Hot carriers generated by plasmons: where are they generated and where do they go from there?

Abstract

A physically transparent unified theory of optically and plasmon-induced hot carrier generation in metals is developed with all the relevant mechanisms included. Analytical expressions that estimate the carrier generation rates, their locations, energy and direction of motion are obtained. Among four mechanisms considered: interband absorption, phonon and defect assisted absorption, electron-electron scattering assisted absorption, and surface -collision assisted absorption (Landau damping), it is the last one that generates hot carriers which are most useful for practical applications in photo detection and photo catalysis.

TiN@TiO2Core–Shell Nanoparticles as Plasmon‐Enhanced Photosensitizers: The Role of Hot Electron Injection

“…For a better understanding of the hot electron generation and injection process in TiN@TiO 2 NPs, and the key factors limiting injection efficiency, we also developed an analytical model for hot electron injection based on a recently developed theory. [ 5 ] The analytical expressions used here support the mechanisms of hot carrier generation and injection in metal–semiconductor heterostructures, and also reveal some advantages that TiN may have in the field of hot‐electron‐mediated photocatalysis.…”

“…The coupling of light into LSPs is usually characterized by absorption efficiency expressed by where d is the depth of the absorbing layer and α is the absorption coefficient. For NPs with an effective plasmon volume of V and a volume concentration of N , α at resonance is roughly [ 5 ] where γ nr and γ rad are the nonradiative and radiative decay rate of LSPs, respectively. Equations () and () indicate that the absorption efficiency of an ensemble of NPs is primarily determined by the filling factor ( NV ) rather than the material itself.…”

“…The nonradiative rate γ nr includes three components: i) Landau damping γ LD , ii) phonon (and defect)‐assisted decay γ ph , and iii) electron–electron scattering γ ee . [ 5 ] The Landau damping rate can be evaluated as [ 5 ] where ν F is the Fermi velocity, E ⟂ ( r ) is the normal component of the electric field E ( r ) at the TiN–TiO 2 interface, and the denominator is the integral of the field over the TiN core. Landau damping is also called surface‐assisted or Kreibig damping, in which reflection at the interface relaxes the momentum conservation rules and allows intraband absorption, generating hot carriers on the surface of TiN.…”

“…[ 1–3 ] More recently, the electrodynamics of plasmon decay process has received increasing attention. [ 4,5 ] Specifically, the nonradiative decay of surface plasmons gives rise to energetic “hot” carriers with much higher energies than electrons or holes at equilibrium states. These hot carriers have been leveraged in enhanced photochemical processes, [ 6 ] with several reports demonstrating their direct involvement in driving chemical reactions, [ 7–9 ] although some of the claims in refs.…”

Fundamental limits of hot carrier injection from metal in nanoplasmonics

“…The work is structured in the following way. Section 2, understandably, if ambitiously, entitled "Genesis", is essentially a very short review of my prior work [43] that has established how the hot carriers are generated by different mechanisms and what is their distribution in energy, space and angular coordinates. But also in this section an often overlooked feature in plasmonics is uncovered -the fact that under most practical conditions only a single SPP is excited on a given nanoparticle.…”