Structural properties of epitaxial films of Fe on Cu and Cu-based surface and bulk alloys

Abstract

Thin films of Fe were grown epitaxially at room temperature on Cu{001}, on the ordered surface alloys Cu{001} c(2×2)- Au and Cu{001} c(2×2)- Pd, and on the bulk alloy Cu 3 Au{001}. The maximum thicknesses attained in well-crystallized Fe films were 18 layers on the first three surfaces but only 3 layers on Cu 3Au {00}. Low-energy electron diffraction (LEED) intensity data from 1-, 2- and 3-layer films on Cu{001&} could not be fitted by models with complete layers of Fe, suggesting that the growth of these ultrathin films was not layer-by-layer. The 12-layer films were found to have a tetragonally distorted face-centered-cubic (fcc) structure with a= 3.61 A ̊ , c= 3.54 A ̊ and 4%-expanded first interlayer spacing. Analysis of the elastic strain gave an equilibrium lattice constant of 3.59 Å for fcc Fe at room temperature. Comparison with lattice constants from total-energy band calculations shows that the Fe cannot be in the nonmagnetic phase, but could be in the ferromagnetic phase, or possibly in an antiferromagnetic phase with the same lattice constant. It is suggested that the first interlayer spacing is enlarged owing to the larger magnetic moment of the first layer.