PENNING IONIZATION ELECTRON-SPECTROSCOPY OF ATOMIC TAPE - AN EXTRATHIN SUPERSTRUCTURE CONSTRUCTED BY INTRAMONOLAYER HYDROGEN-BONDS ON A SOLID-SURFACE

An extrathin molecular superstructure can be constructed by combining planar molecules laid flat and arranged in a monolayer on a solid surf ace. We have introduced hydrogen bonds into a vapor-deposited monolaye r on graphite to form a tapelike superstructure, atomic tape. A planar diamide suitable for linear connection 4,4'-[1,4-phenylenethynylene]d i(benzamide) (PDB) and a reference compound incapable of hydrogen bond formation 4,4'-[1,4-phenylenethynylene] bis(N,N-dimethylbenzamide) (P BDB) were designed and their monolayers were characterized by Penning ionization electron spectroscopy. It is found that the orientation of PDB molecules deposited at 130 K is random but changes to flat on heat ing to 195 K. Unlike the monolayers of PBDB and other larger compounds , the PDB monolayer does not sublime at 295 K. From these results it i s considered that the atomic tape structure is formed by the intramono layer hydrogen bonds of PDB. To elucidate the electronic structure of PDB and PBDB, the Penning ionization electron spectrum of gas phase PB DB was also measured and compared with the monolayer spectra. (C) 1998 Elsevier Science B.V.