Structural characterisation of Fe layers on Co(112̄0)

The structure of thin Fe overlayers on the Co(112̄0) 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 bct modification of the equilibrium bcc phase, with the (001)Fe||(112̄0)Co and [11̄0]Fe||[11̄00]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 bct 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(112̄0) 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 [11̄00] substrate direction.