Effect of Material and Shape of Nanoparticles on Hot Carrier Generation

Nonradiative decay of photoexcited plasmons generates energetic nonthermal charge carriers. These hot charge carriers play a major role in plasmonic photocatalysis and photovoltaics. Therefore, establishing the relationship between the hot carrier generation efficiency and the structural and chemical parameters of nanoparticles is crucial for developing highly efficient plasmonic catalysts and photovoltaic materials. In this study, we compare the quantum efficiency of hot carrier generation between gold (AuNPs) and silver nanoparticles (AgNPs), and spherical (AuNSs) and cubic gold nanoparticles (AuNCs). We construct nanoparticle-on-mirror (NPoM) systems where reactant molecules are positioned in the nanogaps between the nanoparticles and gold films. Excitation of the NPoM at 785 nm, followed by the detection of products using surface-enhanced Raman spectroscopy allows us to measure the plasmon-driven reaction yields. Dividing the reaction yield by the calculated absorption cross section at the excitation laser wavelength provides the efficiency of hot carrier generation per absorbed photon. We reveal that AgNPs are more effective at generating hot carriers than AuNPs, which is consistent with the higher electron-surface scattering rate of AgNPs. The hot carrier generation of AuNCs is marginally better than that of AuNSs, which can be attributed to the enhanced electric fields inside the AuNCs in the nanogap region. This study contributes to a rational design of plasmonic catalysts or photovoltaic materials of higher efficiencies.