Superconducting Tunnel Junction Detectors for Analytical Sciences

Abstract

Superconducting tunnel junction (STJ) detectors exhibit superior detection performance for photons and particles at a high spectroscopic resolution of ∼10 eV, a short dead-time (decay time) of ∼μs, a high quantum efficiency of ∼100%, and a low detection threshold energy of less than 1 eV, which cannot be achieved by conventional detectors. The outstanding detection performance originates from a small superconducting energy gap of ∼meV, which is three orders of magnitude smaller than ∼eV in semiconductors. This paper reports our recent progress in two applications of STJ detectors to fluorescence-yield X-ray absorption fine structure (XAFS) spectrometry for trace light elements in matrices and mass spectrometry (MS) for ions with the same mass/charge-number ratio (m/z) but different charge states and neutral fragments.Index Terms-Mass spectroscopy (MS), superconducting devices, superconducting tunnel junction (STJ), X-ray absorption fine structure (XAFS), X-ray detection. I. INTRODUCTIONS UPERCONDUCTING tunnel junction (STJ) detectors have a sandwich structure of superconductor-insulatorsuperconductor with an insulator thickness of ∼1 nm. The device structure is the same as that of Josephson junctions. For detecting photons or particles, the STJ detectors are operated in the so-called Giaever mode [1], in which the dc Josephson effect is suppressed by applying a small magnetic field of 10-100 G so that the change of quasiparticle tunnel current can be measured. The junctions are biased within the sub-gap region to observe the change of quasiparticle tunnel current.

Heat-Induced Dry Hydrolysis of Sodium Borohydride/Oxalic Acid Dihydrate Composite for Hydrogen Production

“…The hydrogen yield was higher than the theoretical maximum of 4.92 wt %, plausibly due to gaseous contaminants, including carbon monoxide and carbon dioxide, produced by the thermal decomposition of OA at temperatures higher than 100 °C (see Figure S3b). Note that dry hydrolysis of the SB/OA•2H 2 O 44 Figure 5c displays the TCD response to the gaseous products generated by the dry hydrolysis of the SB/OA•2H 2 O composite. The TCD response to hydrogen gas was calibrated with 5, 10, and 30% hydrogen references, and the results showed that the gas products obtained by the dry hydrolytic dehydrogenation of the composite contained mostly pure hydrogen and a small portion of Ar gas without harmful gases that can potentially poison the PEMFC.…”

“…The single peak shown at t R = 1.545 min owing to the flow of the air is either commonly observed in SB/OA·2H 2 O or the air undergoes dry hydrolysis. The peaks assigned to the three most abundant gases in the atmosphere, that is, N 2 ( m / z = 28.1), O 2 ( m / z = 32.1), and Ar ( m / z = 40.1) peaks are clearly observed with small percentages of N ( m / z = 14), O ( m / z = 16), and H 2 O ( m / z = 18) …”

Development of an Energy-Sensitive Detector for the Atom Probe Tomography

“…This can be explained by the difficulty to measure additional physical quantities, while preserving the existing high performances of current APT instruments (Da Costa et al, 2012). Recent developments of position-energy-sensitive detectors (PESDs) greatly compounds this difficulty (Funsten et al, 2004;Buhr et al, 2010;Ohkubo et al, 2014;Fujii et al, 2015), where it can be stated that existing arrays of energy-sensitive cells introduce a very slow response time, that does not go below hundreds of nanoseconds, which is a longway from the few nanoseconds required in APT experiments. This limitation should have the effect of restricting the detection rate and the multi-hit capability of APT instruments.…”

Low Leakage Current Nb-Based Tunnel Junctions with an Extra Top Al Layer

“…On the other hand, Nb/Al/AlO x /Al/Nb junctions, as shown in Fig. 1, are used in X-ray or terahertz detectors because of their low leakage features [3]. The top Al layer is expected to suppress not only the creation of metallic channels in the AlO x insulator, but also to suppress the growth of lower valence niobium oxides on the AlO x because of the chemical reaction between the Nb and AlO x during the deposition of the top Nb electrode.…”