1. Institute for Nanostructure and Solid State Physics Center for Hybrid Nanostructure (CHyN) University of Hamburg Luruper Chaussee 149 22761 Hamburg Germany
2. Present Addresses: Institute of Physical Chemistry Christian-Albrechts-Universität zu Kiel Max-Eyth-Str. 1 24118 Kiel Germany
3. Institute of Physical Chemistry University of Hamburg Grindelallee 177 20146 Hamburg Germany
4. School of Nano Science and Technology Indian Institute of Technology Kharagpur Kharagpur 721302 India