Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994phdt........32s&link_type=abstract
PhD Dissertation, Pennsylvania State Univ. University Park, PA United States
Astronomy and Astrophysics
Astrophysics
Tunnel Junctions, Superconducting Devices, X Ray Detectors, Epitaxy, Polycrystals, X Ray Spectroscopy, Superconducting Films, Energy Gaps (Solid State), X Ray Spectra, Temperature Gradients, Substrates, Astrophysics, Iron Isotopes, Spectral Sensitivity, Niobium, Aluminum, Aluminum Oxides, Ultrahigh Vacuum, Vacuum Chambers, X Ray Sources
Scientific paper
Superconducting tunneling junctions (STJ) show great promise in high energy resolution x-ray spectroscopy for use in x-ray astrophysics. An STJ is a sandwich of an insulator between two superconductors (S-I-S). Such a device has an intrinsic energy resolution an order of magnitude better than any existing semiconductor device, including the charge coupled device (CCD). The potential impact on x-ray astrophysics is enormous, with possible future use on sounding rockets and other as yet undefined satellite missions. This thesis compares two STJ's that have been fabricated using Nb/Al/Al2O3/Nb in the same ultra-high vacuum chamber with the same layer thicknesses with the only difference being that the base layers are either fine grain (polycrystalline) or epitaxial. The testing was done at temperatures between 0.4 K and 4.2 K. The comparison included subgap spectra from an Fe-55 x-ray source. The findings showed that the fine grain junction had a tunnel barrier of much higher quality and yielded higher energy resolution. It was determined that the epitaxial junction was much more sensitive to substrate events. Two peaks were found in the x-ray spectra. Each peak was attributed to x-ray interactions within one or the other superconducting films of the junction.
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