FWF - EMBEDDED - Tuning the electronic properties of SAMs by embedded molecular dipoles

The present project aims at providing an atomic-level understanding of the electronic and structural properties of alkylthiolate based self-assembled monolayers that contain embedded (di)polar functional groups. Such systems are highly interesting both from a fundamental as well as from an application point of view, as the dipolar groups induce a potential discontinuity inside the monolayer electrostatically shifting the energy levels in the regions above and below the dipoles relative to each other. Such SAMs also allow tuning the substrate work-function independent of the docking chemistry and the identity of the SAM-ambient interface in a controlled manner. New insights are expected from combining a number of experimental surface-science techniques with quantummechanical and molecular-dynamics modelling. The former will be used in the group of Michael Zharnikov and include high-resolution X-ray and ultraviolet photoelectron spectroscopy, near-edge absorption fine structure spectroscopy, and Kelvin probe measurements. The simulations, which are to be performed in the group of Egbert Zojer, are ideally complementary to those experiments and include density-functional theory as well as classical force-field based calculations on metal slabs covered on one side by the organic adsorbate. To understand the relationship between the molecular structure and the SAM properties, we will systematically vary the length of the aliphatic chains, the positions of the embedded dipoles, as well as the chemical functionalities giving rise to the dipoles. The molecules will be provided by the group of David A. Allara, where also the infrared reflection absorption spectroscopy will be performed. By combining experiments and simulations we expect in-depths insights into the details of the electrostatic potential shifts between the parts of the SAM above and below the embedded dipoles and how these shifts are linked to the induced changes of the substrate work-function (where preliminary experiments and calculations indicate that this link is not straightforward).