[1
]Department of Physics, University of Oslo, Blindern, P.O. Box 1048, 0316 Oslo, Norway
[2
]Department of Chemistry, University of Oslo, Blindern, P.O. Box 1033, 0315 Oslo, Norway
[3
]Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747
AG Groningen, The Netherlands
[4
]Physics Department, IFE, P.O. Box 40, 2027 Kjeller, Norway
[5
]College of Engineering, Swansea University, Swansea SA1 8PP, U.K.
[6
]Department of Technology Systems, University of Oslo, P.O. Box 70, 2027 Kjeller, Norway