Fe epitaxial layers on Cu 3Au(0 0 1): a structural study by primary-beam diffraction modulated electron emission

Abstract

The structure of Fe films grown on the (0 0 1) surface of a Cu 3Au single crystal at room temperature, has been investigated by means of primary-beam diffraction modulated electron emission (PDMEE), as a function of thickness in the 0–37 monolayers (ML) range. A pseudomorphic, face centered cubic (fcc) structure has been found for films thinner than 4 ML; in an intermediate region of thickness, which extends up to ∼23 ML, two strained phases, with fcc and body centered tetragonal (bct) structure, are present. For thicker films a unique phase of bct type is detected within the chosen information depth of the PDMEE technique. At 37 ML the surface layers of the film show an unstrained body centered cubic (0 0 1) structure with the [1 0 0] crystal direction parallel to the [1 1 0] direction of the substrate. Segregation and intermixing of substrate atoms with the deposit has also been considered. A fraction of the order of one-tenth of ML of Au atoms has been found to segregate on top of films thinner than 4 ML. Au atoms in a concentration of a few percent have been found to be intermixed within the Fe film. In the low coverage region PDMEE data of the Fe/Cu(0 0 1) system have also been acquired for comparison with those obtained on Fe/Cu 3Au(0 0 1).