Abstract
Abstract. 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.
Highlights
Ice covers a much smaller area of our planet than liquid water
We modelled ice–vapour interfaces inside an environmental scanning electron microscope (ESEM), where temperature and humidity values can simulate conditions found in cold climates
We investigated the growth and sublimation of isolated ice crystals, grown in random directions on oxidized silicon wafer, and of polycrystalline films, by real-time, in situ environmental scanning electron microscopy (ESEM)
Summary
Ice covers a much smaller area of our planet than liquid water. Some of this ice is subjected to large seasonal variations in temperature, giving rise to melting and sublimation. Understanding ice melt, flow, sublimation, and evaporation is key in fully understanding the impact of global warming. We focus exclusively on the study of ice–vapour interfaces, as present on snow, glaciers, permafrost soil, and sea ice and in clouds. Our low-humidity conditions are of special relevance for sublimation at the poles and in Greenland, where ice sheets are in contact with air of low humidity, at temperatures well below those of most glaciers on other continents (Bliss et al, 2011). The sublimation (and the redeposition) rate determines whether ice fields can exist at all
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