• Journal of information and communication convergence engineering
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• 제9권6호
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• pp.725-728
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• 2011

Infrared transmission images from GaAs semi insulating wafers were considered for years as directly related to the quantum absorption by electrons on fundamental states of deep centers, especially EL2. The satisfying correspondence of these images with the dislocations revealed by etching or X ray topography or infrared tomography led to the opinion that a strong concentration of EL2 centers was to be expected in the immediate vicinity of the dislocations. More recent work indicates that contrary to the expected behavior the photoqu$\acute{e}$nching of transmission images at T=80K does not appreciably change the image structure itself but more largely the uniform background level of absorption. Such investigations show that the transmission images of isolated dislocations (Indium doped materials) or cell structures of tangled dislocations (undoped materials) can be partly attributed to scattered light; similar operation at T=10K removes the dark features associated to EL2 but still preserves the skeleton of the pattern which is due to scattering. A result of the measurements is that dislocations must not be considered any longer as inexhaustive EL2 reservoirs. The lifetime of the photoqu$\acute{e}$nching mechanism is shown to vary differently for EL2 centers located close to the dislocations or in the matrix. In this paper we will develop the details of infrared image photoqu$\acute{e}$nching experiments in the vicinity of dislocations; undoped and In doped GaAs materials will be shown. These results will be discussed in the light of surface etching experiments.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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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.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.430.2-430.2
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• 2016

The front transparent conductive oxide (TCO) films in thin fill solar cell should exhibit high transparency, conductivity, good surface morphology and excellent light scattering properties. The light trapping phenomenon is limited due to random surface structure of TCO films. The proper control of surface structure and uniform cauliflower TCO films may be appropriate for efficient light trapping. We report light trapping scheme of ICP-RIE glass texturing by SF6/Ar plasma for high roughness and haze ratio of ITO films. It was observed that the variation of etching time, pattern size and Ar flow ratio during ICP-RIE process were important factors to improve the diffused transmittance and haze ratio of textured glass. The ICP-RIE textured glass showed low etching rates due to the presence of metal elements like Al, B, F and Na. The ITO films deposited on textured glass substrates showed the high RMS roughness and haze ratio in the visible wavelength region. The change in surface morphology showed negligible influence on electrical and structural properties of ITO films. The ITO films with high roughness and haze ratio can be used to improve the performance of thin film solar cells.

• 폴리머
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• 제27권4호
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• pp.293-298
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• 2003

제한공간에서 형성되는 폴리(트리메틸렌 테레프탈레이트) (PTT)의 결정구조를 광학현미경, 소각 광산란 및 X-선 회절로 조사하였다. 인자 $\delta$로 대표할 수 있는 배제 성분의 이동거리는 폴리(에틸렌 테레프탈레이트) (PET/PTT) 블렌드의 형태구조 패턴을 결정하는데 중요한 역할을 하였다. 단계 결정화할 경우, PTT 결정화는 앞서 성장한 PET 결정의 구정 사이 영역에서 시작되었으며, 구정 사이 영역이 채워질 때까지 진행하였다. PET 구정 표면은 PTT 결정화에 매우 효과적인 핵 생성 작용을 유도함으로써 transcrystalline 구조의 PTT 결정을 유도하였다. 그 결과 PTT가 많은 상에서 전형적인 구정 구조와 함께 transcrystalline구조가 혼재하는 독특한 형태구조가 관찰되었다. PET 구정의 라멜라 사이나 피브릴 사이의 영역에서는 공간적 제한으로 인하여 PTT분자들의 형태 자유도가 감소하였으며, 이러한 감소 요인은 PET구정 내ㆍ외부에서의 PTT 결정화와 용융 거동에 차이를 유발하였다.

• 대한의용생체공학회:의공학회지
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• 제30권1호
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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.

• 한국대기환경학회지
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• 제30권1호
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• pp.1-17
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• 2014

Temporal variations of optical properties of urban aerosol in Seoul were estimated by the Optical Properties of Aerosols and Clouds (OPAC) model, based on hourly aerosol sampling data in Seoul during the year of 2010. These optical properties were then used to calculate direct radiative forcing during the study period. The optical properties and direct radiative forcing of aerosol were calculated separately for four chemical components such as water-soluble, insoluble, black carbon (BC), and sea-salt aerosols. Overall, the coefficients of absorption, scattering, and extinction, as well as aerosol optical depth (AOD) for water-soluble component predominated over three other aerosol components, except for the absorption coefficient of BC. In the urban environment (Seoul), the contribution of AOD (0.10~0.12) for the sum of OC and BC to total AODs ranged from 23% (spring) to 31% (winter). The diurnal variation of AOD for each component was high in the morning and low in the late afternoon during the most of seasons, but the high AODs at 14:00 and 15:00 LST in summer and fall, respectively. The direct negative radiative forcing of most chemical components (especially, $NO_3{^-}$ of water-soluble) was highest in January and lowest in September. Conversely, the positive radiative forcing of BC was highest in November and lowest in August due to the distribution pattern of BC concentration.

• 한국응용과학기술학회지
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• 제26권2호
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• pp.117-123
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• 2009

Caprylic/Capric triglyceride-in-water emulsions stabilized by Nikkol HCO-60 and HCO-10 were prepared using emulsion inversion point method at different HLB values. Emulsions with various droplet sizes were formed, and emulsion inversion point was detected by electrical conductivity. The change in emulsion droplet sizes and long term stability were monitored using laser scattering method and visual method. The droplet sizes and stability of emulsions were affected by HLB of surfactant. At emulsion inversion point, the water volume fraction increased as the HLB of surfactants decreased. According to our analysis, this resulted from a tendency of forming the W/O (water-in-oil) emulsion as the HLB of surfactants was decreased. The emulsion inversion point was clearly detected by the microscope and the electric conductivity meter. Nanometer-sized emulsion was obtained at the optimum HLB by using emulsion inversion point method. The main pattern of instability of emulsions in HLB 12 and 13 systems was Ostwald ripening. However, The patterns of instability of emulsions below 11 of HLB systems were Ostwald ripening and coalescence. All emulsions produced with surfactants in the range of HLB 8-13, creaming caused by density difference between water phase and oil phase.

• 한국광학회지
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• 제21권6호
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• pp.254-258
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• 2010

타원형 모양의 모드 형태를 갖는 펄스형 레이저 다이오드 (laser diode)의 펄스 형태를 유지하면서 단일 모드 및 Gaussian 형태로 광 모드 변환을 유도하고 광출력을 증폭할 수 있는 기술에 대해서 연구하였다. 실험에서 사용한 펼스형 레이저 다이오드의 구경이 가로는 $300{\mu}m$이며, 세로는 $2{\mu}m$이고 출력은 $1.1mW/cm^2$이다. 렌즈형 광섬유를 사용하여 광결합을 유도하여 단일 모드 및 Gaussian 형태의 출력으로 변환시켰다. 그러나, 다중모드의 펄스형 레이저 다이오드의 출력을 단일모드 렌즈형 광섬유에 결합시키면 출력이 급격하게 감소한다. 따라서 master oscillator power amplifier (MOPA) 기반의 광증폭 기술을 이용하여 레이저 다이오드의 광출력을 증폭시켰다. 증폭 후에도 펄스 성질은 그대로 유지되었고, MOPA구조를 지나 증폭된 광 출력은 $29mW/cm^2$로 측정되었다.

• 한국분무공학회지
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• 제6권1호
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• pp.18-24
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• 2001

Liquid fossil fuel contaminated by water can cause trouble in the combustion processes and affect the endurance of a combustion system. Using an optical sensor to monitor the water content instantaneously in a fuel pipeline is an effective means of controlling the fuel quality in a combustion system. In two component liquid flows of oil and water, the flow pattern and characteristics of water droplets are changed with various flow conditions. Additionally, the light scattering of the optical sensor measuring the water content is also dependent on the flow patterns and droplet characteristics. Therefore, it is important to investigate the detailed behavior of water droplets in the pipeline of the fuel transportation system. In this study, the flow patterns and characteristics of water droplets in the turbulent pipe flow of two component liquids of gasoline and water were investigated using optical measurements. The dispersion of water droplets in the gasoline flow was visualized, and the size and velocity distributions of water droplets were simultaneously measured by the phase Doppler technique. The Reynolds number of the gasoline pipe flow varied in the range of $4{\times}10^{4}\;to\;1{\times}10^{3}$, and the water content varied in the range of 50 ppm to 300 ppm. The water droplets were spherical and dispersed homogeneously in all variables of this experiment. The velocity of water droplets was not dependent on the droplet size and the mean velocity of droplets was equal to that of the gasoline flow. The mean diameter of water droplets decreased and the number density increased with the Reynolds number of the gasoline flow.

• 한국정밀공학회지
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• 제19권3호
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• pp.66-72
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• 2002

Electronic Speckle Pattern Interferometry (ESPI) has been recently developed and widely used because it has advantage to be able to measure surface deformations of engineering components and materials in industrial areas with non-contact. The speckle patterns to be formed with interference and scattering phenomena can measure not only out-of-plane but also in-plane deformations, together with the use of digital image equipment to process the informations included in the speckle patterns and to display consequent interferogram on a computer monitor. In this study, the experimental results of a canti-levered plate using ESPI were compared with those obtained from the simple beam theory. The ESPI results of the canti-levered plate analyzed by 4-step phase shifting method are close to the theoretical expectation. Also, out-of-plane displacements of a spot welded cacti-levered plate were measured by ESPI with 4-step phase shifting technique. The phase map of the spot welded cacti-levered plate is quite different from that of the canti-levered plate without spot welding.