Secondary ion mass spectrometry and x-ray analysis of superconducting Nb/Pd multilayers

We report on accurate structural investigations of sputtered Nb/Pd multilay ers by means of high-resolution secondary ion mass spectrometry and x-ray r eflectivity. The combined use of secondary ion mass spectrometry and x-ray specular reflectivity techniques allows us to study the chemical configurat ion of the interfaces and to relate it to the observed superconducting prop erties. Secondary ion mass spectrometry analyses reveal a distinct Nb and P d modulation and very sharp profiles with abrupt interfaces indicating a ne gligible interdiffusion of Nb and Pd at the interfaces. Moreover, analyzing the features in the Nb and Pd profiles and correlating them to the oxygen distribution in the multilayers and to the low-angle x-ray patterns, thin l ayers (3-4 nm thick) of niobium oxide were noticed at the Nb/Pd interfaces, while no oxide layers at the Pd/Nb interfaces could be detected. The role of this oxide layer in the determination of the crossover between three- an d two-dimensional superconducting behavior in parallel external magnetic fi eld, is discussed. (C) 2000 American Institute of Physics. [S0021-8979(00)0 0902-6].