X-ray diffraction study of lattice strain in Fe/Au(001) superlattice films

X-ray diffraction analyses of Fe/Au(001) superlattice films have revealed a body-centred tetragonal (BCT) structure with c/a=1.1 for Fe layers thinner than 1.0 nm when Au layer thicknesses are 3.0 nm. The perfect in-plane lattice matching was confirmed by off-axial measurements. The observed in-plane lattice parameter, a=0.2875 nm for BCT Fe, is close to the lattice dimension of bulk BCT Fe. However, profile analysis of axial scans have indicated that the Fe(002) lattice spacing along the growth direction has expanded. Such a tetragonal distortion cannot be explained by the normal elastic theory. The observed BCT structure of Fe would be a transient state on the BCC-FCC deformation path stabilized by a size effect or an interface effect. The tetragonal distortion is almost relaxed when Fe layers are thicker than 2.0 nm.