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We present our achievements in the development of superconducting strip-line detectors (SSLDs) with parallel configuration for application in time-of-flight mass spectrometry. We have fabricated 2×2 mm SSLDs by electron beam nano-lithography. In spite of the large area, the detector has a fast time response. To our knowledge our device is the largest cryogenic detector for macromolecules with nanosecond temporal response. Based on the obtained results, our simulations show that the presented parallel SSLD design should be able to cover an area of 4×2 mm while keeping the signal pulse risetime below 1 ns. [ABSTRACT FROM AUTHOR]

An analysis of different strategies for increasing the maximum count rate of superconducting single photon detectors using parallel nanowires is performed with particular emphasis on the expected behaviour when the detector area is increased. We find that for a serial connection of blocks of parallel nanowires, the maximum count rate decreases with the square root of the detector area, whereas it decreases proportional to the detector area for current meandered detectors. Using this design we estimate that a signal pulse falltime of 7.8 ns for a 84 × 84 µm2 parallel detector based on current material parameters should be obtainable. We argue that the slow decrease of count rate with detector area might permit detectors based on parallel nanowires to fully exploit the available cooling power. [ABSTRACT FROM AUTHOR]

We report on a class of low temperature radiation detectors based on superconducting tunnel junctions (STJ5) in which the incoming radiation is absorbed in a long superconducting strip while the readout operation occurs at the two ends of the strip, where two STJs are laterally positioned. These Distributed Read-Out Imaging Devices, or DROIDs, provide spectroscopy, 1-D imaging, single-photon sensitivity, and high quantum efficiency, all in one device. Typically these devices are realized by using Tantalum for the absorber strip and Aluminum for the two STJs. In this way the quasi-particles are created in the Tantalum and subsequently trapped in the Aluminum. As illustrated here, it is possible to fabricate a DROID using a single superconducting material. This choice gives up the trapping effect but has the advantage of eliminating the interface between different superconducting materials. Such a device combines the best quality STJs, large diffusion and lifetime values, with low energy gap for improved energy and position resolution. We report on measurements of current injection done on prototype devices, which demonstrates that STJs can serve as quasi-particle sinks and facilitate charge division in DROIDs. For sufficiently high tunneling rates, DROIDs based on a single material may be able to obtain performances comparable to DROIDs based on two materials. [ABSTRACT FROM AUTHOR]

A novel class of sensors is constituted by radiation detectors based on superconducting tunnel junctions, which could lead in the next future to an advanced instrumentation with an interesting fall out for applications. So far, this area is restricted to LTc superconductors. Among them, niobium has the highest critical temperature and is therefore less demanding in terms of operational temperature. The best performances achieved so far in pure Nb-based junction are far away from the expected theoretical limit. The reason of this discrepancy could be attributed to various problems. Quasiparticle diffusion and edge losses seem to be responsible for the broadening of the signal amplitude spectra so often observed and reported in literature. In this paper we report on efforts to investigate the response to X-Ray of Nb-based superconducting tunnel junctions in terms of a model which includes the quasiparticle diffusion and the edge losses. Our model takes into account the contribution from both the electrodes of the junction and well reproduces the experimental data. [ABSTRACT FROM AUTHOR]

A large-area (200×200 μm2) superconducting stripline detector based on a parallel configuration of superconducting Nb nanowires is presented. We show that the parallel configuration provides a smart way to control the physical nonequilibrium state induced by the molecular impacts, which allows realizing large sensitive area and subnanosecond response at the same time. The experiments were carried out with molecular ions radiation in a keV energy range. The observed rise time was below 400 ps and the relaxation time was 500 ps, the best in this class of superconducting molecular detectors. [ABSTRACT FROM AUTHOR]

We have realized superconducting single photon detectors with reduced inductance and increased signal pulse amplitude. The detectors are based on a parallel connection of ultrathin NbN nanowires with a common bias inductance. When properly biased, an absorbed photon induces a cascade switch of all the parallel wires generating a signal pulse amplitude of 2 mV. The parallel wire configuration lowers the detector inductance and reduces the response time well below 1 ns. [ABSTRACT FROM AUTHOR]

A fast current discriminator, based on Josephson junctions, has been developed to boost the performance of novel type of superconductive detectors in time-of-flight mass spectrometers. The Josephson discriminator could greatly improve the mass resolution in such machines, and it is technologically compatible with the proposed superconductive tunnel junction detector. The effect of intrinsic thermally induced fluctuations in such a device has been investigated to identify the possible operating ranges, in terms of temperature, geometry and materials concerned. Experimental results on the feasibility of the proposed device are also reported. [Copyright &y& Elsevier]

Carbon nanotubes addition to polymer and epoxy material allows to realize a large variety of new types of sensors and actuators. For the development of these devices, a deeper understanding of the basic charge carriers transport mechanisms is needed and low-frequency noise spectroscopy can effectively contribute to this task. The dc and electrical noise characteristics of different polymer/carbon nanotubes composites are analyzed at temperatures from 10 to 300 K. It has been found that a random tunnel junctions resistive networks model describes all the systems under test. A crossover from a two-level tunneling mechanism, at low temperatures, to resistance fluctuations induced by percolative paths, in the high-temperature region, has also been observed. This behavior of the 1/f noise is a general feature of the investigated highly conducting nanocomposites, independent of the specific polymer matrix and nanotube concentration. [ABSTRACT FROM AUTHOR]

The development of a superconductive detector for simultaneous measurement of energy and arrival time is reported. The detector consists of two superconducting tunnel junctions coupled through a passive network. The first junction operates in the quasi-particle regime and measures the energy absorbed by counting the total charge that tunnels. The second junction uses the DC Josephson effect to act as a fast discriminator for the onset of surplus current in the first junction. The feasibility of the detector is demonstrated through simultaneous time and energy measurements of 6 keV X-rays. A model of the detector is presented and numerical simulations show good correspondence with experimental data. [Copyright &y& Elsevier]