Browsing by Author "Johansson, L. -G"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Josephson Junctions Fabricated by Focused Ion Beam from Ex Situ Grown MgB2 Thin Films
    (2004-03) Malisa, Anayesu B.; Valkeapää, M.; Johansson, L. -G; Ivanov, Zdravko
    We prepared MgB2 thin films on SrTiO3 (1 0 0) and Al2O3 (1 1̄ 0 2) substrates by e-beam evaporation of MgB2 pellet. The films were deposited at room temperature and post-annealed at 900 °C in Mg vapour for 5–30 min. Superconducting transition temperatures were observed between 22 and 30 K. Structure and surface morphology of the films were investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM). The films grown on Al2O3 substrates are c-axis oriented while a film grown on SrTiO3 substrate is aligned with the (1 0 1) direction normal to the substrate planes. The films have grain sizes of about 70 nm. The films were patterned into 4 and 8 μm wide microbridges. The microbridges were observed to carry large critical current densities of approximately 1 MA/cm2 at 6.7 K. Focused ion beam (FIB) was used on the bridges in order to fabricate Josephson junctions. A cut 50 nm in width was made across the microbridges followed by an in situ platinum (Pt) deposition into the cut made. SNS-like weak-link junctions were formed in the process.
  • Thumbnail Image
    Item
    Superconductivity in Magnesium Diboride Thin Films
    (2002-04) Ivanova, Z.; Malisa, Anayesu B.; Johansson, L. -G; Komissinski, P. V.
    Mg–B thin films were grown in situ on (1 0 0) SrTiO3 substrates by pulsed laser deposition. Targets pressed from a commercial MgB2 powder had a superconducting transition temperature of 37 K. Films were characterized by atomic force microscopy and susceptibility measurements. First samples showed superconducting onset at 30 K and became superconducting at about 20 K. Films were patterned into microbridges 4–100 μm wide by Ar ion beam milling. Films had large contact resistances, of the order of 500 Ω cm2 in the temperature range 4.2–300 K.