[1] Sapienza Univ Rome, Dept Phys, I-00185 Rome, Italy
[2] Univ Paris Saclay, CNRS UMR 9001, Ctr Nanosci& Nanotechnol C2N, F-91120 Palaiseau, France
[3] IHP Leibniz Inst Innovat Mikroelekt, Technol Pk 25, D-15236 Frankfurt, Germany
[4] Ist Italiano Tecnol IIT, Ctr Life Nanosci, I-00169 Rome, Italy
[5] Univ Leeds, Sch Elect & Elect Engn, Woodhouse Lane, Leeds LS2 9JT, W Yorkshire, England