Nanoscale structure of submicron-thick sputter-deposited Pd films: effect of the adatoms diffusivity by the film-substrate interaction

Pd films were deposited, at room temperature, on Ti and SiO2 substrates by normal (0°) and oblique (36° and 48°) incidence sputtering processes. Scanning electron microscopy was used to analyze the surface and cross morphology of the Pd films so to study the effect of the Pd adatoms surface diffusivity on the films nanostructure. In fact, even if the low homologous temperature (0.17) prescribes that the Pd film grows on both substrates in the Zone I of the structure zone model, some differences are observed: in normal incidence condition, the Pd film on the Ti substrate was found to be formed by tapered grains, while on the SiO2 substrate the Pd film exhibited a columnar morphology with the columns showing a cauliflower shape. Also in the oblique deposition configurations, notable differences in the nanoscale morphology of the Pd films grown in the same conditions are observed on the basis of the supporting substrate. These data suggest that, during depositions, the Pd adatoms diffusivity on the substrate, as determined by the film-substrate interaction both in normal and oblique deposition conditions, is crucial in determining the final film nanostructure. This aspect is semi-quantitatively discussed on the basis of the of the adsorption energy of the Pd atoms on Ti (0.69 eV) and on SiO2 (0.27 eV).