GROWTH AND THERMAL-PROPERTIES OF FCC IRON FILMS ON CU(100)

Specular helium atom scattering has been used to characterise ultra-thin iron films grown epitaxially on a copper (100) substrate. Results are reported for films up to ten monolayers thick for three growth temperatures: 220, 298 and 420 K. In addition we report the results of subsequent thermal treatment of the films. The results suggest that, at low temperatures, growth is diffusion limited and proceeds by the formation of simultaneous multilayers. Near room temperature, growth is more organised but in the early stages, up to approximately three monolayers, films are less well ordered than when slightly thicker. After approximately seven monolayers the quality of the films grown at 298 K deteriorate, possibly as a result of the formation of misfit dislocations. Growth at 420 K proceeds in a layer-by-layer manner but Auger spectroscopy suggests that there is significant intermixing with the substrate at this temperature; that is, the film appears to develop as an epitaxial surface alloy. None of the as-grown films are thermally stable. We present indirect evidence that the alloy film undergoes a spinodal decomposition at low temperatures, leading to the precipitation of an enriched surface layer.