Atomic structure and water arrangement on K-feldspar microcline (001)

Tobias Dickbreder, Franziska Sabath, Bernhard Reischl, Rasmus Väinö Erik Nilsson, Adam S. Foster, Ralf Bechstein, Angelika Kühnle

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Sammanfattning

Cloud properties, such as their reflectivity or their likelihood to precipitate, depend on whether the cloud droplets are liquid or frozen. Thus, understanding the ice nucleation mechanisms is essential for the development of reliable climate models. Most ice nucleation in the atmosphere is heterogeneous, i.e., caused by ice nucleating particles such as mineral dusts or organic aerosols. In this regard, K-feldspar minerals have attracted great interest recently as they have been identified as one of the most important ice nucleating particles under mixed-phase cloud conditions. The mechanism by which feldspar minerals facilitate ice nucleation remains, however, elusive. Here, we present atomic force microscopy (AFM) experiments on microcline (001) taken in ultrahigh vacuum and at the solid-water interface together with density functional theory (DFT) and molecular dynamics (MD) calculations. Our ultrahigh vacuum data reveal features consistent with a hydroxyl-terminated surface. This finding suggests that water in the residual gas readily reacts with the surface. Indeed, corresponding DFT calculations confirm a dissociative water adsorption. Three-dimensional AFM measurements performed at the mineral- water interface unravel a layered hydration structure with two features per surface unit cell. Comparison with MD calculations suggest that the structure observed in AFM corresponds to the second hydration layer rather than the first water layer. In agreement with previous computation results, no ice-like structure is seen, questioning an explanation of the ice nucleation ability by lattice match. Our results provide an atomic-scale benchmark for the clean and water-covered microcline (001) plane, which is mandatory for understanding the ice nucleation mechanism on feldspar minerals.
Originalspråkengelska
TidskriftNanoscale
Volym16
Nummer7
Sidor (från-till)3462-3473
Antal sidor12
ISSN2040-3364
DOI
StatusPublicerad - 2024
MoE-publikationstypA1 Tidskriftsartikel-refererad

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