Which Nanoparticle Shape is the Most Effective in Generating Hot Charge Carriers from Plasmon Excitation?

Abstract

Hot charge carrier generation is one of the most important properties of plasmonic nanoparticles with a wide range of applications, including solar water splitting, photovoltaics, and photocatalysis. Thus, understanding the relationship between the physical parameters of plasmonic nanoparticles and hot carrier generation efficiency is essential for technological advancements. In this study, we investigate how the shape of gold nanoparticles influences the efficiency of generating hot charge carriers from plasmon decay. We synthesize Au nanospheres (AuNSs), Au nanocubes (AuNCs), Au nanorods (AuNRs), and Au nanotriangular prisms (AuNTs) with the same capping ligand and similar size. These nanoparticles are then adsorbed onto selfassembled monolayers of 4-mercaptobenzoic acid (MBA) on gold films to form nanoparticle-on-mirror (NPoM) systems. By irradiating the NPoM at 785 or 633 nm, plasmons are created, and their subsequent decay leads to the production of hot carriers that are used to transform MBA into benzenethiol (BT). We find that AuNRs in NPoM exhibit the highest production of BT, followed by AuNSs ≈ AuNCs > AuNTs when excited at 785 nm. Dividing the reaction yields by the absorption cross section at the specific wavelength determines the hot carrier generation efficiency. For an accurate evaluation of the absorption cross sections, we obtain the calculated scattering spectra that closely match the experimentally measured dark-field single-particle scattering spectra. Using the same calculation parameters, we then determine the absorption cross sections of each NPoM. Based on this approach, we quantify the hot carrier generation efficiency for each NPoM and find that AuNRs are the most effective in generating hot carriers from plasmon excitation compared to any other shapes. These findings provide valuable insights into the design of highly efficient plasmonic photocatalysts.

Hot Electrons in Catalysis

“…The efficiency of hot-electron generation in metallic nanostructures is expected to depend on parameters that govern optical absorption and electron transport, such as the shape, composition, size, and morphology of the nanostructure. This dependence is explored by Kim et al The authors extract hot-carrier-generation efficiencies from rates of plasmon-induced conversion of 4-mercaptobenzoic acid to benzenethiol. They compare these efficiencies for different nanoparticle (NP) shapes, finding that Au nanorods outperform other shapes such as nanospheres, nanocubes, and nanotriangular prisms.…”