Abstract
Localized surface plasmon resonance (LSPR) gas sensors are gaining increasing importance due to their unique tuneable functional properties. Au-WO3−x nanocomposite coatings, in particular, can be outstandingly sensitive to many different gases. However, a proper understanding of their optical properties and the way in which those properties are correlated to their structure/microstructure, is still needed. In this work, Au-WO3 nanocomposite coatings, with Au contents between 0–11 atomic percent, were grown using reactive magnetron co-sputtering technique and were characterized concerning their optical response. The precipitation of Au nanoparticles in the oxide matrix was promoted through thermal annealing treatments until 500 °C. Along with the Au nanoparticles’ morphological changes, the annealing treatments stimulated the crystallization of WO3, together with the appearance of oxygen-deficient WO3−x phases. Through theoretical simulations, we have related the LSPR effect with the different structural and morphological variations (namely, size and distribution of the nanoparticles and their local environment), which were a function of the Au content and annealing temperature. Our results suggest that local voids were present in the vicinity of the Au nanoparticles, for all temperature range, and that they should be present in a wide variety of Au-WO3 nanocomposites. A theoretical study concerning the refractive index sensitivity was carried out in order to predict the optimal coating design parameters for gas sensing experiments.
Highlights
There is an increasing interest in the deposition and characterization of nanocomposite materials containing metallic nanoparticles due to their wide range of applications in different fields of science such as in chemical/biological sensors [1], nonlinear optics [2], solar cells [2], catalysis/photocatalysis [3], or in medical/antibacterial materials [4]
The incorporation of Au nanoparticles into WO3 or WO3−x improves the gas detection sensitivity and selectivity [20] and allows gas sensing by localized surface plasmon resonance (LSPR) [24]
Despite the promising idea of using Au-WO3 nanocomposites as LSPR sensors, there are few publications on the subject and much still remains to be done concerning the optimization of the deposition techniques, the coatings’ design and the fundamental understanding of both optical properties and gas sensing mechanisms of these coatings
Summary
There is an increasing interest in the deposition and characterization of nanocomposite materials containing metallic nanoparticles due to their wide range of applications in different fields of science such as in chemical/biological sensors [1], nonlinear optics [2], solar cells [2], catalysis/photocatalysis [3], or in medical/antibacterial materials [4]. Tungsten trioxide (WO3) is a transition metal oxide that exhibits sub-stoichiometric phase transitions and is considered an n-type semiconductor with a wide band gap It has a high refractive index and shows good corrosion resistance in very strong acid solutions, great optical modulation, good durability, photochromic behaviour, and excellent coloration efficiency [9,10]. Based on theoretical simulations of the refractive index sensitivity, we were able to select the best configuration for LSPR gas sensing
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