Toshiki Kobayashi

Hardness of compositionally nano-modulated TiN films

Compositionally nemo-modulated films have been deposited by a reactive gas flow rate modulation sputtering using a Ti target and N2 gas. The explored modulation periods ranged from 6.7nm to 80nm. The thickness of the moduated layer was 400nm. A TiO2/Ti underlayer with a thickness of 100nm was deposited for the entire sample films. By the X-ray diffraction measurements, it was found that films consisted of polycrystalline Ti and TiN mixtures for the periods longer than 10nm and of monolithic TiN for the periods of 6.7nm and 8nm. The X-ray photoelectron spectroscopy results for the film with a modulation period of 80nm showed that the N concentration in metallic layers was about 30% and that of the nitrided layers was about 45%. The maximum hardness of 11.2GPa was obtained at a modulation period of 10nm for an indenter load of 2.94mN by nanoindentation. This value is larger than that obtained for a monolithic TiN film (8.4GPa).

Effects of ionization power on ion energy distribution in ionized r.f. sputtering measured by an energy-resolved mass spectrometer

Abstract In an ionized sputtering technique, it is crucial to give a proper energy to the particles in order to improve film properties or to enhance directionality of the sputtered particles without causing disorder or other undesired damages to the growing film. In this study, ion energy distribution has been investigated by an energy-resolved mass spectrometer for ionized Ti sputtering in order to discuss effects of coil r.f. power and magnetron cathode r.f. power on energy distribution of Ar+ and Ti+ ions arriving at the substrate. The cathode used in the experiment was a magnetron type with a 55-mm diameter Ti target. Ion energy distribution was measured by PPM-421 Plasma Monitor (Balzers) whose orifice to the ion analysis optics was set in front of the sputtering cathode with a distance of 200 mm. The coil r.f. power and the cathode r.f. power were varied up to 200 W. The experimental results show that energy distribution of Ti+ ions was enhanced from a few tens of eV to more than 100 eV as the coil r.f. power increased. The energy increase of Ti+ ions by an r.f. coil plasma was more drastic for a lower cathode r.f. power. As the cathode r.f. power increases, the energy of Ti+ ions decreased, as a result of quenching of the r.f. coil plasma. The quenching is thought to be induced by the increase in the number of Ti atoms passing through the r.f. plasma region. Energy distribution of Ar+ ions showed similar tendency to that of Ti+ ions.

Smart chemical sensors using ZnO semiconducting thin films for freshness detection of foods and beverages

The sensitivity of the chemical sensor, based on the resistance change of Al2O3-doped and SnO2-doped ZnO (ZnO:Al and ZnO:SnO2) thin film, is studied for exposure to various gases. It is found that the ZnO:Al and ZnO:Sn thin film chemical sensor has a high sensitivity and excellent selectivity for amine (TMA and DMA) gas and ethanol gas, respectively. The ZnO:Al (5.0 wt%) thin film chemical sensor which exhibit a high sensitivity for exposure to odors from rotten sea foods, such as salmon, sea bream, oyster, squid and sardine, responds to the freshness change of these sea foods. The ZnO:SnO2 (78 wt%) thin film chemical sensor which exhibit a high sensitivity for exposure to aroma from alcohols, such as wine, Japanese sake, and whisky, responds to the freshness change of these alcohols.