The ice-vapor interface during growth and sublimation

We employed Environmental Scanning Electron Microscopy (ESEM) in low humidity atmosphere to study the complete scenario of ice growth, coalescence of crystallites, polycrystalline film morphology and sublimation, in the temperature range of −10 ºC to −20 ºC. First, individual ice crystals grow in the shape of micron-sized hexagonal columns with stable basal faces. Their coalescence during further growth 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.