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no~~~/ed~rmTrnhtis.s work was supported financially by the Volkswagenstiftung and the Bundesministerium fur Forschung und Bildung. C. K. and F. M. thank the Fonds dcr Chemischem lndustric for a scholarship. The authors wish to thank Dr J. RPder and Dip]. Chem. K. Martin for recording the LD-TOF mass spectra. Professor Dr N. Karl and Dipl. Phys. C. Gunther for the vapor deposition of the monomolecular layers and Dr R. Strohmaier and Dr J. Petersen for recording the STM images;