1. Materials Science and Engineering Program; Sabanci University; Orhanli Tuzla Istanbul 34956 Turkey
2. Department of Nanostructured Materials; Jožef Stefan Institute; Jamova Cesta 39 Ljubljana 1000 Slovenia
3. Laboratoire de Physique des Solides; Bâtiment 510; CNRS UMR 8502; Université Paris-Sud XI; Orsay F-91405 France
4. Nanotechnology Research and Application Center; Sabanci University; Orhanli Tuzla Istanbul 34956 Turkey