발간논문

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TiO2 photocatalyst with powerful oxidization ability can clean up various environmental pollutions. TiO2 thin films were made to investigate the surface morphology, phase analysis and photocatalytic efficiency. TiO2 thin films were prepared on the Si wafer under various conditions(oxygen partial pressure, working pressrue, D.C. power) by the reactive sputtering process. TiO2 thin films were investigated using XRD, α-step, AFM and a standard plate count method. The deposition rate of TiO2 thin films depended on the particle scattering effect. The surface morphologies of TiO2 thin films showed a columnar structure. The TiO2 films with a good columnar structure were obtained at the optimum processing condition. The Escherichia coli. experiment showed that the excellent crystallinity and the high roughness surface improved the photocatalytic efficiency of TiO2 thin films. The highest efficiency on the bactericidal ability was 78% under UV irradiation. The wetting angle of a water droplet on TiO2 thin films changed from 75˚ to 5˚ under UV light.

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In this study, electronic speckle pattern interferometry (ESPI) was applied to a non-destructive and real-time evaluation of the thermal deformation in a flip-chip package. The displacement resolution of ESPI was improved with magnifying lenses, and ESPI was modified to measure the deformation of micro systems. The flip-chip package thermally deforms with increasing temperature, and the difference in the thermal expansion between the chip and the PCB induces the micro-failure at the solder joint. To evaluate the level of thermal deformation precisely, the horizontal and vertical deformations were measured in the temperature range of 25℃ to 125℃ in situ using the resolution-enhanced ESPI to a sub-micrometer scale. From the experimental results, it was found that the CTE (coefficient of thermal expansion) difference between the chip and the PCB leads to shear strain at the solder joint. In addition, the shear strain could be evaluated at each solder joint. To verify these experimental results, the finite element analysis(FEA) results were compared with the ESPI results. The FEA results were similar to the ESPI results, which confirmed the adequacy of our application.

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Al2O3 is considered as a promising alternative to SiO2 for gate dielectric materials in future Si-based integrated circuits owing to its high dielectric constant and low leakage current. In this study, amorphous Al2O3 films on P type Si(100) at 350℃ have been successfully grown by an atomic layer deposition (ALD) of a top-injection type using Al(CH3)3-trimethylaluminum : TMA and H2O. TMA is a conventional Al precursor and H2O is a conventional oxygen precursor. The growth rate of Al2O3 films was 0.8Å/cycle for all substrates employed under the surface controlled process. According to the AES analysis, the Al2O3 films deposited by TMA contained about 1 at% carbon. The XPS analysis of Al2O3 films grown revealed only an oxidized Al 2p peak and a typical O 1s peak of metal oxides. The electrical properties of Al2O3 films were investigated by I-V measurements. The leakage current values of Al2O3 films were as low as 10^(-9)Å/㎠. The step coverage of the Al2O3 films was about 100% and no reacting layer formed at the top and bottom interfaces.

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The effects of precipitates and alloying elements on impact toughness have been investigated for 30Cr super-ferritic stainless steel welds, in which the total content of carbon and nitrogen was controlled below 250 ppm. The toughness of weld metals was evaluated by sub-size Charpy v-notch impact tests. V-notch tensile test was also undertaken to study crack initiation site and propagation. In order to identify the precipitate phases, its precipitation sites, and morphologies, thin foil, extraction replica and chemical extraction specimens were prepared for TEM analysis. Addition of tungsten in super-ferritic stainless steel weld metals reduced toughness significantly by increasing amount of coarse and angular shaped precipitates such as titanium carbonitride, and successive precipitation along the grain boundary, which provided crack initiation sites and easy propagation. The addition of nickel in the weld metal, however, gave a beneficial effect on the toughness by reducing amount of precipitate and by enhancing formation of fine precipitates.

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This paper presents the main finding of cracking in a Ni-base alloy tube of Hastelloy C-276. It was developed as inter-granular cracking in the heat affected zone(HAZ) or weld metal that occurs during the exposure of welded assemblies to the elevated temperatures. Crack propagation along grain boundaries caused leak failure in the HAZ of socket welding tube. In the HAZ of socket welding, the cracking was not accompanied by coarse carbide precipitation such as Cr23C6 and Cr depleted zone in grain boundary. The intra-grain, however, was inflicted by highly dense dislocations and severe elastic strain fields by thermal stress or strain caused in welding as cooling. These may be caused by carbon diffusion during heating service, and result in construction of high-strengthened matrix in HAZ. The cracking may occur in relatively weak grain boundaries due to grain boundary sliding of the creep condition.

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