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Joong Gill Choi,Oum Ka Won,Chang Yeoul Choi,Hichung Moon,Hyun Sang Shin,Park, Seung Min,Paul Joe Chong Korean Chemical Society 1993 Bulletin of the Korean Chemical Society Vol.14 No.1
The application of time-resolved laser induced fluorescence spectroscopy (TRLIF) to the complexation studies of Eu(III) and Cm(III) with humic substances is described. Using this method, three different spectroscopic characteristics(excitation spectra, emission spectra, and lifetimes) of these aquo ions and their complexes can be directly measured. By observing shifts in the wavelength and changes in the lifetime and intensities of the fluorescence emission, the information on the complexation behavior of humic substances with these trivalent metal cations in an aqueous solution, as well as energy transfer mechanisms, can be obtained. In addition, this method allows precise spectroscopic quantification of the complexation processes at very low concentrations of both components.
Theoretial Studies of Resonance Raman Spectrum of Porphyrin
Choi, Chan-You,Choi, Joong-Gill 동국대학교 1987 論文集 Vol.26 No.-
Resonance Raman 분광법은 hemoprotein에서 보결분자단의 구조관측을 위한 높은 감도와 선택성을 지닌 테크닉이다. 이 분광법으로 얻은 실험결과는 heme의 구조와 metalloporphyrin에서의 여기전자 상태에 대한 새로운 정보를 제공해 준다. "Picket Fence Porphyrin"은 산소분자가 결합되어 있는 hemoprtein에 있어서 대단히 중요한 모델 화합물로 알려져 있다. 본 논문에서는 ring dye laser의 범위안에서 resonace Raman 분광법을 이용하여 이 화합물에 있어서 산소 분자결합에 관계되는 스텍트럼의 변화에 대하여 연구하였다. 이론에서 기대했던 바와 같이 대부분의 Raman modes에서의 여기상태 모양은 O-O(α)Q band에서 최대가 됨이 밝혀졌다. 또한 편극된(polarized) 것과 변칙적으로 편극된 진동들의 편극소거비(depolarization ratio)는 symmetry의 변형으로써 설명될 수 있는 dispersion을 나타내었다. 그러나 산소분자의 결합에 있어서 Fe-O_2 의 stretching vibration은 확인되지 않았으며 산화상태나 스핀상태를 나타내는 어떠한 주파수의 이동도 관찰되지 않았다. 일반적으로 산화상태에서 산화과정의 변화를 직접 예측할 수는 없는 반면, 스핀상태는 높은 스핀에서 낮은 스핀으로 변화하는 것을 기대할 수 있다. 이러한 스핀상태 marker는 전혀 예측하지 못했던 결과이나 만일 짧은 파장을 사용하여 β-band에 더욱 근접한 exciting광선을 이용하면 스핀상태 marker 주파수의 변화는 관찰되리라 예상된다.
Byun, In-Sik,Choi, Ok-Lim,Choi, Joong-Gill,Lee, Sung-Han Korean Chemical Society 2002 Bulletin of the Korean Chemical Society Vol.23 No.11
Kinetic studies on the water-gas shift reaction catalyzed by magnetite/chromium oxide and copper/zinc oxide were carried out by using an in situ photoacoustic spectroscopic technique. The reactions were performed in a closed-circulation reactor system using a differential photoacoustic cell at total pressure of 40 Torr in the temperature range of 100 to $350^{\circ}C.$ The CO2 photoacoustic signal varying with the concentration of CO2 during the catalytic reaction was recorded as a function of time. The time-resolved photoacoustic spectra obtained for the initial reaction stage provided precise data of CO2 formation rate. The apparent activation energies determined from the initial rates were 74.7 kJ/mol for the magnetite/chromium oxide catalyst and 50.9 kJ/mol for the copper/zinc oxide catalyst. To determine the reaction orders, partial pressures of CO(g) and H2O(g) in the reaction mixture were varied at a constant total pressure of 40 Torr with N2 buffer gas. For the magnetite/chromium oxide catalyst, the reaction orders with respect to CO and H2O were determined to be 0.93 and 0.18, respectively. For the copper/zinc oxide catalyst, the reaction orders with respect to CO and H2O were determined to be 0.79 and 0, respectively.
A Direct Detection of $CO_2$ in Sealed-off $CO_2$ Discharge Tube by Optoacoustic Effect
Kim Sung-Ho,Choi Joong-Gill,Cho Ung-In Korean Chemical Society 1994 Bulletin of the Korean Chemical Society Vol.15 No.1
A simple analytical method that allows direct monitoring of small amount of CO$_2$ in a CO$_2$ discharge tube which utilizes the optoacoustic detection technique is described. The dependence of the optoacoustic signal on the mole fraction of CO$_2$ was shown that the system responded linearly to the amount of CO$_2$ present in the miniature discharge cavity equipped with Cu electrodes. It was also found that fraction of dissociated CO$_2$ varied from 14 to 37% of the initial concentration which depended on the current and the pressure in the tube. This simple and easy detection method has proven to possess the practical advantages over the conventional systems for the study of CO$_2$ laser electrodes.
Lim, Jong-Tae,Choi, Ok-Lim,Boo, Doo Wan,Choi, Joong-Gill Korean Chemical Society 2014 Bulletin of the Korean Chemical Society Vol.35 No.3
The wavelength dependence of the photoacoustic signal for n-type GaAs semiconductors in the region of the band-gap energies was investigated. The significant changes in the phase and amplitude of the photoacoustic signal near the band-gap absorption wavelengths were observed to occur when the Si-doping densities in GaAs were varied. Particularly, the first derivatives of the photoacoustic phase vs. wavelength graphs were evaluated and fitted with single Gaussian functions. The peak centers and the widths of the Gaussian curves clearly showed linear relationships with the log values of the Si-doping densities in n-type GaAs semiconductors. It is proposed that the wavelength-dependent PA spectroscopy can be used as a simple and nondestructive method for measuring the doping densities in bulk semiconductors.
광음향 현미경법을 이용한 반도체 표면의 3차원적 구조 분석
이응주,최옥림,임종태,김지웅,최중길,Lee, Eung-Joo,Choi, Ok-Lim,Lim, Jong-Tae,Kim, Ji-Woong,Choi, Joong-Gill 대한화학회 2004 대한화학회지 Vol.48 No.6
반도체 제작 과정에서 증착이나 식각, 회로의 검사 등에서 생겨날 수 있는 미세한 흠집이나 불완전성을 검사하기 위해 광음향 현미경법을 응용하였다. 반도체 표면에서 발생되는 광음향 신호를 측정하여 흠집의 형태와 깊이를 결정함으로써 3차원 영상을 분석하여 그 구조를 밝혔다. 또한 광음향 현미경법을 이용하여 진성 GaAs 반도체의 운반자 운송성질(비방사 벌크재결합 및 비방사 표면재결합)과 열확산도 및 시료 깊이에 따른 3차원 영상을 분석하여 진성 GaAs 반도체 열확산도 측정 시, 빛이 조사되는 표면조건에 따라 광음향신호의 주파수 의존성이 달라짐을 관측하였다. 실험결과 표면상태가 거친 면에서 매끄러운 면으로 갈수록 높은 주파수 의존성을 나타내었다. Si 웨이퍼 위에 임의로 제작되어진 흠집을 만들고 이를 광음향 현미경법으로 측정한 결과 광음향 신호는 변조되는 주파수와 웨이퍼의 열적 특성에 따라 달라지며 이를 통하여 흠집의 형태와 위치 및 크기를 확인하였다. 광음향 현미경은 반도체 소자나 세라믹 물질에 대하여 비파괴 검사와 비파괴 평가에 관한 연구가 가능하며 반도체 공정 과정에서 생겨날 수 있는 시료의 깨짐이나 결함 등을 검사하는데 응용 가능한 분석법임이 증명되었다. In this experiment, a three dimensional structure analysis was carried out to examine the surface defects of semiconductor made artificially on known scale. It was investigated the three dimensional imaging according to the sample depth and the thermal diffusivity as well as the carrier transport properties. The thermal diffusivity measurement of the intrinsic GaAs semiconductor was also analyzed by the difference of frequency-dependence photoacoustic signals from the sample surface of different conditions. Thermal properties such as thermal diffusion length or thermal diffusivity of the Si wafer with and without defects on the surface were obtained by interpreting the frequency dependence of the PA signals. As a result, the photoacoustic signal is found to have the dependency on the shape and depth of the defects so that their structure of the defects can be analyzed. This method demonstrates the possibility of the application to the detection of the defects, cracks, and shortage of circuits on surface or sub-surface of the semiconductors and ceramic materials as a nondestructive testing(NDT) and a nondestructive evaluation(NDE) technique.
Jin-Hyuck Yang,Ji-Woong Kim,최중길,주홍렬,이성한,Joong-Gill Choi 대한화학회 2010 Bulletin of the Korean Chemical Society Vol.31 No.5
The CO2-CH4 reaction catalyzed by Ni/silicon wafers was kinetically studied by using a photoacoustic technique. The catalytic reaction was performed at various partial pressures of CO2 and CH4 (50 Torr total pressure of CO2/CH4/N2) in the temperature range of 500 - 650 oC in a static reactor system. The photoacoustic signal that varied with the CO2 concentration during the catalytic reaction was recorded as a function of time. Under the reaction conditions, the CO2 photoacoustic measurements showed the as-prepared Ni thin film sample to be inactive for the reaction, while the CO2/CH4reactions carried out in the presence of the sample pre-treated in H2 at 600 oC were associated with significant time-dependent changes in the CO2 photoacoustic signal. The rate of CO2 disappearance was measured from the CO2 photoacoustic signal data in the early reaction period of 50 - 150 sec to obtain precise kinetic data. The apparent activation energy for CO2 consumption was determined to be 6.9 kcal/mol from the CO2 disappearance rates. The partial reaction orders, determined from the CO2 disappearance rates measured at various PCO2's and PCH4's at 600 oC, were determined to be 0.33 for CH4 and 0.63 for CO2, respectively. Kinetic data obtained in these measurements were compared with previous works and were discussed to construct a catalytic reaction mechanism for the CO2-CH4 reaction over Ni/silicon wafer at low pressures.