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	Energy-level alignment at strongly coupled organic-metal interfaces Meng-Ting Chen , Oliver T. Hofmann , Alexander Gerlach , Benjamin Bröker , Christoph Buerker , Jens Niederhausen , Takuya Hosokai , Jorg Zegenhagen , Antje Vollmer , Ralph Rieger , Klaus Muellen , Frank Schreiber , Ingo Salzmann , Norbert Koch , Egbert Zojer , Steffen Duhm Journal Of Physics: Condensed Matter DOI: 10.1088/1361-648X/ab0171 Open Access Show Abstract ▼ Abstract: Energy-level alignment at organic-metal interfaces plays a crucial role for the performance of organic electronic devices. However, reliable models to predict energetics at strongly coupled interfaces are still lacking. We elucidate contact formation of 1,2,5,6,9,10-coronenehexone (COHON) to the (111)-surfaces of coinage metals by means of ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, the X-ray standing wave technique, and density functional theory calculations. While for low COHON thicknesses, the work-functions of the systems vary considerably, for thicker organic films Fermi-level pinning leads to identical work functions of 5.2 eV for all COHON-covered metals irrespective of the pristine substrate work function and the interfacial interaction strength.	Jan 2019
I09-Surface and Interface Structural Analysis	Fully atomistic understanding of the electronic and optical properties of a prototypical doped charge-transfer interface Anu Baby , Marco Gruenewald , Christian Zwick , Felix Otto , Roman Forker , Gerben Van Straaten , Markus Franke , Benjamin Stadtmueller , Christian Kumpf , Gian Paolo Brivio , Guido Fratesi , Torsten Fritz , Egbert Zojer Acs Nano 11, 10945-10508 DOI: 10.1021/acsnano.7b05828 Diamond Proposal Number(s): [10370] Open Access Show Abstract ▼ Abstract: The current study generates profound atomistic insights into doping-induced changes of the optical and electronic properties of the prototypical PTCDA/Ag(111) interface. For doping K atoms are used, as KxPTCDA/Ag(111) has the distinct advantage of forming well-defined stoichiometric phases. To arrive at a conclusive, unambiguous, and fully atomistic understanding of the interface properties, we combine state-of-the-art density-functional theory calculations with optical differential reflectance data, photoelectron spectra, and X-ray standing wave measurements. In combination with the full structural characterization of the KxPTCDA/Ag(111) interface by low-energy electron diffraction and scanning tunneling microscopy experiments (ACS Nano 2016, 10, 2365–2374), the present comprehensive study provides access to a fully characterized reference system for a well-defined metal–organic interface in the presence of dopant atoms, which can serve as an ideal benchmark for future research and applications. The combination of the employed complementary techniques allows us to understand the peculiarities of the optical spectra of K2PTCDA/Ag(111) and their counterintuitive similarity to those of neutral PTCDA layers. They also clearly describe the transition from a metallic character of the (pristine) adsorbed PTCDA layer on Ag(111) to a semiconducting state upon doping, which is the opposite of the effect (degenerate) doping usually has on semiconducting materials. All experimental and theoretical efforts also unanimously reveal a reduced electronic coupling between the adsorbate and the substrate, which goes hand in hand with an increasing adsorption distance of the PTCDA molecules caused by a bending of their carboxylic oxygens away from the substrate and toward the potassium atoms.	Sep 2017

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Energy-level alignment at strongly coupled organic-metal interfaces