Epitaxial electrodeposition of Cu2O on Ag substrates in sulfate baths

A series of Cu2O samples were electrodeposited on polycrystalline Ag substrates in an electrolyte containing 0.4 M cupric sulfate and 1.3 M lactic acid at different electrolyte temperatures, pH values, and current densities. The electron backscatter diffraction technique was used to characterize the epitaxial orientation relationship (OR) between the deposited Cu2O films and underlying Ag grains. Epitaxial growth was mostly prohibited for the films deposited at pH 9 and 25 degrees C, whereas epilayers consisting of crystals of a single orientation were deposited on most of the substrate grains at conditions of pH 12/25 degrees C, pH 9/60 degrees C, and pH 12/60 degrees C. In addition to the expected cube-on-cube OR, four more ORs were identified. The existence of multiple ORs was probably a result of coincidence site lattice matching. The adoption of the epitaxial OR for Cu2O films strongly depended on the orientations of the substrate grains. Finally, transmission electron microscopy analysis indicated that the epilayer deposited at 60 degrees C contained a relatively low density of threading dislocations on the order of 10(9) cm(-2) and thus exhibited low electrical resistivity values of 1-3 x 10(3) Omega.cm.