Room-temperature formation of low refractive index silicon oxide films using atmospheric-pressure plasma.

This study aims to apply atmospheric-pressure (AP) plasma to the fabrication of single-layer anti-reflection (AR) coatings with porous silicon oxide. 150 MHz very high-frequency (VHF) excitation of AP plasma permits to enhance the chemical reactions both in the gas phase and on the film-growing surface, increasing deposition rate significantly. Silicon oxide films were prepared from silane (SiH4) and carbon dioxide (CO2) dual sources diluted with helium. The microstructure and refractive index of the films were studied using infrared absorption and ellipsometry as a function of VHF power density. It was shown that significant increase in deposition rate at room temperature prevented the formation of a dense SiO2 network, decreasing refractive index of the resulting film effectively. As a result, a porous silicon oxide film, which had the lowest refractive index of 1.24 at 632.8 nm, was obtained with a very high deposition rate of 235 nm/s. The reflectance and transmittance spectra showed that the low refractive index film functioned as a quarter-wave AR coating of a glass plate.

Mutagenicity of steviol and its oxidative derivatives in Salmonella typhimurium TM677.

Stevioside is natural non-caloric sweetner isolated from Stevia rebaudiana BERTONI, which has been used as a non-caloric sugar substitute in Japan. Pezzuto et al. demonstrated that steviol shows a dose-dependent positive response in forward mutation assay using Salmonella typhimurium TM677 in the presence of metabolic activation system (Aroclor induced rat liver S9 fraction). Our studies were carried out to identify the genuine mutagenic active substance from among the eight steviol derivatives. Steviol indicate almost similar levels of mutagenicity under the presence of S9 mixture, as reported by Pezzuto et al. 15-Oxo-steviol was found to be mutagenic at the one tenth the level of steviol itself under the presence of S9 mixture. Interestingly, specific mutagenicity of the lactone derivative under the presence of S9 mixture was ten times lower than that of the lactone derivative without the addition of S9 mixture.