Simulation of Electron Energy Loss Spectroscopy

The imaging and observation of plasmons at nanoscopic structures is a demanding task, but the change from photons to electrons as an alternative and much more confined probing source opens up new perspectives for experimental measurements. This project focuses on the theoretical description of such experiments with high energetic electrons. The required mathematical formalism will be expanded in two directions: First, a concept of retarded and complex eigenmodes for big nanoparticles is explored, which will allow an intuitive interpretation of the involved physical processes. The 3D reconstruction of electron energy loss data in terms of plasmon tomography will serve as an excellent tool for the comparison of the theoretical findings with experiments carried out by our collaboration partners. Later on, we will focus on tiny nanostructures and small gap distances, where the onset of nonlocal effects can cause big deviations with respect to conventional local calculations. Therefore, a suitable nonlocal model (based on a spatial dependent dielectric function obtained from first principles) will be developed and integrated into our simulation framework. This nonlocal extension will allow systematic predictions for experiments at the edge of currently possible resolutions.

The study of optical phenomena related to the electromagnetic response of metals has led to the development of a thriving and highly interdisciplinary research field called plasmonics. This field is named after the electron oscillations, which propagate along the interface of a metal and a dielectric similarly to the ripples that spread across the surface of a pond after you throw a stone in the water. Plasmonics provides an ideal platform for confining light at the nanoscale and holds a tremendous potential for practical applications. Light-matter interactions have always been a treasure trove for new technical achievements and the promises of plasmonics range from efficient light-harvesting and sensing devices to invisibility with metamaterials, new forms of cancer therapy, novel generations of superfast optical computer chips and data storage. Plasmonics may also form components of a future clean and sustainable society with a transformative impact on the way we drive, manipulate, enhance, and monitor chemical processes. Many of these mechanisms and applications require an improved understanding of the interactions at the nanoscale and the properties of the involved materials. However, the imaging and observation of plasmons at nanoscopic structures is a demanding task, but the change from photons to electrons as an alternative and much more confined probing source opens up new perspectives for experimental measurements. This project focuses on the theoretical description of such experiments with high energetic electrons. The scientific output of this project comprehends many different topics. In total 12 papers in peer-review journals have been published, including one in the prestigious Nature journal as well as one publication in Nature Communications. In 2016 also a book with the title Optical Properties of Metallic Nanoparticles: Basic Principles and Simulation has been published by Springer. It is a general introduction to the research field of plasmonics with a focus on numerical simulations. The main findings of this project include a better understanding of interactions at the nanoscale, the improvement of new imaging techniques based on computer tomography as well as new simulation techniques and new theoretical concepts for the description of plasmonic interactions. Some of these topics have also been adapted for pupils in the science communication project QUANT (http://quant.uni-graz.at/) funded by the FWF. The web platform of QUANT is also available for the public now (only in German).