[1] Institute of Technical Physics, University of Erlangen-Nürnberg, Erwin-Rommel-Str. 1, DE-91058 Erlangen, Germany
[2] Fritz-Haber-Institute, Faradayweg 4-6, DE-14195 Berlin, Germany
[3] Department of Physics, La Trobe University, Bundoora, Vic. 3083, Australia