1. CNR-IMM, Institute for Microelectronic and Microsystems, Campus Ecotekne, Via Monteroni, 73100 Lecce, Italy
2. CNR-Nanotec, Nanotechnology Institute, Campus Ecotekne, Via Monteroni, 73100 Lecce, Italy
3. Mathematics and Physics Department, University of Salento, Via Monteroni, 73100 Lecce, Italy