Atomic Layer Deposition of Dielectric Overlayers for Enhancing the Optical Properties and Chemical Stability of Plasmonic Nanoholes

Fabricating plasmonic nanostructures with robust optical and chemical properties remains a challenging task, especially with silver, which has superior optical properties but poor environmental stability. In this work, conformal atomic layer deposition (ALD) of thin alumina overlayers is used to precisely tune the optical transmission properties of periodic nanohole arrays made in gold and silver films. Experiments and computer simulations confirm that ALD overlayers with optimized thicknesses tune and enhance the transmitted intensity due to refractive index matching effects and by modifying the dielectric properties of each nanohole. Furthermore, encapsulating silver nanohole arrays with thin alumina overlayers protects the patterned surfaces against unwanted oxidation and contamination. The ability to precisely tune the optical properties while simultaneously providing robust chemical stability can benefit a broad range of applications, including biosensing and fluorescence imaging.