1. Department of Physics and Astronomy and Station Q Purdue, Purdue University, West Lafayette, Indiana 47907, USA
2. Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA
3. School of Materials Engineering, Purdue University, West Lafayette, Indiana 47907, USA
4. School of Electrical and Computer Engineering and School of Materials Engineering, Purdue University, West Lafayette, Indiana 47907, USA