Introduction - To understand a mechanism of plasma-surface interaction, there needs analysis of reactions between plasmas and materials. It has long been appreciated that free radicals play important roles for controlling the reactions. The electron-spin-resonance (ESR) technique can detect the radicals - in particular dangling bonds - and thus we have developed methods to utilize the ESR for this purpose [1]. In this study, we focused on ESR detection of free radical on materials interacted with plasmas.

Polymeric materials - An ESR system was connected to a plasma discharge system (2.45 GHz, 50 W) using a quartz tube with an inner diameter of approximately 9 mm. Gas (H2, O2, etc.) was flowed into the quartz tube and the pressure was maintained at approximately 100 Pa in the downflow region. ESR measurements were conducted using a standard X-band (9 GHz) spectrometer with a microwave resonator. The quartz tube and poly(methyl-methacrylate)(PMMA)-ralted polymer (methacrylic acid, ethylacrylate, ethyl-methacrylate, acrylic acid, etc.) film sample were inserted inside the ESR cavity in the down-flow region, typically 20 cm from the plasma discharge.

During exposure of gaseous radicals on the polymer surface, the in situ real-time ESR technique was detected creation of dangling bonds on surface at real time and provided to the microscopic understanding of chemical reactions on surfaces with gaseous radicals during plasma processes. We have successfully obtained information regarding the reaction mechanism with radicals generated by plasma induced surface interactions.

Biological organism - In another, fungal spores of Penicillium digitatum were diluted by sterilized water mixed surfactant (Tween 20) for avoiding clump of spores, and then dried it on a quartz plate. ESR observation of the spores was conducted during oxygen plasma exposure.

Decrease of ESR intensity was corresponded with inactivation behavior where no germination of the spores was observed, eg. no sprout on the mycelia after plasma exposure. Through clarification of individual effects of plasma emission lights, neutral and charged species, this behavior is interpreted that intercellar stable free radical such as quinones was destroyed by exposing oxidizing species generated in the plasmas.

Conclusion - The real time in situ ESR method has a great potential for analyzing the interactions with materials and plasmas.

Acknowledgments - This study was partly supported by the Knowledge Cluster Initiative (the second stage), Tokai region, MEXT.

1. K. Ishikawa et al., J. Phys. Chem. Lett. 2, 1278 (2011).