Materials Science Forum Vols. 510-511

Abstract: Enormous use of ground for various purposes in urban areas has led to disappearance of green-planted surfaces. Considering space constraints, planted roofs become one promising and stabilizing choice to improve amenity and reduce the thermal loads on the building’s shell. However, a critical issue for rooftop garden is the release of pollutants in urban runoff. Not only particles but also dissolved pollutants should be removed from building drainage because of their potential impact on water environment. To add functions for the control of pollutant outflow, bauxsite minerals made of red waste from alumina refineries were incorporated in the rooftop garden as a special soil. The minerals have high trapping capacities for trace metals and other soluble species. Moreover, they are easy to integrate with rooftop garden systems. Based on their equilibrium capacity for removing pollutants, an optimum amount of bauxsite minerals is suggested. The characteristics of rainwater runoff and pollutants release were compared for normal and modified rooftop garden in laboratory scale. As expected, the green roof system with the bauxsite layer reduces the concentration of heavy metals. The technique used in this study is also likely to be implemented in other green surfaces in housing complexes.

Abstract: Nanoporous SiC membrane was developed on the porous alumina plate for the hydrogen separation using preceramic polymers such as polyphenylcarbosilane. The prepared preceramic polymers were characterized with FT-IR, TGA, GPC and XRD. Nanoporous SiC membrane was derived from the preceramic polymer using a spin coating method. The SiC membrane spin coated using 20 wt.% of polyphenylcarbosilane solution in cyclohexane does not show any cracks on the surface after heat treatment at 800oC. The average thickness of the SiC membrane is about 1µm. SiC coated porous alumina possesses asymmetric pore size distribution. There are micropores that originated from porous alumina substrate, and nanopores that derived from amorphous state of SiC membranes. The pore size distribution measurement showed that the sample contains 1-3 nm sized nano pores.

Abstract: A thin film including β-silicon carbide was synthesized by a reaction of silicon monoxide gas and carbon source derived from polyimide film (PIF) at 1400°, 1500°, 1600°, 1700° and 1800°C. Formation mechanism of the SiC film was investigated thermodynamically and kinetically through the relationships among the conversion ratio of SiC, synthesis temperature and time. The formation processes were simulated based on the calculation of differential equations concerning thermodynamic and kinetic constants of 7 chemical equations. The sample obtained had a film shape similar to that of the carbon source film. The results of the time dependence curves of the conversion ratio of SiC calculated from 7 chemical equations, 14 rate constants, 2 diffusion constants, 10 chemical species and 10 differential equations are in good agreement with the experimental results of the SiC conversion ratio as a function of synthesis time. The calculation results of solving each constant suggest that the formation processes of SiC are "rate-controlled reaction at the interface" at the initial stage of the reaction, and then they gradually change to "diffusion-controlling reaction in the reacted region". In the long term synthesis, we recognized that the waste SiO with non-stoichiometric oxygen can also be used as a silicon source.

Abstract: The application of VOC-free materials for building interior is the first step to reduce the contamination level, however, it is practically unavoidable to find a way to eliminate existing pollutants from furniture, adhesives, etc. As a positive way of controlling the air indooors, the air conditioner may be applied with high functional filter, which uses electricity for compulsory air circulation. As an alternative, we modified natural zeolite powder by ion exchange and also by addition of TiO2 photo-catalyst for multifunctional powder to contribute to controlling the indoor air quality. The modified zeolites were applied on the interior non-woven polypropylene sheet to reduce indoor air pollutants not only by adsorption mechanism but also by decomposition mechanism. We studied deodorization of the multi-functional powders and also their coating on non-woven textiles by a Gastec method.

Abstract: To compare with the human cortical bone, the biomimetic properties of nano-hydroxyapatite/polyamide 66 composite (n-HA/PA66) were preliminarily studied qualitatively and quantitatively with TEM, XRD in crystal morphology, phase composition and crystal structure. A series of structure parameters such as cell lattice parameters (a and c), mean crystallite size and micro-strain were calculated to characterize quantitatively the microstructure of n-HA/PA66 and human cortical bone at the atomic level. The results show that n-HA/PA66 is a good biomimetic biomaterial. But there still are some differences between n-HA/PA66 and human cortical bone. Compared to human cortical bone, the crystal microstructure of n-HA/PA66 is denser, the crystal lattice of n-HA is more perfect and the distortion of crystal lattice decreases.

Abstract: Copper via filling is an important factor in 3D stacking interconnection of SiP (system in package). As the packaging density is getting higher, the size of via is getting smaller. When DC electroplating is applied, a defect-free hole cannot be obtained in a small size hole. To prevent the defects in holes, pulse and pulse reverse current was applied in copper via filling. The size of 50, 70, 100
in diameter and 100
in height. The holes were prepared by DRIE method. TaN and Ta was sputtered for copper diffusion barrier. Via specimen were filled by DC, pulse and pulse-reverse current electroplating methods. The effects of additives and current types on copper deposits were investigated. Vertical and horizontal cross section of the via were observed by SEM to find the defects in via. When pulse-reverse electroplating method was used, defect free via were uccessfully obtained.

Abstract: Well-aligned ZnO nanorods were synthesized using metalorganic chemical vapor deposition. Their size was controlled by adjusting the O/Zn precursor ratio. The electrical transport and optical properties of the size-controlled nanorods were investigated. The elelctron concentration and electron mobility in the nanorods are not sensitive to the change of the precursor ratio. In addition, the photoluminescent property is nearly the same regardless of their different sizes. These results suggest that altering the precursor ratio is a way of fabricating size-controlled ZnO nanorods with quite consistent electrical and optical properties.

Abstract: FeSx nanoparticles were synthesized by the chemical vapor condensation (CVC) process using the pyrolysis of iron pentacarbonyl (Fe(CO)5) and sulfur (S). The influence of CVC parameter on the formation of nanoparticle and size distribution was studied. The synthesized nanoparticles consisting of FeS, FeS2 and Fe2O3 were nearly spherical shape and 5~40 nm in mean diameter. Obtained particles were studied by applying the field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) methods. Electrochemical properties of the electrode fabricated with synthesized nanoparticles were evaluated.

Abstract: Hydrogenated amorphous Si (a-Si:H) films were prepared by plasma enhanced chemical vapor deposition (PECVD) techniques, and the effect of nano-structure on the photoluminescence (PL) phenomena of the films was investigated. The films, which were prepared at R.T., contain both amorphous and crystalline phases of 1 ~ 3 nm size nano-crystallites with {100} orientation preference while the films prepared at 500°C are composed of about 6 nm and 150 nm size crystallites. The former exhibit a strong PL intensity near blue light region, while the latter exhibiting little PL phenomena; also, the optical band gap of the former was calculated at 4.2 eV.

Abstract: We studied photoluminescence (PL) and electroluminescence (EL) properties of hydrogenated nanocystalline silicon (nc-Si:H) thin films prepared by applying the plasma enhanced chemical vapor deposition (PECVD) techniques. . A prototype of ITO/nc-Si:H/P-type Si wafer/Al EL devices was illustrated with its fundamental electrical and optical features. The nc-Si:H films exhibited PL spectra in a wavelength range of 350 ~ 700 nm with the maximum intensity at ~ 530 nm, which is attributed to quantum confinement effects (QCE) owing to the presence of nanocrystalline Si. The EL device produced EL spectra with their maximum intensity at ~ 525 nm which are similar to the PL spectra. The light emission is attributed to radiative recombination related to nanocrystalline Si contained in the hydrogenated amorphous Si (a-Si:H).