Polarized Optomechanical Response of Silver Nanodisc Mono layers on an Elastic Substrate Induced by Stretching

A monolayer assembly of silver nanodisks (AgNDs) was fabricated on the surface of a polydimethylsiloxane (PDMS) polymer substrate using the Langmuir-Blodgett technique. Upon stretching the PDMS substrate, the localized surface plasmon resonance (LSPR) spectrum of the AgND monolayer is blue-shifted when the incident light excitation is polarized parallel to the stretching direction. Conversely, a red shift in the LSPR spectrum of the AgND monolayer is observed in the case of light polarization orthogonal to the stretching direction. The magnitude of the shift in the LSPR spectrum is proportional to the degree of stretching of the PDMS substrate. Stretching PDMS in one direction causes its shrinking in the orthogonal direction. Consequently, the interparticle distance between individual AgNDs on the PDMS surface increases in the same direction as the mechanical stretching and simultaneously decreases in the orthogonal direction. The different optical responses of the AgND assembly on the surface of stretched PDMS when excited with different polarization directions is due to the changing strength of the plasmon field coupling, which is inversely proportional to the separation gap between the AgNDs. The experimentally measured LSPR spectra upon stretching the PDMS substrate to different lengths and varying the incident light polarization were confirmed using the discrete dipole approximation calculation technique. The same optical response was obtained for an AgND monolayer sandwiched between two PDMS substrates. Covering the surface of the AgND monolayer on the PDMS substrate with another PDMS layer on top eliminates their deformation after multiple stretching shrinking cycles and increases its chemical stability.