1. Fakultät für Physik and CENIDE, Universität Duisburg-Essen, D-47057 Duisburg, Germany
2. Faculty of Physics, University Vienna, A-1090 Vienna, Austria
3. Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf, D-01328 Dresden, Germany
4. Advanced Materials and Bioengineering Research Centre (AMBER) and School of Chemistry, Trinity College Dublin, College Green, Dublin 2, Ireland
5. Institute of Physics, EIT 2, Faculty of Electrical Engineering and Information Technology, Universität der Bundeswehr München, D-85577 Neubiberg, Germany
6. Institute of Applied Physics, TU Wien, A-1040 Vienna, Austria
7. Department of Applied Physics, Aalto University, P.O. Box 11100, FI-00076 Aalto, Finland