Influence of Ta2O5/Au Thin-Film Thickness on Surface Plasmon Resonance for Gas Sensing: A Numerical Study

Abstract

A theoretical model for a surface plasmon resonance (SPR) gas sensor based on a dielectric–metal structure has been presented in this work. The proposed SPR sensor is numerically analyzed using the Kretschmann configuration and the Fresnel equations at an exciting wavelength of 632.8 nm. The novel configuration presented in this work uses a BK7 semicircular prism coupled with a thin gold (Au) film and a high dielectric constant semiconductor sensing layer of tantalum pentoxide (Ta₂O₅), that give improve in the optical coupling efficiency and enhances surface plasmon excitation. A comprehensive analysis is made between the two types of prisms, semicircular and triangle traditional one, by investigating the influence of metal layer thickness, dielectric material properties, and the number of layers on the SPR sensor performance, using numerical modeling based on MATLAB to evaluate the optimal structural parameters, such as the refractive index, which variate in range (ΔRI = 0, 0.03, 0.06, 0.09, and 0.12) causes in measurable resonance wavelength shifts.The resultant optimized configuration, consisting of a 50 nm Au layer and a 20 nm Ta₂O₅ dielectric layer, achieves a maximum wavelength sensitivity of 2000 nm/RIU and a figure of merit (FOM) of 206 RIU^–1, indicating excellent sensing capability. These results demonstrate that the proposed Ta₂O₅/Au structure integrated with a BK7 semicircular prism offers a promising approach for high-performance SPR-based gas sensing applications.