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

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.