Kei Matsui

Effects of additional vapors on sterilization of microorganism spores with plasma-excited neutral gas

Some fundamental experiments are carried out in order to develop a plasma process that will uniformly sterilize both the space and inner wall of the reactor chamber at atmospheric pressure. Air, oxygen, argon, and nitrogen are each used as the plasma source gas to which mixed vapors of water and ethanol at different ratios are added. The reactor chamber is remotely located from the plasma area and a metal mesh for eliminating charged particles is installed between them. Thus, only reactive neutral particles such as plasma-excited gas molecules and radicals are utilized. As a result, adding vapors to the source gas markedly enhances the sterilization effect. In particular, air with water and/or ethanol vapor and oxygen with ethanol vapor show more than 6-log reduction for Geobacillus stearothermophilus spores.

Effects of humidity on sterilization of Geobacillus stearothermophilus spores with plasma-excited neutral gas

We investigate the effects of relative humidity on the sterilization process using a plasma-excited neutral gas that uniformly sterilizes both the space and inner wall of the reactor chamber at atmospheric pressure. Only reactive neutral species such as plasma-excited gas molecules and radicals were separated from the plasma and sent to the reactor chamber for chemical sterilization. The plasma source gas is nitrogen mixed with 0.1% oxygen, and the relative humidity in the source gas is controlled by changing the mixing ratio of water vapor. The relative humidity near the sample in the reactor chamber is controlled by changing the sample temperature. As a result, the relative humidity near the sample should be kept in the range from 60 to 90% for the sterilization of Geobacillus stearothermophilus spores. When the relative humidity in the source gas increases from 30 to 90%, the sterilization effect is enhanced by the same degree.

Crystallizing compound film on plastics by ion irradiation in plasma

Micro machines are expected in advanced medical instruments for micro surgery. Typical materials for the actuators are shape memory alloys such as TiNi(titanium nickel) and piezoelectric compounds such as PZT(lead zirconate titanate). For future medical application the materials will be required to be deposited directly on the surfaces of plastics in the form of crystalline thin film, since most medical instruments such as catheters for blood vessel surgery are made of polymeric plastics. Then the film will be finished into some micro actuators.

Exact ion energy in plasma immersion ion implantation

Plasma immersion ion implantation (PIII) is used in various industrial fields such as surface modification of materials and sterilization of disease spores. Recently the technology has become utilized for the applications, in which rather lower ion energy is required, such as shallow ion implantation into cutting-edge semiconductor devices of 3 D structure, i.e. so-called Thin FET as well as low temperature crystallization of sputter-deposited film. In the near future the applications will need low ion energy from 500 eV for the Thin-FET implantation to 50 eV for the low temperature crystallization. The ion energy in PIII is, strictly speaking, given by the summation of the pulse bias voltage and the plasma potential. When the bias voltage was as high as several kV for the surface modification of materials, the plasma potential, which is several tens of voltage in usual industrial plasma, could be neglected. However, for the above-mentioned low energy applications, the plasma potential has an important role to determine the ion energy. Until now, in order to determine the ion energy the plasma potential that was obtained when the bias voltage was not supplied was used. In this study we found that plasma potential changed due to the bias voltage for implantation, too. Resultantly, we obtained the exact ion energy for low-energy PIII by correcting the plasma potential with the bias current.

Sterilization of microorganism spores with plasma-excited neutral gas at atmospheric pressure

In recent years, atmospheric pressure plasma has attracted much attention in industrial fields, since it can be easily generated with simple equipment that excludes evacuation systems and, accordingly, it enables continuous processing of various materials in air. The practical use of the specific effects of energetic particles in plasma, such as ions, electrons, and radicals, is expected.

Crystallizing metal compound film on plastics by plasma-based ion implantation

It has been difficult to sputter-deposit crystalline compound directly on a substrate of low heat-resistant material like polymer. In this study a new apparatus is developed which deposits metallic compound film in crystalline structure directly on a substrate at lower temperature than 200°C (473K). The apparatus consists of a magnetron-sputtering deposition system with multi targets as well as of an ion irradiation system which has the same constitution as the plasma-based ion implantation, although the applied voltage is much lower. The crystallization on a low temperature substrate is assumed to arise from the simultaneous irradiation of ions extracted from plasma. In this report very low temperature crystallization of titanium nickel on polyimide substrate at 80°C (353K) was achieved by reducing the substrate heating due to the ion irradiation. The shape memory effect of the sheet was confirmed.