Electrical and Structural Properties of Epitaxial bcc Tantalum Films

Tantalum films have been epitaxially deposited on cleaved MgO (001) surfaces at temperatures above 700°C under high-vacuum conditions. The interstitial impurity content is below 0.5 at.% for thicknesses greater than 1000 Å; the impurity concentration increases with decreasing film thickness, and severe lattice dilation occurs in the very thin film region (250–350 Å). Films of thicknesses greater than 1000 Å have specific resistivities and critical temperatures (16.0 μΩ·cm and 4.30°K, respectively) close to bulk values. Two impurity-stabilized phase transitions produced by electron microscope beam heating are described.