Beam damage to organic material is considerably reduced in cryo-electron microscopy.

Abstract A cryo-electron microscope, equipped with superconducting lenses mounted in a liquid helium-cooled cryostat, was used to study the electron beam-induced damage on various organic crystals. Observations were made with direct imaging and electron diffraction. Thin crystals mounted on carbon film were found to be from 30 to 300 times more beam-resistant at 4 K than at room temperature. The resistance is even higher in favourable cases. Beam damage follows first-order kinetics at the beginning of irradiation; the rate is often lower after more prolonged irradiation. The effect of cryoprotection is reduced with thick crystals, or when the sample is mounted on a plastic film. In these cases the damage increases with increasing flux from 10−2 to 1 electron/A2s. Most of our results can be explained by assuming that cryoprotection in the region of 4 K is strongly dependent on the temperature. Additional factors must be invoked to account for the variations in cryoprotection for heavily irradiated specimens, or for those mounted on plastic films.