1. Microelectronics and Materials Physics Laboratories, University of Oulu, P.O. Box 4500, FIN-90570, Oulu, Finland
2. Office of the Chancellor and Center for Molecular Electronics, Departments of Chemistry & Biochemistry and Physics & Astronomy, University of Missouri-St. Louis, St. Louis, Missouri 63121
3. Department of Physics, JGYTF, University of Szeged, H-6720 Szeged, Boldogasszony sgt. 6, Hungary