Observations of the growth and sublimation of water ice films by variable-energy positron annihilation spectroscopy

The near-surface structure of thin vapor-deposited water ice films during formation and sublimation in vacuum has been probed using in-situ positron annihilation spectroscopy. While amorphous solid water films prepared at 120K are highly dense with low porosity micro- and interconnected meso-pores have been observed in the top few tens of nm of ice films prepared at temperature of 170 – 180K as the films are forming and during sublimation. Responses to these near-surface pores are much more pronounced in films grown at 170 – 180K than in those grown at lower temperatures.