Takeo Nakano

Mode transitions in reactive sputtering of metal (Ti, V) oxides are studied. Under a controlled Ar gas pressure at a flow rate of 10 sccm, direct current sputtering plasma was generated. The oxygen flow rate Q and discharge power P were changed in two ways (Q was varied at fixed P, and vice versa), and the mode transitions were monitored using the state jump in the discharge voltage. When the transition points (P, Q) were plotted as two-dimensional (2D) maps, the metal-to-oxide and oxide-to-metal transition points were found to be located on two corresponding straight lines that passed through the origin, irrespective of how the parameters were varied. The origin of this behavior is discussed and ascribed to the linear relationship between the input power and the sputter etching rate of the target. These results also suggest that the metal-mode, hysteresis, and oxide-mode regions of the 2D map can be determined by a few pilot experiments. By depositing vanadium oxide films under conditions in the oxide-mode region, near its boundary, films with very similar optical properties could be obtained.

Transparent conductive Al-doped Zinc oxide thin films were deposited on glass substrates by conventional radio frequency magnetron sputtering (C-RFMS) and inductively coupled plasma-assisted radio frequency magnetron sputtering (ICP-RFMS) methods. The structural and electrical properties of films were studied as a function of the radial position (r) of the substrate in both methods. A good thickness uniformity was obtained in ICP-RFMS, while a significant decrease in film thickness was observed at r=30 mm (erosion zone) in C-RFMS. The c-axis orientation was achieved in all positions in ICP-RFMS, while crystallinity was degraded at r≧25 mm in C-RFMS. Low resistivity ρ of the order of 10^-4 Ω cm was obtained at all positions in ICP-RFMS, while ρ was rapidly increased at r≧30 mm in C-RFMS. In ICP-RFMS, high-energy ion bombardment is suppressed due to the modified plasma density profile and lower space potential. As for transparency, the sample prepared at r=0 mm in ICP-RFMS showed an average visible transmittance of 81%, higher than that in C-RFMS. Throughout the study, it was demonstrated that ICP-RFMS method was promising to improve the radial distribution of structural, electrical, and optical properties of Al-doped ZnO thin films.

Human embryonic kidney 293T (HEK293T) cells are used in various biological experiments and researches. In this study, we investigated the effect of cell culture environments on morphological and functional properties of HEK293T cells. We used several kinds of dishes made of polystyrene or glass for cell culture, including three types of polystyrene dishes provided from different manufacturers for suspension and adherent cell culture. In addition, we also investigated the effect of culturing on gelatin-coated surfaces on the cell morphology. We found that HEK293T cells aggregated and formed into three-dimensional (3-D) multicellular spheroids (MCS) when non-coated polystyrene dishes were used for suspension culture. In particular, the non-coated polystyrene dish from Sumitomo bakelite is the most remarkable characteristic for 3-D MCS among the polystyrene dishes. On the other hand, HEK293T cells hardly aggregated and formed 3-D MCS on gelatin-coated polystyrene dishes for suspension culture. HEK293T cells adhered on the non- or gelatin-coated polystyrene dish for adherent culture, but they did not form 3-D MCS. HEK293T cells also adhered to non- or gelatin-coated glass dishes and did not form 3-D MCS in serum-free medium. These results suggest that HEK293T cells cultured on non-coated polystyrene dish may be useful for the tool to analyze the characteristics of 3D-MCS.