1. Institut
des Sciences Moléculaires d’Orsay, ISMO, UMR 8214, Université Paris Sud, Bâtiment 351, 91405 Orsay, France
2. Dipartimento
di Ingegneria E. Ferrari, Università di Modena e Reggio Emilia, Via Vivarelli 10, 41125 Modena, Italy
3. CNR-IOM s.s. 14, Km. 163.5 in AREA Science
Park, 34149 Basovizza, Trieste, Italy
4. Solid
State Physics Division, Ioffe Physical-Technical Institute of Russian Academy of Sciences, 26 Polytechnicheskaya str., 194021 St. Petersburg, Russia
5. CNR-INO Area della Ricerca di Pisa - S. Cataldo, via Moruzzi,1, I-56124 Pisa, Italy
6. Department
of Physics, University of Johannesburg, P.O. Box 524, Auckland Park 2006, South Africa