Nanotribological studies of dendrimer-mediated metallic thin films

Recent studies on ultra-thin Au films on dendrimer-mediated substrates showed that the nanohardness of thin metal films is significantly increased by the presence of a dendrimer interlayer. This increase is attributed to the enhanced adhesion and modified growth mode of the dendrimer-mediated Au films as well as the confined nature of the dendrimer interlayer itself. This paper presents the results of extensive nanotribological studies of 10 nm Ti and thin films deposited onto the PAMAM dendrimer-mediated Si wafers using direct current magnetron sputtering. Ramped load nanoscratch tests were performed using a Nano Indenter® II system. X-ray photoelectron spectroscopy was employed to investigate the chemical interactions between the metal films, the interlayers and the environment. The nanoscratch surfaces and friction coefficient profiles for the thin films indicate that the scratch critical load is increased by the presence of dendrimer interlayer; that is the scratch load bearing capacity is improved. This is related to the formation of a mixed nanocomposite and increased interfacial adhesion. Critical load improvement is also related to the generation (size) of the dendrimer. The effect is more pronounced for the thicker G8 dendrimer than that for the G4 dendrimer interlayer. The scratch failure mechanism studied through atomic force microscopy analyses of the scratches tracks is similar to the observed wear behavior of the dendrimer-mediated Cr and Cu films. These results are important for the development and potential application of polymer-mediated metallic thin film tribo-materials.