Structural characterisation of Fe layers on Co(11-20)

The structure of thin Fe overlayers on the Co(11 (2) over bar0) surface has been investigated by low energy electron diffraction (LEED) and by primary-beam diffraction modulated electron emission (PDMEE). Films were prepared by slow Fe deposition at room temperature, up to a nominal coverage of 14 ML. The structure of the layers was the tetragonally distorted bet modification of the equilibrium bcc phase, with the (001)Fe\\(11 (2) over bar0)Co and [1 (1) over bar0]Fe\\[1 (1) over bar 00]Co relationships with the Co substrate. In the low coverage range (0-2 ML) iron forms 3 ML thick islands, that by further Fe deposition increase in thickness and finally coalesce at a coverage as large as 5 ML. The occurrence of a highly distorted bet phase is detected at a nominal coverage of about 2 ML. The final, 14 ML thick film exhibits a 3% contraction along the growth axis with respect to the equilibrium phase. The Fe(001)-Co(11 (2) over bar0) system is a rarely encountered example in which the substrate and overlayer unit meshes exhibit a very large misfit asymmetry in the interface plane. As a consequence, a breakdown of the long-range order occurs in the Fe film along the [1 (1) over bar 00] substrate direction.