Surfactant properties of oxygen in the homoepitaxial growth of Fe: a MDS study

The growth of ultra thin iron films (up to a thickness of 5-6 ML) on O(1 x 1)-Fe/Ag(001) has been investigated by means of He reflectivity (R-He) and metastable de-excitation spectroscopy. The presence of oxygen induces a qua si-ideal layer-by-layer growth at variance with the case of the homoepitaxi al growth of iron on Fe(001). The surface electronic density of states sudd enly changes upon the deposition of the first half of a monolayer. After th e sudden change in the first stages of the growth, the surface density of s tates of both O-2p and Fe-3d states remains essentially unchanged, irrespec tively of the thickness of the deposited film. This provides a clear indica tion that oxygen floats at the surface acting as a surfactant for the growt h of iron on O(1 x 1)-Fe/Ag(001). The stationary fraction of oxygen that re mains on the topmost layer as growth proceeds depends on the substrate temp erature. Post-growth annealing up to 650 K restores the initial coverage of oxygen and the ordered O(1 x 1) phase. (C) 2001 Elsevier Science B.V. All rights reserved.