EPITAXIAL LINES AND THE METASTABILITY OF BCC COBALT

Strains measured by quantitative low-energy electron diffraction for two systems in general pseudomorphic epitaxy are analyzed by means of generalized epitaxial lines. Epitaxial lines are lines of strained film states which characterize a given film-substrate epitaxial system. The lines are plotted on a plane with coordinates giving the shape and size of the film unit cell. A film of Co(001) deposited on a substrate of TiAl(010) strains the square unit mesh of the Co to the rhombic unit mesh of TiAl(010). The calculated strain of bcc Co is a close fit to the measured strain, but the calculated strain of fcc Co lies well beyond the limits of error of the measured strain. Comments are made on the potential usefulness of strain analysis of epitaxial films and on the discontinuous character of epitaxial paths going along epitaxial lines between bcc and fcc structures. © 1995 The American Physical Society.