Initial Oxidation of Tantalum Observed in a Field Ion Microscope

Abstract

The distribution of oxygen atoms diffused into a tantalum crystal as a function of temperature, oxygen pressure, and time has been observed in a field ion microscope. Light oxidation below 450°K causes corrosion of the first atomic layer only, while there is no diffusion into the matrix. The distribution of oxygen interstitials occuring at higher temperature with an activation energy of 1.1 eV is measured by direct counting of surface concentration of interstitials using the field evaporation sectioning technique. Heavy oxidation causes a breakup of the lattice and homogeneously dispersed nuclei of oxide. Tantalum with 1% oxygen content only shows the statistically expected number of interstitial pairs when quenched from 1100°K. In situ annealing between 395° and 360°K causes up to 14.5% of the interstitials to associate in pairs or clusters.