HIGHLY-ORDERED ULTRATHIN FILMS OF QUATERTHIOPHENE ON A AG(111) SURFACE

Ultrathin films of quaterthiophene (4T) were deposited on a Ag(111) su rface by vacuum sublimation and characterized with respect to their ge ometric and electronic properties using several surface-sensitive tech niques. For the monolayer (1 ML), a long-range ordered superstructure is found by electron diffraction (LEED). This is commensurate to the A g(111) surface due to covalent bonding of the ''flat-lying'' 4T molecu le via its pi-system. The bonding properties can be deduced from photo electron spectroscopy results (UPS, XPS). For multilayers (3-20 ML) a gradual decrease of the orientational order is observed by infrared sp ectroscopy and X-ray absorption.