Thermally induced interface changes in W/B4C multilayers

• We reported the influence of the layer thickness on thermal stability of W/B4C multilayers.
• Depending on the layer thickness ratio, the period variation can be positive or negative.
• Diffusion induced structural changes can be minimized by optimizing layers thickness ratio.
• Tungsten carbide and boride phases observed at elevated temperatures.

Multilayer period thickness changes for various thickness ratios, Γ (ratio of W layer thickness to period thickness) as a function of annealing temperatures were studied by grazing incidence X-ray reflectivity (GIXRR), and grazing incidence X-ray diffraction (GIXRD). Both period thickness expansion and compression were observed depending upon Γ and annealing temperatures. Multilayer with the W layer thickness close to the B4C layer has undergone less period thickness changes. Successive appearance and disappearance of multilayer Bragg maxima in GIXRR were observed. Such behavior suggested that redistribution of atomic density within bilayer, the displacement of interface and the multilayer period thickness change as annealing proceeds. GIXRD measurements performed using synchrotron radiation suggested the formation of phases corresponding to tungsten boride and carbide.