Oxide Formation in Evaporated Thin Films of Tantalum

The oxidation of evaporated single crystal Ta films has been carried out in situ in the electron microscope. In order to provide greater assurance that the gas reacting with the Ta film was oxygen rather than nitrogen or carbon vapors residual in the electron microscope column, a vacuum system was designed and assembled to provide auxiliary pumping directly on the sample chamber; a liquid-nitrogen cooled plate was installed in the chamber above the sample to trap contamination; and an oxygen inlet was inserted at the level of the sample itself. Tantalum films of (001) orientation were prepared by evaporation in a separate high-vacuum station, using a 2 kW electron beam gun. Two progressions of oxidation were observed, one under the low oxygen pressure conditions and one under the higher oxygen pressure. The ordered domains producing the 2-fold cubic superlattice are thought to be an early stage of TaO(y), the orthorhombic platelets a later form with the same suboxide designation. (Author).