Porosity and crystallization of water ice films studied by positron and positronium annihilation

The growth, evolution, and annealing of closed and interconnected pores in amorphous and crystalline films of water ice grown under a range of conditions have been studied by variable-energy positron annihilation spectroscopy (VEPAS). By measuring positron and positronium-related annihilation parameters as a function of time and film temperature it is shown that VEPAS has the capacity to yield a wealth of depth-dependent information on film morphology, with particularly promising results on the evolution and annealing of subnanometer closed pores-inaccessible to other techniques-and the study of the energetics of structural and phase changes.