There are some methodological differences from system to system, but Figure 2666a shows an example on how the zero-loss-peak alignment is performed. If the beam-pass ratio is at least 25% (or the selected percentage), the zero loss peak of the energy loss spectrum is considered to have been aligned; otherwise, the zero-loss-peak adjustment process is needed. In this system, an upper-slit beam current detector and a lower-slit beam current detector are employed to the detection of misalignment in order to determine whether the majority of the spectrum intensity falls on the upper slit half or on the lower slit half.
Figure 2666a. An example on how the zero-loss-peak alignment is performed.
The green-boxed inset shows the configuration of the slit.
The zero-loss peak is normally aligned with the Zero-Loss-Peak-Alignment button (the first icon in Figure 2666b) in the Gatan DigitalMicrograph interface.
Figure 2666b. Zero-Loss-Peak-Alignment button indicated by the first icon.
In Figure 2666c (a), the spectrum is formed in the dispersion plane, consisting of a distribution of electron counts (I) versus energy loss (ΔE). All the electrons suffering the same energy loss but traveling in both on-axis and off-axis directions are directed to a focus in the dispersion plane of the spectrometer, which acts as a homogenous magnetic lens as shown in the equivalent schematics in Figure 2666c (b). The object plane of the spectrometer is typically set at the back focal plane (crossover) of the projector lens.
Figure 2666c. (a) Schematic showing magnetic prism, and (b) Equivalent schematics of the magnetic prism. Electrons at various
kinetic energies (due to energy losses induced by interaction with TEM specimen) are focused at the energy-dispersive plane of the spectrometer.