Towards Understanding the Influence of Electron-gas Interactions on Imaging in an Environmental TEM

Prof Jakob B. Wagner
Funding: DTU Cen
The latest generation of environmental transmission electron microscopes (ETEMs) incorporate aberration correction and monochromation, allowing studies of chemical reactions and growth processes with improved spatial and spectral resolution. In order to take full advantage of the improved imaging system by retrieving quantitative information from images acquired in the presence of gas, the propagation of the electron wave in the TEM, including electron scattering by gas molecules has to be understood. The most basic effect on images acquired in the presence of gas is a simple decrease in intensity with increasing gas pressure and scattering

cross-section of the gas molecules. Furthermore, the electrons lose energy when they are scattered by gas molecules leading to a less isochromatic incident electron beam. The figure shows a preliminary measurement of angle-resolved low-loss electron energy loss spectra acquired in the presence of 1100 Pa of Ar in the absence of a specimen.Our on-going work involves the systematic measurements of images, diffraction patterns and energy-loss spectra acquired in the presence of both elemental and molecular gases, for a variety of different beam current densities, accelerating voltages and choices of specimen.

 

Montage of angle-resolved low-loss electron energy-loss spectra acquired from 1100 Pa of Ar in a differentially pumped TEM with no specimen present. The color coding represents the intensity of the signal. 

Jakob Birkedal Wagner
Professor, Scientific director
DTU Cen
+45 45 25 64 71