• Korean Journal of Materials Research
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• v.9 no.9
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• pp.878-882
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• 1999

Structural properties of $Al_xGa_1-_xN$ epilayers grown on (0001) sapphire substrate by plasma induced molecular beam epitaxy are investigated in the range of AlN molar fraction from 0.16 to 0.76. The AlN molar fraction estimated by X-ray diffraction agrees well with that of Rutherford backscattering spectroscopy, showing a good linear relationship. The uniform Auger electron microscopy depth profile and linear dependence of average atomic concentration of all the constituents of AlGaN epilayers on AlN molar fraction imply that the epitaxial growth of $Al_xGa_1-_xN$ layers with variation of AlN molar fraction is well controlled without the compositional fluctuation in depth of the epilayer. It is observed by atomic force microscopy that the surface grain shape of $Al_xGa_1-_xN$ epilayer changes from roundish to coalesced one with increasing AlN molar fraction.

• Korean Journal of Materials Research
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• v.5 no.3
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• pp.357-363
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• 1995

PECVD(Plasma-enhanced Chemical Vapor Deposition)법을 이용하여 증착한 $Ta_{2}$O_{5}$ 박막의 전기적 특성과 미세구조에 미치는 RTA(Rapid Thermal annealing) 후속 고온 열처리의 영향을 조사하였다. $Ta_{2}$O_{5}$ 박막의 미세구조와 interface 거동을 관찰하기 위하여XRD(X-ray Diffractometer), TEM(Transmission Electron Microscope), AES(Auger Electron Spectroscope) 분석을 실시하였으며, 전기적 특성을 관찰하기 위하여 I-V, C-V 측정을 하였다. $600^{\circ}C$에서 60초간 열처리를 실시하였을 경우 가장 우수한 유전 특성 및 누설 전류 특성을 보였으며, 유전 상수는 26이었고 누설 전류는 5 $\times$ $10^{-11}$A/$cm^{2}$이었다. $600^{\circ}C$ 이상의 온도에서 행한 열처리에 의하여 박막의 누설 전류와 유전 특성은 복합적으로 영향을 받았음을 알 수 있었다. 이는 $600^{\circ}C$의 열처리에서 이루어지고있는 박막의 결함감소와 고밀화 현상과 함께 80$0^{\circ}C$ 이상의 열처리에서 발생하는 조밀육방정 결정 구조를 가지는 $\delta$-$Ta_{2}$O_{5}$의 결정화에 기인함을 알 수 있었다. 또한 TEM과 AES분석 결과로부터 이들 박막의 누설 전류와 유전상수의 변화는 열처리에 의하여 일어나는 Ta-O-Si transition층의 생성과 성장에 기인함을 알 수 있었다. 따라서 $Ta_{2}$O_{5}$ 박막의 전기적 특성의 변화는 RTA 후속 열처리에 따른 계면 반응과 결정화 그리고 박막의 조밀화에 그 영향이 있음을 알 수 있었다.

• Korean Journal of Materials Research
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• v.13 no.9
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• pp.567-571
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• 2003

We investigate vanadium (V)-based Ohmic contacts on n-GaN ($N_{d}$=$2.0${\times}$10^{18}$ $cm^{-3}$ ) as a function of annealing temperature. It is shown that the V (60 nm) contacts become Ohmic with specific contact resistances of $10^{-3}$ $- 10^{-4}$ Ω$\textrm{cm}^2$ upon annealing at 650 and $850^{\circ}C$. The V(20 nm)/Ti(60 nm)/Au(20 nm)contacts produce very low specific contact resistances of $2.2 ${\times}$ 10^{-5}$ and$ 4.0${\times}$10^{-6}$ Ω$\textrm{cm}^2$ when annealed at 650 and $850{\circ}C$, respectively. A comparison shows that the use of the overlayers (Ti/Au) is very effective in improving Ohmic property. Based on the current-voltage measurement, Auger electron spectroscopy, glancing angle X-ray diffraction, and X-ray photoemission spectroscopy results, the possible mechanisms for the annealing temperature dependence of the Ohmic behavior of the V-based contacts are described and discussed.d.

• Journal of Animal Environmental Science
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• v.19 no.1
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• pp.9-18
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• 2013

Currently, there was no producing system of TMR for pig feeding in Korea. In this study, we examined unrolling, cutting, and softening for the round bale silage. We designed and developed the prototype system of round bale silage for pig feeding. Unroll method were lower chain conveying and upper belt conveying which includes an hydraulic vertical fodder knife. Gathering and cutting method were rotating auger and flywheel which have 10 cutters, input roller of 280 rpm, and cutter rotating speed of 1,750 rpm. Softening device was rotating hammer in inclined cylinder adjustable to $25^{\circ}C$ and rotating speed up to 1,300 rpm. The prototype system was integrated working for unrolling, cutting, and softening. We found that when the round bale silage in unrolling apparatus cut length of 20 cm to input cutting apparatus, the cutting performance was well in continuous working up to input rate of 1,000 kg/h, the softening apparatus was working well.

• Journal of the Korean Society for Heat Treatment
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• v.9 no.1
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• pp.69-77
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• 1996

The fatigue crack initiation behavior of plasma ion nitrided SACM645 steel was investigated through the rotary bending fatigue test and residual stress measurement by XRD. It was shown by XRD and EPMA that the plasma ion nitrided surface was composed of ${\gamma}^{\prime}(Fe_4N)$phase and ${\varepsilon}(Fe_{2-3}N)$phase, and that the nitrogen atoms existed in Fe matrix in diffusion layer. The OM, SEM and Auger spectroscopy showed that the depth of compound layer, mixed compound and diffusion layer, and diffusion layer was $8{\mu}m$, $30{\mu}m$ and $300{\mu}m$, respectively. However, the microhardness test showed that the depth of hardened layer was $500{\mu}m$. The tensile strength of the ion nitrided SACM645 was lower than that of the unnitrided SACM645, and the ion nitrided specimen was fractured without plastic deformation. The nitrided SACM645 showed much poorer low cycle fatigue properties than the unnitrided one. In rotary bending fatigue, the fatigue strength of the ion nitrided SACM645 was higher than that of the unnitrided specimen, and the fatigue crack initiation sites changed by applied fatigue stress levels. The XRD result showed that the ion nitrided SACM645 has the compressive residual stress from surface to $600{\mu}m$ deep and the tensile residual stress from $600{\mu}m$ to deeper site. It is thought that crack initiation takes place at the point where the total stress of residual stress and applied stress is maximum.

• Journal of the Korean institute of surface engineering
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• v.45 no.6
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• pp.257-263
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• 2012

CrN/AlN multilayer coatings with various bilayer periods in the range of 1.8 to 7.4 nm were synthesized using a closed-field unbalanced magnetron sputtering method. Their crystalline structure, chemical compositions and mechanical properties have been investigated with Auger electron spectroscopy, X-ray diffractometry, atomic force microscopy, nanoindentation, scratch tests. The properties of the multilayer coatings varied strongly depending upon the magnitude of the bilayer period. The multilayer coating with a bilayer period of 1.8 nm showed the maximum hardness and an elastic modulus of approximately 37.6 and 417 GPa, respectively, which was 1.54 times higher than the hardness predicted by the rule of mixture from the CrN and AlN coatings. The hardness of the multilayer coating increased as the bilayer period decreased, i.e. as the rotation speed increased. The Hall-Petch type relationship, hardness being related to (1/periodicity)$^{-1/2}$, suggested by Lehoczky was confirmed for the CrN/AlN multilayer coatings with bilayer period close to the 5-10 nm range. With decreasing bilayer period, the surface morphology of the films became rougher and the critical load of films for adhesion strength gradually decreased.

• Journal of Sensor Science and Technology
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• v.7 no.2
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• pp.83-89
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• 1998

$TiO_{2-x}$ thin film humidity sensors have been fabricated by sputtering method and their physical and hygroscopic characteristics have been investigated. The sputtering conditions and sintering conditions affect the sensor's sensitivity toward humidity. AES and SEM micrographs were taken for the analysis of crystal structures, surface morphology caused by adsorbed water vapour. $TiO_{2-x}$ humidity sensors showed negative impedance-humidity characteristics and the sensor which was fabricated by experimental condition 2(rf power of 200W) showed higher sensitivity and linearity than others. Then the slope of the sensor was about $0.794\;K{\Omega}/%RH$ and the response time of $TiO_{2-x}$ humidity sensors was about 2 min. for adsorption and about 3 min. for desorption at the operating temperature of $30^{\circ}C$.

• Journal of the Korean Geosynthetics Society
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• v.16 no.4
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• pp.163-176
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• 2017

The Discrete Element Method (DEM) has been widely used in civil engineering as well as various industrial fields to simulate granular materials. In this study, DEM was adopted to predict the performance of the face plate-type earth pressure balance (EPB) shield TBM (Tunnel Boring Machine). An analysis of the TBM excavation performance was conducted according to two pre-defined excavation conditions with the different rotation speeds per minute (RPM) of the cutterhead. The TBM model which was used in this study has a 6.64 m of diameter and six spokes. Also, 37 precutters and 98 scrapers at an each spoke were modeled with a real-scale specification. From the analysis, compressive forces at the cutterhead face, shield and cutting tools, resistant torques at the cutterhead face, muck discharge rate and accumulated muck discharge by the screw auger were measured and compared.

• Korean Journal of Materials Research
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• v.12 no.3
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• pp.211-214
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• 2002

Properties of 52/48 PZT films with various thicknesses for piezoelectric micro-electro mechanical systems (MEMS) devices fabricated by multi-coating method on $Pt(3500{\AA})/Ti(400{\AA})/SiO_2(3000{\AA})/Si$(525$\mu\textrm{m}$) substrates were investigated. PZT films were deposited by spin-coating process at 3500 rpm for 30 sec, followed by pyrolysis at 45$0^{\circ}C$ for 10 min producing the thickness of about 120nm. These processes were repeated 4, 8, 12, 16 and 20 times in order to have various thicknesses, respectively. Finally, they were crystallized at $650^{\circ}C$ for 30 min. All thick PZT films showed dense and homogeneous surface microstructures. Thick PZT films showed crystalline structures of random orientations with increasing thickness. Dielectric constants of thick PZT films were increased with increasing film thickness and reached 800 at 100kHz for 2.3$\mu\textrm{m}$ thick PZT film. $P_r\; and\; E_c$ of 2.3$\mu\textrm{m}$ thick PZT films were about 20$\mu$C/$\textrm{cm}^2$ and 63kV/cm. Depth profile analysis by Auger Electron Spectroscopy (AES) of 4800 $\AA$ thick PZT film showed the formation of the perovskite phase on Pt layer by Pb diffusion behavior. It was considered that Pb-Pt intermediate layer promoted PZT (111) columnar structures.

• Korean Journal of Materials Research
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• v.9 no.11
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• pp.1148-1152
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• 1999

An organometallic precursor, hfac(hexafluoroacetylacetonate) Cu(I) DMB (3,3-dimethyl- 1-butene) was synthesized, evaluated and compared with other precursors for metal organic chemical vapor deposition of copper thin films. It was found that at $40^{\circ}C$, the vapor pressure was an order of magnitude higher (about 3 torr) than (hfac) Cu vinyltrimethylsilane (VTMS) and films could be deposited at the substrate temperature of 100-$280^{\circ}C$ with deposition rate substantially higher. The copper films contained no detectable impurities as measured by Auger electron spectroscopy and had a resistivity of about 2.0$\mu\Omega$-cm in the deposition temperature range of 150 to $250^{\circ}C$. From the thermal analysis, (hfac)Cu(I)(DMB) is believed to be quite stable and no appreciable amount of precipitation was observed at $65^{\circ}C$ heating for more than a month.