New design strategies for tuning electrode properties by SAMs

• Applicants: Professor Dr. Andreas Terfort; Professor Dr. Michael Zharnikov
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation ; Solid State and Surface Chemistry, Material Synthesis ; Theoretical Chemistry: Molecules, Materials, Surfaces
• Term: from 2015 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 264761234

Chemically anchored self-assembled monolayers (SAMs) play a crucial role in the area of organic and molecular electronics. They are usually used to modify the electronic properties of interfaces or to act as the active elements of nano-scale devices. Of particular interest in this context are SAMs bonded to metal-electrodes, which, when substituted with polar units at their tails, modify charge-carrier injection. A complication in that context is that due to the dipole-dipole repulsion, SAM-formation in such layers becomes a challenge. To overcome that problem, we will design novel types of SAMs, where the layers are stabilized either by reducing dipole-dipole repulsion via distributing the dipolar units or by inducing hydrogen-bonds between the SAM-forming molecules. To realize the latter approach, we will study systems related to dye molecules like indigo or quinacridone. For such molecules bonded to metal surfaces, e.g., via thiolate anchors, we expect novel properties like work-function modifications of unprecedented magnitude as well as peculiar electronic characteristics arising from the intra-layer chemical and electrostatic coupling. To realize the full potential of the planned research, we will combine the ideally complementary expertise of six research groups: A. Terfort (Univ. Frankfurt) and co-workers will synthesize the required molecules either with distributed dipole moments or the H-bond network forming dyes. M. Zharnikov (Univ. Heidelberg) and his group will devise optimized strategies for growing such SAMs on metal substrates, characterize their structural electronic properties, and together with the group of R. Resel (TU Graz) will study the growth of organic semiconductors on modified electrodes. E. Zojer (TU Graz) and his co-workers will use atomistic modeling to identify the most promising molecular structures guiding the synthetic efforts and to explain experimental observations. K. Zojer (TU Graz) and her students will model, how SAM-modified electrodes are expected to change the charge carrier injection into organic thin-film transistors paying special attention to the role of inhomogenieties in the films electronic properties. Finally, the SAMs designed in this project will be applied in actual device-structures by B. Stadlober and her group (Joanneum Research). All above mentioned research efforts will be intimately linked in close feedback-loops guaranteed by several levels of information exchange. From the tight integration of so many different approaches we expect an unprecedented level of understanding of the electronic and structural properties of the studied systems. This has the potential to significantly impact the way one thinks about self-assembled monolayers and to promote their use in actual organic electronic devices. Moreover, the multi-disciplinary approach and the stimulating research environment will hugely broaden the scientific perspectives of all involved scientists, in particular the students.

• DFG Programme: Research Grants
• International Connection: Austria
• Cooperation Partners: Professor Dr. Roland Resel; Dr. Barbara Stadlober; Dr. Karin Zojer; Professor Dr. Egbert Zojer