Substrate influence on the ordering of organic submonolayers: a comparative study of PTCDA on Ag 110/ and Ag 111/ using HREELS

Vibrational spectra of ultrathin films of perylene-tetracarboxylic-dianhydride PTCDA.on the more open Ag 110. surface and the close-packed Ag 111., as recorded by high-resolution electron energy loss spectroscopy HREELS., are reported. By comparison to density functional calculations of the vibrational frequencies most experimental peaks can be reliably assigned. The internal vibrations of the molecules turn out to be very sensitive towards the effects of the interaction with the substrate. This leads to pronounced differences in the submonolayer spectra from both surfaces. Thus, the results bear some importance in the context of organic epitaxy, which relies on the formation of highly ordered interfaces. q2000 Elsevier Science B.V. All rights reserved