Factors affecting electron beam damage in calcite nanoparticles

Abstract

We report electron fluence thresholds for the degradation of calcite nanoparticles under electron irradiation by both conventional and scanning TEM (CTEM and STEM), using time resolved phase contrast imaging and EDX spectroscopy at both 80 kV and 300 kV accelerating voltages. We show that the degradation pathway of calcite involves disruption of the crystal lattice with the evolution of pores and transformation to calcium oxide and carbon dioxide. Depending on irradiation conditions (CTEM or STEM), the calcium oxide formed can be either amorphous or crystalline, with the formation of the latter apparently being hindered by hydrocarbon contamination build up in STEM. For a given electron flux, irradiation at 300 kV prolongs the characteristic lifetime of the calcite lattice as compared to irradiation at 80 kV but with a corresponding reduction in both image contrast and energy dispersive X-ray (EDX) signal, consistent with the change in inelastic mean free path for electron scattering. STEM offers significant benefits over CTEM, however only in the presence of hydrocarbon contamination, increasing the fluence threshold for the detection of irradiation induced faults in the calcite lattice from 2.7x10 7 enm-2 for 300 kV CTEM to over 1.8x10 8 enm-2 for 300 kV STEM. This work forms a framework for reliable identification of discrete particle crystallinity in nominally amorphous, nanoscale calcium carbonate particles which is of importance for fundamental studies of crystallisation and also for the process control during the synthesis of such surfactant stabilised nanoparticles for application as over-based fuel detergents.

Cathodoluminescent Analysis of Sapphire Surface Etching Processes in a Medium-Energy Electron Beam

“…As a result, the O 2− anion changes its charge state and is displaced from the Al 2 O 3 lattice. Comparing our data (electron energy 40 keV) with the results of [28], where etching was observed at a higher energy of 100 keV and a duration of 30 min, it can be noted that the cross-section of inelastic electron scattering in a dielectric medium, which causes its radiolysis, decreases with increasing electron energy [38,39]. It can be argued that a decrease in the energy of electrons at energies below 100 keV enhances the processes of radiolysis of the sapphire surface.…”

Mineralogy of microbially induced calcium carbonate precipitates formed using single cell drop-based microfluidics

“…6 b) but diffraction patterns did not match any known CaCO 3 polymorphs. Beam damage during TEM resulting in calcium carbonate transformation is fairly common 41 , 42 and could be the reason for the inconclusive TEM analysis.

Figure 6 Visualization of a single vaterite precipitate using FIB-SEM and TEM.

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Analysis of complex, beam-sensitive materials by transmission electron microscopy and associated techniques

“…These alternative approaches will yield differing sensitivities to the electron beam (i.e. differing values of the critical electron fluence), because the type and extent of observed damage varies from loss of atomic order, loss of material to changes in chemistry, and each of these will depend on the predominant damage mechanism responsible for these particular changes (22).…”

“…Alternatively, as shown in figure 5, Hooley et al . [22] compared the radiolytic damage of calcium carbonate nanoparticles (a moderately sensitive, direct-damage inorganic material) by both CTEM and STEM and concluded that hydrocarbon contamination induced by the focused STEM probe was important in mitigating damage, as has been noted by others [70–72]. The build-up of hydrocarbon contamination may protect the specimen in two ways: by improving the conduction of electrons, thus reducing the extent of radiolysis or electrostatic charging by suppressing charge build-up in a similar manner to intentionally deposited carbon coatings [68]; or by preventing the migration of molecular fragments and facilitating their recombination, meaning that there may be some structural damage without significant chemical change [73].…”

“…( b ) Comparison of O : Ca atomic ratios extracted from time-resolved CTEM EDX spectra from both a contaminated and (cleaned) uncontaminated calcite nanoparticle specimen. Adapted from [22]. (Online version in colour.)…”