Temperature effects on morphology and composition of ultrathin heteroepitaxial films: Fe on Ag(100)

We studied the effects of annealing on a 5 ML thick film of iron deposited at 140 K on Ag(100). Surface morphology and elemental composition have been investigated by He scattering and low energy ion scattering spectroscopy. Mild annealing (up to 300-350 K) does not trigger interlayer mixing and is not sufficient to promote a significant improvement of the film order. Annealing-induced segregation of silver at the surface is clearly observed, after slow heating (5 K/min), above 400 K. The surface order neatly improves in the 510-550 K temperature range, while the film is being coated by silver. A close comparison between He scattering and ion spectroscopy measurements after heating up to 550 K and re-cooling at 140 K provides evidence of an annealing stage in which the Fe film is completely wet by silver. Segregation does not represent the equilibrium condition of the system. The experimental results after annealing at high temperatures (T > 650 K) are consistent with a process of Fe precipitation into the bulk of the substrate and after annealing at 700 K the surface becomes structurally and morphologically comparable with the surface of Ag(100) before deposition. (C) 1999 Elsevier Science B.V. All rights reserved.