Preparation of superconducting nanometer structures by means of scanning tunneling microscopy and of layer-by-layer MBE

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.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.