• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.328-331
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• 2000

The effect of the constituent elements and their composition of the seed layer on the properties of the evaporated Zn thin films was investigated. It was carried out by the analysis of the preferred orientation and the grain size, and the corrosion characteristics. Seed layers were prepared by evaporation of Al and AlCu respectively, and here the Cu content as additives of the source materials of seed layers were designed 5 a/o to 20 a/o. The values of full width at half maximum (FWHM) of the (002) x-ray diffraction peaks of Zn decreased by increasing the amount of the additives on Al seed layer, as a results, the grain sizes also decreased. In order to characteristics of Zn thin films evaporated on the various seed layers, electrical resistivity changes with a function of time at the temperature of 40$^{\circ}C$ and the relative humidity of 80%, as a result, the relative resistivity changes were increased by decreasing the grain size and the FWHM values of (002) peaks of Zn.

• Proceedings of the Korea Concrete Institute Conference
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• 1991.10a
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• pp.124-128
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• 1991

Wood, laminates, reinforced concrete, and some special types of metals systems with controlled grain orientation are often orthotropic and at least rectilinearly anisotropic from point to point, if regarded as homogeneous media. Orthotropic bodies where a crack is not associated with a plane of elastic symmetry may be conveniently treated as a crack problem in a generally anisotropic body. At this work, approach for the determination of the stress intensity factors (SIF) of anisotropic body using crack tip singular elements is presented. Caculated values are in good agreement with the others.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.59.1-59.1
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• 2010

Aluminum-induced crystallization (AIC) of amorphous silicon (a-Si) is studied with the structure of a glass/Al/$SiO_2$/a-Si, in which the $SiO_2$ layer has micron-sized laser holes in the stack. An oxide layer between aluminum and a-Si thin films plays a significant role in the metal-induced crystallization (MIC) process determining the properties such as grain size and preferential orientation. In our case, the crystallization of a-Si is carried out only through the key hole because the $SiO_2$ layer is substantially thick enough to prevent a-Si from contacting aluminum. The crystal growth is successfully realized toward the only vertical direction, resulting a crystalline silicon grain with a size of $3{\sim}4{\mu}m$ under the hole. Lateral growth seems to be not occurred. For the AIC experiment, the glass/Al/$SiO_2$/a-Si stacks were prepared where an Al layer was deposited on glass substrate by DC sputter, $SiO_2$ and a-Si films by PECVD method, respectively. Prior to the a-Si deposition, a $30{\times}30$ micron-sized hole array with a diameter of $1{\sim}2{\mu}m$ was fabricated utilizing the femtosecond laser pulses to induce the AIC process through the key holes and the prepared workpieces were annealed in a thermal chamber for 2 hours. After heat treatment, the surface morphology, grain size, and crystal orientation of the polycrystalline silicon (pc-Si) film were evaluated by scanning electron microscope, transmission electron microscope, and energy dispersive spectrometer. In conclusion, we observed that the vertical crystal growth was occurred in the case of the crystallization of a-Si with aluminum by the MIC process in a small area. The pc-Si grain grew under the key hole up to a size of $3{\sim}4{\mu}m$ with the workpiece.

• Journal of the Korean Ceramic Society
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• v.52 no.6
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• pp.441-448
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• 2015

Silicon carbide (SiC) coatings for tri-isotropic (TRISO) nuclear fuel particles were fabricated using a chemical vapor deposition (CVD) process onto graphite. A micro-tensile-testing system was developed for the mechanical characterization of SiC coatings at high temperatures. The fracture strength of the SiC coatings was characterized by the developed micro-tensile test in the range of $25^{\circ}C$ to $1000^{\circ}C$. Two types of CVD-SiC films were prepared for the micro-tensile test. SiC-A exhibited a large grain size (0.4 ~ 0.6 m) and the [111] preferred orientation, while SiC-B had a small grain size (0.2 ~ 0.3 mm) and the [220] preferred orientation. Free silicon (Si) was co-deposited onto SiC-B, and stacking faults also existed in the SiC-B structure. The fracture strengths of the CVD-SiC coatings, as measured by the high-temperature micro-tensile test, decreased with the testing temperature. The high-temperature fracture strengths of CVD-SiC coatings were related to the microstructure and defects of the CVD-SiC coatings.

• Current Photovoltaic Research
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• v.2 no.1
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• pp.1-7
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• 2014

We developed a method of growing thin Si film at $600^{\circ}C$ by hot wire CVD using a very thin large-grained poly-Si seed layer for thin-film Si solar cells. The seed layer was prepared by crystallizing an amorphous Si film by vapor-induced crystallization using $AlCl_3$ vapor. The average grain size of the p-type epitaxial Si layer was about $20{\mu}m$ and crystallographic defects in the epitaxial layer were mainly low-angle grain boundaries and coincident-site lattice boundaries, which are special boundaries with less electrical activity. Moreover, with a decreasing in-situ boron doping time, the mis-orientation angle between grain boundaries and in-grain defects in epitaxial Si decreased. Due to fewer defects, the epitaxial Si film was high quality evidenced from Raman and TEM analysis. The highest mobility of $360cm^2/V{\cdot}s$ was achieved by decreasing the in-situ boron doping time. The performance of our preliminary thin-film solar cells with a single-side HIT structure and $CoSi_2$ back contact was poor. However, the result showed that the epitaxial Si film has considerable potential for improved performance with a reduced boron doping concentration.

• Korean Journal of Metals and Materials
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• v.47 no.9
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• pp.523-532
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• 2009

In this study, four API X80 linepipe steel specimens were fabricated with varying cooling rates and finish cooling temperatures, and their microstructures and crystallographic orientations were analyzed to investigate the effects of cooling conditions on their tensile and Charpy impact properties. All the specimens consisted of acicular ferrite, granular bainite, and secondary phases such as martensite and martensiteaustenite constituent. The volume fraction of secondary phases increased with increasing cooling rate, and the higher finish cooling temperature resulted in the reduction in volume fraction and grain size of secondary phases. According to the crystallographic orientation analysis data, the effective grain size and unit crack path decreased as fine acicular ferrites having a large amount of high-angle grain boundaries were homogeneously formed, thereby leading to the improvement of Charpy impact properties. The specimen fabricated with the higher cooling rate and lower finish cooling temperature had the highest upper shelf energy and the lowest energy transition temperature because it contained a large amount of fine secondary phases homogeneously distributed inside fine acicular ferrites, while its tensile properties well maintained.

• Korean Journal of Materials Research
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• v.30 no.7
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• pp.343-349
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• 2020

NKN [(Na,K)NbO₃] is a candidate lead-free piezoelectric material to replace PZT [Pb(Zr,Ti)O₃]. A single crystal has excellent piezoelectric-properties and its properties are dependent of the crystal orientation direction. However, it is hard to fabricate a single crystal with stoichiometrically stable composition due to volatilization of sodium during the growth process. To solve this problem, a solid solution composition is designed (Na,K)NbO₃-Ba(Cu,Nb)O₃ and solid state grain growth is studied for a sizable single crystal. Ceramic powders of (Na,K)NbO₃-M(Cu,Nb)O₃ (M = Ca, Sr, Ba) are synthesized and grain growth behavior is investigated for different temperatures and times. Average normal grain sizes of individual specimens, which are heat-treated at 1,125 ℃ for 10 h, are 6.9, 2.8, and 1.6 ㎛ for M = Ca, Sr, and Ba, respectively. Depending on M, the distortion of NKN structure can be altered. XRD results show that (NKN-CaCuN: shrunken orthorhombic; NKN-SrCuN: orthorhombic; NKN-BaCuN: cubic). For the sample heat-treated at 1,125 ℃ for 10 h, the maximum grain sizes of individual specimens are measured as 40, 5, and 4,000 ㎛ for M = Ca, Sr, and Ba, respectively. This abnormal grain size is related to the partial melting temperature (NKN-CaCuN: 960 ℃; NKN-SrCuN: 971 ℃; NKN-BaCuN: 945 ℃).

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.11
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• pp.984-989
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• 1998

The ($Sr_{1-x}Ca_x)TiO_3$(SCT) thin films are deposited on Pt-coated electrode($Pt/TiN/SiO_2/Si$) using RF sputtering method with substitutional contents of Ca. The maximum grain of thin films is obtained by substitution of Ca at 15[mol%]. All SCT thin films had (111) preferred orientation. The dielectric constant was increased with increasing the substitutional contents of Ca, while it was decreased if the substitutional contents of Ca exceeded over 15[mol%]. The dielectric constant changes almost linearly in temperature ranges of -80~+90[$^{\circ}C$]. The temperature properties of the dielectric loss have a stable value within 0.02 independent of the substitutional contents of Ca. All SCT thin films used in this study show the phenomena of dielectric relaxation with the increase of frequency, and the relaxation frequency is observed above 200[kHz].

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.2
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• pp.176-180
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• 2006

[ $(Na_{0.5}Bi_{0.5})TiO_3$ ][NBT] thin films were prepared on a highly (100) oriented $LaNiO_3[LNO]$ by sol-gel process. X-ray diffraction patterns of the NBT films annealed above $600^{\circ}C$ for 5 minutes have confirmed a highly (100) oriented growth and pseudocubic structure (a=3.884${\AA}$). The (l00) orientation factor increased from 90 to $99\%$ with increasing soaking time from 5 to 60 minutes at $600^{\circ}C$. The NBT films ($600^{\circ}C$/5 min,) have a flat and dense microstructure with large columnar grains, and their grain size are about 44 nm. The Au/NBT/LNO/Si hetero structure sample show a ferroelectric properties.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.8
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• pp.692-697
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• 2016

This study investigated the effect of surface roughness of zinc oxide (ZnO) layer on the growth of polycrystalline Si layer via an Al-induced layer exchange process. It was found that the growth rate, grain size, crystallization fraction, and preferential orientation of the polycrystalline Si layer were strongly influenced by the surface roughness of the underlying ZnO layer. As the roughness of the ZnO surface increased, a higher growth rate (~40 min) and preferential Si (100) orientation were obtained because of the spatial concentration fluctuations in the Al-Si alloy, induced by the surface roughness of the underlying ZnO layer.