Crystalline AuNP-Decorated Strontium Niobate Thin Films: Strain-Controlled AuNP Morphologies and Optical Properties for Plasmonic Applications

Gold nanoparticle (AuNP) decoration is a commonly usedmethod toenhance the optical responses in many applications such as photocatalysis,biosensing, solar cells, etc. The morphology and structure of AuNPsare essential factors determining the functionality of the sample.However, tailoring the growth mechanism of AuNPs on an identical surfaceis not straightforward. In this study, AuNPs were deposited on thesurface of a perovskite thin film, strontium niobate (SNO), usingpulsed laser deposition (PLD). AuNPs exhibited a dramatic variationin their growth mechanisms, depending on whether they were depositedon SNO thin films grown on magnesium oxide (SNO/MgO) or strontiumtitanate (SNO/STO) substrates. On SNO/MgO, the Au aggregates formlarge NPs with an average size of up to 3500 nm(2). TheseAuNPs are triangular with sharp edges and corners. The out-of-planedirection of growth is favored, and the surface coverage ratio byAuNPs is low. When deposited on SNO/STO, the average size of AuNPsis much smaller, i.e., & SIM;250 nm(2). This reductionin the average size is accompanied by an increase in the number densityof NPs. AuNPs on SNO/STO have a round shape and high coverage ratio.Such an impact from the substrate selection on the AuNP structureis significant when the sandwiched SNO film is below 80 nm thicknessand is weakened for 200 nm of SNO films. X-ray diffraction (XRD) andscanning electron microscopy (SEM) were used to characterize all samples.Strain analysis was used to explain the growth mechanism of AuNPs.The average height of AuNPs was measured by using atomic force microscopy(AFM). Ellipsometry in the visible-near-infrared (vis-NIR)region was used to characterize the optical response of all samples.AuNP-decorated SNO/MgO and SNO/STO thin films exhibit different opticalproperties, with only gold-decorated SNO/MgO samples showing a size-dependentepsilon-near-zero behavior of nanoparticles. These results providean additional route to control the structure of AuNPs. They can beused for various plasmonic applications like the design and developmentof strain-engineered gold-nanoparticle-decorated devices for surface-enhancedRaman spectroscopy (SERS) and photocatalysis.

Automated summary

Gold nanoparticle (AuNP) decoration is a commonly used method to enhance optical responses. This study found that the growth mechanisms of AuNPs vary depending on the substrate, which has a significant impact on the sample's properties.