Hydrogen sensing by plasmon decoupling effect in nanostructured Pd/Au films

Abstract

Plasmon coupling effect occurs in plasmonic nanostructures when interparticle distances are in the order of particle size leading to spectral shifts in the plasmonic band. This effect has been recently highlighted for measurement of fluctuations in the interparticle distance at nanoscale level. In this study, nanostructured thin Au films were deposited on quartz substrates by pulsed laser deposition (PLD) for sensing of hydrogen gas. A blue shift from 730 to 560 nm in LSPR of Au films was observed when substrate temperatures rises from 25 to 600 °C due to variation in morphology of films from a continuous surface composed of tiny agglomerates to granular surface composed of bigger particles with increased interparticle spacing. For plasmon coupling sensing of hydrogen, a thin Pd film was deposited on top of nanostructured Au films. Upon hydrogen exposure, up to12 nm blue shift within few seconds was observed depending on hydrogen concentration. Based on field emission scanning electron microscope (FESEM) images and finite-difference time-domain (FDTD) simulations, this plasmon sensing is explained by hydrogen-induced decoupling due to the formation of surface stresses in Pd, which can affect the LSPR via an increase in interparticle spacing of Au nanoislands. • Nanostructured Au/quartz films were deposited prepared by pulsed laser deposition at different substrate temperatures. • The interparticle distance of Au films increases with temperature, leading to blue shift in the gold plasmonic absorption. • A thin Pd layer as hydrogen catalyst was deposited on Au/quartz samples by DC magnetron sputtering. • Hydrogen interaction led to a further blue shift, which was greater for films with smaller interparticle distance. • Using finite difference time domain (FDTD) simulation, this effect was attributed to a plasmon decoupling effect.