Au nanoparticle monolayers covered with sol-gel oxide thin films: optical and morphological study

Area of Science:

• Materials Science
• Nanotechnology
• Surface Science

Background:

• Submonolayer gold nanoparticles (Au NPs) exhibit unique optical properties influenced by their size, shape, and surrounding environment.
• Thermal annealing is a common method to modify nanoparticle morphology and optical characteristics.
• Functionalized surfaces and thin film coatings can further tune nanoparticle behavior.

Purpose of the Study:

• To investigate the impact of thermal annealing on standalone Au NPs and those coated with NiO and TiO2 thin films.
• To correlate changes in optical properties with structural modifications induced by annealing.
• To explore the potential application of these systems in optical sensing.

Main Methods:

• Characterization techniques including UV-vis absorption, X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), and spectroscopic ellipsometry.
• Controlled thermal annealing of Au NP films with and without metal oxide overlayers.
• Optical sensing experiments using ethanol vapor.

Main Results:

• Surface plasmon resonance (SPR) peak red-shifts and intensifies with increasing Au NP coverage, linked to refractive index.
• Standalone Au NPs sinter at 200 °C, with annealing temperature affecting optical properties.
• NiO and TiO2 coatings significantly red-shift and broaden the SPR band, while suppressing nanoparticle sintering.

Conclusions:

• Metal oxide coatings play a crucial role in stabilizing Au NPs against thermal sintering and modifying their optical response.
• The enhanced optical properties and stability make these Au NP/metal oxide systems promising for optical sensing applications.
• The wavelength-dependent response of Au NPs suggests their utility as tunable optical probes.