Structure, stability and conductivity of aliphatic and aromatic SAM monolayers deposited on aluminum.

Principal Investigator: Daria Marcela Cegiełka
Duration: 2020 - 2024

One of the main trends in the creation of new materials is currently combining inorganic and organic structures (e.g. the development of molecular electronics or tissue engineering). The formation of such hybrid systems inevitably leads to the creation of an interface, most often in the form of a molecule-metal, which becomes an essential part of a given device if we move to the area of nanotechnology. A model system that allows us to analyze the structure and properties of the molecule-metal interface are self-assembled monolayers (SAMs), which are used both in molecular electronics and in biocompatibility issues. So far, most research on SAM systems, along with subsequent applications, has been carried out for monolayers in which the thiol group (-SH) is used to bind molecules to noble metal surfaces (mainly Au) through a covalent bond. The proposed project will investigate SAM monolayers formed on the aluminum surface through ionic bonding via a carboxyl (-COOH) or phosphonic (-PO3H2) group. Although these types of SAMs have recently gained a great interest, the scope of their application is still very limited due to the difficulties in their formation on a very reactive substrate such as aluminum and the insufficient amount of information regarding their structure and properties. As part of the project, it is planned not only to optimize the formation process to create highly ordered structures, but also to use these well-defined systems to analyze their thermal and aging stability, asses their ability to stop the oxidation process of aluminum surface and, related to this task, determine the influence of the substrate and binding group on the conductivity of this type of organic nanostructures. Determining these parameters is crucial for every potential application and it will allow for a much wider utilization of these specific SAM systems. In particular, from the point of view of molecular electronics, it is obviously important to determine the electrical conductivity of both insulating and conducting molecules on the surface of this technologically relevant metal. Aluminum functionalization by SAMs can be, for example, used to modify electrodes in a field-effect transistor system (insulating molecules to modify the gate electrodes, and conducting ones to modify the source and drain electrodes). A less obvious, but equally important parameter in this context is the desired high thermal stability of molecules in the electrical junction due to problems with the dissipation of heat generated at the molecule-metal interface due to the lack of compatibility of vibrational states (different frequency ranges) of organic and inorganic materials.