Optical Generation of Hot Plasmonic Carriers in Metal Nanocrystals: The Effects of Shape and Field Enhancement

Abstract

We investigate theoretically photogeneration of excited carriers in plasmonic nanocrystals. The theory is based on the solution of the quantum equation of motion for the density matrix. Efficient photogeneration of plasmonic electrons and holes in small nanocrystals becomes possible due to the nonconservation of the electron momentum. The confinement and reflection of electrons in small nanocrystals allowed photon-assisted electron transitions with high excitation energies and therefore lead to a large number of energetic carriers. This process is a surface-scattering effect and efficient only for nanostructures with small sizes. Other important factors for the photogeneration effect are the field enhancement and the inhomogeneity of electromagnetic fields inside a plasmonic nanostructure. The plasmonic field effects strongly depend on the shape of the nanocrystal. For example, a plasmonic nanocube is more efficient for the electron photogeneration than a nanosphere and a nanosphere generates more energetic carriers compared to a plasmonic slab. The results obtained here can be used for designing plasmonic nanostructures for solar and photocatalytic applications.