Laser Annealing of Gold Thin Films as a Platform for Plasmonic Sensing Applications

Abstract

The future of the plasmonic devices is heavily challenged by the nanoconstruction schemes of metals which often require rather fast, low-cost, and high-throughput fabrication techniques. Laser annealing is considered to be an unrivaled tool for surface manipulation of thin metallic films, especially with functional plasmonic devices of pre-determined morphology. Herein, a commercial CW CO2 laser, wavelength of 10.6 µm and optimum power of 15W, has been used for surface reconstruction of thin Au films, with an initial film thickness of 15 nm (±3 nm) sputtered on quartz substrates, as plasmonic sensing platforms. The effect of two main laser parameters on the Au film morphology have been explored namely power density and scanning speed. Thermal annealing of Au nanostructured films by the electrical furnace is also been studied. UV-Visible (UV-Vis) spectroscopy characterization measurements is utilized to monitor the the plasmonic induced optical absorption changes with different experimental conditions. Surface annealed Au nanofilms were then used as a plasmonic sensing substrate to detect the size and density variation of Ag NPs, fabricated by pulsed Nd: YAG laser ablation, ith pulse duration of 7 nsec, in DI water with a wavelength of 1064 nm and different laser energies, imbedded in a solution-processed thin dielectric material (CeO2 NPs) to form a composite film. Our plasmonic sensing structure shows a remarkable detection to variable concentrations of Ag NPs reflected by a significant red-shift in the plasmonic resonance absorption of Au nanostructures with laser ablation energy at a fixed number of pulses of 50 (1Hz).