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Energy level alignment at organic/metal interfaces: The role of dielectric layers While organic electronics are on the verge of becoming a major industry the underlying principles on a molecular level are still under debate. Within our work we aim to gain a better insight into the alignment of the electronic levels of organic molecules on metal and dielectric/metal substrates which is important for understanding charge injection at device contacts. In particular we investigate the atomically controlled model system of pentacene (5A) on Ag(100) and MgO(100)/Ag(100) using scanning tunneling microscopy (STM), angle-resolved ultraviolet photoemission spectroscopy (UPS) and density functional theory (DFT). While the former system shows Fermi level pinning through fractional charge transfer (CT) to the lowest unoccupied molecular orbital (LUMO) the latter even features promoted integer CT resulting in a split of the LUMO in a singly occupied (SOMO) and its associated unoccupied molecular orbital (SUMO). |