1. NanoMaterials Group, Department of Applied Physics, Helsinki University of Technology, P.O. Box 5100, Puumiehenkuja 2, 02015 TKK, Finland
2. Center for New Materials, Helsinki University of Technology, P.O. Box 3500, Tietotie 3, 02015 TKK, Finland
3. VTT Biotechnology, P.O. Box 1500, Tietotie 2, 02044 Espoo, Finland