Depth dependent order/disorder transitions in iron-rich thin films grown on i-Al-Pd-Mn studied by medium energy ion scattering

This paper reports a medium energy ion scattering study of the room temperature deposition of Fe on the five-fold surface of i-Al70Pd21Mn9. At low coverage (~ 1 ML) growth results in a disordered alloy film with significant Al content. At higher coverage (~ 11 ML) again an alloy film is formed, but this time with an average composition that slowly varies through the film but is close to stoichiometric Fe3Al. This composition is consistent with magnetic ordering which has been observed in previous experiments on this system. Structural analysis indicates five domains of bcc-like structure in the film, which is oriented with (110) type planes parallel to the five-fold quasicrystal surface. There is a distinct structural transition within the film between a compressed layer near the surface and a slightly expanded layer directly above the quasicrystalline substrate. The sub-surface layer has considerable disorder and the change in layer spacing is attributed to this order/disorder transition within the film. Annealing to 300 °C for 10 min induces a small amount of further up-diffusion of Al into the film and also some segregation of Al to the surface, although structurally the film remains essentially unchanged, with the order/disorder transition occurring at a similar depth.