Amplified Generation of Hot Electrons and Quantum
Surface Effects in Nanoparticle Dimers with Plasmonic Hot Spots
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Abstract
Plasmonic
excitations in optically driven nanocrystals are composed
of excited single-particle electron–hole pairs in the Fermi
sea. In large nanostructures, most of the excited plasmonic electrons
have relatively small excitation energies due to the conservation
of linear momentum. However, small optically driven nanocrystals may
have large numbers of hot electrons with large energies. In this study,
we develop the concept of hot electron generation further by considering
the effect of a plasmonic hot spot. Plasmonic hot spots are areas
in a nanostructure with highly inhomogeneous and enhanced electric
fields. In our model of a nanoparticle dimer, the hot spot region
appears near the gap between the nanoparticles. We then apply the
quantum formalism based on the density matrix to describe this system.
We show that the electromagnetic enhancement and the nonconservation
of linear momentum in the hot spot of the nanoparticle dimer lead
to strongly increased rates of generation of energetic (hot) electrons.
The rates of hot electron generation grow faster than the absorption
cross section and the electromagnetic enhancement factor with the
decrease of the gap between the nanoparticles. This happens due to
the breaking of the linear momentum conservation of electrons in the
hot spot regions. We also show that hot electron generation effect
leads to the quantum mechanism of surface-induced absorption in nanocrystals
that is an intrinsic property of any confined plasmonic system. The
results obtained in this study can be useful for understanding and
designing plasmonic photodetectors and hybrid materials for efficient
photocatalysis