Growth and annealing strategies to control the microstructure of AlN:Ag nanocomposite films for plasmonic applications

A critical comparison of the microstructure, morphology and optical performance of AlN:Ag cermet, nanocomposite films produced by two widely used Physical Vapor Deposition (PVD) techniques, namely Pulsed Laser Deposition (PLD) and Sputtering, and by two post-growth processing techniques, namely thermal and laser annealing is presented. Incorporation of Ag into w-AlN results in disruption of columnar growth, reduction of texture and development of globular grains. The combined X-ray diffraction and X-ray Photoelectron Spectroscopy analyses identified a solubility limit of 4 at.% for Ag into AlN. Further increase of the Ag concentration results in segregation of Ag. Thermal annealing of AlN:Ag results in outdiffusion and self-organization of Ag in nanoparticles with strong plasmonic response. The selective delivery of laser energy to metallic hot spots during laser annealing promotes local over-heating resulting in local crystallization of the AlN matrix enhancing and shifting the localized surface plasmon resonance. Thus, the optical reflectance spectra can be tuned to cover a wide part of the visible range from violet to green. Laser annealing, in particular, can be applied with high spatial selectivity to produce miniature plasmonic devices.