Transmission electron microscopy analysis of CoO degradation induced by electron irradiation.

This study presents an investigation into the electron beam damage phenomenon of CoO under transmission electron microscopy (TEM). It was found that after irradiation at a dose rate of 6.78 × 10 e/nms, CoO crystals exhibited surface reconstruction and faceting features. Electron energy loss spectroscopy (EELS) analysis indicates that the damage process initiates with the desorption of oxygen anions, which subsequently leads to a reduction in the valence state of cobalt cations and corresponding atomic rearrangement. High resolution TEM (HRTEM) reveals that surface faceting, which has an epitaxial relationship with the bulk, could help maintain the crystal lattice of face-centered cubic (fcc) CoO despite Co-O bond breakage upon beam exposure. With a finely focused electron beam, the hole drilling effect was observed. The structural degradation is proposed to arise from inelastic damage that induced partial desorption of oxygen anions and rearrangement of valence-reduced cobalt cations to epitaxially grow on the surface, suggesting an interplay between irradiation damage and material restructuring. The relative phase stability of CoO, combined with its interfacial structure developed upon irradiation, are beneficial to magnetic loss and interfacial polarization loss, thereby rendering CoO a promising candidate as an effective EMW absorber.