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.

This Review discusses the electronic structure of plasmonic resonances in metal nanostructures, clarifying existing misconceptions on the topic. Here we underscore the key property of the plasmonic response in metal nanocrystals: the plasmon and its wave function are mostly composed of a large number of low-energy excitations, which involve electrons near the Fermi level. Simultaneously, some number of high-energy hot electrons are excited in a nanocrystal due to the scattering of electrons by surfaces and in hot spots. It is an established fact that plasmon excitations are well described by classical frameworks, considering the collective oscillation of low-energy carriers moving as the result of classical acceleration. This classical motion is intrinsically dissipative and leads to heating. On the other hand, the generation of hot electrons in nanocrystals is a quantum surface effect. The energy efficiency of such hot-electron processes is always limited. However, there are interesting possibilities for the hot-electron enhancement, which we discuss here in the context of applications for plasmonic photodetectors, photocatalysis, and ultrafast spectroscopy.

Hydrogen storage in chemical compounds is a promising strategy to enable lightweight, high-density, and safe hydrogen technologies. However, the hydrogen release rate from these chemicals is limited by the intrinsic catalytic activity of metal catalysts, which can be enhanced by light irradiation. Here, nanohybrids including a core of plasmonic TiN and multiple Pt nanocrystal catalytic centers are assembled and show, under resonant conditions at 700 nm, hot electron-driven hydrogen evolution from ammonia borane at an apparent quantum yield of 120%. It is also demonstrated that solar irradiation enhances the activity of TiN–Pt nanohybrids by one order of magnitude through two synergistic mechanisms: hot electrons and collective-heating contributions. Using the microscopic calculation of the photo-induced temperature around a single nanocrystal, it is revealed that the collective plasmonic heating regime dominates the macroscopic temperature distribution in the system. The presented data show that plasmonic hot electrons and photothermal heating can be used in synergy to trigger hydrogen release from ammonia borane on demand, providing a general strategy for greatly enhancing the activity of metal catalysts in the dark.

In plasmonics, and particularly in plasmonic photochemistry, the effect of hotelectron generation is an exciting phenomenon driving new fundamental and applied research.However, obtaining a microscopic description of the hot-electron states represents a challenging problem, limiting our capability to design efficient nanoantennas exploiting these excited carriers. This paper addresses this limitation and studies the spatial distributions of the photophysical dynamic parameters controlling the local surface photochemistry on a plasmonic nanocrystal. We found that the generation of energetic electrons and holes in small plasmonic nanocrystals with complex shapes is strongly position-dependent and anisotropic, whereas the 2 phototemperature across the nanocrystal surface is nearly uniform. Our formalism includes three mechanisms for the generation of excited carriers: the Drude process, the surface-assisted generation of hot-electrons in the sp-band, and the excitation of interband d-holes. Our computations show that the hot-carrier generation originating from these mechanisms reflects the internal structure of hot spots in nanocrystals with complex shapes. The injection of energetic carriers and increased surface phototemperature are driving forces for photocatalytic and photo-growth processes on the surface of plasmonic nanostructures. Therefore, developing a consistent microscopic theory of such processes is necessary for designing efficient nanoantennas for photocatalytic applications.

This Perspective concerns the latest developments in the field of chiral nanocrystals (NCs) and metastructures, focusing primarily on plasmonic nanostructures. Such nanomaterials exhibit unusually strong near-field and electromagnetic responses that enable efficient biosensing and light manipulation. Herein we share our thoughts on the latest trends that mark what we call a paradigm shift for the vast and dynamic field of chiroptical materials. The topics to be considered include polarization-sensitive photocatalysis with chiral plasmonic NCs, chiral bioconjugates, DNA-based assemblies, chiral growth, and we also describe the fundamental challenges for optical induction of chirality, transfer of chirality between different scales, and theoretical issues that nanoscience is facing.