1. Department of Physics, Faculty of Science Gazi University, Ankara, Turkey
2. Center Research Laboratory, Application and Research Center, Ankara Yıldırım Beyazıt University, Ankara, Turkey
3. Nanotechnology Research Center, Bilkent University, Ankara, Turkey
4. Department of Physics, Bilkent University, Ankara, Turkey
5. Department of Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey