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Chung Y.K.,Sungkyunkwan University | Jo C.-M.,Sungkyunkwan University | Kim S.K.,Sungkyunkwan University | Kim I.C.,National Institute for Nanomaterials Technology | And 3 more authors.
Journal of the Optical Society of Korea | Year: 2016

A miniaturized FTIR spectrometer based on lamellar grating interferometry is being developed for passive remote-sensing. Consisting of a pair of micro-mirror arrays, the lamellar grating can be fabricated using MEMS technology. This paper describes a method to compute the optical field in the interferometer to optimize the design parameters of the lamellar grating FTIR spectrometer. The lower limit of the micro-mirror width in the grating is related to the formation of a Talbot image in the near field and is estimated to be about 100 µm for the spectrometer to be used for the wavelength range of 7-14 µm. In calculating the far field at the detection window, the conventional Fraunhofer equation is inadequate for detection distance of our application, misleading the upper limit of the micro-mirror width to avoid interference from higher order diffractions. Instead, the far field is described by the unperturbed plane-wave combined with the boundary diffraction wave. As a result, the interference from the higher order diffractions turns out to be negligible as the micro-mirror width increases. Therefore, the upper limit of the micro-mirror width does not need to be set. Under this scheme, the interferometer patterns and their FT spectra are successfully generated. © 2016 Optical Society of Korea.

Park J.H.,Pohang University of Science and Technology | Kim J.K.,POSCO | Lee B.H.,National Institute for Nanomaterials Technology | Seo H.S.,Pohang University of Science and Technology | Kim K.Y.,Pohang University of Science and Technology
Scripta Materialia | Year: 2014

Addition of Zr to low-Cr ferritic stainless steel forms a mixture of ZrC and Fe23Zr6 precipitates that can prevent intergranular corrosion. Transmission electron microscopy and three-dimensional atom probe analysis suggest that the ZrC and Fe23Zr6 mixture prevents intergranular corrosion in two ways: by acting as a strong carbide former to suppress the formation of Cr-carbide and by acting as a barrier against the diffusion of the solute Cr towards the grain boundary. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Jeong H.J.,Pohang University of Science and Technology | Lim N.S.,POSCO | Lee B.H.,National Institute for Nanomaterials Technology | Lee B.H.,Daegu Gyeongbuk Institute of Science and Technology | And 6 more authors.
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2014

Transformation-induced plasticity (TRIP) steels have excellent strain hardening exponents and resistibility against tensile necking using the strain-induced martensite formation that occurs as a result of the plastic deformation and strain on the retained austenite phase. Detailed studies on the microstructures and local mechanical properties, as well as global mechanical properties, are necessary in order to thoroughly understand the properties of TRIP steels with multiple phases of ferrite, bainite, retained austenite, and martensite. However, methods for investigating the local properties of the various phases of the TRIP steel are limited due to the very complicated and fine microstructures present in TRIP steel. In this study, the experimental and numerical methods, i.e., the experimental nanoindenting results and the theoretical finite element analyses, were combined in order to extract the local stress–strain curves of each phase. The local stress–strain curves were in good agreement with the values presented in the literature. In particular, the global plastic stress–strain behavior of the TRIP steel was predicted using the multiple phase unit cell finite element analysis, and this demonstrated the validity of the obtained properties of each local phase. The method of extracting the local stress–strain curves from the nanoindenting curves and predicting the global stress–strain behavior assists in clarifying the smart design of multi-phase steels. © 2014, The Minerals, Metals & Materials Society and ASM International.

Jo C.-M.,Sungkyunkwan University | Choi E.,Sungkyunkwan University | Kim S.K.,Sungkyunkwan University | Kim I.C.,National Institute for Nanomaterials Technology | And 2 more authors.
Bulletin of the Korean Chemical Society | Year: 2015

Microgratings that were designed and fabricated to generate IR absorption spectra of SF6 and NH3 on diffraction into a specific detection angle were tested by correlation spectroscopy. The micrograting diffraction provides a reference spectrum for a target molecule, and its cross-correlation with the transmission spectrum of a gas cell is obtained by varying the diffraction angle. As our optical setup can measure the dispersive transmission spectrum and the correlation spectrum under the same conditions, the two kinds of spectra were compared directly in terms of signal-to-noise ratio (SNR). The SNR's of the correlation spectra were a few times lower than those of the dispersed spectra; therefore, the correlation spectroscopy can hardly be placed above the dispersive spectroscopy with respect to the SNR. The merit of the correlation spectroscopy is that a rather small range of modulation wavelength is needed to identify the target. Therefore, the correlation spectroscopy would be more useful for such target molecules whose spectra consist of broad peaks spread throughout a wide wavelength range. © 2015 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA.

Kim I.C.,National Institute for Nanomaterials Technology | Choi E.,National Institute for Nanomaterials Technology | Kim S.K.,Sungkyunkwan University | Kang Y.I.,Agency for Defense Development | And 3 more authors.
Bulletin of the Korean Chemical Society | Year: 2014

Microgratings whose diffracted field at a fixed angle generate IR spectra of SF6 or NH3 were fabricated by MEMS techniques for the purpose of IR correlation spectroscopy. Each micrograting was composed of 1441 reflecting lines in the area of 19.2 × 19.2 mm2. The depth profile of the line elements was determined with a gradient searching method that was described in our previous publication (J. Mod. Opt. 2013, 60, 324-330), and was discretized into 16 levels between 0 and 6.90 μm. The diffraction field from a given depth profile was calculated with Fraunhofer equation. The fabricated microgratings showed errors in the depth and the width within acceptable ranges. As the result, the diffracted IR spectrum of each micrograting matched well with its target reference spectrum within spectral resolution of our optical setup.

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