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.