Self-assembly of metal-oxide nanostructures: Oxidation of Cu films by in situ UHV-TEM

The effect of temperature on the epitaxial Cu₂O oxide morphology has been investigated by oxidizing Cu(100) thin films at temperatures ranging from 150° to 1000°C. The evolution of the island size and shape was visualized within an in situ ultra high vacuum transmission electron microscope. Dramatically different morphologies of oxide nanostructures can be achieved by an appropriate choice of the oxidation temperature. During oxidation at low temperatures (T < 400°C). the oxide islands adopt triangular shape, but at temperatures higher than 400°C, the islands have a more symmetrical geometry. Of particular interest, quasi-one-dimensional Cu₂O structures with aspect ratios as large as 40:1 were formed at the oxidation temperature of 600°C. The in situ observation data on the elongation of Cu₂O islands agree with the energetic calculations based on the balance between surface and interfacial energies and the elastic stress relaxation in the three dimensional islands.