Observation of residual disorder in the centre of amorphous solid water films after pore collapse at 125 K

The rapid structural re-organisation of porous amorphous solid water, grown to thicknesses in the range 2.5-70 μm by vapour deposition on a copper substrate at 75 K, after heating to 125 K has been found to leave a μm-wide band of residual disorder - for example, nm-sized closed pores - in the centre of the film. This layer was revealed by thinning the film by sublimation and continuously measuring the fraction of 1.5 keV positrons implanted into the film which forms ortho-positronium in the top 150 nm and decays into three gamma photons.