[1] Univ Pisa, Dipartimento Ingn Informaz, I-56122 Pisa, Italy
[2] Quantavis SRL, I-56126 Pisa, Italy
[3] CNR, NEST Lab, Ist Nanosci, I-56127 Pisa, Italy
[4] Scuola Normale Super Pisa, I-56127 Pisa, Italy
[5] Ist Italiano Tecnol IIT, Ctr Nano Sci & Technol, I-20134 Milan, Italy
[6] Ecole Polytech Fed Lausanne EPFL, Inst Elect & Microengn, CH-1015 Lausanne, Switzerland