1. Department
of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235, United States
2. Materials
Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
3. Division
of Electron Microscopic Research, Korea Basic Science Institute, Daejeon 305-806, Republic of Korea
4. Grupo
de Fı́sica de Materiales Complejos, Universidad Complutense, 28040 Madrid, Spain
5. Electronic
Materials Research Center, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea
6. Department
of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996, United States