Yuichiro Takemura

Inactivation of Escherichia coli Using the Atmospheric Pressure Plasma Jet of Ar gas

Germicidal treatments of Escherichia coli on Langmuir–Blodget (LB) agar were performed using the atmospheric pressure plasma jet sources of Ar gas in the ambient air. Shorter distances from the nozzle of the plasma jet device were more effective in achieving higher bactericidal effects on E. coli grown on LB agar. The surface temperature of the agar was monitored and the spectroscopic analysis of the plasma jet was performed in order to evaluate the factors contributing to the bactericidal effect, such as heating, UV emission, and radical formation caused by the plasma jet. Although the plasma jet raised the surface temperature of LB agar up to about 40 °C, the bactericidal effect was not observed. Moreover, the bactericidal effect of UV (200–300 nm) emitted from the plasma jet was negligible compared with the effects of ions and radical species generated by the atmospheric plasma. The results suggest that the ions and radical species generated by the atmospheric pressure plasma jet are critical for high bactericidal effects on E. coli.

Synthesis of Microcrystalline Silicon Films Using High-Density Microwave Plasma Source from Dichlorosilane

The growth of microcrystalline (µc-) Si:H:Cl films was studied using a high-density and low-temperature microwave plasma source and a spoke antenna of a SiH2Cl2–H2 mixture. Spectroscopic ellipsometry and cross-sectional transmission electron microscopy revealed that the µc-Si:H:Cl films with a small volume fraction of void were synthesized from SiH2Cl2 rather than µc-Si:H from SiH4 at a high deposition rate of 20 A/s. These originated from the chemical reactivity of SiHxCly in high-density microwave plasma. The excessive crystallization was suppressed with a small volume fraction of void in SiH2Cl2 plasma compared with that synthesized from SiH4. The fine structure of µc-Si:H:Cl was studied and compared with that of previously studied µc-Si:H synthesized from SiH4 [Jpn. J. Appl. Phys. 38 (1999) 6629].

Decomposition of Methylene Blue by using an Atmospheric Plasma Jet with Ar, N2, O2, or Air

We have performed experiments on the decomposition of methylene blue by using an atmospheric plasma jet with various working gases. The decomposition efficiencies of Ar, N2, and O2 plasmas are almost equivalent; on the other hand, the rate of methylene blue decomposition by air plasma is lower than those by the other plasmas. From the absorption spectra, it has been found that HONO (nitrous acid) is produced by air plasma-liquid reactions. It has been clarified by a series of experiments, where oxygen concentration in N2 plasma is varied, that the concentration of HONO increases and the rate of methylene blue decomposition degrades with increasing oxygen gas flow rate. Furthermore, the presence of nitrate ions and nitrite ions was confirmed by ion chromatography and pH measurement.

Rapid Crystallization of Amorphous Silicon Utilizing the Plasma Annealing at Atmospheric Pressure

The rapid crystallization of amorphous silicon utilizing the rf inductive coupling thermal plasma jet of argon is demonstrated. Highly crystallized a-Si films were fabricated on th -SiO 2 and textured a-Si:H:B/SnO 2 /glass by adjusting the translational velocity of the substrate stage. The H concentration in the films decreased from 10 21 cm -3 to 10 19 cm -3 with no marked increases in oxygen and nitrogen impurity concentrations and defect density. The crystallization proceeds from the bottom to front surface in terms of the volume expansion during the solidification and crystallization of liquid Si.