Submonolayer iron film growth on reconstructed Ir(100)-(5x1)

The early stages of iron film growth on the quasihexagonally reconstructed Ir(100)-(5x1) surface were investigated for deposition temperatures 90-450 K by means of scanning tunnelling microscopy and quantitative low-energy electron diffraction (LEED). For low coverage, single iron atoms diffuse within the one-dimensional troughs formed through the top layer reconstruction. On large step-free terraces a metastable iron phase develops consisting of linear diatomic Fe chains which reside within the troughs and are homogeneously spread over the terrace. With increasing coverage and controlled by temperature, the hexagonal reconstruction is lifted. This surface restructuring proceeds by expelling the 20% extra Ir atoms accommodated in the quasihexagonal layer, whereby a new (5x1) superstructure consisting of equally spaced Ir rows is formed at the very surface. With further deposition, iron fills the space between these rows, eventually leading to an ordered Fe4Ir surface alloy with the completion of the top layer. A quantitative LEED analysis corroborates this model and reveals significant atomic corrugations down to the third layer. It is observed that surface defects of any kind act as nucleation centers for both the film growth and the restructuring process.