Non-pseudomorphous epitaxial growth of fcc Fe on Cu(100) observed by reflection high-energy electron diffraction (RHEED)

A high-precision reflection high-energy electron diffraction (RHEED) analysis of the in-plane lattice spacing of the surface during epitaxial growth of fcc Fe films on a Cu(100) single crystal substrate is presented. As a function of Fe coverage, initially the in-plane fcc Fe lattice spacing is found to decrease drastically until a minimum is reached, while at higher coverages the smaller equilibrium value for bulk fcc Fe (3.59 A), rather than the value of the Cu substrate (3.615 A), is approached. This proves that fcc Fe films on Cu(100) grow strain free and are non-pseudomorphous, contrary to earlier assumptions.