1. Department
of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon 34141, South Korea
2. Department
of Physics, Ewha Womans University, Seoul 120-750, South Korea
3. Department
of Materials Science and Engineering, University of California, Berkeley, California 94720, United States
4. IBM T.J. Watson Research Center, Yorktown
Heights, New York 10598, United States
5. Molecular
Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
6. Materials
Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States