1. Laboratory of Physics, Tokyo Denki University, Saitama 350‐03, Japan
2. Department of Applied Electronic Engineering, Faculty of Science and Engineering, Tokyo Denki University, Saitama 350‐03, Japan
3. Department of Applied Physics, Faculty of Engineering, Tokyo Denki University, Tokyo 101, Japan
4. Department of Chemical Engineering, University of Nebraska‐Lincoln, Lincoln, Nebraska 68588‐0126