The ice–vapour interface during growth and sublimation
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Scanning electron microscopy
We employed environmental scanning electron microscopy (ESEM) in low-humidity atmosphere to study the ice growth, coalescence of crystallites, polycrystalline film morphology, and sublimation, in the temperature range of −10 to −20 ∘C. First, individual ice crystals grow in the shape of micron-sized hexagonal columns with stable basal faces. Their coalescence during further growth results in substantial surface defects and forms thick polycrystalline films, consisting of large grains separated by grain boundaries. The latter are composed of 1 to 3 µm wide pores, which are attributed to the coalescence of defective crystallite surfaces. Sublimation of isolated crystals and of films is defect-driven, and grain boundaries play a decisive role. A scallop-like concave structure forms, limited by sharp ridges, which are terminated by nanoscale asperities. The motivation for this work is also to evaluate ESEM's ability to provide a clean and reproducible environment for future study of nucleation ...