& Organic Electronics Chemisorption, Morphology, and Structure of a n-Type Perylene Diimide Derivative at the Interface with Gold: Influence on Devices from Thin Films to Single Molecules Francesca Ciccullo, [b] Sabine-Antonia Savu, [a] Andrea Gerbi, [c] Maximilian Bauer, [d] Ruslan Ovsyannikov, [d] Antonio Cassinese, [b] Thomas ChassØ, [a] and Maria Benedetta Casu* [a] Abstract: We have investigated thin films of a perylene diimide derivative with a cyano-functionalized core (PDI- 8CN 2 ) deposited on Au(111) single crystals from the mono- layer to the multilayer regime. We found that PDI-8CN 2 is chemisorbed on gold. The molecules experience a thickness- dependent reorientation, and a 2D growth mode with mo- lecular stepped terraces is achieved adopting low deposition rates. The obtained results are discussed in terms of their impact on field effect devices, also clarifying why the use of substrate/contact treatments, decoupling PDI-8CN 2 molecules from the substrate/contacts, is beneficial for such devices. Our results also suggest that perylene diimide derivatives with CN bay-functionalization are very promising candidates for single-molecule electronic devices. Introduction The quest for smart materials has been the focus of intense multidisciplinary efforts in view of their possible use in a number of new applications ranging from medicine to mate- rial science and electronics. In this respect, organic semicon- ductors have shown almost unprecedented success in reaching the market, [1] once the first device was proved. [2] The plastic- based technology has still immense potential and the flavor of strong transformative capabilities, if we think in terms of all kinds of functionality that could be embedded in our everyday environment, such as clothes, food labels, badges, smart cards. [3] One of the greatest strengths of organic semiconduc- tors is their chemical flexibility by synthesis: the concept of chemical surface engineering [4] and design of organic semicon- ductors [5] have been proven to be feasible ways to explore the potential of this class of materials. In this view, substitution is an efficient approach to pursue the goal of tuning properties, and more specifically transport properties, in organic materials; [6] for example, perfluoropentacene is an n-type organic semiconductor in contrast to pentacene, which is a p-type organic semiconductor. [7–9] In addition, with respect to devices, for example, perylene derivates have been proved to yield excellent stable n-channel organic field-effect transistors (OFETs). [10, 11] N,N’-Bis(n-octyl)dicyanoperylene-3,4 :9,10-bis(dicar- boximide), (PDI-8CN 2 , Figure 1) is a perylene diimide derivative that has two cyano (CN) groups directly bound to the aromatic core (bay region) and alkyl chains as substituents on the imide N atoms. The electron-withdrawing CN groups lower the LUMO energy level with respect to the vacuum level, increas- ing the ambient stability, whereas the alkyl chain substituents optimize the crystal packing, improving the transport properties. PDI-8CN 2 yields high performance devices, owing to its high charge mobility (0.1 cm 2 V 1 s 1 ), high ambient stability, and solution processability. [12–18] We intend to contribute to the present understanding of the perylene diimide derivative/metal interface, focusing on the PDI-8CN 2 /Au(111) single-crystal interface. Although signifi- cant research efforts have been devoted to the investigation of the growth mechanisms and chemical interactions at the in- terface between PDI-8CN 2 and SiO 2 gate dielectrics, [15, 19] at the state of the art there is not deep knowledge of the phenom- ena arising at the interface between PDI-8CN 2 and gold, which is the most used metal contact in PDI-8CN 2 -based devices. [15–19] Here, we present the results of our investigation, using several complementary high-resolution techniques (X-ray photoemis- sion spectroscopy (XPS), near edge X-ray absorption fine struc- ture (NEXAFS) spectroscopy, atomic force microscopy (AFM)). We find that PDI-8CN 2 is chemisorbed on gold. The molecules experience a thickness-dependent reorientation; in addition, a 2D growth mode with molecular stepped terraces is [a] S.-A. Savu, Prof. T. ChassØ, Dr. M. B. Casu Institute of Physical and Theoretical Chemistry, University of Tübingen Auf der Morgenstelle 18, 72076 Tübingen (Germany) E-mail : benedetta.casu@uni-tuebingen.de [b] F. Ciccullo, A. Cassinese CNR-SPIN and Department of Physics Science University of Naples Federico II Piazzale Tecchio, 80125 Naples (Italy) [c] Dr. A. Gerbi CNR-SPIN, Corso Perrone 24, 16152 Genoa (Italy) [d] M. Bauer, Dr. R. Ovsyannikov Helmholtz Zentrum Berlin für Materialien und Energie GmbH Elektronenspeicherring BESSY II Albert-Einstein-Str. 15, 12489 Berlin (Germany) Supporting information for this article is available on the WWW under http ://dx.doi.org/10.1002/chem.201404901. Chem. Eur. J. 2015, 21,1–7  2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1 && These are not the final page numbers! ÞÞ Full Paper DOI: 10.1002/chem.201404901