The ice–vapour interface during growth and sublimation

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 and growth on atmospherically relevant nucleators such as materials of biological origin and inorganic materials. Hence, extensive information regarding potential ESEM beam damage and effect of impurities are discussed.This research has been supported by the Ekonomiaren Garapen eta Lehiakortasun Saila, Eusko Jaurlaritza (grant no. PI2013-57), the Ekonomiaren Garapen eta Lehiakorta sun Saila, Eusko Jaurlaritza (grant nos. Elkartek ng15 and Elkartek ng19), and the Ministerio de Economía, Industria y Competitividad, Gobierno de España (grant nos. PID2019-104650GB, MAT2013- 46006-R, and Maria de Maeztu “Units of Excellence” programme MDM-2016-0618)