Non-linear current-voltage characteristics of NS-tunnel junctions prepared by focused ion beam induced deposition

We used a focused Ga-ion beam and the precursor W(CO)6 -injected into a vacuum chamber nearby the focal area of the beam- to create tungsten containing superconducting deposits with a critical temperature of about 5.2 K. The deposits were fabricated onto oxidized aluminum contacts pre-patterned by UV-photolithography. I-V- and V-dI/dV- measurements have been performed between 0.3 K and 6 K using a He3-cryostat. For selected beam energies used during deposition the samples show Josephson-junction like behaviour or tunneling of quasiparticles for temperatures below the superconducting transition of aluminum at about 2 K. In the temperature range between the superconducting transitions of the two electrodes Andreev-reflection was observed.