In EMs, the resolution limit due to chromatic aberration can be estimated by,
Cc -- Chromatic aberration coefficients
λ -- Electron wavelength
ΔE/E -- Relative energy width of the electron beam
We can see that Equation 4241 is related to a beam broadening factor due to chromatic aberration (Cc) of the objective lens because of the finite width of the energy-selecting slit.
Example of estimated resolution limits are shown in Figure 4241. At high accelerating voltages (e.g. 200 kV) the spherical aberration is dominant, while at low accelerating voltages (e.g. 1 kV) the chromatic aberration is dominant. Generally speaking, spherical aberration is the dominant resolution-limiting aberration at accelerating voltages larger than about 100 kV.
Figure 4241. The estimated resolution limits at 1 kV and 200 kV as function of Cs and Ccassuming only one of them is present in each case. The energy width of the beam was assumed to be 0.7 eV.