1. L-NESS and Department of Materials Science, Università di Milano-Bicocca, via R. Cozzi 55, I-20125 Milano, Italy
2. Lpe S.P.A., Sedicesima Strada, I-95121 Catania, Italy
3. Lpe S.P.A., Via Falzarego, 8-20021 Baranzate, Milano, Italy
4. CNR-IMM, sezione di Catania, Stradale Primosole 50, I-95121 Catania, Italy
5. Laboratory for Solid State Physics, ETH Zurich, Otto-Stern Weg 1, CH-8093 Zurich, Switzerland
6. Electron Microscopy Center, Empa, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland