Elucidation of how metal layer deposition conditions impact the optical responses of microgel-based etalon devices to stimuli

Abstract

Poly(N-isopropylacrylamide) (pNIPAm) microgel-based etalons exhibit visual color, and can be fabricated by sandwiching a monolithic microgel layer between two thin metal layers (typically Au). The color of the devices is a direct result of the device structure, and can be dynamically tuned by varying the thickness of the microgel layer in response to external stimuli. For many applications, the robustness of the etalon's structure, the spatial uniformity of the color, and the color change kinetics are of utmost importance. In this investigation, we determined how the composition of the layers that make up the etalon impacts their performance. Specifically, the results indicated that stable etalons can be constructed by simply depositing a layer of Au on top of the microgel layer, as opposed to using a Cr adhesion layer on top of the microgels prior to Au overlayer deposition. We show that thin Au overlayers without a Cr adhesion layer produces Au films that are discontinuous in nature, which in turn directly influences the kinetics of the etalon response. We also confirm that this response pattern holds true for etalon responses to various salt solutions, presenting potential for the future application to alternative analytes of interest.