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We report high resolution Fourier Transform Infrared (FTIR) spectra of nitrogen trifluoride (trifluoroamine, NF3) measured with the Zurich Bruker prototype spectrometer (ZP 2001) and the SLS THz/FTIR setup (2009 prototype) in the range 20–3000 cm - 1 at temperatures between 80 and 120 K using a collisional cooling cell designed with White cell multipath reflection optics and at room temperature (296 K). Except in the far-infrared with instrument limited resolution ( Δ ν FWHM = 0.0008 cm - 1 ) many of the spectra are nearly Doppler limited. Rovibrational transitions were assigned to 13 different vibrational bands and were used then in the fitting procedure. We re-investigated the bands 2 ν 4 , ν 1 , ν 2 + ν 4 , ν 1 + ν 4 , 2 ν 3 and ν 1 + ν 3 , which had been studied before, and we have analyzed the ν 2 + ν 3 , 2 ν 1 , ν 1 + ν 2 + ν 4 , ν 1 + ν 2 + ν 3 , ν 2 + 2 ν 3 , 3 ν 3 , ν 1 + 2 ν 3 bands for the first time. All our analyses refer to the isotopomer 14 NF3.

Transition edge sensor devices made with Mo–Au proximity bilayer thermometers have been fabricated. The bilayers were DC-sputter deposited directly on 250 nm thick pre-etched Si 3 N 4 membranes. Mo was deposited at 700°C, whereas Au was deposited at room temperature in the same pumpdown in order to allow for a good proximity effect. The superconducting transition temperature of devices with 43 nm Mo and 200 nm Au was around 190 mK . The transition width of bilayers deposited on membranes was substantially larger than those measured on samples deposited on the bulk substrate in the same fabrication run (≈2 mK ) . We consider this difference to be the result of a large temperature gradient across the membrane during the deposition process. Devices were tested with a single stage SQUID array kept at 2.2 K . The resolution of a device that has a transition width of 30 mK is 30 eV at 6 keV . A detailed study shows that the detector noise roughly scales with αI 0 , confirming the importance of thermal fluctuation noise in the thermometer.

Superconducting tunneling junction devices are being developed as energy resolving photon counting imagers. We have fabricated a series of Ta/Al/AlOx/Al/Ta devices with variable Al layer thickness, dAl, and measured their response to a weak visible photon source. Single photon sensitivity is observed. We model our system with a set of modified Rothwarf–Taylor equations including quasiparticle losses, trapping, (back)tunneling and calculate the charge responsivity as a function of dAl with one fitting parameter. The quasiparticle loss time for Al and Ta is found to be τ l ( Al )=35 μs and τ l ( Ta )=0.14 μs in our devices, respectively.

We fabricated X-ray detection devices by instrumenting 2 Al/AlO x /Al/Nb tunneling junctions at each end of strips of epitaxial Ta. The Ta strip acts as photon absorber and is a few hundreds of microns long, the Al layers act as quasiparticle traps. The quality of the epitaxial Ta thin film as well as the absorber/trap interface was varied. Devices kept at 550 mK and biased around 300 μV were irradiated by 6 keV photons. The total charge collected by both junctions varies with the energy released by absorbed photons, depends on various quasiparticle loss processes, and is a function of the bias voltage of the tunneling devices. Our arrangement enables to distinguish between energy resolution degrading mechanisms occuring in the Ta absorber and those present in the vicinity of the tunneling junctions.

We are developing small arrays of microcalorimeters based on transition edge sensors made with Mo/Au bilayers deposited on silicon nitride membranes and Au absorbers. The superconducting transition of the bilayers is adjusted to be around 130 mK with a transition width better than a millikelvin by use of the proximity e!ect between the Au and Mo "lms. We built a dilution refrigerator and wired it for 2 channel operation in order to study thermal coupling issues between thermometers within the array. The device fabrication procedure as well as preliminary results are presented. ( 2000 Elsevier Science B.V. All rights reserved.

A new Nb/AlO x /Nb trilayer process for X-ray detector applications has been developed. The process employs a movable mechanical slit which, after the sputter deposition of the base Nb electrode followed by a thin layer of Al and its oxidation, is shifted to a second position where the Nb counter electrode is deposited. The overlap area of the two electrodes forms the junction are after final patterning by standard photolithography and reactive ion etching. The best junctions so far obtained have, at 4.2 K, typically a quality factor of 42 mV with a Josepshon current density of 1200 A/cm 2 , and a tunneling time τ tun in the range of 50 to 500 ns. We discuss several aspects of this technique in comparison with the selective niobium anodization process (SNAP) and the selective niobium etching process (SNEP).

A whole wafer fabrication procedure using selective etching of refractory materials to produce Nb- or Ta/Al/AlO x Al/Nb tunneling X-ray detectors is discussed. Fabrication aspects and preliminary results are presented.

Results from a comparison between current-voltage data measured on Nb/Al/AlO x /Al/Nb tunneling junctions to a proximity effect model proposed by Golubov et al. [J. Low Temp. Phys. 70 (1988) 83] are used to get an estimation of the quasiparticle collection as a function of the Al-film thickness (4 and 120 nm) in X-ray detectors.

Laser ablated thin YBa 2 Cu 3 O 7 (YBCO) films on SrTiO 3 substrates were used to fabricate step edge Josephson junction arrays. After forming the substrate into a checkerboard arrangement of steep mesas of lattice parameter 7.5μ m , a YBCO film was deposited and patterned into a square network with the same lattice parameter. The arrays thus consist of 10 3 ×10 3 wires, 1.5 μ m wide and some 10 6 junctions at the sites of the steps. In a perpendicular magnetic field the conductance of the arrays shows up to 40 periodic oscillations, the periodicity corresponding to one flux quantum per array unit cell.

Pulsed laser deposition (PLD) was used to grow superconducting Ta-films with critical temperatures close to bulk values (4.5 K) on sapphire substrates. Results are compared with films grown by e-beam evaporation. The PLD method allows the growth of superconducting Ta-films on substrates kept at ambient temperature but film surfaces are plagued by sub-micron particles. On the other hand, e-beam evaporation results in smooth surfaces but requires a substrate temperature of the order of 400 ° C for producing high-quality superconducting films. Critical temperatures, residual resistance ratios, and crystal structure are presented.

The feasibility of using of current-biased superconducting strips for radiation detection is investigated. Narrow Ta strips are exposed to 5.5 MeV α-particle radiation and the rise-time of the induced voltage pulses is measured as function of temperature and bias current. The rise-time of the voltage signal strongly depends on the site on the strip which is hit by the α-particle. In order to determine the spatial resolution of a superconducting strip detector, position-sensitive measurements were performed. The maximum lateral resolution estimated so far is 25μm in a 7μm wide, 340 nm thick and 0.6 mm long Ta-strip.

The observation of quantum interference transitions in the dynamic resistance of a large two-dimensional array of proximity-effect junctions driven by superposed dc- and rf-currents is reported. It is shown that, under the synchronizing effect of the rf-field, the array behaves as a superposition of coherent quantum oscillators connected in series.