1. Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden, Department of Biology and Chemical Engineering, Mälardalens University, Box 325, SE- 631 05 Eskilstuna, Sweden, Materials Physics, Royal Institute of Technology, Electrum 229, SE-164 40 Kista, Sweden, and MAX-lab, University of Lund, Box 118, SE- 221 00 Lund, Sweden