1. Consiglio Nazionale delle Ricerche, Istituto per la Microelettronica e Microsistemi, Strada VIII, n. 5, Zona Industriale, I-95121, Catania, Italy
2. HUN-REN Centre for Energy Research, Institute of Technical Physics and Materials Science, Konkoly-Thege M. út 29-33, Budapest, 1121, Hungary
3. Department of Physics, Chemistry and Biology (IFM), Linköping University, 581 83 Linköping, Sweden