1. Institute for Nanoscience and Engineering, University of Arkansas 1 , Fayetteville, Arkansas 72701
2. Material Science and Engineering Program, University of Arkansas 2 , Fayetteville, Arkansas 72701
3. Department of Electrical Engineering, University of Arkansas 3 , Fayetteville, Arkansas 72701
4. Microelectronics-Photonics Program, University of Arkansas 4 , Fayetteville, Arkansas 72701
5. Department of Physics, University of Arkansas 5 , Fayetteville, Arkansas 72701