Structural evolution of Fe-Al multilayer thin films fordifferent annealing temperatures

Abstract

The phase formation during thermal annealing of Fe/Al multilayerthin films prepared by electron-beam evaporation, with an overallatomic concentration ratio of Fe:Al = 1:1, has been studiedby Rutherford backscattering spectrometry (RBS), x-ray diffractionspectroscopy (XRD), and conversion-electron Mössbauer spectroscopy(CEMS). At the annealing temperature of 473 K some degree of atomicmixing between Fe and Al layers is revealed only by CEMS. At 573 Ka large degree of atomic mixing is indicated also by RBS, leading tothe nucleation and growth of the B2 FeAl intermetallic phase, asdetected by means of XRD and CEMS. At 673 K all Fe atoms havereacted and the multilayer film is transformed into a defective B2phase. Annealing at higher temperature increases the structuralorder of the B2 phase. We suggest that the observed phase formationoccurs in three stages: (1) formation of a thin intermixedlayer between Fe and Al in the as-deposited sample; (2) Al migrationinto the initial intermixed layer; (3) B2 phase growth at theinterface between the intermixed layer and the Fe layer.