1. Applied Physics Program, University of Michigan, 450 Church St, Ann Arbor, Michigan 48109, USA
2. Electrical Engineering and Computer Science Department, University of Michigan, 1301 Beal Ave, Ann Arbor, Michigan 48109, USA
3. Department of Physics, Temple University, 1925 N. 12th St, Philadelphia, Pennsylvania 19122, USA
4. Materials Science and Engineering Department, University of Michigan, 2300 Hayward St, Ann Arbor, Michigan 48109, USA