1. Selçuk University, Faculty of Arts and Sciences, Department of Physics, TR-42049 Campus, Konya, Turkey
2. Ankara University, Faculty of Sciences, Department of Physics, TR-06100 Tandoĝan, Ankara, Turkey
3. Ankara University, Faculty of Engineering, Department of Engineering Physics, TR-06100 Tandoĝan, Ankara, Turkey
4. Institute for Material Science, Darmstadt University of Technology, Petersenstraße 23, D-64287 Darmstadt, Germany