Electron Beam Damage Monitored by EELS
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In some cases, the beam damage of the specimens in TEM measurements can be monitored by observation of energy-loss near-edge structure (ELNES), for instance, in the damage process of CeO2 specimens. The electron beam damage induces the changes in the spectral shape of a CeO2 specimen in thickness of 0.17λ within a few seconds. λ is inelastic mean free path. Figure 2644 shows the damage sequence from fresh CeO2 (A) to damaged CeO2 (H) with such thickness. After H, the edge showed no further changes with increase of electron dose. The M5 and M4 maxima and the peaks Y and Y' are associated with Ce4+. The electron-beam damaged CeO2 presents Ce M4,5 and O K-edge shapes that are consistent with reduction to a Ce3+ oxide. During the beam-damage process the spectrum of CeO2 changes as below:
         i) Decreases in energies of the M5 and M4 maxima,
         ii) Changes in shape of the near-edge structure,
         iii) Inversion of the M5 to M4 branching ratio,
         iv) Increase in the M5 to M4 area ratio.

damage sequence from fresh (A) to damaged (H) CeO2 from such specimen

Figure 2644. The damage sequence from fresh CeO2 (A) to damaged CeO2 (H) in thickness of 0.17λ. The estimated doses in each case are (A) 3 x 105 e/Å2; (B) 6 x 105 e/Å2; (C) 2 x 106 e/Å2; (D) 3 x 106 e/Å2; (E) 7 x 106 e/Å2; (F) 1 x 107 e/Å2; (G) 2 x 107 e/Å2; and (H) 5 x 107 e/Å2. [1]

[1] L.A.J. Garvie and P.R. Buseck, Determination of Ce4+/Ce3+ in electron-beam-damaged CeO2 by electron energy-loss spectroscopy, Journal of Physics and Chemistry of Solids 60 (1999) 1943–1947.