Scanning Transmission Electron Microscopy in a Scanning Electron Microscope: Electron-Beam Broadening, Contamination, and Investigation of ZIF-8 by Correlative Electron Microscopy

Scanning transmission electron microscopy (STEM) at low electron energies in scanning electron microscopes has several advantages: The lower energies (typically ≤ 30 keV) in scanning electron microscopy (SEM) compared to the commonly used energies of 80 keV - 300 keV in STEM imaging yield enhanced contrast for light materials and reduced knock-on damage. The many detectors in a scanning electron microscope enable correlative imaging of surface and bulk properties of the same specimen regions. Scanning electron microscopes are also more readily available in research laboratories due to the lower price compared to classical STEM instruments. Hence, STEM in scanning electron microscopes, abbreviated as STEM-in-SEM, is a viable alternative to high-energy STEM in dedicated STEM instruments for analyses down to the nanometer scale. However, some characteristics of STEM-in-SEM, like contamination and electron-beam broadening in specimens, are more severe at lower electron energies. Both of these issues are quantitatively analyzed in this work.
Another part of this thesis is concerned with studying the surface-mounted metal-organic framework (SURMOF) ZIF-8 by STEM and transmission electron microscopy (TEM) at electron energies of 200 keV and 300 keV. ... mehrThe applied techniques include STEM tomography, nanobeam electron diffraction, and energy-dispersive X-ray spectroscopy (EDXS). Because ZIF-8 is highly susceptible to be damaged by electron irradiation, low-dose imaging conditions need to be used to preserve its crystalline structure. In addition, ZIF-8 is usually prepared on bulk substrates, from which it needs to be detached for TEM imaging by a potentially damaging procedure. To turn this preparation step obsolete, ZIF-8 was deposited directly on TEM grids covered by amorphous carbon films in a layer-by-layer synthesis approach. Future studies on SURMOF growth can profit from the TEM-sample preparation technique and correlative microscopy described in this thesis.