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Thick specimens in the CEM and STEM. Resolution and image formation.
Ultramicroscopy
|July 1, 1975
Summary
A new theory explains image formation in thick specimens for electron microscopes. Scanning transmission electron microscopes (STEM) offer superior resolution for thick samples compared to conventional electron microscopes (CEM).
Area of Science:
- Materials Science
- Electron Microscopy
- Physics
Background:
- Resolution in transmission electron microscopy (TEM) is often limited by plural scattering in thick amorphous specimens.
- Understanding image formation in thick samples is crucial for accurate material characterization.
Purpose of the Study:
- To develop a theoretical framework for resolution and image formation in thick amorphous specimens.
- To compare the performance of scanning transmission electron microscope (STEM) and conventional electron microscope (CEM) for thick samples.
Main Methods:
- Developed an analytic theory for plural incoherent scattering applicable to various materials and beam voltages.
- Considered eight operating modes: four for STEM and four for CEM.
- Applied modulation transfer function (MTF) for image quality assessment.
Main Results:
- The developed theory accurately describes electron scattering and is applicable to both thin and thick specimens.
- STEM demonstrates significant advantages over CEM for imaging thick specimens.
- A 90 keV STEM provides image quality comparable to a 1 MeV CEM for a 1-micron carbon film.
Conclusions:
- STEM offers superior resolution for thick amorphous specimens compared to CEM.
- Energy filtering in CEM can improve resolution but reduces signal intensity and usable thickness.