Chemical bonding of PTCDA on Ag surfaces and the formation of interface states

We present a detailed investigation of the interface bonding of 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) on Ag(1 1 1) and Ag(1 1 0) surfaces by a combination of structural and electronic techniques (SPA-LEED, STM, TPD, UPS, HR-XPS, and NEXAFS) thus obtaining a consistent picture of the adsorption behaviour of PTCDA/Ag in the monolayer regime. The interaction with silver is strong and leads to the formation of new common hybrid orbitals in the monolayer, which are interface states for PTCDA films on Ag, involving at least LUMO, HOMO, and HOMO-1, and the Ag 5s- and 4d-states. This chemisorption is based on a covalent interaction between metal and molecular states, and can unambiguously be distinguished from mere van-der-Waals bonding.