Nanoscale Visualization of a Photoinduced Plasmonic Near-Field in a Single Nanowire by Free Electrons

Abstract

Swift electrons can undergo inelastic interactions not only with electrons but also with near-fields, which may result in an energy loss or gain. Developments in photon-induced near-field electron microscopy (PINEM) enable direct imaging of the plasmon near-field distribution with nanometer resolution. Here, we report an analysis of the surface plasmonic nearfield structure based on PINEM observations of silver nanowires. Single-photon order-selected electron images revealed the wavelike and banded structure of electric equipotential regions for a confined near-field integral associated with typical absorption of photon quanta (nℏω). Multimodal plasmon oscillations and second-harmonic generation were simultaneously observed, and the polarization dependence of plasmon wavelength and symmetry properties were analyzed. Based on advanced imaging techniques, our work has implications for future studies of the localized-field structures at interfaces and visualization of novel phenomena in nanostructures, nanosensors, and plasmonic devices.

Efficiently accelerated free electrons by metallic laser accelerator

“…In experimental measurements of two-colour excitation, two laser beams with frequencies and could produce visible asymmetric structural features in the EELS spectra 45 . Furthermore, the secondharmonic (SH) eld would cause asymmetric features in the EELS spectrum of the PINEM experiment, as predicted theoretically by Konečná et al 46 The spatial distribution of the SH elds in silver nanowires after fs-pulsed laser excitation have been observed directly in real space by PINEM 47 . The occurrence of high-harmonic generation in this bowtie structure was demonstrated in previous works 41,42,48 .…”

Nanoscale-Femtosecond Imaging of Evanescent Surface Plasmons on Silver Film by Photon-Induced Near-Field Electron Microscopy

“…In the work of Vanacore et al, the PINEM signal is produced by the coupling between the electron pulse and the semi-infinite light field formed by light wave reflection at the silver film surface, while the PINEM signal is mainly from the coupling between the electron pulse and the surface plasmon field in our work. PINEM of nanostructures including silver nanowires and nanorods and carbon nanotubes has been widely used to identify the temporal and spatial overlaps between pump laser pulse and probe electron pulse in the 4D UEM. ,, However, the surface plasmons of them are strongly polarization dependent, and the polarization of the laser pulse should be perpendicular to the longitudinal axis of the nanostructures to maximize the near-field excitation, making the use of this method limited and tedious. In contrast, there is no polarization dependence of the PINEM signal for the silver film, namely, the polarization of the incident fs laser can be arbitrary, making the silver film a better platform for identifying the time zero of 4D UEM.…”

Accelerating Quantum Materials Development with Advances in Transmission Electron Microscopy

“…315 In Figure 7d, the polarization-dependent plasmonic response of an Ag nanowire can be resolved via ultrafast EM with fs temporal resolution on the nm length scale. 319,320…”

“…Nanowire diameter 110 nm; scale bar 100 nm. Adapted from ref . Copyright 2021 American Chemical Society publishing group.…”