112-pixel arrays of high-efficiency stj x-ray detectors
DESCRIPTION
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). - PowerPoint PPT PresentationTRANSCRIPT
112-Pixel Arrays ofHigh-Efficiency STJ X-ray Detectors
Stephan FriedrichMatthew Carpenter
LLNL (Detector Testing)
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.
John HallRobin Cantor
Star Cryo (Fabrication)
Jack HarrisBill Warburton
XIA (Electronics)
Synchrotron ScienceALS, SSRL
Superconducting Tunnel Junction Detectors
Al2O3
200×200 μm2
Nb
Ta AbsorberAl
SiO2 AlTa
X-ray Photon
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)
Energy resolution ∆EFWHM = 2.355√(εE(F+1+1/<n>)
Si Substrate
SiO2
STJ Operating Principle
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Signal = Current pulse
Al Al Ta TaAlOx
ΔAl
ΔTa
STJ Performance (as of LTD-14)
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Single-pixel spectrum of MnO + Fe7(CN)18 on Al Resolution vs. Count Rate
At the Synchrotron, We Need Efficiency
Single Pixel
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36 Pixels200 x 200 µm2 112 pixels of 200 x 200 µm2 STJs
For details on fabrication, ask Robin Cantor at the STAR Cryoelectronics booth.
⇒ Matt Carpenter(Monday talk)
Options: 1) Increase area/pixel 2) Thicker Ta absorber 3) Arrays: Detectors, readout
Scalable 32-Pixel STJ Preamplifier
New preamp has same noise, but is small,cheap ($25 in parts), and remote-controlled.
Existing preamp works fine, but is too big, too expensive (~$1k) and bias is manual.
RF
Rdyn Vbias
en
IX
Vout=IXRF
STJ
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STJ Preamp Controller
Rdyn Vbias from DAC
en
IX
Vout=IXRF
New: 32 channelsOld: Single channel
Small, Cheap, Remote-Controlled Preamp
For details, ask Bill Warburton at XIA LLC06/26/2013 LTD-15, Pasadena
Simultaneous bias scan of all pixels:Average current provides I(V)… … rms fluctuations measure noise.
X-ray Spectra at LLNLWith old single-channel preamp:
27 of 32 pixels tested have high resolution (rest is either open or shorted).
With new 32-channel XIA preamp(and 32-pixel digitizer / DSP board):
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More X-ray Spectra from Same 112 Pixel array
26 of 32 pixels tested have high resolution (rest is either open or shorted). 06/26/2013 LTD-15, PasadenaTa STJs seem to trap flux more easily than Nb STJs.
With old single-channel preamp:With new 32-channel XIA preamp(and 32-pixel digitizer / DSP board):
Sum Spectra
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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
53 pixels of 112-pixel STJ array, 165 nm Ta absorber
X-ray Absorption Spectroscopy with STJs
Electron yield:Sample surfacesModerate bgnd.
SynchrotronMonochromatic,intense X-ray beam
Sample xAbsorption µx(E)
DetectionThree options:
Monochromator
Transmission:Thin samplesHigh background
Fluorescence:Bulk samplesLow background
Fluorescence-detected XAS provides highest sensitivity,if the detector used can separate the fluorescence of interest with high efficiency.
Scan energy of X-ray beam, measure absorption (by transmission, e-yield or X-ray yield)
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Sample
corelevels
valencelevels
vacuum
Organic Photovoltaics (“Plastic Solar Cells”)• Cheap, light, cheap, flexible, cheap… • Not as efficient yet, ~12% max in the lab• Efficiency depends on microstructure
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Glass substrate
Ca/Ag electrode
ITO electrodePEDOT:PSS
P3HT - PCBM
Bulk hetero-jct.active layer
For details, ask Adam Moulé at UC Davis
Ca-L-edge Absorption Spectrumwith Ca electrode removed.
Organic Photovoltaics (oPV)Ca XAS of organic PV material (PCBM)
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Ca diffuses from electrode into active area! Electrode materials can serve as dopants.
C XAS: Occupancy at EF changes: Doping!
S. Mauger et al., Adv. Funct. Mater. 23, 1935 (2013)
EV(oPV)=-6.1eV
EC(oPV)=-3.7eV
EF(Ca)=-2.9eV
Band
gap EF(Ag)=-4.6eV
Energy levels:
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)
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