Plasmon excitation by fast electron probes
Scanning transmission electron microscopy (STEM) uses fast electron beams as probes for imaging and spectroscopic investigation of solid state matter. Fast electrons passing through or nearby a sample can loose small fractions of their energy which can be measured by electron energy loss spectrometry (EELS). The probability of losing energy corresponding to a certain excitation frequency is a characteristic fingerprint which identifies a variety of excitations in solids. Moreover, the localized nature of the electron beams allows to obtain spatially resolved spectral information which altogether makes STEM-EELS a unique tool for spectroscopic imaging that helps to understand the nature of complex excitations of matter at the nanoscale.
The particular interest of our group lies in the so called low-loss energy region corresponding to the visible and infrared range of the electromagnetic spectrum. At low energies it is possible to excite plasmonic and phononic excitations that are particularly relevant in nanophotonics and plasmonics. To that end we have worked especially on the development of analytical and numerical methods that allow for theoretical interpretation of low-loss EELS. We have studied EELS spectral response of plasmonic systems in different geometries and materials as well as electron beam-induced manipulation of plasmonic nanoparticles. Our current research in EELS is focused on the description of phononic excitations in state of the art photonic systems such as Van der Waals crystals.