5 July 1996 Preparation of superconducting nanometer structures by means of scanning tunneling microscopy and of layer-by-layer MBE
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Thin films of YBCO were patterned down to the sub-micrometer scale by means of electro-beam lithography (EBL). A resist system based on amorphous carbon layers was developed, which allows the production of uncovered high-Tc superconductor microstructures. With this method we generated microbridges with a width of minimum 200 nm and a length of up to 5 micrometers. The layered structure of high Tc superconductors enables a further modification of the microbridges on the nm-scale into lateral weak-links by means of a scanning tunneling microscope (STM) using high tunneling currents in the range of nA and fast scanning modes ('etching'). This modification was carried out in N2-atmosphere after the YBCO microstructures were sputtered in Ne-atmosphere. In UHV we did not observe any etching process. Using atomic layer-by-layer MBE we have prepared BiSrCaCuO thin films and vertical S-N-S junctions on SrTiO3 substrates at 720 degrees C in 2(DOT)10-5 mbar ozone pressure. 40 nm thick Bi-2212 films showed an inductively measured Tc of 84 K. Thinner films have Tc values of 64 K and 46 K for 15 nm and 10 nm thick films, respectively. We present in-situ-STM images of the surface topography and TEM investigations of the dependence of the substrate/film interface on the first deposited layer. The S-N-S junction was made with Bi-2201 as barrier material and showed quasiparticle tunneling dI/dU-U characteristic. We estimated 2(Delta) (0)/kBTc to 3.5-4 with a non BCS- like linear temperature dependence.
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L. Buschmann, L. Buschmann, Holger Hoffschulz, Holger Hoffschulz, J. Dressen, J. Dressen, H. Stahl, H. Stahl, B. Decker, B. Decker, F. Nouvertne, F. Nouvertne, R. Barth, R. Barth, Bernd Spangenberg, Bernd Spangenberg, Heinrich Kurz, Heinrich Kurz, Gernot Guentherodt, Gernot Guentherodt, } "Preparation of superconducting nanometer structures by means of scanning tunneling microscopy and of layer-by-layer MBE", Proc. SPIE 2697, Oxide Superconductor Physics and Nano-Engineering II, (5 July 1996); doi: 10.1117/12.250250; https://doi.org/10.1117/12.250250

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