1. Solid
State Physics and NanoLund, Lund University, Box 118, SE-221 00, Lund, Sweden
2. Center
for Electron Nanoscopy, Technical University of Denmark, DK 2800 Kgs. Lyngby, Denmark
3. Laboratory
of Mathematics, Physics and Electrical Engineering, Halmstad University, Box 823, SE-301 18 Halmstad, Sweden