Nanoscopic Feldspar Islands on K-Feldspar Microcline (001)

Feldspar minerals are abundant rock-forming minerals playing a central role in environmental processes such as silicate weathering and ice nucleation in mixed-phase clouds. These processes typically take place at the feldspar-water interface, which is why the micro- and nanoscopic surface topology is of major importance to understand them. However, especially in the field of ice nucleation on feldspar surfaces, most experimental studies are limited to the micrometer scale, while the ice nucleation sites are expected to be nanometre sized. Here, we report an intrinsic island structure observed on microcline (001). High-resolution atomic force microscopy (AFM) images taken in ultra-high vacuum show nanometre-sized islands on the terraces and at the step edges. Atomic scale images revealing a very similar contrast and identical lattice parameters on the terrace and on the islands suggest that these islands are an intrinsic feature of the microcline surface. Moreover, AFM at the solid-liquid interface demonstrates that the observed nanostructure is stable in water. As the existence of islands significantly increases the density of edge and kink sites, the observed nanostructure might have important implications for surface reactivity and potentially ice nucleation efficiency.