HREM of electron-beam-induced damage in l-Ta 2O 5

Abstract

Samples of l-Ta 2O 5 exposed to a high current density electron beam were observed by high resolution electron microscopy (HREM) to reduce to suboxide and metallic Ta phases. Data are presented for crystals aligned along [001], [020], [200], and [130], in which surface areas are seen to reduce to Ta 2O, TaO 2, bcc Ta, or a β-Ta phase via an amorphous intermediate phase. The driving force appears to involve desorption of oxygen stimulated by electronic transitions (DIET), and the possible involvement of the “infinitely adaptive nature” of the initial l-Ta 2O 5 structure in the damage process is discussed. Comparison of results obtained from an ultrahigh vacuum HREM to those from a conventional HREM suggests that contamination effects in lower vacuum systems influences the reliability of the results, especially in complex systems like Ta&1bO. Finally, the results follow a symmetry selection rule, which explains why l-Ta 2O 5 does not reduce to the monoxide phase as observed in similar experiments with TiO 2, V 2O 5, and Nb 2O 5.