Optimized epitaxial growth of Fe on Ag(001)

We report on a comprehensive study of the growth of 5-nm-thick epitaxial Fe(001) films on Ag(001) substrates which are deposited on Fe-precovered GaAs(001) wafers. We characterize the films in situ by scanning tunneling microscopy, low-energy electron diffraction, X-ray photoelectron spectroscopy, and depth profiling to obtain information about the geometrical and chemical surface structure. We find that the surface morphology is improved by either growing or postannealing the films at elevated temperatures. During deposition at and above room temperature, however, an atomic exchange process is activated that results in a thin Ag film (up to 1 ML) ''floating'' on top of the growing Fe film. We propose and confirm a growth procedure that yields clean, Ag-free surfaces with a morphology superior to the other films. This optimized recipe consists of two steps: (i) low-temperature growth of the first 2 nm in order to form a diffusion barrier for the Ag substrate atoms, and (ii) high-temperature deposition of the final 3 nm to take advantage of the improved homoepitaxial growth quality of Fe at elevated temperatures. The relevance of these results with respect to magnetic properties of multilayers is discussed.