INFLUENCE OF ENVIRONMENTAL SATURATION AND ELECTRIC-FIELD ON GROWTH AND EVAPORATION OF EPITAXIAL ICE CRYSTALS

Experimental studies of ice grown epitaxially from the vapor phase on covellite (CuS) and AgI substrates in air shows that growth sometimes occurs as thin crystals whose thickness can be measured by their interference color when viewed under vertical white illumination. Some crystals fail to thicken while growing laterally. Their growth rate is twice as fast on AgI as on CuS under identical conditions. Non-thickening crystals can be induced to thicken by increase of excess vapor density; a few crystals fail to thicken by water saturation. Lateral growth rate is enhanced and non-thickening crystals are also induced to thicken by application of a dc electric field. Results are interpreted in terms of a reduced growth rate caused by strain at the ice-substrate interface leading to an increase of crystal vapor pressure. This is consistent with a smaller misfit and lower strain for AgI substrates compared with CuS. Electric field gives rise to local ionization and mass flow towards the growing crystal, giving an effectively larger excess vapor density. This interpretation is consistent with the enhanced evaporation rates observed in the presence of an electric field. Ice crystal growth habit dependence on environmental conditions is examined in light of these results. © 1979.