EPITAXIAL STRAIN AND THE GROWTH OF CU(001) ON FE(001)

In order to study the role of epitaxial strain in stabilizing a body-c entered cubic (bcc) modification of Cu, we have made high-resolution, in situ measurements of the in-plane elastic film strain associated wi th epitaxial growth of Cu(001) on Fe(001). Using grazing-incidence x-r ay scattering with synchrotron radiation, we observe in-plane elastic strains in the Cu as large as 7.6% occurring at a coverage of 2 equiva lent monolayers. These tensile strains tetragonally distort the face-c entered cubic (fcc) Cu lattice, resulting in a body-centered tetragona l structure. A true bcc structure is not observed. As the film grows t hicker, the epitaxial strain decays in a continuous, monotonic manner resulting in a slightly strained fcc structure by 10 equivalent monola yers. The observed strain relaxation agrees with equilibrium theory, s uggesting that the growth of bcc Cu is contingent upon kinetic barrier s to misfit dislocation nucleation and/or movement.