1. NanoMaterials Group, Department of Applied Physics and Center for
New Materials, Aalto University, P.O. Box
15100, FI- 00076 Aalto, Espoo, Finland
2. COMP/Applied Physics, Aalto University, P.O. Box 1100, FI-00076 Aalto, Finland
3. Department of Physics, University of Helsinki, P.O. Box 43, FI-00014 Helsinki, Finland