1. Unit of Naples-Institute for Microelectronics and Microsystems, Via P. Castellino 111, 80131 Naples, Italy, Department of Physical Sciences and Department of Organic Chemistry and Biochemistry, University of Naples “Federico II”, Via Cinthia 4, 80126, Naples, Italy, and LYCRIL − INFM-CNR, Via P. Bucci, Cubo 33/B, 87036 Arcavacata di Rende, Cosenza, Italy