1. Foundation for Research and TechnologyHellas, Institute of Electronic Structure and Laser, P.O. Box 1527, Heraklion Crete, Greece; Department of Chemistry, University of Athens, 157 01 Zografou Athens, Greece; Fakultät für Physik und Geowissenschaften, Universität Leipzig, D-04103 Leipzig, Germany; and Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139