1. School of Physics, Centre for Research on Adaptive Nanostructures and Nanodevices, Trinity College Dublin, College Green, Dublin 2, Ireland
2. Institut des Matériaux Jean Rouxel (IMN), CNRS, Université de Nantes, BP32229 Nantes, France
3. Department of Physics, University of Umeå, 901 87 Umeå, Sweden
4. Kavli Institute of NanoScience, Delft University of Technology, P.O. Box 5046, 2600 GA, Delft, The Netherlands
5. LPS, CNRS8502, Université Paris-Sud, Bat. 510, 91405 Orsay Cedex, France
6. Department of Chemistry, University of Oslo, P.O. Box 1033, Blindern, 0315 Oslo, Norway