1. a Research Laboratory of Precision Machinery and Electronics , Tokyo Institute of Technology , Nagatsuda, Midoriku , Yokohama , 227 , Japan
2. b Hitachi Research Laboratory, Hitachi Ltd. , Saiwai-cho, Hitachi , Ibaraki-ken 317 , Japan
3. c Department of Materials Science and Engineering , Tokyo Institute of Technology , Nagatsuda, Midoriku , Yokohama 227 , Japan
4. d Research Laboratory of Precision Machinery and Electronics , Tokyo Institute of Technology , Nagatsuda, Midoriku , Yokohama 227 , Japan