1. Nanotechnology Research Center, Bilkent University, 06800 Bilkent, Ankara, Turkey
2. Department of Nanotechnology and Nanomedicine, Hacettepe University, 06800 Beytepe, Ankara, Turkey
3. Department of Physics Engineering, Hacettepe University, 06800 Beytepe, Ankara, Turkey
4. Department of Electrical and Electronics Engineering and Department of Physics, Bilkent University, 06800 Bilkent, Ankara, Turkey