A direct observation of nanometer-size void dynamics in an ultra-thin water film

Here we report the direct dynamic observation of electron beam induced nucleation of nanometer-diameter voids in a thin water film (<12 nm) on a hydrophilic substrate using an in situ TEM platform tailored towards imaging of liquids. The growth dynamics of these nano-voids in a thin water film reveal that there is a critical diameter below which voids are unstable and close up. However, the coalescence of several of such small and unstable voids allows for pathway to form larger and stable voids. A simple model based on the minimization of free energy explains our experimental observations.