Quantitative analysis of knock-on and thermal damage of biological specimens by electron irradiation in transmission electron microscopy |
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| Affiliation: | 1. Electrical Engineering Department, Kogakuin University, 1-24-2, Nishishinjuku, Shinjuku-ku, Tokyo, Japan;2. Hitachi Naka Works, Ichige, Katsuta-city, Ibaragi-ken, Japan;3. Hamamatsu University, School of Medicine 3600, Handa-Cho, Hamamatsu-city, Japan;4. Department of Anatomy, Gunma University, School of Medicine, Maebashi-city, Gunma-ken, Japan;1. Laboratorium für Elektronenmikroskopie, Karlsruher Institut für Technologie (KIT), Engesserstr. 7, 76131 Karlsruhe, Germany;2. CellNetworks, BioQuant, Universität Heidelberg, Im Neuenheimer Feld 267, 69120 Heidelberg, Germany;1. Central Facility for Electron Microscopy, Group of Electron Microscopy of Materials Science, University of Ulm, 89081 Ulm, Germany;2. Electrical Engineering Institute, Ecole Polytechnique Federale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland;1. Max Planck Institute of Biophysics, Department of Structural Biology, Max-von-Laue-Str. 3, D-60438 Frankfurt, Germany;2. Caesar Research Center, Ludwig-Erhard-Allee 2, D-53175 Bonn, Germany;3. University College London, Division of Biosciences, Gower Street, London WC1E 6BT, UK;4. University of Frankfurt, Physikalisches Institut, Max-von-Laue-Str. 1, D-60438 Frankfurt, Germany |
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| Abstract: | High-energy electrons are able to transfer momentum to nuclei, which results in displacement on to the interstitial lattice sites with a maximum transferred energy of 4 · 104 eV for carbon at 100 keV. Moreover, most of the energy dissipated in energy losses is converted into heat, which results in melting and evaporation.The specimen temperature rise was calculated by the heat conduction theory and confirmed by the specimen drift due to the thermal damage. The damage can be reduced by a small area of illumination, the use of a metal-coated microgrid and small area scanning.A further displacement due to the knock-on collision and the resulting etching rate of biological specimens was measured. The damage is proportional to the current density in c cm-2 at the specimen. The allowable maximum dose was obtained from the measurement of an etching rate with the weight loss and dry density of the specimens.It was found that the images affected by the electron irradiation, in which -H, C-H, C-N bonds break molecules in proteinaceous biological specimens are removed, and the remaining molecules are changed to stable carbon-rich molecules by deposition, polymerization and contamination. In addition, defect images were observed in high contrast, when compared with unaffected images taken with a small area scanning method. |
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