1. Institut für Physik & IRIS Adlershof, Humboldt-Universität zu Berlin, Newtonstr. 15, 12489 Berlin, Germany
2. Helmholtz-Zentrum
Berlin für Materialien und Energie GmbH, Albert-Einstein-Str. 15, 12489 Berlin, Germany
3. Engineering
Department “E. Ferrari”, University of Modena e Reggio Emilia, Via Vignolese 905, 41125 Modena, Italy
4. Department
of Physics, University of Johannesburg, PO Box 524, Auckland Park 2006, South Africa