Gold-Aluminum Thin Films as an Alternative to Pure Metals for Plasmon Resonance Sensors

Noble metal alloys have been widely investigated as an alternative to pure metals for improving the optical response of optoelectronic devices in the visible range of the electromagnetic spectrum. However, their use is hardly extended to the ultra-violet (UV) range. As an alternative, aluminum (Al)-based alloys could expand the functionality of photonic devices into the UV range. In this work, we fabricate and measure the dielectric constant of binary mixtures of gold (Au) and Al thin films. The films were deposited on a glass substrate via the co-sputtering method. The dielectric functions were measured using spectroscopic ellipsometry. We investigated how the optical response of the samples changed under a wide range of temperatures, from 25°C to 200°C. Also, we performed AFM, SEM, XRD, and EDS measurements. We demonstrate that, in all our cases, a bimetallic material outperforms their pure metal counterparts in the near-IR range after the temperature treatment, e.g., Al0.51Au0.49 shows an increased quality factor of its surface plasmon polariton (QSPP) than pure Au and Al. To verify our calculations, we measured the SPP of pristine and temperature treated samples.