Damage of Materials due to Electron Irradiation
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This book (Practical Electron Microscopy and Database) is a reference for TEM and SEM students, operators, engineers, technicians, managers, and researchers.



The extent of electron-beam damage in electron microscopes, e.g. high voltage TEMs, depends on some factors such as the probe current density, accelerating voltage, chemistry and structure of the solid, and type and concentration of defects in the specimens.

Among charged particles, electrons possess the smallest mass, which minimizes the structural damage that they cause in the specimen. However, when energetic electrons interact with SEM samples or pass through a thin film in TEM, they still lose their energy, mainly through heating, electrostatic charging, displacement damage, sputtering, ionization damage (radiolytic), inelastic collision (knock-on), and hydrocarbon contamination processes [1], as shown in Figure 4543. These phenomena are often called “radiation damages” in a less precise form. In EM analysis, ionization damage and sputtering are more common than displacement damage.

Almost all materials undergo the displacement of atoms above a specific energy threshold, and electrons with energies smaller than this critical displacement energy only make the sample atom vibrate in its site and dissipate energy as phonons. Direct displacement of atoms from the crystal lattice creates point defects. In radiolytic damages based on the inelastic scattering, an increase in excitation energy can produce bond breaking of certain materials such as polymers and alkali halides. The damages which affect the structure and/or the chemistry of the specimen depend mainly on the energy of the electron beams. The ionization effect decreases significantly with increasing accelerating voltage up to 100 kV and stays low at higher voltage [2]. Therefore, when a material can undergo a radiolytic process, knock-on damage is insignificant and vice versa. For most metals, for example, the threshold of displacement energy is about 20 to 30 eV [1]; therefore knock-on damage in the TEM does not occur for accelerating voltages less than 300 kV.

Damage of Materials due to Electron Irradiation

Figure 4543. Schematic diagram of radiation damage.

In TEM analysis, most ceramics and catalysts suffer radiation damages under electron beams with accelerating voltages of 80-300 kV (especially in FEG TEMs due to high current densities), while most of metallic materials are not affected by such incident electron beams.




[1] L. W. Hobbs, in:J. J. Hren, J. I. Goldstein, D. C. Joy (Eds.),Introduction to Analytical Electron Microscopy, PlenumPress, NewYork, 1979, p.437.
[2] R. Csencsits, R. Gronsky, Ultramicroscopy 23 (1987) 421.



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