Optical measurement of directional strain by scattering from nano-disk pairs aligned on an elastomer

We propose a strain measurement method utilizing light scattered by a pair of nano-disks onto an elastomer sheet. Such nanoparticle pairs exhibit a scattering spectrum that is dependent on the gap distance and the incident light polarization. We utilized this behavior by forming nano-disk pairs with a diameter of 105 nm and a gap of 20-50 nm on a polydimethylsiloxane (PDMS) sheet so that the gap could be altered with strain. The axial direction of the nano-disk pair could be identified by finding the peak wavelength maximum while rotating the polarization angle. Under tensile strain, the peak wavelength decreased from 674 nm at a strain of 0% to 637 nm at a strain of 9.5%, with a peak-shift sensitivity of -3.4 nm/% strain. Under compression strain, the peak wavelength increased from 681 nm at a strain of 0% to 705 nm at a strain of -3.8%, and the peak-shift sensitivity was -16 nm/% strain for strains of 0 to -1%. These experimentally determined peak scattering wavelength positions and peak-shift directions are consistent with the simulation results. This method offers wireless measurements of in situ strain on a nanometric scale.