Abstract
We present analysis and quantification of electron beam sensitivity in calcite in order to identify damage thresholds under which bright field TEM imaging, selected area electron diffraction and scanning TEM should be performed. A large reduction in damage under TEM was found when operating at 300 kV rather than 200 kV, suggesting that the irradiation induced degradation of calcite to calcium oxide is dominated by radiolysis. At 300 kV, bright field STEM imaging was able to retain lattice information at higher fluences than was possible using TEM and, although damage was still seen to occur, there was no observation of the formation of crystalline calcium oxide.
Highlights
Calcium carbonate or calcite is of widespread interest as a structural biomaterial and for its environmental and industrial importance, which has led to extensive research into its formation and properties
We present analysis and quantification of electron beam sensitivity in calcite in order to identify damage thresholds under which bright field TEM imaging, selected area electron diffraction and scanning TEM should be performed
A large reduction in damage under TEM was found when operating at 300 kV rather than 200 kV, suggesting that the irradiation induced degradation of calcite to calcium oxide is dominated by radiolysis
Summary
Calcium carbonate or calcite is of widespread interest as a structural biomaterial and for its environmental and industrial importance, which has led to extensive research into its formation and properties. Whilst a heavily researched material, calcium carbonate is well known for its sensitivity under electron irradiation in both conventional and scanning TEM damaging through its radiolytic decomposition to calcium oxide. Recent reports have provided partial quantification of the damage process [1,2,3], the purpose of this study is to use calcite as a model material to compare damage under different conditions and operating modes (e.g. TEM and STEM) and develop damage limitation strategies which may be applicable to other electron beam sensitive systems [4,5]. Materials Calcite nanoparticles were produced through the carbonation of calcium oxide suspended in water [6]. The particles were dried and suspended in ethanol prior to deposition onto a either a holey carbon or lacy carbon film (Agar Scientific Ltd) for 200 kV experiments, and an ultrathin amorphous carbon or graphene oxide film (EM Resolutions Ltd) for 300 kV experiments, all supported on copper TEM grids
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