Transport of hot carriers in plasmonic nanostructures

Abstract

Plasmonic hot carrier devices extract excited carriers from metal nanostructures before equilibration, and have the potential to surpass semiconductor light absorbers. However their efficiencies have so far remained well below theoretical limits, which necessitates quantitative prediction of carrier transport and energy loss in plasmonic structures to identify and overcome bottlenecks in carrier harvesting. Here, we present a theoretical and computational framework, Non-Equilibrium Scattering in Space and Energy (NESSE), to predict the spatial evolution of carrier energy distributions that combines the best features of phase-space (Boltzmann) and particle-based (Monte Carlo) methods. Within the NESSE framework, we bridge first-principles electronic structure predictions of plasmon decay and carrier collision integrals at the atomic scale, with electromagnetic field simulations at the nano-to mesoscale. Finally, we apply NESSE to predict spatially-resolved energy distributions of photo-excited carriers that impact the surface of experimentally realizable plasmonic nanostructures at length scales ranging from tens to several hundreds of nanometers, enabling first-principles design of hot carrier devices.Surface plasmon resonances shrink optics to the nano scale, facilitating strong focusing and localized absorption of light [1][2][3][4][5]. Decay of plasmons generates energetic electrons and holes in the material that can be exploited for applications including photodetection, imaging and spectroscopy [6-12], photonic energy conversion, and photocatalysis [13][14][15][16][17][18]. However, these applications require carriers that retain a significant fraction of their energy absorbed from the plasmon, which is typically two orders of magnitude larger than the thermal energy scale. Experimentally, the energy distributions of hot carriers that critically impact their efficiency of collection cannot be measured directly, but must instead be inferred indirectly from optical response in pump-probe measurements, [19][20][21] from photo-current measurements, [22,23] or from redox-reaction chemical markers.[24] This critically necessitates theoretical prediction of charge transport in metal nanostructures far from equilibrium, which presents a major challenge for current computational methods [25][26][27][28].In extremely small nano-scale systems, electron dynamics require a full quantum mechanical treatment, and several classes of techniques have been developed for quantum transport simulations. In diagrammatic many-body perturbation theory, quantum transport can be described using the non-equilibrium Greens function (NEGF) formalism [29], which has been applied extensively to electron transport in molecular junctions [30]. atoms in rarefied gases [31], nanoscale metal interconnects [32], and small plasmonic nanoparticles [33]. Open quantum system approaches applied to photons have simi- * prineha@seas.harvard.edu † sundar@rpi.edu larly enabled efficient prediction of retardation and radiative effects on plasmon resonance...

Probing nanoscale spatial distribution of plasmonically excited hot carriers

“…18 ). It indicates that the hot holes with higher energy could only be collected within a shorter distance, agreeing with the reported simulation result due to the shorter mean free path of hotter carriers 9 , 11 . At −0.6 V, the energy barrier is only about 0.1 eV lower than the excitation laser energy (1.96 eV).…”

“…After generation in the nanoscale localized and strongly enhanced plasmonic electric field, the hot carriers can only travel a few tens of nanometers before they lose their energy by thermalization via the electron–electron scattering and electron–phonon scattering, which has been revealed by the theoretical calculation 9 , 10 . The consequent spatial distribution of the hot carriers may determine the active area on the surface, which is crucial to efficiently capture the hot carriers for achieving highly efficient SP-based catalysts or optoelectronic devices 5 , 9 , 11 . Recently, the spatial distribution of hot carriers has been visualized via ex situ scanning electron microscope or florescence imaging of the reaction or stained products of the hot carriers-induced reaction 11 – 14 .…”

Mapping Photoemission and Hot-Electron Emission from Plasmonic Nanoantennas

“…33,42,43 Jermyn et al for example, have recently reported the results of models for the energetic and spatial distributions of hot electrons in Au nanorods that are in excellent agreement with HSQ exposures observed in this work. 43 In this work, we coarsely estimate the energy of hot electrons generated in the nanoantennas by calculating resistive losses and assuming that on the timescale of the laser pulse all power dissipated by resistive loss is carried 6 by conduction electrons in Au. Based on these assumptions and approximations, we hypothesize that hot electrons 1.5 eV above the Fermi level of Au may have sufficient energy to initiate the dissociation of water, which subsequently drives hydrolysis and crosslinking of HSQ.…”

“…The recent report by Jermyn et al shows that the distribution of hot carriers is expected to peak at the center of nanorod antennas. 43 These hot electrons may carry sufficient energy to dissociate species on the Au surface via mechanisms such as dissociative electron attachment. 59,60 Dissociation of water due to hot electrons could play an important role in the crosslinking of HSQ, as water dissociation products would support the hydrolysis of silane groups in HSQ.…”

Silver-Copper Oxide Heteronanostructures for the Plasmonic-Enhanced Photocatalytic Oxidation of N-Hexane in the Visible-NIR Range

“…The reduced dimensions of the heteronanostructures minimize the probability of undergoing another relaxation/recombination process [68]. While the injection of hot electrons (using n-type semiconductors such as TiO 2 ) is the most accepted plasmon-driven charge transfer mechanism, there exist recent interesting studies claiming the importance of hot holes in other plasmonic-based systems [73,86,92,97,134,135,136,137] such as Au-NiO x , Au-pGaN [73], Au nanorods coated with a CoO nanoshell [138], Au nanostructures [101,139,140], or Ag-BiOCl hybrids [86,137].…”