Vibrational and electronic properties of an organic-metal interface: HREELS study of PTCDA/Ag(111)

Aromatic molecules are applied in organic electronic devices such as LEDs and FETs. Knowledge concerning the vibrational properties of an organic-metal interface in relation to its electronic properties is (often) lacking. We present an HREELS study of the interface formation between PTCDA molecules and Ag(111). We show that PTCDA molecules in the first ML chemisorb with their perylene cores to Ag(111) with a nearly flat molecular orientation. Charge transfer between perylene and Ag(111) is observed. Additionally, the electronic structure of chemisorbed PTCDA molecules differs completely from that of molecules in a multilayer. The dispersion of the Ag(111) surface plasmon shows that the electrons in the Ag(111) surface become ‘less free’ upon chemisorption of PTCDA. Furthermore, the dispersion of the HOMO-LUMO electronic excitations and the possible role of phonon coupling in the temperature regime between 140-300K will be presented and discussed for different thickness of the epitaxially grown films of PTCDA.