1. Centre for Materials Science and Nanotechnology (SMN), University of Oslo, P.O.B. 1126 Blindern, NO-0318 Oslo, Norway
2. Department of Physics, University of Oslo, P.O.B. 1048 Blindern, NO-0316 Oslo, Norway
3. SINTEF Materials and Chemistry, Forskningsveien 1, NO-0314 Oslo, Norway