Structure, bonding, and growth at a metal-organic interface in the weak chemisorption regime: Perylene-Ag(111)

Organic semiconductors on single-crystalline metal surfaces are model systems for injection contacts in organic field-effect transistors (OFET) and light-emitting diodes. They allow us to classify possible metal-organic interaction scenarios and to elucidate general tendencies, which most likely will also be found at metal-organic interfaces in real devices. In this contribution, we report a comprehensive investigation of the interface of perylene, a promising material for OFETs, with the close-packed noble metal surface Ag(111), using high-resolution electron energy loss spectroscopy, low-energy electron diffraction, and scanning tunneling microscopy as surface analytical techniques. The most important findings are: In the monolayer, molecules are oriented flat and form an incommensurate, most probably fluid overlayer. The molecules interact electronically with the substrate and become weakly metallic. Scanning tunneling microscopy reveals a propensity of perylene molecules toward a specific adsorption site on Ag(I I I), if the influence of intermolecular interactions is inhibited. Film growth at room temperature is similar to Stranski-Krastanov type. Finally, co-planar adsorption of perylene on Ag(l 11) is metastable, and annealing the monolayer at 420 K leads to a structural transformation of the film. The perylene-Ag(111) interface can therefore be classified as weakly interacting.