We have discovered useful physical, mechanical, and chemical behavior in experiments on dendrimer-metal nanocomposite films. Most of the work has centered on nanocomposite systems of the form substrate (Si wafer with native oxide)/dendrimer monolayer/adlayer (vapor-deposited ultrathin metal film). Dendrimers are three-dimensional, highly ordered, tree-like branched macromolecules with specific structures in the core and outer shell. They can be synthesized with highly controllable sizes (they are essentially monodisperse) determined by the core type, extent of branching, and nature of the end groups. The spontaneous absorption of dendrimers monolayers on technological surfaces from mumol ethanolic solutions makes monolayer deposition relatively simple. Among the important findings reported is evidence for dramatically enhanced quality (superior flatness and adhesion) of metal films deposited on dendrimer monolayers. The dendrimer monolayer modifies metal overlayer film growth, such that relatively unreactive metals show smaller gain size when evaporated onto the monolayer than when sputter deposited. XPS studies clearly show that the metal layer penetrates the dendrimer adlayer. Indeed, deposition of reactive metals (Al, Co, Cr, Ti) onto amine-terminated, amido-branch dendrimer monolayers results in metal nitride and carbide formation at room temperature. More recent work confirms that the overlayer deposition disrupts the polymeric structure of the monolayer (bond breaking), even when the metal is relatively unreactive (e.g., Cu). The presence of the monolayer and formation of a nanocomposite have a significant effect on the mechanical properties of the ultrathin film. We have observed very striking differences in the wear modes associated with nanoscratch events on metal layers with and without a dendrimer interlayer. Dramatic effects on the nanotribological performance of dendrimer monolayer-mediated Au and Cu films are also observed.
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