Tailoring core size, shell thickness, and aluminium doping of Au@ZnO core@shell nanoparticles†

Abstract

Plasmonic materials, such as gold nanoparticles (AuNPs), exhibit significant extinction and near-field enhancement across the visible and near-infrared spectrum, attributable to localized surface plasmon resonances (LSPRs). Epsilon-near-zero (ENZ) materials, such as aluminium doped zinc oxide (AZO) are known in non-linear optics for their ability to generate and manipulate light-matter interactions through processes like higher harmonic generation. Combining doped ZnO with plasmonic materials therefore holds promise for enhancing non-linear efficiencies and tuning their operational wavelengths. To date, however, only top-down structures based on plasmonically decorated thin ENZ films have been realized, and no colloidal and scalable route to obtain these hybrid materials has been reported yet. Here, we introduce a novel colloidal synthesis approach for fabricating Au@AZO core@shell nanoparticles with tunable core size, shell thickness, and dopant concentration, allowing for the spectral alignment of the LSPRs of the AuNPs with the non-linear optical properties of the AZO shells. Our method involves the colloidal synthesis of gold cores followed by an ascorbic acid-assisted process to deposit polycristalline ZnO and AZO shells, resulting in core diameters ranging from 25 to 69 nm, shell thicknesses from 16 to 47 nm, and aluminium doping levels between 0 and 4 at%. Our procedure widens the range of hybrid plasmonic nanostructures that can be colloidally synthesised, opening new possibilities for the large scale fabrication of high-performance nanomaterials for integration in photonic, photocatalytic, and sensing applications.