Wettability and crystalline orientation of Cu nanoislands on SiO2 with a Cr underlayer

Cu thin films were grown by sputter deposition on SiO2 substrates with a Cr underlayer that is known to improve the adhesion between Cu and SiO2. The initial stage of Cu growth was investigated using transmission electron microscopy. Results showed that non-wetting spherical Cu nanoislands were formed with a random crystalline orientation on Cr/SiO2, and evolved into a randomly oriented polycrystalline thin film. These results were then compared with our previous results on the initial growth of Cu on SiO2 with and without a Ti underlayer. A quantitative model was proposed to explain the difference in dependence of the wettability of microscopic nanoislands and that of the adhesion of macroscopic thin films on interfacial interactions and surface energies.