Detection of H2 using plasmonic amplification of surface photoacoustic (SPA) waves generated in Pd nanoparticle-deposited GaN piezotransistive microcantilevers has been investigated using a pulsed 520 nm laser. Using 1.5 nm thickness of the Pd functionalization layer, H2 detection down to 1.5 ppm was demonstrated with a high signal-to-noise ratio, underscoring the feasibility of sub-ppm level detection using this novel sensing method. Adsorption of H2 in Pd nanoparticles (NPs) changes their plasmonic absorption spectra because of Pd lattice expansion, in addition to changing their work function. The high sensitivity exhibited by the SPA-based H2 detection method is attributed to a combination of changes in the plasmonic spectrum and work function of Pd NPs and was observed to be a strong function of Pd thickness, biasing conditions, and probe laser power. A comparison of the SPA-based detection technique with traditional chemidiode and chemiresistor sensors, integrated in the functionalized piezotransistor, indicated a superior detection performance of the former.
Keywords: GaN microcantilevers; Pd nanoparticles; hydrogen sensing; photoacoustics; piezotransistive.