Hrtem and Eels Studies of Reacted Materials From Caf2 by Electron Beam Irradiation

Abstract

ABSTRACTThe change of calcium fluoride (CaF2) by electron beam irradiation has been investigated in TEMs operated at 200 kV. By irradiation fluorine is desorbed rapidly from CaF2 crystal. Although plasmon peaks in EELS spectra suggest the formation of Ca metal, no evidence for the existence of Ca metal is found in electron diffraction pattern or HRTEM images. This is due to perfect topotactic formation of Ca metal from CaF2 with a similar crystal structure and closely similar lattice parameters. Irradiation also forms amorphous material near the edge of Ca/CaF2 and randomly oriented CaO crystallites grow from the amorphous material. This amorphous material is regarded as hydroxide formed through the reaction of Ca and water, considering the residual gas composition and the formation rate of the material.