1. Institute for Microelectronics and Microsystems, IMM-CNR, Stradale Primosole n 50, 95121 Catania, Italy, Dipartimento di Scienze Chimiche, Università di Catania, INSTM UdR Catania, Viale A. Doria 6, 95125 Catania, Italy, and Institute of Inorganic Methodologies and of Plasmas, IMIP-CNR and INSTM UdR Bari, via Orabona 4, 70125, Bari, Italy