• 한국광학회지
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• 제12권2호
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• pp.143-149
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• 2001

Lithium triborate$(LiB_3O_5, LBO)$ 결정을 이용하여 파장가변 티타늄 사파이어 레이저로부터 내부공진기 구조를 이용한 진동수 배가를 수행하였다 효과적인 진동수 배가를 수행하기 위해서 자체 개발한 파장가변 티타늄 사파이어 레이저를 이용하여 기본파의 중심 파장 및 파장 변화에 대한 LBO 결정의 스펙트럼 선폭 및 각선폭 등을 측정하였으며 내부공진기 방법을 이용하여 진동수 배가된 제2고조파 출력 특성 및 파장 가변성 등을 측정하였따. 800nm의 기본파 파장에서 LBO 결정의 $\theta$방향에 대한 스펙트럼 선폭 및 각선폭은 각각 1.54nm.cm 및 3.8mard.cm으로 확인되었다. 또한 내부공진기 구조를 이용한 진동수 배가 결과, 기본파의 출력이 800nm에서 185mW일때 400nm에서 스펙트럼의 반치폭이 0.089nm인 5.3nW의 제2고조파 출력을 얻을 수 있었고, 진동수 배가된 출력의 파장가변 영역은 397nm-403nm로 확인되었다.

• 대한금속재료학회지
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• 제50권8호
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• pp.605-611
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• 2012

ZnO nanostructures were grown on R-plane sapphire substrates with seed layers annealed at different temperatures ranging from 600 to $800^{\circ}C$. The properties of the ZnO nanostructures were investigated by scanning electron microscopy, high-resolution X-ray diffraction, UV-visible spectrophotometer, and photoluminescence. For the as-prepared seed layers, ZnO nanorods and ZnO nanosheets were observed. However, only ZnO nanorods were grown when the annealing temperature was above $700^{\circ}C$. The crystal qualities of the ZnO nanostructures were enhanced when the seed layers were annealed at $700^{\circ}C$. In addition, the full width at half maximum (FWHM) of near-band-edge emission (NBE) peak was decreased from 139 to 129 meV by increasing the annealing temperature to $700^{\circ}C$. However, the FWHM was slightly increased again by a further increase in the annealing temperature. Optical transmittance in the UV region was almost zero, while that in the visible region was gradually increased as the annealing temperature increased to $700^{\circ}C$. The optical band gap of the ZnO nanostructures was increased as the annealing temperature increased to $700^{\circ}C$. It is found that the optical properties as well as the structural properties of the rod-shaped ZnO nanostructures grown on R-plane sapphire substrates by hydrothermal method are improved when the seed layers are annealed at $700^{\circ}C$.

• 한국의학물리학회지:의학물리
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• 제33권4호
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• pp.63-71
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• 2022

Purpose: To clarify the relationship between the diameter of the simulated bead and the Z-resolution of the tomosynthesis image. Methods: A simulated bead was placed on a 1,024×1,024×1,024-pixel base image. The diameters were set to 0.025, 0.05, 0.1, 0.2, 0.3, 0.7, 1.0, and 1.3 mm. A bead was placed at the center of the base image and projected at a simulated X-ray angle range of ±45° to obtain a projected image. A region of interest was placed at the center of the bead image and the slice sensitivity profile (SSP) was obtained by acquiring pixel values in the z-direction. The full width at half maximum of the SSP was defined as the Z-resolution and the frequency response was obtained by the 1-D Fourier transform of the SSP. Results: Z-resolution increased with increasing bead diameter. However, there was no change in Z-resolution between 0.025 and 0.1 mm. The frequency response was similar to that of the Z-resolution, with a significant difference between 0.1 and 0.2 mm diameter. Conclusions: Z-resolution is dependent on the diameter of the bead, which should be selected considering the pixel size of the tomosynthesis image.

• 한국전기전자재료학회논문지
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• 제14권6호
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• pp.445-454
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• 2001

The stochiometric mix of evaporating materials for the CuInSe$_2$ single crystal thin films was prepared from horizontal furnace. To obtain the single crystal thin films, CuInSe$_2$ mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the Hot Wall Epitaxy(HWE) system. The source and substrate temperature were 62$0^{\circ}C$ and 41$0^{\circ}C$, respectively. The crystalline structure of single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). The carrier density and mobility of CuInSe$_2$ single crystal thin films measured from Hall effect fby van der Pauw method are 9.62x10$^{16}$ cm$^{-3}$ , 296$\textrm{cm}^2$/V.s at 293 K, respectively. From the photocurrent spectrum by illumination of perpendicular light on the c-axis of the CuInSe$_2$ single crystal thin film we have found that he values of spin orbit splitting ΔSo and the crystal field splitting ΔCr were 6.1 meV and 175.2 meV at 10K, respectively. From the photoluminescence measurement on CuInSe$_2$ single crystal thin film we observed free excition (Ex) existing only high quality crystal and neutral bound exiciton (D$^{\circ}$,X) having very strong peak intensity. Then, the full-width-at-half-maximum(FWHM) and binding energy of neutral donor bound excition were 7meV and 5.9meV, respectivity. by Haynes rule, an activation energy of impurity was 50 meV.

• 한국전기전자재료학회논문지
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• 제19권7호
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• pp.605-610
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• 2006

We have investigated $Al_{0.25}Ga_{0.75}As/In_{0.2}Ga_{0.8}As$ structures for pseudomorphic high electron mobility transistor(pHEMT), which were grown by molecular beam epitaxy(MBE) and consequently annealed by rapid thermal anneal(RTA), using Hall measurement, photoluminescence, and transmission electron microscopy (TEM). According to intensity and full-width at half maximum maintained stable at the same energy level, the quantized energy level in $Al_{0.25}Ga_{0.75}As/In_{0.2}Ga_{0.8}As$ quantum wells was independent of the RTA conditions. However, the Hall mobility was decreased from $6,326cm^2/V.s\;to\;2,790cm^2/V.s\;and\;2,078cm^2/V.s$ after heat treatment respectively at $500^{\circ}C\;and\;600^{\circ}C$. The heat treatment which is indispensable during the fabrication procedure would cause catastrophic degradation in electrical transport properties. TEM observation revealed atomically non-uniform interfaces, but no dislocations were generated or propagated. From theoretical consideration about the mobility changes owing to inter-diffusion, the degraded mobility could be directly correlated to the interface scattering as long as samples were annealed below $600^{\circ}C$ lot 1 min.

• 한국진공학회지
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• 제10권3호
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• pp.374-379
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• 2001

MBE를 이용하여 GaAs위에 InAs 양자점을 성장시키고 Ga, As, In, As의 순서로 셔터를 교대로 열어주는 방식으로 3주기 반복하여 InGaAs 층을 성장시키고 그 위에 다시 GaAs층을 성장시킨 시료(시료번호: QDl)에 대하여 온도를 변화시키며 열처리를 수행한 후 그 광학적 특성을 분석하였다. 기존의 다른 그룹들의 연구결과처럼, InAs 양자점을 성장시키고 GaAs 에피층을 barrier층으로 성장시킨 경우, 열처리 온도가 증가함에 따라 발광피크는 단파장쪽으로 이동하는 것을 확인하였다. 반면에, InGaAs층을 포함하고 있는 QDI 시료의 경우, 발광 피크의 위치가 열처리 온도가 $600^{\circ}C$가 될 때까지는 장파장 쪽으로 이동하다가, 그 이상의 온도에서는 단파장 쪽으로 이동하는 현상을 관찰하였다. 또한, 발광피크의 반치폭도 열처리 온도가 증가하면서 감소하는 경향을 보이다가 다시 증가되는 경향을 보이고 있다.

• 한국진공학회지
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• 제10권1호
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• pp.22-26
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• 2001

Plasma assisted molecular beam epitaxy(PAMBE)를 사용하여 Si 기판위에 성장시킨 AlN 박막에 대하여 성장온도 및 기판의 방향성에 따른 박막의 결정성 변화를 분석하였다. Reflection high energy electron diffraction(RHEED) 패턴을 이용하여 성장 중의 결정성을 관찰하였고, 성장 후에는 X-ray diffraction(XRD), double crystal X-ray diffraction(DCXD), transmission electron microscopy/diffraction(TEM/TED)분석을 하였다. $850^{\circ}C$이상의 온도에서 Si(100)위에 성장된 AlN박막은 육방정계의 c축 방향으로 우선 배향되어 있음을 확인하였으며 Si(111)위에 성장된 AlN박막의 경우 AlN(0001)/Si(111), AlN(1100)/Si(110), AlN(1120)/Si(112)의 결정방위를 가지고 성장하였음을 확인하였다. 또한 Si(111) 기판 위에서는 전위와 적층결함 등 많은 결정결함에 의해 DCD패턴의 반치폭이 2$\theta$=$36.2^{\circ}$에서 약 3000arcsec에 이르는 등 결정성은 좋지 않았으나 AlN박막이 단결정으로 성장된 것으로 나타났다.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2003년도 춘계종합학술대회
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• pp.88-92
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• 2003

본 논문에서는 Al 하부전극 상에서 RF magnetron sputtering 기술을 이용한 ZnO 박막 증착 및 공정온도가 ZnO 결정성장에 미치는 영향을 고려하여 제작한 FBAR 소자에 대한 연구를 발표한다. 결과적으로, 20$0^{\circ}C$의 공정온도에서 주상형 결정립(columnar grain)을 가지고 c축 우선 배향된 ZnO 박막을 얻을 수 있었다. 이렇게 얻은 ZnO 박막을 FBAR 소자에 적용하여 제작한 결과, 2.05GHz의 공진 주파수에서 ~19.5dB의 반사손실을 보였다.

• Journal of Astronomy and Space Sciences
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• 제33권2호
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• pp.137-146
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• 2016

The correlation between meteorological data collected at the optical wide-field patrol network (OWL-Net) Station No. 1 and the seeing of satellite optical observation data was analyzed. Meteorological data and satellite optical observation data from June 2014 to November 2015 were analyzed. The analyzed meteorological data were the outdoor air temperature, relative humidity, wind speed, and cloud index data, and the analyzed satellite optical observation data were the seeing full-width at half-maximum (FWHM) data. The annual meteorological pattern for Mongolia was analyzed by collecting meteorological data over four seasons, with data collection beginning after the installation and initial set-up of the OWL-Net Station No. 1 in Mongolia. A comparison of the meteorological data and the seeing of the satellite optical observation data showed that the seeing degrades as the wind strength increases and as the cloud cover decreases. This finding is explained by the bias effect, which is caused by the fact that the number of images taken on the less cloudy days was relatively small. The seeing FWHM showed no clear correlation with either temperature or relative humidity.

• IEIE Transactions on Smart Processing and Computing
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• 제6권1호
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• pp.66-70
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• 2017

Radioactive materials are used in medicine, non-destructive testing, and nuclear plants. Source localization is especially important during nuclear decommissioning and decontamination because the actual location of the radioactive source within nuclear waste is often unknown. The coded-aperture imaging technique started with space exploration and moved into X-ray and gamma ray imaging, which have imaging process characteristics similar to each other. In this study, we simulated $21{\times}21$ and $37{\times}37$ coded aperture collimators based on a modified uniformly redundant array (MURA) pattern to make a gamma imaging system that can localize a gamma-ray source. We designed a $21{\times}21$ coded aperture collimator that matches our gamma imaging detector and did feasibility experiments with the coded aperture imaging system. We evaluated the performance of each collimator, from 2 mm to 10 mm thicknesses (at 2 mm intervals) using root mean square error (RMSE) and sensitivity in a simulation. In experimental results, the full width half maximum (FWHM) of the point source was $5.09^{\circ}$ at the center and $4.82^{\circ}$ at the location of the source was $9^{\circ}$. We will continue to improve the decoding algorithm and optimize the collimator for high-energy gamma rays emitted from a nuclear power plant.