1. Department
of Precision and Microsystems Engineering, Research Group of Micro
and Nano Engineering, Delft University of Technology, Mekelweg
2, 2628 CD Delft, The Netherlands
2. Department
of Materials Engineering, KU Leuven, Kasteelpark Arenberg 44, B-3001 Leuven, Belgium
3. Imec, Kapeldreef 75, B-3001 Leuven, Belgium
4. IKS-Department
of Physics, KU Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium
5. Department
of Physics, University of Jyväskylä, P.O. Box 35, FI-40014 Jyväskylä, Finland