Efficiency of Hot-Electron Generation in Plasmonic Nanocrystals with Complex Shapes: Surface-Induced Scattering, Hot Spots, and Interband Transitions

Abstract

The generation of hot electrons is an intrinsic property of all plasmonic nanocrystals under illumination. However, the number of such excited electrons will strongly depend on the shape, material, and excitation wavelength. In this paper, we develop a practical self-consistent formalism to describe the generation of energetic electrons in a plasmonic nanocrystal with an arbitrary shape. We apply our formalism to gold nanospheres, nanorods, and nanostars. Among the investigated shapes, the nanostar geometry demonstrates the best performance, with an internal energy efficiency of ∼25%. This superior capability of hot-electron generation in the nanostars comes from the following factors: strong hot spots in the red spectral region, isotropic optical response, and the absence of interband transitions at the plasmonic resonance. Spherical gold nanocrystals show strong interband absorption at the plasmon resonance, and the related efficiency of the generation of hot holes in the d band can reach a level of 70%. By analyzing the energy performance of nanocrystals under CW illumination, we show that the most relevant parameter to consider is the rate of hot-electron generation, whereas the steady-state numbers of thermalized and nonthermalized electrons play secondary roles. The physical principles formulated in this study can be used to design a variety of plasmonic nanomaterials for applications in photocatalysis and photodetection.