1. Institute for Nanoscience and Engineering, University of Arkansas, Fayetteville, Arkansas 72701, United States
2. Materials Science and Engineering, University of Arkansas, Fayetteville, Arkansas 72701, United States
3. Department of Electrical Engineering, Arkansas State University, Jonesboro, Arkansas 72467, United States
4. Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, United States
5. Department of Electrical Engineering, University of Arkansas, Fayetteville, Arkansas 72701, United States