Solid State Phenomena Vols. 124-126

Abstract: In this study, we intend to synthesize the new bio-glass composition with fluoride additions, such as CaF2 and MgF2, instead of Na2O in bio-glass ceramic composition based on 45S5 (46.1SiO2-26.9CaO-24.4Na2O-2.6P2O5, mol%). Also, we intend to increase the SiO2 content up to 50 mol% to enhance the mechanical properties. When B2O3 (4 mol%) was added as a Na2O substitution, thermal expansion coefficient was decreased at the sintering temperature (650~950 oC). Compared to the low flexural strength (57±3 MPa) and vickers hardness (4.6 GPa) of sintered bio-glass ceramics without fluoride and B2O3, bio-glass ceramics substituted with 10mol% MgF2 for Na2O showed more higher mechanical properties (flexural strength: 141±5 MPa, vickers hardness: 5.6 GPa). Thermal expansion coefficient of bio-glass ceramics with the ion substitutions (Ca2+, Mg2+ and B3+) was decreased from 16×10-6/oC to 9.4~10×10-6/oC (~400 oC).

Abstract: Pure Mg, binary Mg-5.6wr%Al, Mg-1.0wt%Si and Mg-7.5wt%Zn alloys were coated by plasma electrolytic oxidation (PEO) method, and their wear properties were investigated and discussed based on surface roughness, thickness and component of coatings. All coatings showed porous layer with some volcano top-like pores on the surface and the non-uniform thickness. The coatings on Mg-Al, Mg-Si and Mg-Zn alloys were composed of primarily MgO and Al2O3, SiO2, ZnO, respectively. The coating layer on Mg-Si alloy was thicker than that of Mg-Al and Mg-Zn alloys, while it was less rough. The wear resistance of pure Mg and Mg alloys was improved by PEO method and the coated Mg alloys showed better wear resistance compared to the coated pure Mg. In particular, the coated Mg-Zn alloy revealed the best wear resistance, while the coated Mg-Si alloy had poor wear resistance despite much thicker coating layer.

Abstract: Ceramic coatings were synthesized on pure Mg and binary Mg-7.1wt%Al alloy by plasma electrolytic oxidation (PEO) technique, and the effect of current ratio, C2/C1, ranging from 0.2 to 0.85 on their mechanical and electrochemical properties was investigated. As the C2/C1 ratio increased, the thickness of the coating layer increased, while surface roughness was almost unchanged. The hardness and wear resistance had a marked tendency to increase with increasing C2/C1 ratio and Mg-Al alloy showed higher hardness and wear resistance at all C2/C1 ratios compared to pure Mg. The weight loss of the pure Mg and Mg-Al alloy in 3.5%NaCl solution was reduced by coatings. However, it had no dependence on the C2/C1 ratio. The wear resistance of the coated Mg-Al alloy was better than that of the coated pure Mg.

Abstract: The anodic titania nanotubular films for photocatalyst were synthesized by anodic oxidation in HF electrolyte, and the photocatalytic properties of anodic TiO2 layer were investigated. The self organized anodic TiO2 film consisting of nanotubes with diameter of 100-150 nm as photocatalyst can be obtained by electrochemical method at a constant potential of 20 V for 40 min in HF solution. In order to improve the photocatalytic efficiency the anodic titania nanotube was heat treated at 550oC for 1h. In the evaluation of dye degradation, heat treated catalyst shows much higher efficiency than non-heat treated one.

Abstract: We report the observation of the carbon nanostructures simply obtained from the sol-gel process using zirconium alkoxide with subsequent heat-treatment. A Raman study showed that the well-defined D and G active modes in multi-walled carbon nanotube similarly appeared in the sample prepared at 350
and 400
. Those disappeared when the sample was heat-treated above 450
, at which its phase fully transformed to zirconia. We observed through HRTEM that either sphere or tube-like carbon nanostructure appeared dispersedly or in a cluster among the oxide aggregates at 350
and 400
. Our study demonstrated that both of the two carbon nanostructures occurred in an intermediate related to carbonization, which may exist during the heat-treatment even in air

Abstract: The epitaxial growth conditions of CeO2 and Y2O3 single buffer layers on textured Ni tapes were examined using rf magnetron sputtering, and the process conditions for the sequential and mixture buffer layers of these two materials were investigated respectively in order to develop a more simplified buffer architecture. The CeO2 single layer exhibited a well developed (200) epitaxial growth at Ar/10%O2 gas below 450°C, although the epitaxial property was decreased with increasing layer thickness. With regard to the deposition of Y2O3 on Ni, the epitaxial growth was not successful. The epitaxy of Y2O3 on Ni was very sensitive to the O2 gas pressure during sputtering. The repeated sequential architecture of the CeO2 and Y2O3 layers exhibited a good epitaxial property at 400°C/(Ar/10%O2) for the initial CeO2 layer and 700°C/Ar and 700°C/(Ar/10%O2) for the subsequent Y2O3 and CeO2 layers, respectively. The Y-doped CeO2 buffers with (200) epitaxy were successfully obtained by the co-sputtering of Ce and Y metals in a reactive gas condition, and the maximum target Y/Ce ratio for the epitaxy was about 1/10.

Abstract: The electronic structure and defect states of 6.25% transition metal (TM = Fe and Co) doped rutile titanium dioxide were investigated by ab initio ultrasoft pseudopotential plane wave method based on density functional theory. When a Fe or Co atom was substituted for a Ti site of TiO2 lattice, additional unoccupied 3d-states of TM appeared as defect states in band-gap and occupied 3d-states represented metallic behavior (half-filled states).It was found that two occupied defect states and one half-filled defect state were the 3d-states of TM from the calculation of band decomposed charge density. The higher unoccupied states were hybridized with unoccupied oxygen 2p-states and located at the middle of band-gap.

Abstract: In general, Electrostatic chuck (ESC) was used to fix and clamp the silicon wafer with electrostatic force in the semiconductor fabrication process. Recently, due to their excellent chemical and plasma stability and high thermal conductivity, sintered ceramics has been used as an insulator material in the configuration of ESC. However, metals of high melting point, such as Mo, W, still used for electrode materials. Because of the thermal mismatch between metal electrode and ceramic insulator, micro cracks were produced at the interface during sintering process of ceramic or its operation process with high temperature, which leads to reduce the life time of ESC. To improve the compatibility between metal and ceramic, mesh type metal electrode was used in ESC but this type of electrode results in inhomogeneous electrostatic force. Homogeneous clamping force is very important to determine the final quality of semiconductor. We have investigated a ceramic electrostatic chuck composed of conducting ceramic electrode of titanium nitride instead of metal electrode. Aluminum nitride was added to titanium nitride to control the thermal expansion coefficient. This composite electrode shows not only a good electrical conductivity but also an excellent compatibility to dielectric layer. Compatibility between the electrode and dielectric layer enable to design the electrode with continuous sheet type which leads to homogeneous electrostatic force. Electrostatic force of ceramic ESC with conducting ceramic electrode was about 1700gf/4inch wafer when the applied voltage was DC 3kV.

Abstract: The effect of ScSZ - YSZ composite on stabilization and electrical conductivity has been investigated. Composite of (8YSZ)x(10ScSZ)(1-x)(x=0~1) were mixed by wet milling process and sintered at 1400°C for 5h and characterized by XRD, SEM, dilatometry and impedance spectroscopy. the long-term stability of the electrolyte materials was examined at 900°C for up to 1000h. The cubic phase shifts from an YSZ character to a ScSZ character with increase in percentage of ScSZ. The conductivity of composite with increasing ScSZ content is slightly higher than YSZ. Especially, above 50wt% ScSZ composition exhibited higher electrical conductivity. All compositions showed conductivity degradation after annealing at 900°C for 1000h.