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We have investigated two-dimensional arrays of overdamped Josephson junctions that have been fabricated in Nb/Al/sub 2/O/sub 3//Nb-technology, together with microwave coupling structures. Different arrays have shown to emit coherent microwave radiation by using microwave-coupled on-chip detectors. Low-temperature scanning electron microscopy is used to study the coupling of the microwave radiation to an on-chip load. From the appearance of Shapiro steps in the current vs. voltage curves of detector junctions for different degrees of disorder in the array-junctions, margins of the spread in the critical currents of the Josephson junctions for coherent oscillation can be drawn. [ABSTRACT FROM PUBLISHER]

Nb-based superconducting tunnel junctions are being developed as high energy resolution X-ray detectors. Unfortunately, loss of excess quasiparticles at the edges, combined with lateral diffusion, results in an inhomogeneous response. To study this degradation of energy resolution, we manufactured detectors with a Ta trap in the top or bottom electrode away from the tunneling barrier. Excess quasiparticles in this so-called killed electrode will be trapped effectively and thus removed from the tunneling process. The X-ray spectra of the active electrode can be fitted with a model based on classical diffusion of quasiparticles. On junctions with a killed bottom electrode also Low Temperature Scanning Electron Microscopy (LTSEM) measurements have been performed. The X-ray spectra and the LTSEM scans are consistent with each other and with the model. The energy resolution of the junctions presented here is limited by loss of quasiparticles at the edges. [ABSTRACT FROM PUBLISHER]

Low-Temperature Scanning Electron Microscopy (LTSEM) has been successfully applied to the investigation of the local superconducting properties of thin films and Josephson junctions as well as to the study of more complex superconducting circuits. Since many superconducting devices and circuits can be operated successfully only in low ambient magnetic fields, we have built a liquid nitrogen cooled low temperature stage with improved magnetic shielding for the temperature range between 77 and 130 K. For effective magnetic shielding we use a superconducting YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// tube in addition to several Mumetall shields. We established further improvements such as an in-vacuum motorized x-y-slide, which allows us to shift the sample with a minimum step width of 1.5 /spl mu/m. We present first test measurements of the transport properties of a high T/sub c/ dc SQUID that demonstrate the functionality of the new stage. [ABSTRACT FROM PUBLISHER]