1. Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556, USA
2. Department of Physics, Korea University, Seoul 136-701, South Korea
3. Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556, USA
4. Notre Dame Integrated Imaging Facility, University of Notre Dame, Notre Dame, Indiana 46556, USA
5. School of Electrical and Computer Engineering, Cornell University, Ithaca, New York 14853, USA
6. Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853, USA