The Different Observation Modes in Electron Microscopy (SEM, TEM, STEM) - Sample Preparation Topic for Transmission Electron Microscopy - page 54

- Electrons transmitted by elastic scattering are used in TEM or TEM/STEM
to identify the microstructure through the combination of conventional modes:
bright-field, dark-field, weak-beam, microdiffraction, lattice fringe, and high-
resolution imaging modes. They will be used to obtain structural imaging, crys-
tallography, chemical and spectroscopic imaging, and chemical and spectroscopic
data.
- Electrons transmitted by inelastic scattering will be used to identify the chemical
nature of the elements, the nature of chemical bonds, and the atomic environment
(EELS in a TEM, TEM/STEM, or STEM).
Table 3.2 lists the different responses to the electron-matter interaction, the char-
acteristics of these signals, the image information, the equipment used, as well as
the resolution of these images.
For bulk samples , the SEM will make it possible to study morphology with good
resolution (1 nm), as well as to perform semi-quantitative or quantitative elemental
analysis on the scale of a few nanometers. The latest-generation SEMs produce even
better results, as they are equipped with FEG electron sources.
If good resolution power is desired, then it is necessary to limit the excited vol-
ume. To do this, it is necessary to work on thin samples in TEM, TEM/STEM, or
STEM. The goal is to be able to fully characterize the specimen, i.e., to precisely
determine the texture and the local microstructure, as well as to be able to determine
the local chemistry of particles a few nanometers in size.
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