Structural aspects of superlattices of Fe-W, Fe-Mo, and Fe-Nb metals

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Abstract
X-ray diffraction and Mössbauer absorption results are reported for the layered structures Mo/Fe, Nb/Fe, and W/Fe, with layer periodicities in the range 0.5–50 nm. The films are amorphous for periodicities of 0.5–2 nm, but with composition modulation, and are crystalline with coherency in the growth direction for periodicities of 2–50 nm. The superlattice diffraction patterns are in agreement with a one-dimensional model, provided the effects of depositing part-plane layers are taken into account. In the intermediate region near periodicities of 2 nm, mixed crystalline and amorphous phases are observed, with sharp diffraction patterns from the crystalline regions. It is suggested that the lattice mismatch is taken up by deposition defects for periodicities above 3 nm, and by these defects and columnar boundaries with the amorphous phase for periodicities near 2 nm.