Electrodeposition of ordered semiconductor metal oxide nanostructures and epitaxial thin films

This dissertation presents an investigation of the electrodeposition of ordered semiconductor metal oxide nanostructures and epitaxial thin films. Epitaxial ZnO nanopillars with grain sizes less than 100 nm have been electrodeposited onto Au(111), Au(110) and Au(100) single crystal substrates. Epitaxial growth of Cu₂O films on single crystalline Si(001) has been achieved using electrodeposition. This is an unexpected result because there is a strong driving force for the oxidation of Si to form a native amorphous SiO ₂ layer. The large lattice mismatch between film and substrate is reduced from −21.4% to +11.2% by the formation of a Cu₂O(001)[100]//Si(001)[110] orientation relationship, in which the film is rotated 45° around the common [001] axis. A lateral overgrowth mechanism has been proposed.; A unique feature of electrodeposition is the ability to control the orientation and morphology of electrodeposited films by controlling the solution pH or the electrode overpotential. These degrees of freedom are not available in vapor deposition. The last two papers in this dissertation present epitaxial growth of Cu₂O thin films and nanocrystals with tunable morphologies on InP(001) substrates using electrodeposition. The formation of a Cu ₂O(001)[100]//InP(001)[110] orientation relationship reduces the lattice mismatch from −27.2% to 2.9%. The morphologies of the thin films and nanocrystals are determined by the solution pH. Pyramidal crystals are observed at pH 9 and cubelike crystals are observed at pH 12.