Interface Structure and Solid State Reactions of Fe/Zr Multilayers
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Interface Structure and Solid State Reactions of Fe/Zr Multilayers Bruce M.Clemens' and D.L.Williamson' * Physics Department. General Motors Research Laboratories Warren, Michi-
gan 48090-9055 ** Department of Physics, Colorado School of Mines, Golden Colorado 80401
Abstract Iron zirconium multilayer films were prepared by electron beam evaporation and by sputter deposition. Layer thicknesses were varied from 50 monolayers of each constituent down to 2 monolayers. Conversion electron Mossbauer spectroscopy, x-ray diffraction, and Auger spectroscopy have been used to characterize multilayers in the as-deposited and annealed state. Amorphous phase formation occurs during thermal anneals, and samples with layer thicknesses of 5 monolayers or less of each constituent are amorphous as deposited. Amorphous interfaces are observed in all samples, with this interface region being larger in the electron beam evaporated samples than in the sputter deposited samples.
Introduction The first iron-based amorphous alloy formed by the process of solid state reaction has been reported[l]. Elemental layers of crystalline Fe and Zr were partially transformed to an amorphous phase by a solid state anneal. More recently, complete transformation of Fe/Zr multilayers with an average composition of Fe5oZr 50 was observed, with evidence that this process produced a phase separated amorphous alloy[2]. Solid state formation of amorphous alloys has been observed in several early transition metal-late transition metal pairs. Metastable free energy diagrams have been used to demonstrate that, due to the large negative heat of mixing typical of these alloy systems, the amorphous phase has a lower free energy than the two phase starting material[l.3.41. It has also been observed that one element is the dominant moving species in the reaction[5.6J. Amorphous phases have also been observed in metal multilayers when the layer thickness is less than about 10 atomic planes of each constituent per layer. This has been observed in multilayer pairs where the large atomic structural mismatch precludes epitaxy between the layers, including Ti/Ni[4l. Zr/Ni[4]. Hf/Cu[7,8], and Nb/Co[9]. Absence of long range crystalline order is even observed at small layer thicknesses in Mo/Ni multilayers. where at larger layer thicknesses the interfaces are crystalline[10]. In this paper we investigate the structure and properties of Fe/Zr multilayers in both the annealed and as deposited state. We have prepared several samples with different layer thicknesses by both electron-beam evaporation and dc magnetron sputter deposition. A Mossbauer technique known as conversion electron Mossbauer spectroscopy. CEMS[11J. is used to examine the state of the Fe. X-ray diffraction is used to determine the crystal structure of the layers and to examine the composition modulation. Auger electron electron spectroscopy is used to characterize the composition modulation and possible contamination by oxygen and carbon. We compare the amorphous phase produced by solid state reaction duri
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