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  • 1
    Electronic Resource
    Electronic Resource
    NbN/MgO/NbN edge-geometry tunnel junctions (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 81-83 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the fabrication and low-frequency testing of the first edge-geometry NbN/MgO/NbN superconducting tunnel junctions. The use of an edge geometry allows very small junction areas to be obtained, while the all-NbN electrodes permit operation at 8–10 K with a potential maximum operating frequency above 1 THz. Edge definition in the base NbN film was accomplished utilizing Ar ion milling with an Al2O3 milling mask, followed by a lower energy ion cleaning step. This process has produced all-refractory-material tunnel junctions with areas as small as 0.1 μm2, resistance-area products less than 21 Ω μm2, and subgap to normal state resistance ratios larger than 18.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101760
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  • 2
    Electronic Resource
    Electronic Resource
    Superconducting phonon spectroscopy using a low-temperature scanning tunneling microscope (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 946-948 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the first observation of phonon density of states effects in a superconductor using a low-temperature scanning tunneling microscope (STM). The phonon effects were observed using a STM spectroscopy method to measure dItunneling /dV vs V for the tunnel junction formed by the Au STM probe and a superconducting Pb sample.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.100815
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  • 3
    Electronic Resource
    Electronic Resource
    Observation of adsorbate-induced surface states by elastic electron tunneling spectroscopy (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 58 (1985), S. 2266-2269 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electronic structure induced by adsorbates at the interface of Al/AlOx/Au tunnel junctions has been observed by elastic electron tunneling spectroscopy. Strong structures appearing in the tunneling spectra above ∼1 eV after exposure to I, Hg, Bi, and organohalides, have been interpreted in terms of adsorbate-induced surface states. The spectroscopic capabilities of elastic electron tunneling spectroscopy may be useful in the area of chemical detection. In the broader sense, the observation of adsorbate-induced unoccupied electronic states below the vacuum energy, makes elastic electron tunneling spectroscopy a potentially useful technique for the study of surfaces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.335944
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  • 4
    Electronic Resource
    Electronic Resource
    Length scaling of bandwidth and noise in hot-electron superconducting mixers (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 3344-3346 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Mixing experiments have been performed at frequencies from 4 to 20 GHz on Nb thin-film superconducting hot-electron bolometers varying in length from 0.08 to 3 μm. The intermediate frequency (IF) bandwidth is found to vary as L−2, with L the bridge length, for devices shorter than (square root of)12 Le−ph≈1 μm, with Le−ph the electron-phonon length. The shortest device has an IF bandwidth greater than 6 GHz, the largest reported for a low-Tc superconducting bolometric mixer. The conversion efficiencies range from −5 to −11 dB (single sideband, SSB). For short bridges, the mixer noise temperature is found to be as low as 100 K (double sideband, DSB), with little length dependence. The local oscillator power required is small, ≈10 nW. Such mixers are very promising for low-noise THz heterodyne receivers. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116052
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  • 5
    Electronic Resource
    Electronic Resource
    Large bandwidth and low noise in a diffusion-cooled hot-electron bolometer mixer (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 1558-1560 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Heterodyne measurements have been made at 533 GHz using a novel superconducting hot-electron bolometer in a waveguide mixer. The bolometer is a 0.3 μm long niobium microbridge with a superconducting transition temperature of 5 K. The short length ensures that electron diffusion dominates over electron-phonon interactions as the electron cooling mechanism, which should allow heterodyne detection with intermediate frequencies (if) of several GHz. A Y-factor response of 1.15 dB has been obtained at an if of 1.4 GHz with 77 and 295 K loads, indicating a receiver noise temperature of 650 K DSB. The −3 dB rolloff in the if response occurs at 1.7 GHz. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115698
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  • 6
    Electronic Resource
    Electronic Resource
    Low noise in a diffusion-cooled hot-electron mixer at 2.5 THz (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 1567-1569 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The noise performance of a Nb hot-electron bolometer mixer at 2.5 THz has been investigated. The devices are fabricated from a 12-nm-thick Nb film, and have a 0.30 μm×0.15 μm in-plane size, thus exploiting diffusion as the electron cooling mechanism. The rf coupling was provided by a twin-slot planar antenna on an elliptical Si lens. The experimentally measured double sideband noise temperature of the receiver was as low as 2750±250 K with an estimated mixer noise temperature of (approximate)900 K. The mixer bandwidth derived from both noise bandwidth and IF impedance measurements was (approximate)1.4 GHz. These results demonstrate the low-noise operation of the diffusion-cooled bolometer mixer above 2 THz. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.119967
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  • 7
    Electronic Resource
    Electronic Resource
    Low-noise 1 THz niobium superconducting tunnel junction mixer with a normal metal tuning circuit (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 1714-1716 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We describe a 1 THz quasioptical SIS mixer which uses a twin-slot antenna, an antireflection-coated silicon hyperhemispherical lens, Nb/Al-oxide/Nb tunnel junctions, and an aluminum normal-metal tuning circuit in a two-junction configuration. Since the mixer operates substantially above the gap frequency of niobium (ν(approximately-greater-than)2Δ/h∼700 GHz), a normal metal is used in the tuning circuit in place of niobium to reduce the Ohmic loss. The frequency response of the device was measured using a Fourier transform spectrometer and agrees reasonably well with the theoretical prediction. At 1042 GHz, the uncorrected double-sideband receiver noise temperature is 840 K when the physical temperature of the mixer is 2.5 K. This is the first SIS mixer which outperforms GaAs Schottky diode mixers by a large margin at 1 THz. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115915
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  • 8
    Electronic Resource
    Electronic Resource
    Performance limitations of niobium-based submillimeter-wave quasiparticle mixers operating near the gap frequency (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 424-426 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have measured the noise temperature of heterodyne receivers employing Nb/AlOx/Nb tunnel junction mixers at frequencies ranging from 70% to 93% of the gap frequency of niobium (∼700 GHz). The sensitivity of the receiver is decreased by the overlap of the n=1 and n=2 photon steps of opposite sign. At bias voltages where these photon steps overlap, there is an increase in receiver noise up to 50%. Theoretical calculations using the Tucker theory agree well with the observed mixer performance. This overlap already affects the receiver operation for best performance at frequencies well below 700 GHz. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.114620
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  • 9
    Electronic Resource
    Electronic Resource
    Dispersion in Nb microstrip transmission lines at submillimeter wave frequencies (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 2712-2714 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have measured the effects of dispersion on the resonant mode frequencies of open-ended Nb-SiOx-Nb microstrip transmission lines over a frequency range from 50 to 800 GHz. Submicron Nb/Al-AlOx/Nb Josephson junctions were used as both voltage-controlled oscillators and detectors to sample the high order modes of the resonators. The resonator modes are equally spaced up to about 550 GHz where the mode spacing start to decrease gradually to a minimum above the gap frequency fg≈700 GHz and then increases. Results are in good agreement with the expected theoretical behavior based on the Mattis–Bardeen conductivity of the superconductor line.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.108069
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  • 10
    Electronic Resource
    Electronic Resource
    A low-noise 492 GHz SIS waveguide receiver (1992)
    Springer
    International journal of infrared and millimeter waves 13 (1992), S. 785-798 
    Details
    ISSN: 1572-9559
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this paper we discuss the design and performance of an SIS waveguide receiver which provides low noise performance from 375 to 510 GHz. At its design frequency of 492 GHz the receiver has a double sideband noise temperature of ∼172 K. By using embedded magnetic field concentrators, we are able to effectively suppress Josephson pair tunneling. Techniques for improving receiver performance are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01011595
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