1. Department of Physics, University of Jyväskylä, P.O. Box 35, Jyväskylä 40014, Finland
2. Department of Micro- and Nanosciences, Aalto University School of Electrical Engineering, P.O. Box 13500, FI-00076 AALTO, Finland
3. ASM Microchemistry Oy, Pietari Kalmin katu 1 F 2, FIN-00560 Helsinki, Finland