Hot electron chemistry is of paramount significance because of its applicability to photocatalytic reactions, solar energy conversion, and waste decomposition. The nonradiative decay of excited plasmons in gold nanoparticles (AuNPs) generates highly energetic nonthermal electrons and holes that can induce chemical reactions when transferred to nearby molecules. In this study, we explore the relationship between AuNP size (26−133 nm) and the plasmoninduced reaction yield. To isolate the size from other structural parameters, we prepare perfectly round gold nanospheres (AuNSs) with narrow size distributions. The use of a nanoparticle-on-mirror configuration, in which the reactant molecules (4-mercaptobenzoic acid) are positioned in nanogaps between the AuNSs and a Au film, promotes the generation of hot carriers and allows the highly sensitive detection of the reaction products (benzenethiol) using surface-enhanced Raman spectroscopy. We show that the reaction yield increases as the AuNS size increases up to 94 nm and then decreases for larger AuNSs. This peculiar Λ-shaped size-dependent reactivity can be explained by considering both the plasmonic absorption efficiency of AuNSs and the decay rate of plasmons via electron-surface scattering. The product of the calculated absorption cross section and the inverse of the AuNS size reproduces our experimental results remarkably well. These findings will contribute to the design of highly efficient plasmonic photocatalysts and photovoltaic devices.

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.

The plasmonic properties of gold nanoparticles (AuNPs), such as color tunability, electric field generation, hot carrier generation, and localized heating, are significantly enhanced in the nanogaps between AuNPs. Therefore, the...

Gold nanoparticles (AuNPs) are widely used as biological imaging agents, colorimetric sensors, surface‐enhanced Raman spectroscopy (SERS) substrates, photothermal anti‐cancer agents, visible wavelength photocatalysts, and photovoltaic materials. These applications are based on the plasmonic properties of AuNPs. Therefore, a fundamental understanding of the origin of the plasmonic behavior of AuNPs allows us to control the properties of AuNPs and widen their applications. In this review, we discuss the origin of the color, SERS, and hot‐carrier generation of AuNPs. We start with the free‐electron Drude model and the dielectric constant of AuNPs, which defines the material properties. We then explain the mechanism that determines the colors of bulk and nanosized gold, enhancement of the electric fields outside the AuNPs, and generation of hot carriers during the decay of plasmons.

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.