Regensburg 2013 – wissenschaftliches Programm

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MI: Fachverband Mikrosonden

MI 1: Topical Session: Using Transmission Electron Microscopy to Unravel the Mysteries of Materials I - Joint Session with MM

MI 1.1: Topical Talk

Montag, 11. März 2013, 10:15–10:45, H4

The potential of valence electron energy-loss spectroscopy to probe local optical properties and band structure information in scanning transmission electron microscopy — •Rolf Erni — Electron Microscopy Center, Empa, Swiss Federal Laboratories for Materials Science and Technology, CH-8600 Dübendorf, Switzerland

Valence electron energy-loss spectroscopy (VEELS) in scanning transmission electron microscopy (STEM) offers the possibility to measure band structure information and in particular band gap and transition energies of materials with (sub-)nanometer spatial resolution. Although the technique has been used to reliably identify dielectric information of various bulk and nanomaterials, VEEL spectra contain a wealth of spectral contributions which can complicate the extraction of the desired information. Retardation effects, such as Cerenkov losses, or the excitation of guided light modes as well as surface and finite-size effects can alter the bulk dielectric function contained in VEEL spectra. The dielectric theory describing these effects has been known for a long time, but the incorporation of these effects into routine simulations has not yet become standard. For materials of known dielectric function, it is possible to analyze the origin of individual spectral signatures. This allows for predicting possible spurious effects of unknown materials. The present contribution provides an overview of the applicability of VEELS for the study of nanomaterials, interface and surface effects, combining experiments with simulations which are adequate to address spectral signatures that are not describable by the common energy-loss function of bulk materials.