An In Situ TEM Study of the Diffusivity of Gold Atoms in Nanocomposite Thin Films by Zirconia Co-Deposition: Implication for Neuromorphic Devices

Abstract

This study explores the thermal evolution and depercolation processes in nanocomposite gold and zirconia thin films with a focus on their potential applications in neuromorphic devices. The behavior of gold nanostructured thin films under thermal stimuli, with and without zirconia inclusions, was examined utilizing both in situ heating transmission electron microscopy, upon low electron dose conditions, and molecular dynamics simulations. The initial experiments on pure gold films revealed a progressive retraction of gold clusters starting just above 100 °C, driven by thermally activated solid-state dewetting. This process continued up to 1000 °C, resulting in a significant reduction of the substrate area covered by gold from 47 to 10%. Introducing zirconia into the gold films notably altered their thermal stability. Indeed, the presence of zirconia clusters limited the diffusivity of gold atoms, increasing the temperature threshold for depercolation and enhancing the film’s thermal stability. Molecular dynamics simulations corroborated these findings, showing a marked decrease in gold diffusivity when codeposited with zirconia: its inclusion reduced it by approximately a factor of 3, mainly due to zirconia’s high melting point. Finally, this stabilization effect was found to be more pronounced when experimentally observed in films with higher zirconia content, where the depercolation process was significantly impeded. These results highlight the potential of zirconia as a stabilizing agent in nanostructured materials, enhancing the thermal resilience of the nanostructured gold films. They provide a viable pathway to tuning the thermal behavior of gold in nanocomposite thin films, paving the way for the development of energy-efficient neuromorphic devices capable of dynamic topological changes and autonomous task execution.