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112-Pixel Arrays of High-Efficiency STJ X-ray Detectors

112-Pixel Arrays of High-Efficiency STJ X-ray Detectors. Synchrotron Science ALS, SSRL. Stephan Friedrich Matthew Carpenter LLNL (Detector Testing). John Hall Robin Cantor Star Cryo (Fabrication). Jack Harris Bill Warburton XIA (Electronics).

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112-Pixel Arrays of High-Efficiency STJ X-ray Detectors

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  1. 112-Pixel Arrays ofHigh-Efficiency STJ X-ray Detectors Synchrotron Science ALS, SSRL Stephan Friedrich Matthew Carpenter LLNL (Detector Testing) John Hall Robin Cantor Star Cryo (Fabrication) Jack Harris Bill Warburton XIA (Electronics) This work was funded by DOE grants DE-SC0006214, DE-SC0002256 and SC-0002256. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

  2. Superconducting Tunnel Junction Detectors STJ Operating Principle X-ray Photon Ta AlAl Ta AlOx Al O Ta Absorber 2 3 Al Al SiO 2 Ta Nb ΔTa SiO 2 ΔAl Si Substrate Signal = Current pulse 200×200 μm2 Energy resolution ∆EFWHM = 2.355√(εE(F+1+1/<n>) Small energy gap (Δ≈ 1meV) ⇒ (Comparably) high energy resolution (<10 eV FWHM) Short excess charge life time (~µs) ⇒ (Comparably) high count rate (>5,000 counts/s) LTD-15, Pasadena

  3. STJ Performance (as of LTD-14) Single-pixel spectrum of MnO + Fe7(CN)18 on Al Resolution vs. Count Rate LTD-15, Pasadena

  4. At the Synchrotron, We Need Efficiency Options: 1) Increase area/pixel 2) Thicker Ta absorber 3) Arrays: Detectors, readout Single Pixel 36 Pixels 200 x 200 µm2 112 pixels of 200 x 200 µm2 STJs ⇒ Matt Carpenter (Monday talk) For details on fabrication, ask Robin Cantor at the STAR Cryoelectronics booth. LTD-15, Pasadena

  5. Scalable 32-Pixel STJ Preamplifier RF Old: Single channel New: 32 channels STJ Preamp Controller STJ en Vout=IXRF IX Rdyn en Vout=IXRF Vbias IX Rdyn Vbias from DAC Existing preamp works fine, but is too big, too expensive (~$1k) and bias is manual. New preamp has same noise, but is small, cheap ($25 in parts), and remote-controlled. LTD-15, Pasadena

  6. Small, Cheap, Remote-Controlled Preamp Simultaneous bias scan of all pixels: Average current provides I(V)… … rms fluctuations measure noise. For details, ask Bill Warburton at XIA LLC LTD-15, Pasadena

  7. X-ray Spectra at LLNL With new 32-channel XIA preamp (and 32-pixel digitizer / DSP board): With old single-channel preamp: 27 of 32 pixels tested have high resolution (rest is either open or shorted). LTD-15, Pasadena

  8. More X-ray Spectra from Same 112 Pixel array With new 32-channel XIA preamp (and 32-pixel digitizer / DSP board): With old single-channel preamp: 26 of 32 pixels tested have high resolution (rest is either open or shorted). LTD-15, Pasadena Ta STJs seem to trap flux more easily than Nb STJs.

  9. Sum Spectra 53 pixels of 112-pixel STJ array, 165 nm Ta absorber With old setup, rise time discrimination can be used to veto bottom layer events. ⇒ a) Implement veto in XIA DSP, or b) Make STJs with thicker Ta absorber LTD-15, Pasadena

  10. X-ray Absorption Spectroscopy with STJs Synchrotron Monochromatic, intense X-ray beam Sample x Absorption µx(E) Detection Three options: vacuum valence levels Electron yield: Sample surfaces Moderate bgnd. Fluorescence: Bulk samples Low background core levels Monochromator Sample Transmission: Thin samples High background Scan energy of X-ray beam, measure absorption (by transmission, e-yield or X-ray yield) Fluorescence-detected XAS provides highest sensitivity, if the detector used can separate the fluorescence of interest with high efficiency. LTD-15, Pasadena

  11. Organic Photovoltaics (“Plastic Solar Cells”) • Cheap, light, cheap, flexible, cheap… • Not as efficient yet, ~12% max in the lab • Efficiency depends on microstructure Ca-L-edge Absorption Spectrum with Ca electrode removed. Bulk hetero-jct. active layer Ca/Ag electrode P3HT - PCBM PEDOT:PSS ITO electrode Glass substrate For details, ask Adam Moulé at UC Davis LTD-15, Pasadena

  12. Organic Photovoltaics (oPV) Ca XAS of organic PV material (PCBM) C XAS: Occupancy at EF changes: Doping! Energy levels: EF(Ca)=-2.9eV EC(oPV)=-3.7eV EF(Ag)=-4.6eV Band gap EV(oPV)=-6.1eV Ca diffuses from electrode into active area! Electrode materials can serve as dopants. S. Mauger et al., Adv. Funct. Mater. 23, 1935 (2013) LTD-15, Pasadena

  13. 112-Pixel Ta-STJ X-ray Detector Arrays • ~5 to ~10 eV FWHM below ~1 keV, ~5000 counts/s per pixel • 112-pixel arrays have high uniformity, 8-9 eV FWHM, ~75% yield (STAR Cryo) • Computer-controlled 32-channel pre-amplifier and digitizer cards (XIA LLC) • Chemical analysis of dilute samples (e.g. organic solar cells with UC Davis) LTD-15, Pasadena

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