Physical Principles of Electron Microscopy: An Introduction to TEM ...

130 Chapter 5
inelastic collisions to bring them to rest and also the probability of inelastic
scattering is inversely proportional to E0. A 1-keV electron penetrates only
about 50 nm into carbon and less than 10 nm into gold. The interaction
volume therefore becomes very small at low incident energy; see Fig. 5-3.
interaction
volume
increasing E 0
increasing Z
penetration
depth
Figure 5-3. Schematic dependence of the interaction volume and penetration depth as a
function of incident energy E0 and atomic number Z of the incident (primary) electrons.
Figure 5-4. Penetration of (a) 30-keV, (b) 10-keV and (c) 3-keV electrons into aluminum (Z =
13) and (d) 30-keV electrons into gold (Z = 79). Note that the dimensional scales are
different: the maximum penetration is about 6.4 �m, 0.8 �m, and 0.12 �m in (a), (b), and (c),
and 1.2 �m in (d). These Monte Carlo simulations were carried out using the CASINO
program (Gauvin et al., 2001) with 25 primary electrons and an incident-beam diameter equal
to 10 nm in each case.