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Tunable Plasmonic Thermal Emitter Using Metal-Coated Elastomeric Structures

This project was focused on the creation of a gold-coated grating structure capable of inducing a surface plasmon polariton within the mid-infrared region, enhancing emissions at specific wavelengths based on the grating periodicity. The grating structure was formed on a silicone elastomer, polydimethylsiloxane (PDMS), in order to give the structure, the ability to have the periodicity dimensions of the grating altered by applying a stress, thereby changing the location of the emission enhancement, giving the device the potential to be used as an infrared strain sensor. Creation of the structure employed a top-down, micro-scale fabrication technique referred to as Direct Laser Writing (DLW). Using a light-sensitive, negative-tone photoresist material, a grating was patterned onto a glass substrate via photopolymerization, in which areas exposed to an ultraviolet (UV) laser were rendered insoluble by forming cross-links on the portions of the resist which interacted with the UV source. This grating was then placed under a custom-designed mold which was then filled with liquid PDMS and cured for 3 hours at 60°C to cure (harden or cross-link) and leaving an inverse elastomer pattern behind once the cured PDMS was peeled off the substrate. Upon coating the structure with a ~80 nm thick layer of gold, a Fourier Transform infrared (FTIR) spectrometer was used to measure the thermal emissions spectrum of the sample grating at a high temperature (~200°C) and under different strains. These spectra were then analyzed to look for selective emission enhancements caused by the grating structure due to the inducing of a surface plasmon polariton (SPP), as well as changes in the location and nature of these enhancements based on applied strains. Final results showed two sets of enhancement behaviors with the application of uniaxial strain: a shifting of the region of peak emission enhancement to higher wavelengths, and a broadening of the region of enhancement. However, more testing is needed in order to determine the precise causes of the behavior and to quantify it in such a way that it could be turned into a functioning sensor device.
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