This book (Practical Electron Microscopy and Database) is a reference for TEM and SEM students, operators, engineers, technicians, managers, and researchers.
During the collision process between incident electrons and a nucleus, if the energy (E) received by an atomic nucleus exceeds the atomic surface-binding energy Es, surface atoms can be removed in an average time, given by,
<T> ~ e/(σsJ) ------------------- [4408a]
J -- The current density of the incident electron beam,
σs -- The cross section of sputtering (or called knock-on).
The sputtering cross section can be given by, 
A -- The atomic mass number,
Z -- The atomic number,
E -- The energy received by an atomic nucleus due to the collision between the incident electrons and the nucleus,
E0 -- The energy of incident electrons.
Cross-sections (σ) of surface sputtering in conducting materials induced by electron irradiation is from 10-22 to 10-21 cm2.
Conventional wisdom suggests that a low operating voltage (<100 kV) in TEMs is optimal for reducing radiation damage, but the calculated profiles as a function of incident electron energy E0 in Figure 4408 demonstrate the minimum displacement cross-sections for lithium atoms in the elemental Li, lithiated graphite (LiC6) and graphite are not at low operating voltages.
Figure 4408. The displacement cross-sections for lithium atoms in the elemental Li, lithiated graphite (LiC6) and graphite as a function of incident electron energy E0.
Ed is the displacement
 Chadderton, L.T., 1965. Radiation Damage in Crystals, Methuen,
 FengWang, Jason Graetz, M. Sergio Moreno, Chao Ma, LijunWu, Vyacheslav Volkov, and Yimei Zhu, Chemical Distribution and Bonding of
Lithium in Intercalated Graphite:
Identification with Optimized Electron
Energy Loss Spectroscopy, ACS Nano, 5 (2), (2011) 1190.