1. Nanoscale Engineering Division, Department of Physics, Chemistry and Biology, Linköping University, Linköping SE 581 83, Sweden
2. Institut Pprime, Département Physique et Mécanique des Matériaux, UPR 3346 CNRS, Université de Poitiers, SP2MI, 11 Bvd M. et P. Curie, F86073 Poitiers Cedex 9, France
3. Department of Mechanical and Structural Engineering and Materials Science, University of Stavanger, N-4036 Stavanger, Norway