Size-Dependent Hot Electron Injection at Single-Nanoparticle Level

The hot electron injection (HEI) effect has been widely applied in photocatalytic and photodetection systems; however, its efficiency is often low. Since the plasmonic response of every nanoparticle is the basis for the collective photocurrent results, it is imperative to examine the HEI processes at the single-particle level and to develop a theoretical model. Here, with the use of photoirradiated Kelvin probe force microscopy, the size effect of Au nanoparticles (AuNPs) was experimentally investigated at the single-particle level for the first time. Moreover, a comprehensive plasmonic injection model was developed to directly correlate the AuNP size to HEI efficiency. This theory captures the essential processes of hot electron generation and transport, and its results are consistent with the experimental measurements. Remarkably, the surface potential generated by the HEI is approximately linear to the nanoparticle diameter; the HEI current grows rapidly with increasing AuNP size, showing an increase of 3 orders of magnitude when the AuNP size varies from 10 to 60 nm; and the injection efficiency is inversely proportional to the particle size. This research may clarify plasmonic light harvesting processes for high-efficiency photocatalytic and photodetection systems.