The interplay between interface structure, energy level alignment and chemical bonding strength at organic–metal interfaces

• DOI: 10.1039/c4cp04595e
• Publication Date: 2014-11-19T17:08:07Z
• Authors: M. Willenbockel; D. Lüftner; B. Stadtmüller; G. Koller; C. Kumpf; S. Soubatch; P. Puschnig; M. G. Ramsey; F. S. Tautz
• Keywords: HOMO/LUMO; Chemisorption

What do energy level alignments at metal-organic interfaces reveal about the metal-molecule bonding strength? Is it permissible to take vertical adsorption heights as indicators of strengths? In this paper we analyse 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) on three canonical low index Ag surfaces provide exemplary answers these questions. Specifically, employ angular resolved photoemission spectroscopy for a systematic study two uppermost frontier states in ordered monolayer phases PTCDA. Data are analysed using orbital tomography approach. This allows unambiguous identification character states, and also discrimination between inequivalent species. Combining experimental information with DFT calculations generic Newns-Anderson chemisorption model, highest occupied lowest unoccupied molecular orbitals (HOMO LUMO) respect vacuum levels bare molecule-covered surfaces. reveals clear differences states. particular, all LUMO is subject considerable bond stabilization through interaction π-electron system metal, consequence which becomes occupied. Moreover, observe larger more open Most importantly, our analysis shows that both binding energies overall molecule linked strength chemical sense stronger leads shorter energies.