Adsorption, Diffusion and Structure Formation of Water on Calcite: Fundamental Processes in Wetting of an Omnipresent Mineral Surface

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Water at surfaces is omnipresent both in nature and technology. Therefore, solid-water interfaces are pivotal in a broad range of fields, including, e.g., geochemistry, environmental chemistry as well as catalysis. Ice nucleation at surfaces is a particularly interesting phenomenon in this context, which has been studied since centuries. Yet, many fundamental questions regarding the physico-chemical mechanisms responsible for water adsorption and structure formation at surfaces remain poorly understood.Calcite is a particularly interesting substrate to study water nucleation phenomena, since it represents the most abundant carbonate on earth. It plays a major role in many every day's life and industrial processes, including such diverse fields as scale inhibition, oil recovery, or construction. Despite the importance of the calcite-water interface, very little is known about the molecular-scale details of water adsorption, diffusion and structure formation on this surface. This lack of information is mostly due to the fact that calcite, being an electrically insulating material, represents a major challenge for classical surface science techniques. In this respect, dynamic atomic force microscopy carried out in ultra-high vacuum has proven to constitute an ideally suited technique to obtain atomic resolution on bulk insulator surfaces.The goal of the project is unravelling fundamental steps in water adsorption, diffusion and structure formation on the natural cleavage plane of calcite, namely calcite (10.4), kept in ultra-high vacuum. We will determine basic parameters in water adsorption such as free energy and entropy of adsorption as well as water monomer diffusion barriers. To elucidate temperature-dependent water structure formation, we will study water cluster formation and diffusion as well as temperature-dependent mono- and multilayer growth. Experiments with both light (H2O) and heavy (D2O) water are planned to shed light onto the influence of hydrogen bonding in these structures.In summary, the project aims at elucidating the basic physical mechanisms in water adsorption, diffusion as well as structure formation and growth on calcite (10.4) by recording AFM data at low and variable temperatures. These insights are expected to provide important fundamental input for understanding the reactivity of water-calcite interfaces in a broad range of different areas.