Abstract
Superconducting tunnel junction (STJ) detectors are promising for energy-dispersive X-ray spectroscopy. We are developing array detectors with a sensitive area of 4 mm 2, which consist of 100 of Nb/Al/AlO x /Al/Nb STJs having a size of 200 × 200 μm 2 in order to obtain a good statistic for a short measurement time while keeping an excellent energy resolution for element selection in X-ray material analysis. In the course of this development, we analyzed the microstructures of the layers of Nb, Nb/Al, Nb/Al/AlO x /Al and Nb/Al/AlO x /Al/Nb deposited on Si substrates by using AFM (Atomic Force Microscope) and cross-sectional TEM (Transmission Electron Microscope). We found that the grain sizes of the polycrystalline films and the interface boundaries in the top electrodes are quite different from those in the bottom electrodes in a nanometer scale. It is expected that these different microstructures cause different heights of the pulse signals for the X-ray photon absorption events in the top and bottom electrodes.
Published Version
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