1. Catalan Institute of Nanotechnology, Campus UAB, 08193 Bellaterra (Barcelona),
Spain
2. Department of Physics, University College Cork, College Road, Cork, Ireland
3. Department of Physics, Universitat Autonoma de Barcelona, 08193 Bellaterra
(Barcelona), Spain
4. VTT Technical Research Centre of Finland, PO Box 1000, 02044 VTT, Espoo, Finland
5. Institut d’Electronique,
de Microélectronique et de Nanotechnologie (IEMN), Université de Lille 1, France
6. LDOM, Faculté des Sciences, Université Mohamed 1, Oujda, Morocco
7. Institució Catalana de Recerca i Estudis Avançats (ICREA), 08010
Barcelona, Spain