1. R&D Center for Innovative Material Characterization, University of Tsukuba 1 , 1-1-1 Tennodai, Tsukuba 305-8573, Japan
2. Institute of Pure and Applied Sciences, University of Tsukuba 2 , 1-1-1 Tennodai, Tsukuba 305-8573, Japan
3. Metrology Systems Research & Development Dept., HITACHI High-Tech Corporation 3 , 552-53 Shinkocho, Hitachinaka-shi, Ibaraki-ken 312-8504, Japan