1. Materials Institute, The Scientific and Technological Research Council of Turkey (TUBITAK)-Marmara Research Center (MAM), Gebze/Kocaeli 41470, Turkey
2. Department of Physics, Gebze Technical University, Gebze/Kocaeli 41400, Turkey
3. Nanotechnology Research Center, Gebze Technical University, Gebze/Kocaeli 41400, Turkey