Chapter/Index: Introduction | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Appendix
| Knock-on processes need some energy transfer for atomic displacement to create Frenkel pair, which is normally more than 10 eV for atoms in a bulk crystal, while atom removal from the surface requires significantly less energy. Energetic electron induced elastic scattering can also enhance diffusion of atoms at the surface [1] or vacancy migration in the bulk, which have relatively high cross sections and thus require small energy of the order of 1eV or less. In order to avoid radiation damage caused by atom displacements in electron microscopes (EMs), the energy (accelerating voltage) of the incident electrons must be smaller than the threshold energy for knock-on processes, which lies in the range between 100 and 300 keV for most solid materials.
[1] Y. Ma, L.D.Marks,in: G. W. Bailey (Ed.), Proc. 44th Ann. Meet. Electron Microsc. Soc.Am., San Francisco Press,San Francisco, 1986.
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