1. NANOTAM-Nanotechnology Research Center, Bilkent University, 06800 Ankara, Turkey
2. Department of Electrical and Electronics Engineering, Bilkent University, 06800 Ankara, Turkey
3. Department of Physics, Bilkent University, 06800 Ankara, Turkey
4. UNAM-Institute of Materials Science and Nanotechnology, Bilkent University, Ankara, Turkey