Unique structural and mechanical properties of ultrathin au films grown on dendrimer-mediated substrates

Evidence is presented here for very significant improvements in film quality when Au is deposited on a self-assembled monolayer of amine-terminated poly(amidoamine) (PAMAM) dendrimers (generation G8) on SiOx. In addition, the nanomechanical response of the monolayer dendrimer film itself and the Au/dendrimer bilayer configuration is reported for the first time. Ultrathin (12.5 nm) Au grown on the native oxide of Si(100) results in an apparently continuous but poorly adherent film with vertical RMS roughness, approximate to1 nm, and occasional, very much larger scale (approximate to 75 nm) features. Dendrimer-mediated Au films have substantially reduced roughness (approximate to0.4 nm) and no large-scale features. Nanoindentation studies demonstrate surprisingly large differences in the mechanical responses of Au films with and without a dendrimer interlayer. The nanoindentation hardness (a measure of resistance to plastic deformation) of the dendrimer-mediated 12.5-nm Au film is significantly higher than that of the 12.5-nm Au layer alone. This mechanical strengthening is attributed to the compressed and confined nature of the dendrimer interlayer and points to the possibility of using hybrid organic/inorganic nanocomposites as tribomaterials.