1. International Iberian Nanotechnology Laboratory, 4715-330 Braga, Portugal
2. Wihuri Physical Laboratory, Department of Physics and Astronomy, University of Turku, FI-20014 Turku, Finland
3. Mechanical Engineering Department and IDMEC, Instituto Superior Técnico, University of Lisbon, Av. Rovisco Pais, 1049-001 Lisboa, Portugal
4. Materials Science and Engineering Program, University of Texas at Austin, Austin, Texas 78712, United States
5. Centro de Física das Universidades do Minho e do Porto, Universidade do Minho, 4710-057 Braga, Portugal