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  • 1
    Electronic Resource
    Electronic Resource
    Investigation of epitaxial niobium based superconducting tunnel junction detectors
    Amsterdam : Elsevier
    Physica B: Physics of Condensed Matter 194-196 (1994), S. 1663-1664 
    Details
    ISSN: 0921-4526
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0921-4526(94)91331-5
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  • 2
    Electronic Resource
    Electronic Resource
    S-Cam: A spectrophotometer for optical astronomy: Performance and latest results (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 4582-4591 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: S-Cam is a cryogenic optical camera for ground-based astronomy designed around a 6×6 array of superconducting tunnel junctions. It has been conceived as a technology demonstrator, aimed at proving the potential of a new generation of single photon counting detectors for ground-based telescopes and as a possible precursor to a future space-based instrumentation. The camera is based on a 6×6 array of Ta–Al Josephson junctions, operating at about 350 mK and individually read out. For each detected photon, the absorption position, the arrival time, and the corresponding energy are measured. This allows for recording an image and simultaneously obtaining spectrophotometric information from the observed objects. In this article we provide an overview of the latest cryogenic detector performance, an up-to-date description of the S-Cam system, and a summary of the results obtained both during testing at ESTEC and during actual observations at the William Herschel Telescope in La Palma (Canary Islands, Spain). An example of the novel astronomical data obtained during the latest observation campaigns (December 1999 and April 2000) is also described. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1326055
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  • 3
    Electronic Resource
    Electronic Resource
    Design and performance of a portable 3He cryogenic system for ground based instrumentation (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 4088-4096 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The availability of compact cryogenic refrigerators is of importance for the development of both ground and space-borne instrumentation based on cryogenic detectors. In this article we report on the design and performance of a complete ground based cryogenic system consisting of a 3He cryosorption refrigerator, and designed to cool a 6×6 element detector array of tantalum based superconducting tunnel junctions (STJs). The refrigerator provides an operating temperature of 330 mK, with a hold time in excess of 7 h. The system is designed to be portable, to provide a very stable focal plane, and to minimize the use of magnetic materials. Such a system has been used to host the focal plane assembly of S-Cam, the first optical camera for ground based astronomy utilizing an array of STJs, recently installed at the William Herschel Telescope, in La Palma. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149303
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  • 4
    Electronic Resource
    Electronic Resource
    X-ray detection by superconducting tunnel junctions via phonon propagation in the substrate (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 7362-7369 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The x-ray performance of Nb-Al-AlOx-Al-Nb superconducting tunnel junctions deposited on sapphire has been studied for phonon mediated detection of x rays absorbed in the substrate in the energy range 750 to 6000 eV. Two separate channels of phonon propagation can be identified. One produces a discrete signal peak, due to high frequency phonons originating from the x-ray absorption sites in a shallow layer below the junction. The other contributes to a monotonic signal tail, due to low frequency phonons, reaching the junction after diffusive or multiple scattering at surfaces. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361452
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  • 5
    Electronic Resource
    Electronic Resource
    High-resolution x-ray spectra measured using tantalum superconducting tunnel junctions (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 3359-3361 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The spectral response of a 100×100 μm2 tantalum based superconducting tunnel junction to 5.9 keV x-ray photons from a 55Fe source has been studied. In full illumination the energy resolution for the Mn Kα line complex is 56 eV, dominated by spatial nonuniformity in the response of the detector. When illuminating selectively a 5–10 μm diam spot in the center of the detector, the energy resolution improves to 22 eV, corresponding to 15.7 eV for the individual Mn Kα1 and Mn Kα2 lines. This exceeds the predicted theoretical energy resolution of 7.3 eV for this type of device by only a factor of ∼2. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121603
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  • 6
    Electronic Resource
    Electronic Resource
    Transmission electron microscopy and atomic force microscopy analysis of Nb-Al-AlOx-Nb superconducting tunnel junction detectors (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 4099-4106 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The performance of photon detectors based on superconducting tunnel junctions are related to their current - voltage (I-V) curve characteristics and, ultimately, to the quality of the thin tunnel barriers (of order 1 nm) which separate the two superconducting thin films. Both the optimization of the spectroscopic performance of these detectors and the development of a reproducible and high yield fabrication route, require a better understanding of barrier quality and growth techniques. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) provide valuable tools for the investigation of the barrier region and for the control of the quality of the different thin films and related interfaces. In this paper, the results of a TEM and AFM evaluation of Nb-Al-AlOx-Nb tunnel junctions are reported, together with their interpretation on the basis of the I-V curve performance at low temperature (T≥0.3 K). Thickness disuniformities of the Al plus AlOx overlayer and evidence of barrier defects have been found, which may place constraints on the spectroscopic performance of such devices. Through the use of TEM it has also been possible to confirm the epitaxial nature of the Nb base electrode. The junction counter electrode however appears to be polycrystalline, with a columnar morphology and an average grain width of 40 nm. The overall structure of the various layers may well place constraints on the tunneling characteristics of the device. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359492
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  • 7
    Electronic Resource
    Electronic Resource
    NbN–Nb–Al superconducting tunnel junctions as photon counting detectors (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 5536-5542 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Asymmetric NbN–Nb–Al–AlOx-Al–Nb superconducting tunnel junctions have been investigated as photon counting detectors at x-ray and ultraviolet (UV)-visible wavelengths. The inclusion of a thin NbN passivation layer on the top electrode of the devices in place of the natural niobium oxides has reduced the quasiparticle loss rates, thereby enhancing the probability of multiple tunnel processes. As a consequence, the detector responsivity has increased from 900e−/eV, up to values in excess of 2000e−/eV in the temperature range 0.3–0.8 K. Such a responsivity level has allowed single photon counting performance at wavelengths as long as 700 nm and at operating temperatures as high as 830 mK. The devices show a linear response in the UV-visible range, while at 6 keV the expected nonlinearities in the energy response and moderate energy resolution similar to that found in Nb–Al junctions are observed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.367384
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  • 8
    Electronic Resource
    Electronic Resource
    Response linearity of Nb tunnel junction detectors for photon energies from 1.5 to 6.4 keV (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 2490-2493 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent experimental results show a linear energy response in high quality Nb-Al-AlOx-Nb superconducting tunnel junction detectors for photon energies between 1.5 and 6.4 keV. The experimental data are based on both direct x-ray illumination and on the escape and re-absorption of fluorescent photons created in the junction electrodes and in the silicon substrate. The observed linearity of the energy response raises questions on the validity of some theoretical models which describe the relaxation process occurring in a superconducting thin film after x-ray photoabsorption. Such models generally predict nonlinear effects due to large quasiparticle number densities and short recombination times.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357607
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  • 9
    Electronic Resource
    Electronic Resource
    The suppression of phonon induced noise in niobium superconducting tunnel junction x-ray detectors (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 2574-2579 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An investigation into the phonon contamination of x-ray sensitive superconducting tunnel junctions arising from the x-ray photoabsorption in various substrates has been conducted. Results are presented on the design of a superconducting tunnel junction (STJ) which substantially reduces or even eliminates phonon induced noise from the substrate. Such noise is the predominant feature in x-ray spectra from junctions due to the bulk of the photons being absorbed in the substrate rather than in the thin superconducting film. The design involves the choice of a suitable buffer sandwich between the substrate and the STJ. Such a buffer would appear not only to attenuate the phonons created in the x-ray photoabsorption in the substrate but also to scatter the phonons inelastically, introducing a frequency down-conversion. Such a process ensures that few phonons of energy sufficient to break Cooper pairs in the superconducting film of the STJ enter the junction. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361124
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  • 10
    Electronic Resource
    Electronic Resource
    Optimization of superconducting tunnel junction based x-ray detectors (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 6774-6779 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Current research into x-ray detection using superconducting tunnel junctions indicates that the poor spectral resolution obtained so far, in comparison with theoretical expectations, is partly due to the excellent acoustic coupling of the junction and substrate. The substrate acts both as a source of noise and as a heat sink for the nonequilibrium junction, thus masking the intrinsic response of the superconducting electrodes to photoexcitation. A new design for a superconducting tunnel junction based on an x-ray detector is presented. The design effectively decouples the substrate and junction and should therefore eliminate many causes of spectral degradation, bringing resolution closer to that predicted theoretically, and thus allowing experimental investigation of the intrinsic superconducting film response to x-ray photoexcitation. An outline of the way in which the design can be optimized geometrically to achieve the decoupling is given. Further optimization of the intrinsic film response to x-ray photons is achieved through the introduction of specific absorbing and trapping regions to improve both the quantum efficiency and charge output of the new design. The use of "pairing potential barriers'' within the electrode leads will also improve the intrinsic resolution of this device.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355076
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