Final Report Summary - THEOFUN (Theoretical studies on the functionalisation of metal surfaces with organic and biological complexes under electrochemical conditions) Compared to surfaces under UHV conditions, electrochemical systems combine a whole variety of additional effects. These range from nanostructured materials over the presence of the electrolyte and the multi-component environment to conditions of finite temperature, pressure, and electrode potential. Due to this complexity our knowledge about the ongoing processes is mostly limited to the macroscopic regime. However, nowadays theoretical methods are able to provide a deeper insight into structures and processes at the atomistic level, which together with experiments could lead to a better understanding. This project aimed to understand the functionalisation of metal surfaces with organic and biological complexes under electrochemical conditions and to explore the stability and electronic properties of these materials under realistic conditions.In the first part of the project we concentrated on developing suitable methods, which were then applied to investigate the interaction within the interface. Regarding the method development, a multi-scale approach was implemented that allows interfaces as complex as electrochemical double-layers to be modeled self-consistently now. While all approaches that have been reported in literature so far are based on some rather system-influencing approximations, our approach is now able to avoid such unphysical assumptions. Further, we have developed a reactive molecular-dynamics forcefield within the ReaxFF framework that is general enough to describe the interactions in a large class of organic and biological molecules. This multi-scale approach was already applied to study the structure and properties of 4-mercaptopyridine self-assembled monolayers on Au single crystal electrodes, which were then used to deposit metal islands up to a full monolayer on top, leading to a kind of sandwich structure. The “free-hanging” metal islands show unique electronic properties, and are used for investigations of electrocatalytic reactions now. In addition, these islands have successfully been used as templates to grow organic molecules on top. Subsequent experiments confirmed our theoretical predictions. Further, we have studied the adsorption of thymine and thiothymine on Au- and Pt-electrodes. Motivated by corresponding experiments we could also explain the observed potential-induced structural changes of the adsorbates from a standing-up to a lying-down configuration.Finally, we the morphology and electronic structure of DNA-functionalized electrodes, as well as the influence of an applied electrode potential was investigated. These systems were also used as (bio-)sensors in order to reveal the details of the electrochemical double layer.
