On the oxidation of CaF2 in transmission electron microscope

Electron stimulated oxidation of CaF2 in transmission electron microscope has been thoroughly studied using various electron microscopy techniques, including imaging, electron diffraction and electron energy-loss spectroscopy. It found that the electron irradiation induced CaO locate on the edge of specimen. The oxidation process is associated with desorption of F by electron irradiation, and originates from O impurities in the specimen. Driven by electric field produced by electron irradiation, the O ions inside bulk diffuse to the edge region, occupying the interstitials of metallized Ca lattice. Therefore, the accumulation of O along the edge of specimen results in forming CaO.

► This study provides a detailed study of oxidation process in CaF2 in TEM.
► It discoversthat the O source foroxidation is theinternal O impurity.
► Oxidation is caused by diffusion of O from bulk to the edge of TEM specimen.
► The driving force for the O diffusion is the electric fielddue to irradiation.
► Electric field proceeds by ejection of secondary and Auger electrons.