1. Faculty of Mechanical Engineering, Brno University of Technology, Brno 616 69, Czech Republic
2. Central European Institute of Technology—CEITEC, Brno University of Technology, Brno 612 00, Czech Republic
3. IONTOF GmbH, Heisenbergstr. 15, 48149 Münster, Germany
4. Department of Applied Physics, Eindhoven University of Technology, Eindhoven 5600 MB, The Netherlands