• 한국진공학회:학술대회논문집
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• 한국진공학회 1994년도 제6회 학술발표회 논문개요집
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• pp.43-43
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• 1994

We studied chemical reactio of Eu metal on the in situ cleaved CdTe(110) surface by pphotoemission sppectroscoppy using synchrotron radiation. The chamber was maintained with base ppressure $\leq$2${\times}$10-10 mb during the expperiment. The expperiment was carried out in pphoton Factory in Jappan. Core level pphotoemission sppectroscoppy was carried out with Al K${\alpha}$ Line. The CdTe simiconductor was determined to be pp-typpe with low dopping concentration from Hall measurement. We found that there are two reacted pphases of Te with Eu (related to divalent Eu and trivalent Eu, resppectively) from least square fitting of Te 4d sppectra, but three is no indication of Cd reaction. Trivalent Eu exists after roughly one monolayer depposition (600 sec. depposition time is considered as one monolayer), which is also observed at Eu 3d core level sppectra. Overlayer Eu is metallized after roughly 2 monolayers depposition, as can be deduced from the fact that metallic edge near Fermi level begins to appear. The intensity of core-level of Te decreases expponentially at the initial stage (near one monolayer) and after one monolayer depposition it decreases more slowly due to Te out-diffusion. We categorized the growth mode of Eu on CdTe as S-K growth mode (cluster formation after one monolayer deppisition) from the relative intensity pplot of Te 4d normalized to the cleaved surface. At cleaved surface band bending is already established due to surface defects. At first 100 sec. depposition time the shift toward lower binding side by 0.6 eV is found at all core level sppectra of all elements in semiconductor. This shift is considered as the re-adjustment of surface Fermi level to the pposition induced by Eu metal (0.2 eV above the valence band maximum).

• Bulletin of the Korean Chemical Society
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• 제34권11호
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• pp.3335-3339
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• 2013

Boron-doped ZnO (BZO) nanorods were grown on quartz substrates using hydrothermal synthesis, and the temperature-dependence of their photoluminescence (PL) was measured in order to investigate the origins of their PL properties. In the UV range, near-band-edge emission (NBE) was observed from 3.1 to 3.4 eV; this was attributed to various transitions including recombination of free excitons and their longitudinal optical (LO) phonon replicas, and donor-acceptor pair (DAP) recombination, depending on the local lattice configuration and the presence of defects. At a temperature of 12 K, the NBE produces seven peaks at 3.386, 3.368, 3.337, 3.296, 3.258, 3.184, and 3.106 eV. These peaks are, respectively, assigned to free excitons (FX), neutral-donor bound excitons ($D^{\circ}X$), and the first LO phonon replicas of $D^{\circ}X$, DAP, DAP-1LO, DAP-2LO, and DAP-3LO. The peak position of the FX and DAP were also fitted to Varshni's empirical formula for the variation in the band gap energy with temperature. The activation energy of FX was about ~70 meV, while that of DAP was about ~38 meV. We also discuss the low temperature PL near 2.251 eV, related to structural defects.

• 한국진공학회지
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• 제19권6호
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• pp.483-488
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• 2010

스핀코팅 방법을 이용하여 다양한 농도의 전구체로 ZnO 나노 섬유질 박막(ZnO nano-fibrous thin films)을 성장하였고, 그에 따른 표면 및 광학적 특성 변화를 scanning electron microscopy (SEM)와 photoluminescence (PL)을 이용하여 측정하였다. 전구체 농도가 0.4 mol (M) 이하 일 때는 성장률이 낮아 ZnO 핵생성만이 되었고, 0.6 M 이상일 때 ZnO 박막은 나노섬유질 구조가 되었다. 전구체 농도가 더욱 증가함에 따라 ZnO 나노 섬유질의 굵기가 굵어졌고 ZnO 박막의 두께도 단계적으로 두꺼워졌다. 전구체 농도가 증가함에 따라 ZnO 나노 섬유질 박막의 photoluminescence (PL)의 근밴드가장자리 광방출(near-band-edge emission) 피크 세기와 full-width at half-maximu (FWHM)이 증가하였고, 깊은 준위 광방출(deep-level mission) 피크는 적색편이(red-shift)하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.337-337
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• 2013

ZnO seed layers were deposited on a quartz substrate using the sol-gel method, and B-doped ZnO (BZO) nanorods with different B concentrations ranging from 0 to 2.5 at.% were grown on the ZnO seed layers by the hydrothermal method. The structural, optical, electrical propertiesof the ZnO and BZO nanorods were investigated using field-emission scanning electron microscopy, X-ray diffraction (XRD), photoluminescence (PL), ultraviolet-visible spectroscopy, and hall effect. The ZnO and BZO nanorods grew well aligned on the surface of the quartz substrates. From the XRD data, it can be seen that the B doping is responsible for the distortion of the ZnO lattice. The PL spectra show near-band-edge emission and deep-level emission, and they also show that B doping significantly affects the PL properties of ZnO nanorods. The optical band gaps are changed by B doping, and thus the Urbach energy value changed with the optical band gap of the ZnO nanorods. From the hall measurements, it can be observed that the values of electrical resistivity, carrier concentration, and mobility are changed by B doping.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 학술대회 논문집 전문대학교육위원
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• pp.35-39
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• 2000

$ZnIn_2S_4$ and $ZnGaInS_4:Er^{3+}$ single crystals crystallized in the rhombohedral (hexagonal) space group $C_{3v}^5(R3m)$, with lattice constants $a=3.852{\AA},\;c=37.215{\AA}$ for $ZnIn_2S_4$, and $a=3.823{\AA}$, and $c=35.975{\AA}$ for $ZnIn_2S_4:Er^{3+}$. The optical absorption measured near the fundamental band edge showed that the optical energy band structure of there compounds had a direct and indirect band gap, the direct and indirect energy gaps are found to be 2.778 and 2.682 eV for $ZnIn_2S_4$, and 2.725 and 2.651eV for $ZnIn_2S_4:Er^{3+}$ at 293 K. The photoluminescence spectra of $ZnIn_2S_4:Er^{3+}$ measured in the wavelength ranges of $500nm{\sim}900nm$ at 10 K. Eight sharp emission peaks due to $Er^{3+}$ ion are observed in the regions of $549.5{\sim}550.0nm,\;661.3{\sim}676.5nm$, and $811.1{\sim}834.1nm$, and $1528.2{\sim}1556.0nm$ in $CdGaInS_4:Er^{3+}$ single crystal. These PL peaks were attributed to the radiative transitions between the split electron energy levels of the $Er^{3+}$ ions occupied at $C_{2v}$, symmetry of the $ZnIn_2S_4$ single crystals host lattice.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 학술대회 논문집 전문대학교육위원
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• pp.56-59
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• 2000

$CdGaInS_4$ and $CdGaInS_4:Er^{3+}$ single crystals crystallized in the rhombohedral(hexagonal) structure. with lattice constants $a=3.913{\AA},\;c=37.245{\AA}$ for $CdGaInS_4$, and $a=3.899{\AA}$ and $c=36.970{\AA}$ for $CdGaInS_4:Er^{3+}$. The optical absorption measured near the fundamental band edge showed that the optical energy band structure of these compounds had a direct and indirect band gap. the direct and indirect energy gaps are found to be 2.771 and 2.503 eV for $CdGaInS_4$, and 2.665 and 2.479 eV for $CdGaInS_4:Er^{3+}$ at 10 K. The temperature dependence of the optical energy gap was well represented by the Varshni equation. In $CdGaInS_4$, the values of ${\alpha},\;{\beta}$ of the direct and the indirect energy gap were found to be $7.57{\times}10^{-4}eV/K$. $6.53{\times}10^{-4}eV/K$ and 240K. 197K. and the values of ${\alpha}$ and ${\beta}$ of the direct and the indirect energy gap in the $CdGaInS_4:Er^{3+}$ were given by $8.28{\times}10^{-4}eV/K,\;2.08{\times}10^{-4}eV/K$ and 425 K, 283 K, respectively.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 제4회 영호남학술대회 논문집
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• pp.97-100
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• 2002

$CdGaInS_{4}:Er^{3+}$ single crystal crystallized in the rhombohedral. with lattice constants a = 3.899 $\AA$ and c = 36.970 $\AA$ for $CdGaInS_{4}:Er^{3+}$. The optical absorption measured near the fundamental band edge showed that the optical energy band structure of this compound had a direct and indirect band gaps. the direct and indirect energy gaps are found to be 2.665 and 2.479eV for $CdGaInS_{4}:Er^{3+}$ at 10 K. The photoluminescence spectra of $CdGaInS_{4}:Er^{3+}$ measured in the wavelength ranges of 500 nm~900 nm and 1500~1600 nm at 10 K. Eight sharp emission peaks due to $Er^{3+}$ ion are observed in the regions of 549.5~560.0nm. 661.3~676.5nm. 811.1~ 834.1 nm and 1528.2~1556.0 nm in $CdGaInS_{4}:Er^{3+}$ single crystal. These PL peaks were attributed to the radiative transitions between the split electron energy levels of the $Er^{3+}$ ions occupied at $C_{2v}$ symmetry of the $CdGaInS_4$ single crystals host lattice.

• 대한원격탐사학회지
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• 제37권4호
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• pp.699-717
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• 2021

South Korea is pushing for the advancement of crop production technology to achieve food self-sufficiency and meet the demand for safe food. A medium-sized satellite for agriculture is being launched in 2023 with the aim of collecting and providing information on agriculture, not only in Korea but also in neighboring countries. The satellite is to be equipped with various sensors, though reference data for ground information are lacking. Hyperspectral remote sensing combined with 1st derivative is an efficient tool for the identification of agricultural crops. In our study, we develop a system for hyperspectral analysis of the ground-based reflectance spectrum, which is monitored seven times during the cultivation period of three soybean crops using a PSR-2500 hyperspectral sensor. In the reflection spectrum of soybean canopy, wavelength variations correspond with stages of soybean growths. The spectral reflection characteristics of soybeans can be divided according to growth into the vegetative (V)stage and the reproductive (R)stage. As a result of the first derivative analysis of the spectral reflection characteristics, it is possible to identify the characteristics of each wavelength band. Using our developed monitoring system, we observed that the near-infrared (NIR) variation was largest during the vegetative (V1-V3) stage, followed by a similar variation pattern in the order of red-edge and visible. In the reproductive stage (R1-R8), the effect of the shape and color of the soybean leaf was reflected, and the pattern is different from that in the vegetative (V) stage. At the R1 to R6 stages, the variation in NIR was the largest, and red-edge and green showed similar variation patterns, but red showed little change. In particular, the reflectance characteristics of the R1 stage provides information that could help us distinguish between the three varieties of soybean that were studied. In the R7-R8 stage, close to the harvest period, the red-edge and NIR variation patterns and the visible variation patterns changed. These results are interpreted as a result of the large effects of pigments such as chlorophyll for each of the three soybean varieties, as well as from the formation and color of the leaf and stem. The results obtained in this study provide useful information that helps us to determine the wavelength width and range of the optimal band for monitoring and acquiring vegetation information on crops using satellites and unmanned aerial vehicles (UAVs)

• 한국결정성장학회지
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• 제9권2호
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• pp.180-184
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• 1999

수집 Bridgman 법을 이용하여 $Mg_{0.15}Zn_{0.85}Te$ 와 $Mg_{0.15}Zn_{0.85}Te:Co^{2+}$(0.001%) 단결정을 성장시켰다. 성장된 시료들에 대하여 광흡수 특성을 연구하였다. 광흡수결과 $Mg_{0.15}Zn_{0.85}Te$단결정에서는 exciton과 관련된 흡수 peak들이 나타났으며, 이 peak들은 온도증가와 함께 장파장쪽으로 이동하였고, 100K이상의 온도에서 excitionic band gap의 온도계수 $-5.8{\times}10^{-4}\;eV/K$eV/K 이었다. $Mg_{0.15}Zn_{0.85}Te$ : $Co^{2+}$단결정에서는 $Co^{2+}$이온에 기인된 $A-band:^4A_2(^4F) {\to}^4T_1(^4F),\; B-band:\; ^4A_2(^4F){\to}^4T_1(^4P)$의 intracenter 전이와 흡수단 부근에서 charge transfer에 기인한 photoionization transition에 관련된 C-band를 6--~770nmdnk 파장영역에서 관측하였다. 이들을 결정장 이론과 Lucovsky formular에 의해 결정장 매개변수와 Racah 매개변수, 전하이동 에너지 값을 결정하였다.

• 한국지리정보학회지
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• 제15권4호
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• pp.1-14
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• 2012

하천은 육지 표면에서 일정한 물길을 따라 흐르는 물줄기를 의미하며, 하천 매핑 작업은 하천유역의 지형 변화 연구 및 하천 유역의 홍수 모니터링 연구 등에 매우 중요한 역할을 한다. 그러나 하천의 수위변화로 인한 유역 내 지표면의 수위 및 유량의 불균일성 등으로 인하여, 기존의 지반조사 기술은 하천 매핑 작업에 효과적이지 않다. 공간 정보 자료는 해당 지역에 접근하지 않고도 해당 지역에 관한 지형적인 정보를 획득할 수 있어서, 하천 지형 조사 및 하천 측량 등 하천 유역의 지형연구에 굉장히 유용하게 쓰일 수 있다. 본 연구에서는, 각각의 다른 파라미터를 사용하여 영상분류 기법 중의 하나인 ISODATA(Iterative Self_Organizing Data Analysis) 분류기법을 적용하여 RapidEye 영상으로부터 하천을 추출하는 방법을 제시하였다. 우선, RapidEye 영상으로부터 NIR(Near InfraRed) 밴드 영상과 NDVI(Normalized Difference Vegetation Index) 영상을 생성한 뒤, 이를 각각의 파라미터로 설정한다. 생성된 각각의 영상에 ISODATA 기법을 적용한 뒤, 후처리 과정을 통하여 각각의 영상으로부터 하천을 추출하도록 한다. 각각의 영상에서 추출한 하천의 경계선 또한 Sobel 에지 추출 기법을 통하여 추출된다. 점검 점들을 이용하여 정확도 검증을 수행한 결과, NIR 밴드로부터 추출한 하천의 정확도가 NDVI 영상으로부터 추출한 하천의 정확도보다 더 높다는 것을 알 수 있다.