Interface quality and thermal stability of laser-deposited metal/MgO multilayers

Metal/MgO multilayers (metal of Fe, Ni80Nb20, and Ti) with bilayer periods in the range 1.2-3.0 nm have been prepared by pulsed laser deposition and characterized by both hard and soft-x-ray reflectometry. The interface roughness is found to be < or = 0.5 nm in all the samples and is nearly independent of the total number of deposited bilayers. The interface roughness, however, depends on the absolute thickness of the individual layers and increases from approximately 0.3 nm for a 3.0-nm period to approximately 0.5 nm for a bilayer period of 1.2 nm. The multilayers are found to be highly stable up to temperatures as high as 550 degrees C. The hard-x-ray reflectivity of the multilayers decreases for T > 300 degrees C, whereas the layered structure is stable up to 550 degrees C. The reflectivity in the water window region of soft x rays, lambda = 3.374 nm, was found to be 0.4% at an angle of incidence of approximately 54 degrees for multilayers with 60 bilayers at a period of approximately 2.1 nm.