Structural characterization of Fe/Ag bilayers by RBS and AFM

Fe/Ag thin films are intensively investigated due to their special magnetic properties. Recently a deposition-order dependent asymmetric interface has been found. When iron is grown on silver, the interface is sharp, while the growth of Ag on Fe results in a long, low-energy tail of the Ag peak in the Rutherford backscattering spectrometry (RBS) spectra. The main purpose of this paper is to show that the low-energy Ag tail is caused by grain boundary diffusion, and that, when elevating the growing temperature of the Ag layer this effect becomes more significant. Two sets of polycrystalline and epitaxial Fe/Ag bilayers were prepared simultaneously onto Si(1 1 1) and MgO(1 0 0), respectively. The iron layers were grown at 250 °C and annealed at 450 °C in both sets, while the Ag layer was grown in the first set at room temperature (RT) and in the second set at 250 °C (HT). The sample composition, the interface sharpness and the quality of the epitaxy were studied by Rutherford backscattering spectrometry (RBS) combined with channeling effect. The surface morphology was determined by atomic force microscopy (AFM). RBS spectra show that in the case of RT samples the epitaxial MgO/Fe/Ag bilayer has sharp, well-defined interface, while for the polycrystalline Si/Fe/Ag sample the silver peak has a low-energy tail. Both the Fe and Ag peaks smeared out in the case of HT samples. AFM-images show that the RT samples have a continuous Ag layer, while the HT samples have fragmented surfaces. The RBS spectra taken on the HT samples were successfully simulated by the RBS-MAST code taking into account their fragmented structures.