Structural properties of Fe-Ni/Cu/Fe-Ni trilayers on Si (100)

TL;DR

This study examines the structural characteristics of Fe-Ni/Cu/Fe-Ni trilayers on silicon, revealing phase transformations and improved layer quality after annealing, with implications for magnetic and electronic applications.

Contribution

It provides detailed analysis of phase changes and structural properties of Fe-Ni/Cu/Fe-Ni trilayers on Si(100), including effects of annealing and alloy composition.

Findings

Invar trilayers transform to fcc structure after annealing.

Layered structures are maintained in both as-deposited and annealed states.

Bragg reflections become sharper post-annealing, indicating improved crystallinity.

Abstract

We investigate the structural properties of Fe$_{1-x}$Ni$_x$/Cu/Fe$_{1-x}$Ni$_x$ ( $x=0.5$, non Invar and $x=0.36$, Invar) trilayers deposited on Si~(100)~at room temperature using dc magnetron sputtering technique in ultra high vacuum conditions taking high purity Fe, Ni and Cu metals with Cu layer thickness 4, 6 and 8 nm for each alloy composition. The structure of the alloy films of the trilayers was investigated using x-ray diffraction and the thickness \& roughness of the layers were obtained by x-ray reflectivity measurement. Both the as prepared and annealed trilayers exhibit layered structure. The as deposited Fe-Ni alloy in non Invar trilayer exhibits only fcc structure whereas in Invar alloy it exhibits a mixed fcc and bcc phases. Interestingly after annealing at 425$^0$C in ultra high vacuum, the Invar alloy completely transformed to fcc structure for all Cu thicknesses. In both Invar and non Invar trilayers, the Bragg reflections corresponding to Fe-Ni alloy layers become sharp after annealing. The induced structural transformation in Invar trilayer is explained using enhanced diffusion of Fe and Ni atoms at high temperatures.