Fabrication Of Ag Nano-film Hybride Structures Based On PAA Template And Their Optical Properties

Noble metal nanostructures have special optical properties due to localized surface plasmon resonance (LSPR), such as the selected optical absorptions and scattering and the electromagnetic enhancement and so forth. Further, extensive research has discovered that the optical properties of nanostructure depend not only on materials but also on geometry. Metamaterials based on plasmonic elements are particularly efficient as absorbing media, because both the electrical and the magnetic properties of a metamaterial can be tuned by structured design. Incorporating plasmonic nanostructures and electromagnetic metamaterials into absorber systems has been employed effectively to govern the light-matter interactions, which introduce important applications in solar cells, photovoltaics, photocatalyst, molecular detections and thermal emitters and so on. In this work, we fabricated hybrid nanostructures based on Ag films by nanoimprinting, anodic anodization, thermal evaporation and atom layer deposition, the optical properties of the hybrid nanostructures were studied.Firstly, highly ordered ultrathin Porous Anodic Alumina (PAA) substrate was fabricated by nanoimprinting and anodic anodizing. Ag/PAA hybrid structures with single Ag nanoparticle located in the pore were synthetized by thermal evaporation and annealing treatment. Different annealing temperature and time were introduced to study the Ag/PAA morphology related optical absorption property. It was found that the Ag/PAA hybrid structures had a strong and broad-band absorption in both ultraviolet and visible light regions owing to the geometry trapping of PAA substrate as well as the LSPR of Ag nanoparticles. The optical absorption spectra showed that the highest absorption of the Ag/PAA hybrid structure was found on that with 30 nm thick Ag film without annealing treatment, which possessed the highest absorption of 90.3% at 525 nm, and the lowest absorption of 70.3% at 1080 nm.Secondly, the nano-tapered Ag/PAA hybrid structure was conveniently fabricated by a multistep anodizing and etching pore-widening method and thermal evaporation of a Ag film. The influence of silver film thickness and annealing process on morphology and optical properties of Ag/PAA hybrid structure were investigated. The result showed that the Ag/PAA hybrid structures had a strong and broad-band absorption in both ultraviolet and visible light regions owing to the geometry trapping of inverted nanotaper structure as well as the LSPR of Ag nanostructures. The SERS intensity was strongly dependent on the annealing-induced formation of Ag particles and interparticle nanogaps. With the increase of silver thickness, the intensity of optical absorptions became weaker. After annealing treatment, the optical. absorptions decreased due to the influence of size and intervals between Ag nanoparticles. Inversely, the SERS intensity was increased stongly.Finally, the TiO2/Ag/PAA nanocomposite structures were fabricated successfully by thermal evaporation and atomic layer deposition (ALD) on inverted tapered PAA substrates. The Ag film thickness, temperature of TiO2 deposited, multilayer of Ag and TiO2 films and annealing process were investigated to study the TiO2/Ag/PAA optical properties. The UV-Vis-NIR spectra showed that the highest absorption of the TiO2/Ag/PAA nanocomposite structure was found on that with 30 nm thick Ag film and 20 nm thick TiO2 film prepared at the ALD temperature of 75 ℃, which possessed the highest absorption of 99.0% at 475 nm, and the lowest absorption of 82.5% at 800 nm. Furthermore, the TiO2/Ag/PAA nanocomposite structure had strong absorptions about 80.2% at 1060 nm and 1860 nm.