• Advances in nano research
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• 제4권3호
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• pp.229-249
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• 2016

In this paper, buckling characteristics of nonhomogeneous functionally graded (FG) nanobeams embedded on elastic foundations are investigated based on third order shear deformation (Reddy) without using shear correction factors. Third-order shear deformation beam theory accounts for shear deformation effects by a parabolic variation of all displacements through the thickness, and verifies the stress-free boundary conditions on the top and bottom surfaces of the FG nanobeam. A two parameters elastic foundation including the linear Winkler springs along with the Pasternak shear layer is in contact with beam in deformation, which acts in tension as well as in compression. The material properties of FG nanobeam are supposed to vary gradually along the thickness and are estimated through the power-law and Mori-Tanaka models. The small scale effect is taken into consideration based on nonlocal elasticity theory of Eringen. Nonlocal equations of motion are derived through Hamilton's principle and they are solved applying analytical solution. Comparison between results of the present work and those available in literature shows the accuracy of this method. The obtained results are presented for the buckling analysis of the FG nanobeams such as the effects of foundation parameters, gradient index, nonlocal parameter and slenderness ratio in detail.

• Advances in nano research
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• 제4권3호
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• pp.197-228
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• 2016

In the present study, thermo-electro-mechanical vibration characteristics of functionally graded piezoelectric (FGP) Timoshenko nanobeams subjected to in-plane thermal loads and applied electric voltage are carried out by presenting a Navier type solution for the first time. Three kinds of thermal loading, namely, uniform, linear and non-linear temperature rises through the thickness direction are considered. Thermo-electro-mechanical properties of FGP nanobeam are supposed to vary smoothly and continuously throughout the thickness based on power-law model. Eringen's nonlocal elasticity theory is exploited to describe the size dependency of nanobeam. Using Hamilton's principle, the nonlocal equations of motion together with corresponding boundary conditions based on Timoshenko beam theory are obtained for the free vibration analysis of graded piezoelectric nanobeams including size effect and they are solved applying analytical solution. According to the numerical results, it is revealed that the proposed modeling can provide accurate frequency results of the FGP nanobeams as compared to some cases in the literature. In following a parametric study is accompanied to examine the effects of several parameters such as various temperature distributions, external electric voltage, power-law index, nonlocal parameter and mode number on the natural frequencies of the size-dependent FGP nanobeams in detail. It is found that the small scale effect and thermo-electrical loading have a significant effect on natural frequencies of FGP nanobeams.

• 한국재료학회지
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• 제30권2호
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• pp.81-86
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• 2020

MoO₃ metal oxide nanostructure was formed by hydrothermal synthesis, and a perovskite solar cell with an MoO₃ hole transfer layer was fabricated and evaluated. The characteristics of the MoO₃ thin film were analyzed according to the change of hydrothermal synthesis temperature in the range of 100 ℃ to 200 ℃ and mass ratio of AMT : nitric acid of 1 : 3 ~ 15 wt%. The influence on the photoelectric conversion efficiency of the solar cell was evaluated. Nanorod-shaped MoO₃ thin films were formed in the temperature range of 150 ℃ to 200 ℃, and the chemical bonding and crystal structure of the thin films were analyzed. As the amount of nitric acid added increased, the thickness of the thin film decreased. As the thickness of the hole transfer layer decreased, the photoelectric conversion efficiency of the perovskite solar cell improved. The maximum photoelectric conversion efficiency of the perovskite solar cell having an MoO₃ thin film was 4.69 % when the conditions of hydrothermal synthesis were 150 ℃ and mass ratio of AMT : nitric acid of 1 : 12 wt%.

• 설비공학논문집
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• 제24권3호
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• pp.281-287
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• 2012

The internal oxide scale of twelve superheater and reheater tubes were tested which were serviced for 30,000~120,000 hours in thermal power plants. The oxide scale was formed in three layers. The Cr-rich area was observed beneath the original metal surface. The hematite ($Fe_2O_3$) phase was formed on the outer surface. The intermediate layer was magnetite ($Fe_3O_4$). The thickness of Cr-rich layer was about half of the total scale. All layers grew during the operation hour of the plant. The thickness of thickest scale was 0.2mm in superheater tubes. This can increase the tube metal temperature about $7^{\circ}C$ more than initial state. $7^{\circ}C$ tube metal temperature can reduce tube life about 30%, but the boiler tube's design margin is big enough therefore it has been analyzed that it would not effect on the life span.

• 한국전기전자재료학회논문지
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• 제28권12호
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• pp.821-825
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• 2015

Anti-reflective (AR) thin film was fabricated on a glass substrate by sol-gel method. The coating solution was synthesized with TEOS (tetraethlyorthosilicate) and poly ethylene glycol (PEG, 4.0 wt%). As the withdrawal speed of coating was changed from 0.1 mm/sec to 0.3 mm/sec, the thickness and refractive index of prepared thin films were changed. The reflectance and transmittance of coating glass fabricated by the withdrawal speed of 0.1 mm/sec were 0.62% and 95.0% in visible light range. The refractive index and thickness of single layer thin film were n= 1.29 and ca. 99.0 nm.

• 한국표면공학회지
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• 제40권5호
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• pp.225-233
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• 2007

Effects of alloying elements on the corrosion layer formation of Pb-grid/active materials interface has been researched for improvement of corrosion resistance of Pb-Ca alloy. For this research, various amounts of alloying elements such as Sn, Ag and Ba were added to the Pb-Ca alloys and investigated their corrosion behaviors. Batteries fabricated by using these alloys as cathode grids were subjected to life cycle test. Overcharge life cycle test was carried out at $75^{\circ}C$, 4.5 A, for 110 hrs. with KS standard (KSC 8504). And then, after keeping the battery with open circuit state for 48 hr, discharge was carried out at 300A for 30 sec. Corrosion morphology and interface between Pb-grid and active materials were investigated by using ICP, SEM, WDX, and LPM. Corrosion layer of Pb-Ca alloy got thicken with increasing Ca content. For Pb-Ca-Sn alloy, thickness of corrosion layer decreased as Sn and Ag content increased gradually. In case of Pb-Ca-Sn-Ba alloy, thickness of corrosion layer decreased up to 0.02 wt% Ba addition, whereas, it was not changed in case of above 0.02 wt% Ba addition.

• 한국수소및신에너지학회논문집
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• 제16권4호
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• pp.372-378
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• 2005

Ni/YSZ ($Y_2O_3$-stabilized $ZrO_2$) composite powder for a cathode material in high temperature electrolysis(HTE) was synthesized by a mechanical alloying method with Ni and YSZ powder. Microstructure of the composite and cell thickness for HTE reaction has been analyzed with various techniques of XRD, SEM to investigate effects of fabrication conditions. Employing the composite material, furthermore, the unit cell for HTE has been studied to evolve hydrogen from water. XRD patterns showed that the composites after wet mechanical alloying were composed of respective nano-sized crystalline Ni and YSZ. While ethanol as additive for mechanical alloying increased to $20\;{\mu}m$ of average particle size of the composites, alpha-terpineol effectively decreased to sub-micro size of that. This study has been found out the evolution of hydrogen by HTE reaction employing the fabricated cathode material, showing 1.4 ml/min of $H_2$ generation rate as increasing $20\;{\mu}m$ of cathode thickness.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2000년도 International Symposium on Magnetics The 2000 Fall Conference
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• pp.251-265
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• 2000

S $m_{2}$F $e_{17}$ $N_{x}$ film magnets using a S $m_{2}$F $e_{17}$ target were prepared at $N_{2}$ gas atmosphere using a Nd-YAG laser ablation technique. The effect of nitrogen pressure, deposition temperature, pulsation time and film thickness on the structure and magnetic properties of S $m_{2}$F $e_{17}$ $N_{x}$ film were studied. Increasing the nitrogen pressure up to 5 atm. was confirmed to lead the formation of complete S $m_{2}$F $e_{17}$ $N_{x}$ compound. Optimized magnetic properties with the nitrogenation temperature ranging over 500-53$0^{\circ}C$ could be obtained by extending the nitrogenation time up to 4 hours. Relatively low coercivities of 400~600 Oe were exhibited from the S $m_{2}$F $e_{17}$ $N_{x}$ films having the thickness of 50~100 nm while 4$\pi$ $M_{s}$ of 10~12 kG could be achieved. In-plane anisotropic characteristic, which was the basic goal in this study, was achieved by controlling the nitrogenation parameters.ameters.ers.ameters.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 하계학술대회 논문집 Vol.8
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• pp.7-8
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• 2007

We investigated the characteristics of UTB-SOI pMOSFETs with SOI thickness ($T_{SOI}$) ranging from 10 nm to 1 nm and evaluated the dependence of electrical characteristics on the silicon surface orientation. As a result, it is found that the subthreshold characteristics of (100)-surface UTB-SOI pMOSFETs were superior to (110)-surface. However, the hole mobility of (110)-surface were larger than that of (100)-surface. The enhancement of effective hole mobility at the effective field of 0.1 MV/ccm was observed from 3-nm to 5-nm SOI thickness range.

• 비파괴검사학회지
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• 제34권6호
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• pp.457-466
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• 2014

This paper presents an analytic and numerical simulation of the generation and propagation of pico-second ultrasound with nano-scale wavelength, enabling the production of bulk waves in thin films. An analytic model of laser-matter interaction and elasto-dynamic wave propagation is introduced to calculate the elastic strain pulse in microstructures. The model includes the laser-pulse absorption on the material surface, heat transfer from a photon to the elastic energy of a phonon, and acoustic wave propagation to formulate the governing equations of ultra-short ultrasound. The excitation and propagation of acoustic pulses produced by ultra-short laser pulses are numerically simulated for an aluminum substrate using the finite-difference method and compared with the analytical solution. Furthermore, Fourier analysis was performed to investigate the frequency spectrum of the simulated elastic wave pulse. It is concluded that a pico-second bulk wave with a very high frequency of up to hundreds of gigahertz is successfully generated in metals using a 100-fs laser pulse and that it can be propagated in the direction of thickness for thickness less than 100 nm.