Imaging feldspar microcline and the first stages of ice nucleation at the atomic scale Giada Franceschi, Luca Lezuo, Andrea Conti, Florian Mittendorfer, Michael Schmid and Ulrike Diebold Institute of Applied Physics, TU Wien, Austria Feldspar microcline (KAlSi 3 O 8 ) is a prominent mineral in the Earth’s crust and is present as dust particles in the atmosphere, where it nucleates ice with great efficiency. To unravel the greater ice-nucleating efficiency of microcline compared to other silicate dust particles, numerous studies have investigated the interaction of microcline with water. However, the relative importance of crystallographic orientations, lattice match between ice and microcline, cation composition, and defects for the ice-nucleating properties remain debated. Here, we present experimental surface studies of microcline and its interaction with water at low temperature. The surfaces were prepared by cleaving in ultrahigh vacuum (UHV) and analyzed with non-contact atomic force microscopy (nc-AFM) and x-ray photoelectron spectroscopy (XPS). The results provide direct views of the atomic- scale structure of microcline, exposes a hexagonal array of K + ions upon cleaving. Dosing water at 100K causes hydroxylation of the dry surface followed by the growth of a partially ordered water layer – possibly the onset of ice nucleation. The experimental results are interpreted with support from DFT calculations.
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