1. Sandia National Laboratories, Albuquerque, New Mexico 87123, United States
2. Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque87123, New Mexico United States
3. Department of Electrical and Computer Engineering, University of Texas at Austin, Austin, Texas 78712, United States
4. Department of Electrical and Computer Engineering, University of New Mexico, Albuquerque, New Mexico 87131, United States
5. Department of Information Engineering, University of Padova, Padua 35122, Italy
6. Walter Schottky Institut, Technische Universitat Munchen, Garching 85748, Bavaria , Germany