Regensburg 2004 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 1: Supraleitung: Herstellung und Charakterisierung
TT 1.2: Vortrag
Montag, 8. März 2004, 09:45–10:00, H20
Thickness dependence of superconducting properties of ultra-thin Nb and NbN films — •Konstantin Il’in1, Michael Siegel1, Alexei Semenov2, Andreas Engel2, Heinz-Wilhelm Hübers2, Eugen Hollmann3, Gregory Gol’tsman4, and Boris Voronov4 — 1Institut für Mikro- und Nanoelektronische Systeme, Universität Karlsruhe, Karlsruhe — 2DLR Institut für Planetenforschung, Berlin — 3Forschungszentrum Jülich GmbH, Jülich — 4MSPU, Moscow, Russia
We studied systematically superconducting properties of Nb and NbN films widely used in modern detector technology. The films with a thickness from 3.5 to 100 nm were deposited by reactive magnetron sputtering. The Ginzburg-Landau coherence length and the electron diffusion constant have been obtained from the temperature dependence of the second critical magnetic field, HC2. We have found that diffusivity in ultra-thin films reduces with thickness. The non-linear temperature dependence of HC2 of NbN films at temperatures close to TC was attributed to the granular structure of the films. At low temperatures, where the normal core of a magnetic vortex is smaller than the grain size, HC2 depends linear on temperature. The grain size of 40-80 nm was estimated from the crossover temperature, where the dependence of HC2 on temperature changes from linear to non-linear behaviour. We found that grain size and its dependence on film thickness is determined by sputtering conditions.