1. Department of Physics, Case Western Reserve University, 10600 Euclid Avenue, Cleveland, OH 44106, USA
2. Nanotechnology Research Center, Bilkent University, 06800 Ankara, Turkey
3. Department of Physics, University of Calabria, CNR-Nanotec, Licryl Laboratory, 87036 Rende, Italy
4. Colegio de Ciencias e Ingeniería, Universidad San Francisco de Quito, Avenida Diego de Robles s/n y Pampite, Cumbayá, 1712841 Quito, Ecuador