample magnetometer) 측정을 수행하였다. 이러한 연구 결과는 향후 자성나노입자와 그라핀과의 복합화를 위한 기저 기술로 활용가능하리라 판단된다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.424-424
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• 2008

Dye-sensitized Solar Cell (DSC) is a new type of solar cell by using photocatalytic properties of $TiO_2$. The electric potential distribution in DSCs has played a major role in the operation of such cells. Models based on a built-in electric field which sets the upper limit for the open circuit voltage(Voc) and/or the possibility of a Schottky barrier at the interface between the mesoporous wide band gap semiconductor and the transparent conducting substrate have been presented. $TiO_2$ thin films were deposited on the FTO substrate by Nd:YAG Pulsed Laser Deposition(PLD) at room temperature and post-deposition annealing at $500^{\circ}C$ in flowing $O_2$ atmosphere for 1 hour. The structural properties of $TiO_2$ thin films have investigated by X-ray diffraction(XRD) and atomic force microscope(AFM). Thickness of $TiO_2$ thin films were controlled deference deposition time and measurement by scanning electron microscope(SEM). Then we manufactured a DSC unit cells and I-V and efficiency were tested using solar simulator.

• 한국신재생에너지학회:학술대회논문집
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• 2007.11a
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• pp.297-300
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• 2007

In this study, we have attempted a new method to enhance the coloring of dye on the $TiO_2$ surface in the dye sensitized solar cell. In the conventional coloring process in a dye sensitized solar cells, dye is absorbed by the covalent bond between TiO2 and dye molecule while the photo-electrode coated with $TiO_2$ layer is soaked in dye solution for about 12-24 hours. But this process takes long time, so we have researched more effective and faster way than the conventional process by applying electric field. Three kinds of electric power such as direct voltage, alternating voltage and pulse voltage were applied to the transparent conducting oxide during the coloring process. As a result, we achieved improved power, fill factor and efficiency of dye-sensitized solar cell in case of applying direct voltage and pulse voltage. In contrast, alternating voltage tend to reduce the dye adsorption on the $TiO_2$ surface and hence the efficiency. We measured the absorption spectra of dye by UV-VIS spectrophotometer before and after soaking the $TiO_2$ in the dye and found no characteristic change in the dye was observed. In this study, we researched on shortening time of coloring process which spent much time in the whole process.

• Journal of Environmental Health Sciences
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• v.36 no.4
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• pp.337-341
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• 2010

The modified simultaneous differential staining technique, which enables double staining of cartilage and bones, needs to be improved to prevent soft tissues from being damaged during the staining process. Key factors influencing the extent to which soft tissues are damaged include the fixative used, macerating time, potassium hydroxide concentration, incubation temperature and the removal of skin from specimens. Here we describe a protocol that enables the hardening of tissues during bleaching and maceration. We also describe a method for objectively measuring rates of cartilage and bone growth. The use of formalin as a fixative rendered soft tissues more rigid due to the resulting chemical bonds formed between proteins. Blotted specimens were immersed in 1% potassium hydroxide (KOH) and incubated at $37^{\circ}C$ for 1 day (smaller specimens) or 2-3 days (larger specimens). The 1% KOH solution was also used as the diluent solution for the subsequent immersion in a graded series of 30%, 50%, 70%, 90%, 100% glycerol solutions, a procedure that made soft tissues even more transparent and hardened. It was not necessary to remove the skin of specimens shorter than 2 cm, since the macerating solution could easily penetrate their thin skin layer and continuously remove those pigments hindering visibility. Since excessive osmosis is another factor that can damage soft tissues in the macerating process by causing the rupture of those cells not able to withstand the osmotic pressure, here it was minimized by balancing the salt concentration between the interior and exterior of cells with the addition of 0.9% sodium chloride (NaCl) in the macerating solution. Finally, to determine the proportions of cartilage and bone growth, photographs of the stained specimens were taken with a dissecting microscope and sections corresponding to the cartilage and bones were cut out from the printed pictures and weighed. Our results show that this method is suitable for the objective evaluation of bone and cartilage growth.