Interface asymmetry in AlN/Ni and Ni/AlN interfaces: A study using resonant soft X-ray reflectivity

X-ray waveguides are layered structures consisting of a low Z material sandwiched between two high Z materials. The performance of such waveguide structures is influenced by quality of interfaces formed by low and high Z materials. Electric field intensity calculations for Ni/AlN/Ni waveguide structure suggest them as a promising candidate for such applications. We have optimized design parameters of this trilayer structure to trap wave field of 8 keV energy and studied interface properties of two interfaces viz. Ni-on-AlN and AlN-on-Ni by depositing different bilayer samples on Si substrate. AlN-on-Ni bilayer grown on Si substrate gives a good contrast for grazing incidence X-ray reflectivity (GIXRR) measurements using Cu Ka photons but Ni-on-AlN bilayer on Si substrate comes out as a single layer system in GIXRR measurement due to poor contrast between AlN and Si optical constants. To overcome this situation, we have applied resonant soft x-ray reflectivity near Ni L-edge region using soft x-ray reflectivity beamline at Indus-2 synchrotron source. It has been observed that an interlayer is formed in case of AlN-on-Ni interface due to diffusion of AlN or Al and N atoms separately into Ni layer, whereas in case of Ni-on-AlN interface, either AlN molecules or Al and N atoms diffuse into top Ni layer without formation of any interlayer.