1. Solid State Physics Department, Jozef Stefan Institute, Jamova ulica 39, SI-1000 Ljubljana, Slovenia
2. Faculty of Applied Natural Sciences and Cultural Studies, OTH Regensburg, 93053 Regensburg, Germany
3. Faculty of Mathematics and Physics, University of Ljubljana, Ljubljana SI-1000, Slovenia
4. Department of Electrochemical Materials, J. Heyrovsky Institute of Physical Chemistry, Dolejskova 3, Prague 8, 182 23, Czech Republic
5. Institute for Experimental and Applied Physics, University of Regensburg, 93053 Regensburg, Germany