Thermal properties of thin and thick Ni ₃ Al cluster assembled layers: An atomic scale simulation study

Diffusion properties at inner surfaces and interfaces of Ni ₃ Al nanostructured materials are investigated by means of classical molecular dynamics with a second moment tight-binding potential. Model samples as prepared by low energy cluster beam deposition (LECBD) on a metal substrate are used. The first consists in a cluster layer interacting with the substrate. The second is a fragment of the first, to which periodic boundary conditions are applied in order to approximate an infinitely thick layer. Half of the atoms are either located at pore surfaces or at cluster interfaces. As a consequence of temperature, the model thick film undergoes strong compaction, which is identified as the result of coalescence. The effect is less pronounced for the cluster film on a substrate, suggesting the latter to contribute to the nanostructured layer stability. The comparison of the diffusion properties of these samples is made. For both samples, atomic diffusion at surfaces and interfaces is found particularly fast and the diffusion coefficient obeys an Arrhenius law with an activation energy of 0.3eV, similar to that found in liquid Ni ₃ Al.