1. Department of Physics, Centre for Materials Science and Nanotechnology, University of Oslo, PO Box 1048, Blindern, N-0316 Oslo, Norway
2. NOMATEN Centre of Excellence, National Centre for Nuclear Research, A. Soltana 7, 05-400 Otwock-Świerk, Poland
3. Royal Institute of Technology, KTH-EECS, Electrum 229, SE-164 40 Stockholm, Sweden