1. Advanced Materials Department, Jožef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia
2. Department for Nanostructured Materials, Jožef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia
3. Condensed Matter Physics Department, Jožef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia
4. Jožef Stefan International Postgraduate School, Jamova cesta 39, 1000 Ljubljana, Slovenia
5. Faculty of Science and Technology and MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands