• Proceedings of the KSME Conference
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• 2005.11a
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• pp.25.2-25.2
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• 2005

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2465-2470
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• 2007

We have analyzed the three-dimensional thermal conduction in anisotropic materials using nonsymmetric-Fourier transforms. And a complete theoretical treatment of the photothermal deflection spectroscopy has been performed for thermal conductivity measurement in anisotropic medium. Thermal conductivity tensor was determined by the deflection angle and phase angle with the relative position between the heating and probe beams. The influence of the parameters, such as modulation frequency of the heating beam, the thermal conductivity tensor, was investigated.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.6
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• pp.804-812
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• 2003

This paper introduces optical methods for in-situ measurement of surface temperature and pressure transient in thermal processes having nanosecond time scales. In the temperature measurement, a p -Si thin film whose refractive index is calibrated as a function of temperature is embedded beneath the sample surface and the photothermal reflectance is monitored for estimating the surface temperature. The pressure transients are measured using the photoacoustic optical deflection method. The experimental technique is used to analyze the nanosecond laser induced vaporization process that is central to numerous engineering and bio-medical applications. Based on the experimental results, discussions are made on the experimental technique and the physical mechanisms of laser-driven explosive vaporization phenomena.

• Journal of the Korean Vacuum Society
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• v.8 no.2
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• pp.153-157
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• 1999

The dependence of the absorption edge of wurtzite $Al_xGa_{1-x}N$ on alN mole fraction has been studied. The AlN mole fraction was varied from 0 to 1. The absorption coefficients at room temperature were determined by transmission and photothermal deflection spectroscopy. Photothermal deflection spectroscopy can be applied to determine the low absorbance values. From the results, the effective bandgaps of $Al_xGa_{1-x}N$ alloys were determined by choosing corresponding photon energies of the positions of the absorption coefficient of $6.3\times10^4\textrm{cm}^{-1}$ at the absorption curves of the $Al_xGa_{1-x}N$ alloys. From the energy position of the absorption coefficient versus AlN mole fraction, a bowing parameter of 1.3eV was determined. The bowing parameter agreed quite well with the measured effective bandgaps of AlGaN alloys.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.138-143
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• 2000

A new method of measuring the thermal diffusivity of solid material at room temperature with photothermal displacement method is proposed. The influence of the parameters on phase lag was studied. From the minimum position of phase of measured deflection with respect to the pump beam the thermal diffusivity of the materials can be obtained. The minimum position of phase is determined using multiparameter least-square regression fitting. The experimental values for different samples obtained by applying new method are in good agreement with the literature values.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.3
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• pp.296-304
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• 2001

A new method of measuring the thermal diffusivity of solid material at room temperature using photothermal displacement is proposed. The influence of the parameters, such as radius and modulation frequency of the pump beam and the sample thickness, was studied. From the minimum position of phase of measured deflection with respect to the pump beam, the thermal diffusivity of the materials can be obtained. The position where phase has the minimum value is determined using multiparameter least-square regression fitting. The experimental values for different samples obtained by applying the new method are in good agreement with the literature values.

• Journal of Energy Engineering
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• v.10 no.1
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• pp.63-70
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• 2001

재료의 열확산계수를 비접촉적인 방법으로 구하기 위하여 광열편향법에 대한 3차원 모델을 해석하였다. 이 방법은 가열빔이 재료에 광학적으로 흡수될 때 검사빔의 초기궤적이 시편과 시편주의 매질의 온도상승으로 인하여 나타나는 굴절지수의 구배에 의하여 검사빔이 편향되는 원리를 이용하는 것이다. 기존의 연구에서는 주로 가열빔과 검사빔의 상대거리를 변화시키면서 편향의 위상각을 측정하여 열확산계수를 결정하였다. 하지만 본 연구에서는 고정된 상대거리에서 가열빔의 변조주파수를 변화시키면서 편향의 위상각을 계산하여 열확산계수를 구할 수 있는 관계식을 제시하였다. 본 연구에서 제시한 열확산계수 결정 방법은 다른 방법에 비하여 실험과 해석이 간단하고 비교적 측정하기가 어려운 상대거리에 영향을 받지 않는 방법이다.

• Bulletin of the Korean Chemical Society
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• v.24 no.3
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• pp.318-324
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• 2003

A time-resolved probe beam deflection (PBD) technique was employed to study the energy relaxation dynamics of photofragments produced by photodissociation of $CH_3I$ at 266 nm. Under 500 torr argon environment, experimental PBD transients revealed two energy relaxation processes; a fast relaxation process occurring within an acoustic transit time (less than 0.2 ㎲ in this study) and a slow relaxation process with the relaxation time in several tens of ㎲. The fast energy relaxation of which signal intensity depended linearly on the excitation laser power was assigned to translational-to-translational energy transfer from the photofragments to the medium. As for the slow process, the signal intensity depended on square of the excitation laser power, and the relaxation time decreased as the photofragment concentration increased. Based on experimental findings and reaction rate constants reported previously, the slow process was assigned to methyl radical recombination reaction. In order to determine the rate constant for methyl radical recombination reaction, a theoretical equation of the PBD transient for a radical recombination reaction was derived and used to fit the experimental results. By comparing the experimental PBD curves with the calculated ones, the rate constant for methyl recombination is determined to be $3.3({\pm}1.0)\;{\times}\;10^6\;s^{-1}torr^{-1}$ at 295 ± 2 K in 500 torr Ar.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1988.05a
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• pp.33-34
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• 1988

Recent developments in characterization techniques for solar cells are reviewed. First, general rules of material selection for solar cells such as $CuInSe_2$ and amorphous silicon of photovoltaic application are studied. Secondly, a method to obtain correct cell efficiency measurements under AM1 condition is introduced. Thirdly, various characterization techniques for solar cells are discussed. A special emphasis is given to up-scaling and computer control of the characterizations in the following systems; cell I-V characteristics for cell efficiency and other cell parameters, spectral response for quantum efficiency, surface photovoltage for diffusion length of minority carriers, and photothermal deflection for density of states in energy gaps.

• Solar Energy
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• v.17 no.2
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• pp.55-66
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• 1997

The structural and optoelectronic properties of polycrystalline CdS films up to several microns in thickness, fabricated by three different methods, are compared to one another for the purpose of preparing CdTe/CdS solar cells. All films were deposited on an indium tin oxide on glass substrate. The three methods are: 1) alternated spraying of cation and anion solution at room temperature; 2) spray pyrolysis with substrate temperature up to $500^{\circ}C$; 3) chemical bath deposition (CBD). Deposited films were thermally treated in various ways. All films showed a well-developed wurtzite structure. Films grown by the alternated-spray method and the chemical bath method consist of randomly-oriented crystallites with dimensions <0.5 microns. Annealing at $400^{\circ}C$ increases the crystallite size slightly. Films which were grown by pyrolysis at substrate temperatures from $400^{\circ}C\;to\;500^{\cir\c}C$ were oriented in the <002> direction. For growth by pyrolysis at $500^{\circ}C$, the surface is rough on a lateral scale of 0.1 to 0.3 microns. The optical band gap and defect states are investigated by optical absorption, photoluminescene, Raman, and photothermal deflection spectroscopies.