Electron beam-induced damage in tellurium dioxide

In this work, structural and compositional changes in α-TeO₂, also known as paratellurite, were studied as function of 300 kV electron beam exposure. Firstly, the mean free path for electron scattering in α-TeO₂ was measured, to enable local specimen thickness measurement and estimation of scattering probabilities. A value of λ = 155 nm ± 6 nm was obtained, for the specific experimental conditions as detailed in the text. Then, high resolution TEM images and EEL spectra were acquired as a function of electron beam exposure, and the material changes were recorded. Differing behaviors, ranging from complete specimen etching, reduction to elemental tellurium, or no effect, were observed depending on the specific specimen and illumination conditions that were employed. Markedly different material changes were observed under broad illumination (TEM mode) and focused probe illumination (STEM mode). In STEM mode, a threshold effect in the applied electron dose rate was observed. For the conditions employed, with a beam current of 45 pA or less, there was no significant damage to the specimen. In TEM mode, it was observed that specimen damage was enhanced at the periphery of the illuminating electron beam area, and proceeded more rapidly in thicker regions of the specimen. Under certain illumination conditions, a stable network of tellurium oxide and elemental tellurium was formed. While only a small fraction of the parameter space governing electron-beam induced damage has been investigated, the results to date indicate that specimen charging and induced electric fields are the dominant mechanism of damage in this insulating material.