Energy resolution of 12 eV at 5.9 keV from Al-superconducting tunnel junction detectors

An energy resolution of DeltaE = 12 eV [full width at half maximum (FWHM)] has been measured for the Mn-55 K-alpha1 line (E = 5.9 keV) using a superco nducting lead absorber (90x 90x 1.3 mum(3)) readout by a single aluminum su perconducting tunnel junction (100x 100 mum(2)). The total detector area ha s been illuminated, while a slit mask of 150 mum width was used to partiall y shadow the detector leads and substrate area from impinging x rays. The t otal electronic noise contribution was measured as DeltaE(elec) = 4 eV (FWH M). The superconducting tunnel junction is located on a Si3N4 membrane of t hickness 0.3 mum, the lead absorber is separated from the superconducting t unnel junction's top layer by a thin layer of natural aluminum oxide. No de viations from linear energy response were observed in the energy range betw een E = 1.74 keV and E = 6.49 keV. The same resolution was obtained for a s ingle aluminum superconducting tunnel junction, where the influence of subs trate events was suppressed by a metallic buffer layer between tunnel junct ion and substrate. The escape of recombination phonons into the substrate c auses small nonlinearities in the tunnel junction's energy response. (C) 20 01 American Institute of Physics.