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# Electron beam sensitivity of mica

van Berkum, Tess (2018) Electron beam sensitivity of mica. Bachelor's Thesis, Applied Physics.

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Mica is a mineral that has a naturally flat surface with basal and outstanding cleavage, which makes it a good substrate for high quality film growth. In order to study the structure of these thin layers different geometries can be examined by (scanning) transmission electron microscopy ((S)TEM), namely plan-view and cross-section geometries. In this paper a dual beam system is used for preparing TEM-lamellas. The goal of the experiment is to investigate the electron beam sensitivity of mica when it is viewed in cross-section by a (S)TEM. It was found that mica has a certain electron dose threshold in order to conclude if it is damaged or not. The threshold lies in the electron dose range of $4.1 * 10^{-7}$ pC/$\mu$m$^2$ and $8.6 * 10^{-7}$ pC/$\mu$m$^2$ by 30 kV electrons. Furthermore an observation was made that the diffraction patterns vanish inhomogeneously, the out-plane lines decrease earlier than the in-plane lines when the electron dose increases. An equation of a sigmoidal logistic function, $y = A2 + (A1-A2)/(1 + (x./x0)^p)$, is found to express the vanishing of in-plane diffraction lines when the electron dose increases. The benefit of controlling the electron beam damage of mica is that the study of thin layers can be improved.