Self-Assembled Monolayers
Self-assembled monolayers (SAMs) are ordered molecular assemblies formed by the adsorption of amphiphilic, surfactant-type molecules on solid surfaces. The substrate is generally immersed into a dilute solution of the film molecules or suitable precursors thereof and a monolayer film forms spontanously in a time span of a few minutes to a few hours.
A typical amphiphilic molecule (octadecyltrichlorosilane), consisting of a long-chain alkyl group (C18H37) and a polar head group (SiCl3), which forms SAMs on various oxidic substrates.
The driving force for the surface aggregation and self-assembly is i) a covalent bond formation of the film molecules with the substrate surface via suitable functional groups and ii) intermolecular, van der Waals-type interactions between the hydrocarbon chains of the film molecules.
Formation of Self-Assembled Monolayers
According to the type of film-substrate bonding, SAMs can be grouped into the following categories:
- Organosulfur compounds (thiols, thioethers, disulfides etc.) on late transition metals (gold, silver, copper, mercury)
- Organosilicon compounds (alkylchlorosilanes, alkylalkoxysilanes) on metal and nonmetal oxides (Al2O3, TiO2, SnO2, SiO2, glass)
- Fatty acids on metal oxides (AgO, CuO, Al2O3)
- Alkylphosphonic acids on metal and nonmetal surfaces primed with coordinating transition metal ions (Zr4+, Hf4+, Cu2+, Zn2+)
The research in our group focusses on the preparation and characterization of such monolayer films as well as on the development of novel applications, which are based on the unique feature of these films that the surface properties can be selectively tuned to practical demands by just a single layer of molecules.