Low temperature scanning electron microscopy of superconducting thin films and Josephson junctions

By extending scanning electron microscopy to the temperature regime of liquid helium and nitrogen a powerful technique for the imaging of the local properties of superconducting thin films and Josephson junctions is obtained. Low temperature scanning electron microscopy (LTSEM) allows one both to investigate interesting physical phenomena in superconducting thin film samples with a spatial resolution of about 1 mu m and to perform a functional test of superconducting devices and circuits at their operation temperature. We discuss the technical and physical background of the LTSEM imaging technique including the electron optical and cryogenic requirements, the interaction of the electron beam with the superconducting sample, the dynamics of the electron beam induced non-equilibrium state, and the electron beam induced signal. The origin of spatial structures in superconducting thin films and Josephson junctions and their spatially resolved analysis by LTSEM is reviewed. The use of LTSEM in the functional test of both low- and high-temperature superconducting thin films, devices, and circuits is summarised.