1. School of Electrical and Computer Engineering, Cornell University, Ithaca, New York 14853, USA
2. Department of Material Science and Engineering, Cornell University, Ithaca, New York 14853, USA
3. Novel Crystal Technology, Inc., Sayama 350-1328, Japan
4. Kavli Institute at Cornell for Nanoscale Science, Cornell University, Ithaca, New York 14853, USA