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The direct imaging of Josephson- and Abrikosov-Vortices trapped in bicrystalline YBa2Cu3O7 washer direct current superconducting quantum interference devices (dc SQUIDS) is presented. The dc SQUIDs, which contain regular arrays of micrometer holes or antidots, were directly imaged with a standard scanning electron microscope that is equipped with a liquid nitrogen cryostage. The technique permits the simple visualization of vortices at spatial resolutions of about 1 micrometer.

The fabrication of a prototype imaging X-ray detector is presented. The detector is composed of aluminum/aluminum oxide/aluminum/niobium superconductive tunnel junctions sputtered directly on a high purity niobium single crystal with an RRR of about 15000. The detector has the potential to offer high energy resolution in addition to a high quantum efficiency, large detection area and improved imaging capabilities. The spatial and temporal response of the detector has already been derived.

Electron beam and laser beam scanning microscopy are two typical methods used to electrically characterize thin films and junctions. A study compared the electron- and laser-beam scanning techniques in an electrical characterization of high critical temperature, thin film Josephson junctions. The purpose of the experiment is to develop spatially resolved methods for electrically characterizing thin films and junctions, which is crucial for further advances in physics and applications of high temperature semiconductors.

Research was conducted to examine a novel type of self-synchronizing two-dimensional Josephson junction arrays based on special symmetry breaking network architectures. The calculations prove that the Josephson oscillators mutually synchronize into a coherent in-phase state and that such arrays can emit maximum coherent microwave power in the entire theoretically expected frequency range. Experimental results indicate that the symmetry breaking array architecture will be applicable for an implementation with Josephson junctions made from high critical temperature superconductors.

A study was conducted to analyze double peak phenomenon in superconducting tunnel junction x-ray detectors. Square junctions were fabricated by the dc-sputtering of aluminum surface by photolithographic patterning using reactive ion etching. Results indicated that the double peak correlated with the dynamics of quasiparticles resulting from x-ray absorption events. In addition, the double peak phenomenon was influenced by by bias voltage and magnetic history.

A study was conducted to examine superconducting tunnel junctions supporting various multilayer structures by low temperature scanning electron microscopy. A trapping layer from utilized to eliminate the response of the base electrode in the junctions. Results indicated the possibility of separating different quasiparticle loss processes by determining the quasiparticle lifetimes of junctions with various film thicknesses at different temperatures.

A study was conducted to examine the two-dimensional arrays of overdamped Josephson junctions under microwave irradiation. Arrays of 10 Josephson junctions were utilized in the study while the electron beam was determined at a frequency of 20 kHz. Results indicated that the critical current spread influences the arrays' behavior under microwave irradiation. They also indicated a close association between the dynamic resistance and frequency locked junctions.

Niobium-based superconducting tunnel junctions are proposed for high energy resolution x-ray detectors. Inhomogeneous response, however, results from lateral diffusion and the loss of excess particles at the edges. Detectors with a Ta-trap were developed to analyze the energy resolution degradation. The approach successfully trapped the killed electrode and removed it from the tunneling process.

A detailed study was conducted on two-dimensional arrays of overdamped Josephson junctions based in Nb/Al2O3/Nb-technology. Microwave-coupled on-chip detectors reveal that the arrays emit coherent microwave radiation. The coupling of microwave radiation to an on-chip load was examined using low-temperature scanning electron microscopy. A method for deriving the margins of the critical current spread of the junctions for coherent oscillation is described.

Low-temperature scanning microscopy is used to obtain two-dimensional images of vortex dynamics in two-dimensional overdamped Josephson junction arrays at zero applied magnetic field. A vortex model is then employed to characterize the images. Results show that vortex-vortex interaction becomes for evident in the arrays as the bias current increases. Nucleation of current-induced vortices at the array boundaries also occurs at bias currents slightly above the critical current.

The magnetic field dependence of the supercurrent density in YBa2Cu3O7-delta Grain Boundary Josephson Junctions is investigated by measuring the thermal noise induced slope of the devices' current-voltage characteristics. The measurements are conducted in the large magnetic field range between zero and 12 T. Results show that the supercurrent density has strong inhomogeneities on small length scales in the nanometer regime.

Low temperature scanning electron microscopic studies of the higher order zero field steps of long inline and overlap Josephson junctions suggest the possible occurrence of several stable states in the presence of more than one fluxon in the junction. The occurrence is associated with different spacing among fluxons during their propagation. The emitted radiation spectrum is associated with the variation in these dynamic states. Numerical simulations attribute fluxon interaction with plasma oscillations to the observed behavior.

The characterization of the current density distribution in an edge-shaped region of a planar YBa2Cu3O7-[Delta] flux transformer is reported for the first time. The analysis was performed by means of three-dimensional computation of the electromagnetic field. In addition, experimental studies using low-temperature scanning electron microscopy were carried out. It is shown that the current density distribution in edge regions deviates strongly from the symmetric case, which is established in the case of straight conductors. The results of calculation and measurement are discussed with respect to consequences for the design of flux transformers for SQUID systems.

Low temperature scanning electron microscopic technique is employed for the spatially resolved investigation of single-electron tunneling (SET) circuits. Signals from various parts of the circuits are imaged with the help of circuit voltage, recording as a function of the beam coordinates. Charge trapping near SET-transistor induces memory effect. The efficiency of this technique is demonstrated with a system having 11 electrons.

A superconducting circuit and microfabrication technology were combined in an advanced cryoelectronic detection system. Superconducting tunnel junctions with thin silicon membrane window substrates were used to for the formation of the detector system. The estimation of ionizing radiation-generated excess quasiparticles was the basis of the system's operation. The utility of the combination was demonstrated.

The performance of Josephson junctions and superconducting integrated circuits operating at a spatial resolution of one micrometer was evaluated by low temperature scanning electron microscopy. Two dimensional arrays of coherently oscillating Josephson junctions coupled to a detector junction were used in the investigation. Results show that the linear properties of the junctions are strongly dependent on the prevailing boundary conditions.

The interaction of fluxons with Abrikosov vortices in long quasi-one-dimensional Josephson junctions was investigated. An electron beam technique was used to inject an Abrikosov vortex into a long Josephson junction. The interaction force between the vortex and the fluxons in the junction was then measured using the critical current values. Results show that the trapped magnetic flux quanta induced by the vortex-fluxon interaction has a strong influence on the performance of the Josephson junction.

The movement of fluxon between the superconducting electrodes of a Josephson junction was studied. Long linear Josephson junctions were subjected to a relatively high magnetic field. The current-voltage curves were then obtained by a sequential crossing of the junctions with an applied electron beam generated by a flux-flow oscillator. Results indicate that the movement of fluxon in the junction induces large narrow band radiation in the frequency range of 62 to 77 gigahertz.

The temporal and spatial characteristics of irradiated Nb/AlOx/NB tunnel junction detectors were studied. The detectors, which were fabricated by the Selective Niobium Etching Process, were irradiated by electrons of different energies using Low Temperature Scanning Electron Microscopy. The homogeneity of the detector response to radiation was then analyzed to determine its influence on the detectors' energy resolution. Results show that the irradiation process causes a degradation of the junctions' energy resolution.

X-ray photoelectron spectroscopy was used to investigate the chemical composition of the surfaces and interfaces of NbN-MgO-NbN trilayers prepared by magnetron sputtering. The results showed that oxygen ions and atoms were generated in the MgO barrier layer and resulted in strong plasma oxidation during the deposition process. Adsorption layers of hydroxides on the MgO resulted in the formation of niobium oxide components. Annealing of the NbN-Mgo layers prior to the deposition of the top electrode effectively prevented the formation of niobium suboxide layers and microshorts.

With low-temperature scanning electron microscopy, the magnetic flux states in high critical temperature Josephson junctions have been imaged. The experiments were performed with [YBa.sub.2][Cu.sub.3][O.sub.7-δ] thin-film grain boundary Josephson junctions fabricated on [001] tilt [SrTiO.sub.3] bicrystals. For applied magnetic fields parallel to the grain boundary plane, which correspond to local maxima of the magnetic field dependence of the critical current, the images clearly show the corresponding magnetic flux states in the grain boundary junction. The spatial modulation of the Josephson current density by the external magnetic field is imaged directly with a spatial resolution of about 1 micrometer., Grain boundaries in the high temperature superconductors are known to act as weak links limiting the transport-critical current density of polycrystalline materials[1]. Whereas the weak links of grain boundaries are [...]

The emission spectrum of two-dimensional Josephson junction arrays was investigated. A low temperature scanning electron microscope was used in measuring the junctions' direct current (dc) and radio frequency properties. The measurements were obtained by coupling the array emission to a detector junction via a dc blocking stripline capacitor. Results reveal that the high coherent power emitted by the two-dimensional arrays is caused by an internal resonance in the array unit cells.

The effect of the acceptor concentration on the avalanche breakdown electric field was investigated. The results showed that the avalanche breakdown electric field increased linearly with the concentration of doping acceptors. The mechanics of the electric breakdown changed as the material increased in purity. Breakdown behavior became different when the sample length was equal to or less than the inelastic scattering length.

Spatially Resolved Observation of Supercurrents Across Grain Boundaries in YBaCuO Films A DETAILED UNDERSTANDING OF THE electronic properties of the grain boundaries in superconducting [YBa.sub.2.Cu.sub.3.O.sub.7] is important both for fundamental [...]