Epitaxial Films and Nanostructures

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The proposed research program will explore two recent unexpected discoveries associated with two particular examples of oxide substrates being used to support epitaxial structures. The first case involves a gold film evolving into epitaxial gold nanoparticles on a spinel substrate. There is a large surface energy associated with the gold spinel surface. This energy drives the dewetting of the gold at modest temperatures with the gold film breaking up into nanometer scale particles as expected. However, gold and spinel have a near lattice match so that at somewhat higher temperatures the gold nanoparticles rotate such that they are aligned with the underlying substrate. At yet higher temperatures, a self-limited chemical reaction takes place, forming an epitaxial bilayer of gold oxide. There is strong evidence that this bilayer represents an equilibrium complexion i.e. that it provides the lowest free energy interface between the gold and spinel crystalline states. The evidence is that with annealing at higher temperatures or longer times the bilayer does not appear to grow, the adhesion of the gold nanoparticle increases dramatically and that the estimate of the surface tension from the contact angle is greatly reduced. If equilibrium complexions could be introduced or approximated at the interface of insulating layers and metallization layers then the reliability of many semiconductor could be improved.