Plasmonic device using backscattering of light for enhanced gas and vapour sensing

Based on recent experimental and theoretical results obtained with gold-glass nanocomposite films, we propose a plasmonic device which uses the backscattering of light in order to make a highly sensitive gas/vapour sensor. The backscattered reflectance is used as the sensing signal since it has been shown, under certain conditions, that this component of the diffracted light is much more sensitive to a change of refractive index in the surrounding medium than the specular component. In addition, the backscattering presents an azimuthal angular dependency which is viewed as an advantage for practical implementation. The device consists of three planar layers. First, a glass substrate acting as incidence medium. Then a dielectric layer with a reduced refractive index with respect to the substrate is added which acts as a leaky-waveguide in order to maximize light coupling into the third sensing layer. The third layer is composed of gold nanopillars embedded in a dielectric matrix. Through numerical simulations, 2D periodic square and hexagonal arrays of gold nanopillars are compared in order to point out the influence of the nanocomposite arrangement in the photonic response. Moreover, disorder is introduced into these arrays in order to highlight the robustness of the sensing principle with respect to defects in the particle arrangement and size. For the purpose of gas/vapour sensing, we study the backscattered reflectance as it changes according to modifications in the dielectric environment at the external surface due to adsorption from gas or vapour. We determine the optimized device parameters and incidence angles.