TY - JOUR
T1 - Controlling the Spatial and Momentum Distributions of Plasmonic Carriers
T2 - Volume vs Surface Effects
AU - Pettine, Jacob
AU - Meyer, Sean M.
AU - Medeghini, Fabio
AU - Murphy, Catherine J.
AU - Nesbitt, David J.
N1 - Funding Information:
This work has been supported by the Air Force Office of Scientific Research (FA9550-15-1-0090) with additional funds for laser and apparatus development provided by the National Science Foundation Physics Frontier Center (PHY-1734006). Support for nanoparticle synthesis and characterization in the C.J.M. laboratory has been funded by the National Science Foundation (CHE-1608743). The authors would like to thank Dr. J. G. Hinman for contributions to the synthetic procedures and Prof. H. Petek for discussions regarding this work.
Publisher Copyright:
© 2021 American Chemical Society.
PY - 2021/1/26
Y1 - 2021/1/26
N2 - Spatial and momentum distributions of excited charge carriers in nanoplasmonic systems depend sensitively on optical excitation parameters and nanoscale geometry, which therefore control the efficiency and functionality of plasmon-enhanced catalysts, photovoltaics, and nanocathodes. Growing appreciation over the past decade for the different roles of volume- vs surface-mediated excitation in such systems has underscored the need for explicit separation and quantification of these pathways. Toward these ends, we utilize angle-resolved photoelectron velocity map imaging to distinguish these processes in gold nanorods of different aspect ratios down to the spherical limit. Despite coupling to the longitudinal surface plasmon, we find that resonantly excited nanorods always exhibit transverse (sideways) multiphoton photoemission distributions due to photoexcitation within volume field enhancement regions rather than at the tip hot spots. This behavior is accurately reproduced via ballistic Monte Carlo modeling, establishing that volume-excited electrons primarily escape through the nanorod sides. Furthermore, we demonstrate optical control over the photoelectron angular distributions via a screening-induced transition from volume (transverse/side) to surface (longitudinal/tip) photoemission with red detuning of the excitation laser. Frequency-dependent cross sections are separately quantified for these mechanisms by comparison with theoretical calculations, combining volume and surface velocity-resolved photoemission modeling. Based on these results, we identify nanomaterial-specific contributions to the photoemission cross sections and offer general nanoplasmonic design principles for controlling photoexcitation/emission distributions via geometry- and frequency-dependent tuning of the volume vs surface fields.
AB - Spatial and momentum distributions of excited charge carriers in nanoplasmonic systems depend sensitively on optical excitation parameters and nanoscale geometry, which therefore control the efficiency and functionality of plasmon-enhanced catalysts, photovoltaics, and nanocathodes. Growing appreciation over the past decade for the different roles of volume- vs surface-mediated excitation in such systems has underscored the need for explicit separation and quantification of these pathways. Toward these ends, we utilize angle-resolved photoelectron velocity map imaging to distinguish these processes in gold nanorods of different aspect ratios down to the spherical limit. Despite coupling to the longitudinal surface plasmon, we find that resonantly excited nanorods always exhibit transverse (sideways) multiphoton photoemission distributions due to photoexcitation within volume field enhancement regions rather than at the tip hot spots. This behavior is accurately reproduced via ballistic Monte Carlo modeling, establishing that volume-excited electrons primarily escape through the nanorod sides. Furthermore, we demonstrate optical control over the photoelectron angular distributions via a screening-induced transition from volume (transverse/side) to surface (longitudinal/tip) photoemission with red detuning of the excitation laser. Frequency-dependent cross sections are separately quantified for these mechanisms by comparison with theoretical calculations, combining volume and surface velocity-resolved photoemission modeling. Based on these results, we identify nanomaterial-specific contributions to the photoemission cross sections and offer general nanoplasmonic design principles for controlling photoexcitation/emission distributions via geometry- and frequency-dependent tuning of the volume vs surface fields.
KW - Monte Carlo
KW - angle-resolved photoemission
KW - gold nanorods
KW - multiphoton photoemission
KW - single particle
KW - ultrafast
KW - velocity map imaging
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U2 - 10.1021/acsnano.0c09045
DO - 10.1021/acsnano.0c09045
M3 - Article
C2 - 33427462
AN - SCOPUS:85099932234
VL - 15
SP - 1566
EP - 1578
JO - ACS Nano
JF - ACS Nano
SN - 1936-0851
IS - 1
ER -