Towards the epitaxial growth of Au thin films on MgO substrates for plasmonic applications

Surface plasmon polaritons (SPPs) in Au thin films are nowadays intensively exploited for sensing applications that leverage the strong optical field confinement at the metal/dielectric interface and the easy functionalization of the Au surface. Moreover, Au thin films represent one of the common starting points for the top-down nanofabrication of plasmonic nanostructures supporting localized resonances. In this framework, strategies for the growth of high-quality Au films on transparent substrates are crucial and not yet fully established. In this study, we exploit MgO(001) substrates for the growth of thin (about 45 nm) Au films, also including an additional buffer layer of Fe. We successfully demonstrate Au samples with reduced roughness and presenting low-energy electron diffraction features, indicating a high degree of crystalline ordering. This is supported by the experimental evidence of an increased (by almost a factor of 3) propagation length compared to a reference Au sample grown on standard glass slides, which is however still significantly lower than the one expected from first principles.