1. Center for Research on Interface Structures and Phenomena and Department of Applied Physics, Yale University, New Haven, Connecticut 06511, USA
2. Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43210, USA
3. Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio 43210, USA
4. Department of Mechanical Engineering and Materials Science, Yale University, New Haven, Connecticut 06511, USA