1. International Iberian Nanotechnology Laboratory (INL) Braga 4715‐330 Portugal
2. Dipartimento di Fisica Università di Roma La Sapienza Roma 00185 Italy
3. Displax S.A. Rua Soldado Manuel Pinheiro Magalhães, 68 Braga 4715‐167 Portugal
4. Mechanical Engineering Department and IDMEC Instituto Superior Técnico University of Lisbon Av. Rovisco Pais Lisbo 1049‐001 Portugal
5. Materials Science and Engineering Program The University of Texas at Austin Austin TX 78712 USA
6. Departamento de Física Universidade do Minho Braga 4710‐057 Portugal