TEM preparation methods and influence of radiation damage on the beam sensitive CaCO3 shell of Emiliania huxleyi

• TEM plan-view and cross-section preparation methods were developed and adjusted for E. huxleyi.
• H2O thinning for plan-view samples is a very gentle method to obtain electron transparent samples.
• FIB sectioning for cross-section samples is very appropriate for coccoliths like E. huxleyi.
• Electron beam stability investigations of calcite were done by BF imaging, HRTEM, SAD and EELS.
• The samples are stable for several minutes, when using 300 kV and parallel illumination.

The ultrastructure of biologically formed calcium carbonate crystals like the shell of Emiliania huxleyi depends on the environmental conditions such as pH value, temperature and salinity. Therefore, they can be used as indicator for climate changes. However, for this a detailed understanding of their crystal structure and chemical composition is required. High resolution methods like transmission electron microscopy can provide those information on the nanoscale, given that sufficiently thin samples can be prepared. In our study, we developed sample preparation techniques for cross-section and plan-view investigations and studied the sample stability under electron bombardment. In addition to the biological material (Emiliania huxleyi) we also prepared mineralogical samples (Iceland spar) for comparison. High resolution transmission electron microscopy imaging, electron diffraction and electron energy-loss spectroscopy studies revealed that all prepared samples are relatively stable under electron bombardment at an acceleration voltage of 300 kV when using a parallel illumination. Above an accumulated dose of ∼105 e/nm2 the material – independent whether its origin is biological or geological – transformed to poly-crystalline calcium oxide.