[1] Department of Physical Electronics, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-ku, Tokyo 152-8552, Japan
[2] Department of Electrical Engineering, Dong-A University, 840 Hadan2-dong, Saha-gu, Busan 604-714, Korea, Republic of
[3] SORST, Japan Science and Technology Agency, Tokyo 152-8552, Japan
[4] National Center for Nanomaterials Technology, Pohang University of Science and Technology, Korea, Republic of