EXAFS study of the local order in metastable fcc iron films

Surface EXAFS is used to determine the crystallographic structure of iron films prepared by deposition on Cu(100). These metastable films have structural and vibrational properties strongly dependent on their thickness and on their growth temperature. A well defined fee structure is obtained in films grown at a temperature higher than 350 K and in thick films (8 monolayers) grown at room temperature. The thinner films (2 to 5 monolayers) grown at room temperature do not have an fee structure: the first shell radial distribution function is very broad and anisotropic. The origin of this first shell broadening can be random static disorder in the layer or a well defined reconstruction inducing different nearest neighbour distances. These different crystallographic structures are apparently connected to the different magnetic properties measured in these films.