Abstract
Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn layers of several μm thickness on bulk niobium have been prepared by heating the niobium samples in a saturated tin vapor at 1050°c. The layers have been analyzed by scanning electron microscopy and electron microprobe analysis; furthermore, measurements of penetration depth λ(T), pinning, critical field B <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c2</inf> (T), rf surface resistance R(T) and rf peak field have been carried out. As a result λ(T=0) ≃ 170 nm, Ginzburg-Landau parameter <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\kappa \simq 18</tex> , London penetration depth λ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</inf> = 40 nm, coherence length ξ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</inf> = 40 nm and mean free path ℓ = 2 nm have been found by using the values 2Δ/kT <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> = 4.2 and B <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> (0) = 0.54T. These material parameters - in connection with weak flux pinning - indicate quite homogeneous Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn layers. With the cavity measurements a surface resistance R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">res</inf> (3 GHz) = 1.7 . 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-7</sup> Ohm could be achieved; the highest observed electric surface field so far was <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E\max,surf. = 14</tex> MV/m. The apparently good quality of the Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn oxide interface is indicated by the BCS like λ(T)-dependence and the comparably weak electron loading of Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn cavities.
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