1. Seiko Epson Corporation, Fujimi Plant, 281 Fujimi, Fujimi‐Machi, Suwa‐Gun, Nagano, Japan
2. Seiko Epson Corporation, Research and Development Department, 3‐3‐5 Owa Suwa‐Shi Nagano, Japan
3. Research Center of Ion Beam Technology, Hosei University, Kajino‐Cho, Koganei‐Shi, Tokyo, 184 Japan