• Journal of the Korean Vacuum Society
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• v.7 no.4
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• pp.348-354
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• 1998

To investigate an influence of the thermal preheating for the substrates exerted on the heteroepilayers, the ZnTe epilayers are grown on the GaAs (100) at the substrate temperature of 450~$630^{\circ}C$ by hot wall epitaxy (HWE). For this purpose, double crystal rocking curve (DCRC) and photoluminescence (PL) are measured. The full width at half maximum of DCRC are the smallest in the ZnTe epilayers grown on the GaAs thermally etched at around both $510^{\circ}C$ and $590^{\circ}C$. However, at around $550^{\circ}C$ they increase due to the reconstruction of the atoms in the surface. And they increase due to the oxide layer at below $490^{\circ}C$ and due to the surface defects at above $610^{\circ}C$. From PL analysis, the full width at half maximum of the light hole exciton $X_{1s,th}$ and of the second-order Raman line increase at around $550^{\circ}C$. With the increasing preheating temperature, the intensities of Y-bands and of the oxygen bound exciton (OBE) peak related to an oxide layer on the GaAs surface generally decrease. From these experimental results, it's confirmed that the GaAs substrate thermally etched influences the ZnTe pilayers.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.32-32
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• 2009

Silicon carbide (SiC) is a wide-bandgap semiconductor that has materials properties necessary for the high-power, high-frequency, high-temperature, and radiation-hard condition applications, where silicon devices cannot perform. SiC is also the only compound semiconductor material. on which a silicon oxide layer can be thermally grown, and therefore may fabrication processes used in Si-based technology can be adapted to SiC. So far, atomic force microscopy (AFM) has been extensively used to study the surface charges, dielectric constants and electrical potential distribution as well as topography in silicon-based device structures, whereas it has rarely been applied to SiC-based structures. In this work, we investigated that the local oxide growth on SiC under various conditions and demonstrated that an increased (up to ~100 nN) tip loading force (LF) on highly-doped SiC can lead a direct oxide growth (up to few tens of nm) on 4H-SiC. In addition, the surface potential and topography distributions of nano-scale patterned structures on SiC were measured at a nanometer-scale resolution using a scanning kelvin probe force microscopy (SKPM) with a non-contact mode AFM. The measured results were calibrated using a Pt-coated tip. It is assumed that the atomically resolved surface potential difference does not originate from the intrinsic work function of the materials but reflects the local electron density on the surface. It was found that the work function of the nano-scale patterned on SiC was higher than that of original SiC surface. The results confirm the concept of the work function and the barrier heights of oxide structures/SiC structures.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.27.1-27.1
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• 2011

The recent extensive research of one-dimensional (1D) nanostructures such as nanowires (NWs) and nanotubes (NTs) has been the driving force to fabricate new kinds of nanoscale devices in electronics, optics and bioengineering. We attempt to produce silicon oxide nanowires (SiOxNWs) in a simple way without complicate deposition process, gaseous Si containing precursors, or starting material of $SiO_2$. Nickel (Ni) nanoparticles (NPs) were applied on Si wafer and thermally treated in a furnace. The temperature in the furnace was kept in the ranges between 900 and $1,100^{\circ}C$ and a mixture of nitrogen ($N_2$) and hydrogen ($H_2$) flowed through the furnace. The SiOxNWs had widths ranging from 100 to 200 nm with length extending up to ~10 ${\mu}m$ and their structure was amorphous. Ni NPs were acted as catalysts. Since there were no other Si materials introduced into the furnace, the Si wafer was the only Si sources for the growth of SiOxNWs. When the Si wafer with deposition of Ni NPs was heated, the liquid Ni-Si alloy droplets were formed. The droplets as the nucleation sites induce an initiation of the growth of SiOxNWs and absorb oxygen easily. As the droplets became supersaturated, the SiOxNWs were grown, by the reaction between Si and O and continuously dissolving Si and O onto NPs. Photoluminescence (PL) showed that blue emission spectrum was centered at the wavelength of 450 nm (2.76 eV). The details of growth mechanism of SiOxNWs and the effect of Ni NPs on the formation of SiOxNWs will be presented.

• Korean Journal of Materials Research
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• v.12 no.11
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• pp.865-869
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• 2002

We investigated the reaction stability of titanium, cobalt and their bilayer films with side-wall spacer materials of SiO$_2$ for the salicide process. We prepared Ti 350 $\AA$, Co 150 $\AA$, Co 150 $\AA$/Ti 100 $\AA$ and Ti 100 $\AA$/Co 150 $\AA$ films on 1000 $\AA$-thick thermally grown SiO$_2$ substrates, respectively. Then the samples were rapid thermal annealed at the temperatures of $500^{\circ}C$, $600^{\circ}C$, and $700^{\circ}C$ for 20 seconds. We characterized the sheet resistance of the metallic layers with a four-point probe, surface roughness with scanning probe microscope, residual phases with an Auger depth profilometer, phase identification with a X-ray diffractometer, and cross-sectional microstructure evolution with a transmission electron microscope, respectively. We report that Ti reacted with silicon dioxide spacers above $700^{\circ}C$, Co agglomerated at $600^{\circ}C$, and Co/Ti, Ti/Co formed CoTi compound requiring a special wet process.

• Journal of Information Display
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• v.6 no.2
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• pp.16-18
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• 2005

Hybrid insulator pentacene thin film transistors (TFTs) are fabricated with thermally grown oxide and cross-linked polyvinylalcohol (PVA) including surface treatment by dilute ploymethylmethacrylate (PMMA) layer on $n^+$ doped silicon wafer. Through the optimization of $SiO_2$ layer thickness in hybrid insulator structure, carrier mobility is increased to more than 35 times than that of the TFT which has only a gate insulator of $SiO_2$ at the same electric field. The carrier mobility of $1.80cm^2$/V-s, subthreshold swing of 1.81 V/decade, and $I_{on}/I_{off}$ current ratio> $1.10{\times}10^5$ are obtained less than -30 V bias condition. The result is one of the best reported performances of pentacene TFTs with hybrid insulator including cross-linked PVA layer as a gate insulator at relatively low voltage operation.

• Journal of the Korea Institute of Military Science and Technology
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• v.23 no.5
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• pp.435-443
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• 2020

Thermal barrier coating(TBC) applied to fighter and turbine engines is a technology that improves the durability of core parts by lowering the surface temperature of base material. The thermal stress caused by mis-match of the coefficient of thermal expansion between the top coating and the TGO interface is the main cause of TBC breakage. Since the thermal stress is dependent on the microstructure of the TBC, designing microstructure of TBC can improve the durability as well as lower the thermal stress. In this study, the effect of coating thickness, volume of porosity and vertical cracking on the thermal stress was analyzed through finite element analysis. Through the analysis results, a design range of a microstructure that can improve the durability of thermal barrier coating by lowering thermal stress is proposed.

• Corrosion Science and Technology
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• v.5 no.4
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• pp.141-148
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• 2006

The chemical composition and the semiconducting properties of the passive films formed on Alloy 690 in various film formation conditions were investigated by XPS, photocurrent measurement, and Mott-Schottky analysis. The XPS and photocurrent spectra showed that the passive films formed on Alloy 690 in pH 8.5 buffer solution at ambient temperature, in air at $400^{\circ}C$, and in PWR condition comprise $Cr_2O_3$, $Cr(OH)_3$, ${\gamma}-Fe_2O_3$, NiO, and $Ni(OH)_2$. The thermally grown oxide in air and the passive film formed at high potential (0.3 $V_{SCE}$) in pH 8.5 buffer solution were highly Cr-enriched, whereas the films formed in PWR condition and that formed at low potential (-0.3 $V_{SCE}$) in pH 8.5 buffer solution showed relatively high Ni content and low Cr content. The Mott-Schottky plots exhibited n-type semiconductivity, inferring that the semiconducting properties of the passive films formed on Alloy 690 in various film formation conditions are dominated by Cr-substituted ${\gamma}-Fe_2O_3$. The donor density, i.e., concentration of oxygen vacancy, was measured to be $1.2{\times}10^{21}{\sim}4.6{\times}10^{21}cm^{-3}$ and lowered with increase in the Cr content in the passive film.

• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.4
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• pp.259-265
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• 2016

This paper presents a study on the use of pulsed phase thermography in the measurement of thermal barrier coating thickness with a numerical simulation. A multilayer heat transfer model was ussed to analyze the surface temperature response acquired from one-sided pulsed thermal imaging. The test sample comprised four layers: the metal substrate, bond coat, thermally grown oxide and the top coat. The finite element software, ANSYS, was used to model and predict the temperature distribution in the test sample under an imposed heat flux on the exterior of the TBC. The phase image was computed with the use of the software MATLAB and Thermofit Pro using a Fourier transform. The relationship between the coating thickness and the corresponding phase angle was then established with the coating thickness being expressed as a function of the phase angle. The method is successfully applied to measure the coating thickness that varied from 0.25 mm to 1.5 mm.

• Journal of the Korean Ceramic Society
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• v.55 no.6
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• pp.608-617
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• 2018

The effects of the purity and monoclinic phase of feedstock powder on the thermal durability of thermal barrier coatings (TBC) were investigated through cyclic thermal exposure. Bond and top coats were deposited by high velocity oxygen fuel method using Ni-Co based feedstock powder and air plasma spray method using three kinds of yttria-stabilized zirconia with different purity and monoclinic phase content, respectively. Furnace cyclic thermal fatigue test was performed to investigate the thermal fatigue behavior and thermal durability of TBCs. TBCs with high purity powder showed better sintering resistance and less thickness in the thermally grown oxide layer. The thermal durability was found to strongly depend on the content of monoclinic phase and the porosity in the top coat; the best thermal fatigue behavior and thermal durability were in the TBC prepared with high purity powder without monoclinic phase.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.7
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• pp.569-575
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• 2008

In this study, disk type of thermal barrier coating system for gas turbine blade was isothermally aged in the furnace changing exposure time and temperature. For each aging condition, bond tests for three samples were conducted for evaluating degradation of adhesive or cohesive strength of thermal barrier coating system. For as-sprayed condition, the location of fracture in the bond test was in the middle of epoxy which have bond strength of 57 MPa. As specimens are degraded by thermal aging, bond strength gradually decreased and the location of failure was also changed from within top coat at the earlier stage of thermal aging to the interface between top coat and TGO at the later stage due to the delamination in the coating.