Observing the Formation of Ice and Organic Crystals in Active Sites.

Heterogeneous nucleation is vital to a wide range of areas as diverse as ice nucleation on atmospheric aerosols and the fabrication of high-performance thin films. There is excellent evidence that surface topography is a key factor in directing crystallisation in real systems, however the mechanisms by which nanoscale pits and pores promote nucleation remain unclear. This dataset supports a study in which we use natural cleavage defects on Muscovite mica to investigate the activity of topographical features in the nucleation from vapour of ice and various organic crystals. Direct observation of crystallisation within surface pockets using optical microscopy, and also interferometry, both demonstrate that these sharply acute features provide extremely effective nucleation sites, and allows us to determine the mechanism by which this occurs. A confined phase is first seen to form along the apex of the wedge, and then grows out of the pocket opening to generate a bulk crystal after a threshold saturation has been achieved. Ice nucleation proceeds in a comparable manner, although our resolution is insufficient to directly observe a condensate prior to the growth of a bulk crystal. This dataset provides new insight into the mechanism of crystal deposition from vapour on real surfaces, where this will ultimately enable us to use topography to control crystal deposition on surfaces. It is also particularly relevant to our understanding of processes such as cirrus cloud formation, where such topographical features are likely candidates for the “active sites” that make clay particles effective nucleants for ice in the atmosphere.