Breakdown of the bi-dimensional symmetry in bct Fe layers by epitaxy on Co(1 1 2̄ 0) surface

The structure of thin Fe overlayers on the Co(1 1 2̄ 0) surface has been investigated by low energy electron diffraction (LEED) and by primary-beam diffraction modulated electron emission (PDMEE), as a function of the Fe coverage (6–50 ML) and of the substrate temperature (between room temperature and 300°C). The structure of the layers was the tetragonally distorted bct modification of the equilibrium bcc phase, with the (0 0 1)Fe||(1 1 2̄ 0)Co and [1 1̄ 0]Fe||[1 1̄ 0 0]Co relationships with the Co substrate. The Fe(0 0 1)–Co(1 1 2̄ 0) system exhibits 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 1̄ 0 0] substrate direction.