1. Nanoelectronics, Faculty of Engineering, Kiel University, 24143 Kiel, Germany
2. Chair of Functional Nanomaterials, Faculty of Engineering, Kiel University, 24143 Kiel, Germany
3. Synthesis and Real Structure Group, Faculty of Engineering, Kiel University, 24143 Kiel, Germany
4. Central Laboratory of Solar Energy and New Energy Sources, Bulgarian Academy of Sciences, 1784 Sofia, Bulgaria