Silicates, i.e., minerals containing Si and O as well as other ions, are ubiquitous on our planet. They largely compose the rocks we stand on, and are active in sequestrating atmospheric CO2. Through weathering processes, they transform into clays and create soils, providing essential nutrients for plant growth. Furthermore, they exist as airborne dust particles in the atmosphere, where they influence ice nucleation and cloud formation, profoundly impacting global weather patterns.
Most of these phenomena are regulated by reactions at silicate surfaces: small molecules thereby adsorb and react to form new molecules or minerals or both. The atomic details of silicate surfaces – e.g., their composition, crystallographic orientation, atomic structure, active/defect sites, and charge distribution – will determine the precise reaction paths and rates.
To date, knowledge about silicate surfaces is limited due to technical reasons – the strong insulating nature of these minerals makes it challenging for scanning probe techniques. However, recent developments in atomic force microscopy (AFM) allow us to overcome the hurdles and tap into the surface chemistry of silicates and its relevance for many important natural processes. In our labs, we employ constant-height non-contact AFM with a qPlus sensor in UHV to investigate the surfaces of different silicates at the atomic level. We complement these studies by area-averaging spectroscopic techniques such as X-ray photoelectron spectroscopy and ab-initio theoretical modeling.
© CC BY 4.0 Giada Franceschi/IAP
Muscovite mica, a common 2D aluminosilicate, offers a nice example. Facile cleaving occurs between planes of K ions. In our labs, we have resolved the distribution of these K ions – neither disordered nor fully ordered – and investigated its relation to the underlying Al ions.
- G. Franceschi, P. Kocán, A. Conti, S. Brandstetter, J. Balajka, I. Sokolović, M. Valtiner, F. Mittendorfer, M. Schmid, M. Setvín, U. Diebold
Resolving the intrinsic short-range ordering of K+ ions on cleaved muscovite mica
Nature Communications 14, 208 (2023); doi: 10.1038/s41467-023-35872-y
Feldspars are a group of minerals that form more than 50% of the rocks in the crust of the Earth; nevertheless, only very little is known about them. We are currently working on K-feldspars (KAlSi3O8) to understand the role of the surface chemistry of these materials in the context of atmospheric ice nucleation. Soon, you can read here more about our newest results!
Projektass.in Dott.mag. Dr.in rer.nat. Giada Franceschi
Research Unit of Surface Physics