1. The Center for Solar Energy Research and Applications (GÜNAM), Middle East Technical University, 06800 Ankara, Turkey
2. Department of Micro and Nanotechnology, Middle East Technical University, 06800 Ankara, Turkey
3. Department of Physics, Middle East Technical University, 06800 Ankara, Turkey
4. Department of Metallurgical and Materials Engineering, Middle East Technical University, 06800 Ankara, Turkey