1. IMM-Instituto de Microelectrónica de Madrid (CNM-CSIC); Isaac Newton 8, PTM E-28760 Tres Cantos Madrid Spain
2. Department of Applied Physics; Brazilian Center for Physics Research; Urca, Rio de Janeiro 22290-180 Brazil
3. International Iberian Nanotechnology Laboratory (INL); Av. Mestre Jose Veiga 4715-330 Braga Portugal