Ag films deposited on Si and Ti: How the film-substrate interaction influences the nanoscale film morphology

Submicron-thick Ag films were sputter deposited, at room temperature, on Si, covered by the native SiO layer, and on Ti, covered by the native TiO layer, under normal and oblique deposition angle. The aim of this work was to study the morphological differences in the grown Ag films on the two substrates when fixed all the other deposition parameters. In fact, the surface diffusivity of the Ag adatoms is different on the two substrates (higher on the SiO surface) due to the different Ag-SiO and Ag-TiO atomic interactions. So, the effect of the adatoms surface diffusivity, as determined by the adatoms-substrate interaction, on the final film morphology was analyzed. To this end, microscopic analyses were used to study the morphology of the grown Ag films. Even if the homologous temperature prescribes that the Ag film grows on both substrates in the zone I described by the structure zone model some significant differences are observed on the basis of the supporting substrate. In the normal incidence condition, on the SiO/Si surface a dense close-packed Ag film exhibiting a smooth surface is obtained, while on the TiO/Ti surface a more columnar film morphology is formed. In the oblique incidence condition the columnar morphology for the Ag film occurs both on SiO/Si and TiO/Ti but a higher porous columnar film is obtained on TiO/Ti due to the lower Ag diffusivity. These results indicate that the adatoms diffusivity on the substrate as determined by the adatom-surface interaction (in addition to the substrate temperature) strongly determines the final film nanostructure.