1. Ruhr-University Bochum, Faculty of Mechanical Engineering,
Institute for Materials, 44801 Bochum, Germany
2. Institute
of Solid State Physics, Vienna University of Technology, Wiedner
Hauptstrasse 8-10, 1040 Vienna, Austria
3. ISM−CNR Area della Ricerca Roma1, Via Salaria km 29.300, C.P. 10, 00016 Monterotondo Scalo (RM), Italy