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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

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.


Superconducting tunnel junction detectors
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


Stj performance as of ltd 14
STJ Performance (as of LTD-14)

Single-pixel spectrum of MnO + Fe7(CN)18 on Al

Resolution vs. Count Rate

LTD-15, Pasadena


At the synchrotron we need efficiency
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


Scalable 32 pixel stj preamplifier
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


Small cheap remote controlled preamp
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


X ray spectra at llnl
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


More x ray spectra from same 112 pixel array
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.


Sum spectra
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


X ray absorption spectroscopy with stjs
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


Organic photovoltaics plastic solar cells
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


Organic photovoltaics opv
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


112 pixel ta stj x ray detector arrays
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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