Continuous Wave Resonant Photon Stimulated Electron Energy-Gain and Electron Energy-Loss Spectroscopy of Individual Plasmonic Nanoparticles

Abstract

The unique optical properties of surface plasmon resonances in nanostructured materials have attracted considerable attention, broadly impacting both fundamental research and applied technologies ranging from sensing and optoelectronics to quantum computing. Electron energy-loss spectroscopy (EELS) in the transmission electron microscope has revealed valuable information about the full plasmonic spectrum of these materials with nanoscale spatial resolution. Here we report a novel approach for experimentally accessing the photon-stimulated electron energy-gain and stimulated electron energy-loss responses of individual plasmonic nanoparticles via the simultaneous irradiation of a continuous wave laser and continuous current, monochromated electron probe. Stimulated gain and loss probabilities are equivalent and increase linearly in the low-irradiance range of 0.5 × 108 to 4 × 108 W/m2, above which excessive heating reduces the observed probabilities; importantly in our low-irradiance regime, the photon energy must be tuned in resonance with the plasmon energy for the stimulated gain and loss peaks to emerge. Theoretical modeling based on Fermi’s golden rule elucidates how the plasmon resonantly and coherently shuttles energy quanta between the electron probe and the radiation field and vice versa in stimulated electron energy-loss and -gain events. This study opens a fundamentally new approach to explore the quantum physics of excited-state plasmon resonances that does not rely on high-intensity laser pulses or any modification to the EELS detector.

Near field excited state imaging via stimulated electron energy gain spectroscopy of localized surface plasmon resonances in plasmonic nanorod antennas

“…Table 2 summarizes the M x max numbers estimated from the peak fits of the spectra taken at the spontaneous EELS intensity maximum positions for each mode. Note that while higher light-driven plasmon populations are realized in high-irradiance pulsed experiments 57 , the values realized here are consistent with previous low irradiance cw experiments 59 .…”

“…Several approaches have been developed to model photon stimulated EEL and EEG phenomena 48 – 51 , 57 , 59 . As has been demonstrated previously 59 , sEELS and sEEGS is approximately proportional to the product of the optical extinction cross section (σ) and the spontaneous EELS intensity (Γ EELS ). Thus it is instructive to compare the resultant EEL and extinction spectra for the geometries studied.…”

“…Pulsed and continuous wave (cw) photothermal heating and excitation can both be achieved. In particular, we have studied the recrystallization, grain growth, phase separation, and dewetting of an Ag 0.5 Ni 0.5 film 58 , and resonant cw sEEG and sEEL in nanostructures resulting from a dewet silver film 59 .…”

Attosecond metrology in a continuous-beam transmission electron microscope

“…Space-time imaging or spectroscopy with photon-induced near-field electron microscopy ( 6 ), time-resolved holography ( 8 ), electron-electron diffraction ( 16 , 17 ), waveform electron microscopy ( 9 ), quantum state reconstruction ( 23 ), or laser-assisted electron spectroscopy ( 30 ) may therefore be advanced to attosecond time resolution to study, for example, metamaterials, photonic integrated circuitry, solar energy convertors, or photocatalytic materials on the basis of the underlying electrodynamics in space and time. Continuous-wave laser illumination of complex materials is feasible at intensities of 10 4 to 10 6 W/cm 2 ( 31 , 32 ) and with field strengths of ~10 6 V/m, enough to produce substantial holographic image distortions ( 9 ) or spectral changes in photon-induced near-field electron microscopy ( 6 , 31 ). Nanosecond excitation can be used for alleviating thermal load ( 33 ).…”

In Situ Laser Synthesis of 2D WSe2 Within TEM

“…Here we report how a prototype setup allows laser illumination to be coupled into transmission electron microscopes (TEM) for real-time observations of two-dimensional (2D) materials synthesis and processing. The configuration and ability of in situ photon delivery system was reported previously [1][2] . Amorphous atoms and molecules were deposited at room temperature on TEM grids by pulsed laser deposition.…”