Spectral field mapping in plasmonic nanostructures with nanometer resolution

Abstract

Plasmonic nanostructures and -devices are rapidly transforming light manipulation technology by allowing to modify and enhance optical fields on sub-wavelength scales. Advances in this field rely heavily on the development of new characterization methods for the fundamental nanoscale interactions. However, the direct and quantitative mapping of transient electric and magnetic fields characterizing the plasmonic coupling has been proven elusive to date. Here we demonstrate how to directly measure the inelastic momentum transfer of surface plasmon modes via the energy-loss filtered deflection of a focused electron beam in a transmission electron microscope. By scanning the beam over the sample we obtain a spatially and spectrally resolved deflection map and we further show how this deflection is related quantitatively to the spectral component of the induced electric and magnetic fields pertaining to the mode. In some regards this technique is an extension to the established differential phase contrast into the dynamic regime.

Spatial Resolution of Coherent Cathodoluminescence Super-Resolution Microscopy

“…13 We note that also electron energy loss spectroscopy (EELS) has been used to reveal nanoscale optical features in plasmonic nanostructures, also aided by the very small electron beam spot size in the transmission electron microscopes on which EELS microscopy is carried out. 20−26 The exact spatial resolution that can be experimentally achieved with CL and how close plasmon field profiles, and optical mode profiles in general that are derived from the measurements, approach theoretical profiles has remained unresolved.…”

Recent Advances in Transmission Electron Microscopy for Materials Science at the EMAT Lab of the University of Antwerp

“…Pulsed electron sources have allowed to observe the dynamical behaviour of reproducible phenomena with femtosecond resolution [ 121 ]. Even more recently, by analysing the angular distribution of inelastically scattered electrons, effectively joining EELS and momentum-resolved STEM, Krehl et al have measured the thus-far elusive transverse field produced by localized surface plasmon resonances [ 122 ].…”

Probing the Radiative Electromagnetic Local Density of States in Nanostructures with a Scanning Tunneling Microscope

“…12,13 The lateral component may be determined from the lateral deflection of the inelastically scattered electrons. 14 In a related technique, cathodoluminescence, where again a high-energy electron beam is used for excitation, the resulting emitted light is detected and it is the projected R-EM-LDOS that is probed, [15][16][17][18] though dark modes may also be detected through a combination of methods. 19 Other techniques for mapping the EM-LDOS are based on the use of fluorescent probes, [20][21][22][23][24][25][26][27] two-photon luminescence 28,29 and/or scanning near-field optical microscopy.…”