1. CNR-IMM, Unit of Agrate Brianza, Via C. Olivetti 2, Agrate Brianza I-20864, Italy
2. Università del Piemonte Orientale ‘‘A. Avogadro’’, Viale T. Michel 11, Alessandria I-15121, Italy
3. Institute of Microelectronics of Barcelona (IMB-CNM, CSIC), Bellaterra 08193, Spain
4. CEMES-CNRS, Université de Toulouse, CNRS, Toulouse 31055, France