Energetics of nanoscale films with self–assembled oxide/metal pillars in nitride matrix

Abstract

Vertically aligned nanocomposite (VAN) thin films consisting of NiO and Au nanopillars in a TiN matrix exhibits excellent optical anisotropy and tunability along with strong magneto–optical coupling properties. A recent experimental study showed that NiO deposited on a template of TiN matrix containing Au nanopillars nucleates NiO pillars on the already existing Au pillars. Due to the oxygen–deficient NiO, Au and Ni interdiffusion develops a unique Au shell/NiO core structure in the top region and segregated agglomerates of Ni in the lower Au pillars. As a step toward understanding the growth of such a multi–phase film configuration, we report a comparative energetic investigation confirming that configurations with interdiffusion of Au and Ni is energetically favorable compared to other possible configurations without the interdiffusion of Au and Ni. In this work, a thermodynamic model accounting for elastic energy due to lattice mismatch strain, capillarity effects, and interfacial and chemical energies is utilized to compare various film configurations energetically. Among all the configurations examined, the ones that closely resemble the experimental observations possessed the least energy. It was also found that Au–Ni interdiffusion is immediate upon the deposition of oxygen–deficient NiO on TiN–Au template, and a critical ratio of Au and NiO pillar heights favors core–shell structure. These findings are vital for understanding the formation mechanisms of complex VANs and future designs of new three–phase VAN structures with complex morphologies.