Plasmonic Strain Sensors Based on Au-TiO2 Thin Films on Flexible Substrates

This study aimed at introducing thin films exhibiting the localized surface plasmon resonance (LSPR) phenomenon with a reversible optical response to repeated uniaxial strain. The sensing platform was prepared by growing gold (Au) nanoparticles throughout a titanium dioxide dielectric matrix. The thin films were deposited on transparent polymeric substrates, using reactive magnetron sputtering, followed by a low temperature thermal treatment to grow the nanoparticles. The microstructural characterization of the thin films' surface revealed Au nanoparticle with an average size of 15.9 nm, an aspect ratio of 1.29 and an average nearest neighbor nanoparticle at 16.3 nm distance. The plasmonic response of the flexible nanoplasmonic transducers was characterized with custom-made mechanical testing equipment using simultaneous optical transmittance measurements. The higher sensitivity that was obtained at a maximum strain of 6.7%, reached the values of 420 nm/epsilon and 110 pp/epsilon when measured at the wavelength or transmittance coordinates of the transmittance-LSPR band minimum, respectively. The higher transmittance gauge factor of 4.5 was obtained for a strain of 10.1%. Optical modelling, using discrete dipole approximation, seems to correlate the optical response of the strained thin film sensor to a reduction in the refractive index of the matrix surrounding the gold nanoparticles when uniaxial strain is applied.

Automated summary

This study introduces a thin film with reversible optical response that exhibits localized surface plasmon resonance (LSPR) phenomenon under repeated uniaxial strain. Gold nanoparticles were grown throughout a titanium dioxide dielectric matrix to prepare the sensing platform. The flexible nanoplasmonic transducers showed a higher sensitivity and transmittance gauge factor at maximum strain, indicating a reduction in the refractive index of the matrix surrounding the gold nanoparticles. Optical modeling using discrete dipole approximation suggests a correlation between the optical response of the strained thin film sensor and the reduction in refractive index.