Diffusion-induced recrystallization during the early stages of solid-state dewetting of Ni-Pt bilayers

We report the phenomenon of diffusion-induced recrystallization (DIR) in the Ni-Pt bilayers deposited on sapphire substrate and annealed at the temperature of 950°C. The as-deposited bilayers were nanocrystalline and exhibited mazed bicrystal microstructure. Short (shorter than 1 min) anneals at 950°C resulted in heterogeneous intermixing, with the isolated intermixed regions containing randomly oriented new grains of varying concentrations being spread in the original bilayer with little intermixing. This intermixing mode was discussed in terms of DIR phenomenon. Further annealing resulted in preferential growth of {111}- and {100}-oriented grains with random in-plane orientations at the expense of the randomly textured matrix formed during DIR, with a clear advantage of the {111}-oriented grains at the later stages of grain growth. Long annealing at the temperature of 1000°C resulted in full solid state dewetting of the bilayer and formation of homogeneous faceted single crystalline Ni-Pt nanoparticles. The majority of nanoparticles exhibited {111} orientation, while a minority of smaller nanoparticles had a {100} orientation. An additional ordering annealing at 550°C reversed the distribution of the particle orientations, with the majority of small nanoparticles exhibiting the (001) orientation and L10 long-range order. These findings demonstrate that the DIR process plays an important role in the diffusion intermixing of Ni-Pt bilayers and in the final geometry of metal nanoparticles formed during solid-state dewetting.