V. Lacquaniti et al., ANALYSIS OF THE INTERFACES OF STACKED JOSEPHSON-JUNCTIONS BY ATOMIC-FORCE MICROSCOPY, IEEE transactions on applied superconductivity, 7(2), 1997, pp. 2419-2422
The surface properties of vertical stacks of Nb/(Al-AlOx/Nb)(n) Joseph
son junctions have been investigated by Atomic Force Microscopy (AFM).
The results indicate that the roughness of the AlOx layers is nearly
constant and independent of the surface features of the underlaying Nb
films. The superposition of several Nb and Al-AlOx films has an overa
ll smoothing effect on their surfaces, as indicated by the strong redu
ction of the rms roughness in a stack of junctions with respect to tha
t of the base Nb film. The height-height correlation function shows th
at the rms roughness increases on small sampling lengths I (l < 20 mn)
as l(alpha) with alpha approximate to 0.85 for both Nb and AlOx. The
interface profiles between the Al-AlOx and Nb electrodes have been rec
onstructed from AFM data, and a reasonable agreement with anodization
spectroscopy profiles has been found.