Effect of Hydrogen Pressure on the Size of Nickel Nanoparticles Formed during Dewetting and Reduction of Thin Nickel Films

We report a study of the formation of nickel nanoparticles by the dewetting of nickel metal films under different reduction conditions. The effects of both film thickness and temperature of dewetting on the size distributions of Ni nanoparticles are in agreement with previously reported studies. However, our work evidences that the hydrogen pressure applied during the reduction process has a drastic influence on the size of the formed Ni nanoparticles, the hydrogen pressure effect being all the more important that the film thickness is small. We interpret this effect by the formation of nickel metal hydride displacing the surface free energy balance of the system in favor of the dewetting. Moreover, the replacement of hydrogen by an inert gas allows us to rule out Ostwald's ripening as the mechanism originating the sintering of the nanoparticles.