Irradiation-induced densification of cluster-assembled thin films

The growth and modification of nanocluster-assembled thin films were studied using molecular-dynamics simulations. Porous thin films of copper were grown through sequential deposition of 50 Cu-711 nanoclusters on a Cu (100) substrate. Irradiation of these films with Xe and Au ions, at energies ranging 5-30 keV, was then carried out with the aim of increasing their density. Results show that heavy-ion irradiation can successfully be used in the densification of initially underdense thin films. With ion ranges tuned to the thickness of the thin films, densities approaching that of bulk copper were achieved at fluences as low as 50x10(12) ions/cm(2). Densification was caused by local melting in individual clusters and the resulting viscous flow of atoms into voids within the films. Nanocrystallinity was preserved as recrystallization occurred according to crystal orientations of the pre-existing clusters.