Surface plasmon resonance response of Au-Al thin films and their potential for use in gas, water, and biological sensors*

Surface plasmon resonance (SPR)-based sensors take advantage of the SPR response of certain metals to identify minor changes in the index of refraction of the sensing medium, most often to detect the presence/concentration of some other substance. Owing to the small scale of these changes, sensors rely on materials, such as Au, whose SPR response is both well-defined, with a small full width at half maximum (FWHM) and large peak height, and highly sensitive to smalll changes. In this work, we calculate the sensitivity to a change in the index of refraction of the sensing material, FWHM, and peak height of the SPR responses of four different thicknesses of various AuAl alloyed thin films, including pure ones, fabricated through the co-sputtering method. We analyze these three metrics for three different sensing media, air, water, and a biological environment, for both fixed incident wavelength and fixed incident angle. This analysis yielded that Au_0.85Al_0.15 was most comparable to Au, having a higher sensitivity and similar FWHM/peak height for each sensing medium and sensor type. For a fixed incident angle, while all alloys had larger FWHMs, they outperformed the pure materials in terms of sensitivity for all three sensing media.