1. Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235, USA
2. Department of Physics and Materials Science, University of Memphis, Memphis, Tennessee 38152, USA
3. Department of Electrical Engineering and Computer Science, Vanderbilt University, Nashville, Tennessee 37235, USA
4. Vanderbilt Institute of Nanoscale Science and Engineering, Vanderbilt University, Nashville, Tennessee 37235, USA
5. Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA