1. Laboratory for Micro- and Nanotechnology, Paul Scherrer Institut, CH-5232 Villigen-PSI, Switzerland
2. Institute of Applied Physics, University of Bern, CH-3012 Bern, Switzerland
3. Laboratory of Metal Physics and Technology, Department of Materials, ETH Zurich, CH-8093 Zurich, Switzerland
4. VTT Technical Research Centre of Finland, P.O. Box 1000, FIN-02044 Espoo, Finland