Nanotribological Studies of Dendrimer-Mediated Metallic Thin Films
X. Li, G.Wei, M. Curry, J. Zhang, S.C. Street, M.L. Weaver
Center of Materials for Information Technology, The University of Alabama, Box 870209, Tuscaloosa, AL 35487-0209
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. We have extended our MRSEC-enabled multidisciplinary research on the nanotribology of dendrimer-mediated metallic films to investigate the roles of different dendrimer interlayers on the tribomechanical response of reactive metallic films. Extensive nanotribological studies were conducted on 10 nm Ti and Al thin films deposited onto PAMAM dendrimer mediated Si wafers using direct current (DC) magnetron sputtering. Ramped load nanoscratch tests were performed using a Nano Indenter® II system. X-ray photoelectron spectroscopy (XPS) was employed to investigate the chemical interactions between the metal films, the interlayers, and the environment. In agreement with our prior investigations, the nanoscratch surface 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 increase is attributed to the formation of a mixed nanocomposite region and increased interfacial adhesion in the dendrimer-mediated films. Critical load improvement is also related to the generation (size) of the dendrimer. The effect is more pronounced for the thicker G8 dendrimer than for the G4 dendrimer interlayer (see Figure 1, below). It is speculated that this difference is related to the relative volume fractions of dendrimer, metal and nanocomposite in each system.