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

摘要

Metal/MgO multilayers (metal of Fe, Ni_(80)Nb_(20), 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 ≤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 ≈0.3 nm for a 3.0-nm period to ≈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℃. The hard-x-ray reflectivity of the multilayers decreases for T>300℃, whereas the layered structure is stable up to 550℃. The reflectivity in the water window region of soft x rays, λ=3.374 nm, was found to be 0.4% at an angle of incidence of ≈54° for multilayers with 60 bilayers at a period of ≈2.1 nm.