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(111), 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(111) 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.