Annealing of amorphous ice films

Shear modulus and internal friction of amorphous water ice films of ≈ 1 μm thickness formed by vapor deposition below 100 K onto a silicon double paddle oscillator were measured, and their annealing up to 160 K was studied. As the deposition temperature decreases to 50 K, the shear modulus decreases to less than 5% of its bulk value, explained by increasing porosity, which exceeds 60% at 50 K. The internal friction, which is temperature independent below 10 K, as is common to all amorphous solids, increases with decreasing deposition temperature, i.e., with increasing porosity. During annealing at a constant temperature, the internal friction decreases with a logarithmic time dependence. Even after annealing at 160 K, when the film is fully dense, and its shear modulus has reached its bulk value, its internal friction is still over one order of magnitude larger than that of films deposited at substrate temperatures at which the films form as crystals. Thus, annealing amorphous ice does not lead to the same kind of order as is achieved by depositing crystalline ice.