Fig. 3: Finding the sensor parameters with the highest FoM through particle swarm optimization.

a Schematic of the working principle and the associated figure-of-merit, FoM, of our plasmonic sensor. b Sketches of the four parameters defining the architecture of the Pd nanodisk arrays and their range used for the particle swarm optimization (PSO) algorithm. In this four-dimensional searching space, 10 populations are generated at random and let evolve iteratively through the PSO algorithm to find a sensor with the highest FoM, as defined in (a). c Evolution of the FoM for each of the 10 populations through 15 iterative generations. Clearly, in each generation, each population finds structures with higher FoM. At the end, one of the populations reaches the highest FoM of 0.11. d Extinction spectra of the optimized sensor (d = 124 nm, h = 20 nm, a = 376 nm, t_PMMA = 300 nm) calculated for Pd (light gray) and PdH_0.125 (dark gray) nanodisk arrays. e Calculated FoM of nanodisk arrays with particle diameters d and array pitches a in close proximity to the ones determined for the optimized sensor (star symbol). The FoM exhibits ~10% variance from the optimized sensor, which indicates that a rather constant FoM can be achieved during the fabrication of the sensor.