Iron multilayers on Cu(100) - A case of complex reconstruction investigated by quantitative LEED

Epitaxial growth of iron on Cu(100) leads to the formation of fee iron whereby as function of film thickness a variety of different structures is observed. As detected by full dynamical LEED structure analyses using tensor LEED these structures are rather complex. In the coverage regime below 5 monolayers all iron layers are reconstructed both vertically and in-plane. Above 5 monolayers only the top layer is reconstructed until a martensitic transformation at about 10 monolayers leads to the formation of a bcc(110) surface. The structures found correlate nicely with known magnetic properties. Surprisingly, the in-plane lattice parameter of the fee iron layers was found to be 2.52 Angstrom, i.e. smaller than the value of 2.55 Angstrom known for bulk copper layers. However, a re-investigation of clean Cu(100) also yields a 1% in-plane contraction of copper surface layers compared to bulk layers, i.e. the clean copper surface - at least after conventional preparation procedures - relaxes under its surface stress. In conclusion, the growth of Fe on Cu(100) has to be regarded as pseudomorphic.