Controlling Hot Electron Spatial and Momentum Distributions in Nanoplasmonic Systems: Volume versus Surface Effects

TL;DR

This study investigates how nanoplasmonic system geometry and excitation parameters influence hot electron distributions, distinguishing volume and surface contributions to optimize design for applications like catalysis and photovoltaics.

Contribution

It provides direct experimental and theoretical insights into volume versus surface photoemission mechanisms in gold nanorods, enabling better control of hot electron distributions.

Findings

Volume excitation dominates in certain geometries.

Surface excitation becomes significant with red-detuned lasers.

Design principles for nanoplasmonic systems are proposed.

Abstract

Hot carrier spatial and momentum distributions in nanoplasmonic systems depend sensitively on the optical excitation parameters and nanoscale geometry, which therefore determine the efficiency and functionality of plasmon-enhanced catalysts, photovoltaics, and nanocathodes. A growing appreciation over the past decade for the distinction between volume- and surface-mediated photoexcitation and electron emission from such systems has underscored the need for direct mechanistic insight and quantification of these two processes. Toward this end, we use angle-resolved photoelectron velocity mapping to directly distinguish volume and surface contributions to nanoplasmonic hot electron emission from gold nanorods as a function of aspect ratio, down to the spherical limit. Nanorods excited along their longitudinal surface plasmon axis exhibit surprising transverse photoemission distributions due to the dominant volume excitation mechanisms, as reproduced via ballistic Monte Carlo modelling. We further demonstrate a screening-induced transition from volume (transverse) to surface (longitudinal) photoemission with red detuning of the excitation laser and determine the relative cross-sections of the two mechanisms via combined volume and surface multiphoton photoemission modelling. Based on these results, we are able to identify geometry- and material-specific contributions to the photoemission cross-sections and offer general principles for designing nanoplasmonic systems to control hot electron excitation and emission distributions.