application of ltds to synchrotron radiationltd-10.ge.infn.it/trasparencies/f/f01_acapito.pdf ·...

F. d’Acapito LTD-10 Conference 1

The GILDA CRG at ESRF

Application of LTDs to Synchrotron Radiation

F. d’AcapitoINFM – OGG c/o ESRF GILDA CRG B.P.220 F-38043 Grenoble (France)



Layout

• Introduction & comparison • Present & near future applications

– X-ray Absorption Spectroscopy– X-Ray Fluorescence analysis

• Future applications– X-ray emission spectroscopy– Resonant Inelastic X-ray scattering– X-ray Raman Scattering

• Conclusion



+ and - of LTD detectors

+ Low energy resolution+ Absence of geometrical constraints (scattering angles, beam size, ..)+ No critical mechanical alignment+ In vacuum operation

- Low count rate- Reduced solid angle- Applicability to hard X-rays ?



Energy–resolving x-ray detectors

LTD (STJ) SemiconductorSolid State

Crystalanalyzers



Energy–resolving x-ray detectors

106cps

103 cps

104 cps

105 cps

Count Rate

10-4 sr0-1020TES *

10-3 sr0.1-100.2Bragg/Grating

10-4 sr0 - 1?10STJ *

10-2 sr0.3-120150-300HP-Ge, Si:Li

Solid angle

E (keV)

∆E (eV)

Type

* Couple high resolution to no geometrical constraints



Application fields

-X-ray emission spectroscopy-Resonant Raman Scattering-Non resonant Raman scattering

00.5

11.5

22.5

33.5

4

0 5 10 15 20 25 30 35 40

K le

vel N

atur

al W

idth

(eV)

Atomic number Z

Xtalspectrometer

resol.

-X-ray absorption spectroscopy-X-ray fluorescence analysis

0

200

400

600

800

1000

0 10 20 30 40 50

Kαααα line spacing

Ekα

(Z+1

) - E

k α(Z

) (eV

)

Atomic Number Z

2 FWHM

Physical parameters defining the energy resolution



Present & near futureapplications



X-ray Absorption Spectroscopy

0

500

1000

1500

2000

18000 20000 22000 24000 26000 28000

Fluo

resc

ence

Yie

ld (c

ps)

Energy (eV)

Pd Kα

PdKβ +

Compton Elastic

-0.1

0

0.1

0.2

0.3

0.4

0.5

24000 24250 24500 24750 25000Abs

orpt

ion

Coe

ffici

ent (

Arb.

Uni

ts)

Energy E (eV)

Monochromatic X-raysof energy E

Sample

X-ray spectrum coming from the sample

EXAFS spectrum

Local Structure

( ) [ ]∑ −−•∝f

if hEEirifw νδε2

exp v)



Fluorescence flux

X-ray beam: Intensity=1012 ph/s @ 6540 eV

Sample: concentration=1015 Mn / cm2

Detector: Collection solid angle=10-3 sr

K fluorescence Flux: 104 ph/s

(Neglecting elastic + compton)



Soft X-ray region - XAS

STJ detector for soft x-ray fluorescence(Friedrich et al. RSI 73 (2002), 1629.)

XAS experiment (InGaAsN at the N k edge)Lordi et al. PRL 90 (2003), 145505



Hard X-ray region -fluorescence

Fluorescence spectrum of a Re foilF. Gatti et al SRN 3 (2003), in press.

See also Poster F03

TES detector300*400*25 µm3 Sn absorber

TES sensor an Al/Ag multilayerCount rate ≈ 100cps

Ω ≈ 10-8 sr



Cu Kα

Co Kα&

Fe Kβ

Fe KαMn Kα

Ni Kα

Ni KβCoKβ

FWHM = 70 eV

Fluorescence analysis

4000 5000 6000 7000 8000 90000

2000

4000

6000

8000

10000

12000

14000

elastico

Ca Kα1

Ni Kα1Co K

α1

Fe Kα1

Cu Kα1

D52_rosso D78_oro

Cou

nts

Energy (eV)HP-Ge detector

Sample of XVI centuryitalian pottery.

TES Detector



Wafer surface impurity analysis

Intentionally contaminated Si wafer. Measurement done with a Si:Li detector, ∆E=140 eV.P. Pianetta et al. RSI 66 (1995), 1293

•Control of industrial processes•Synch. Radiation source•Total reflection condition•Detection limit: 108 – 1012 at/cm2

High resolution desirableHigh count rate (>105 cps)



Future applications



High resolution x-ray emission spectroscopy

• Kα and (much more) Kβ lines exhibit variations linked to the chemical environment

• Variations are greater than the natural linewidth of the K state

•The achievement of energy resolution of the order of 1-2 eV could give access to the several exprimental techniques techniques

Levels of x-ray fluorescence transitions

n=1

2

3

4



Mn K fluorescence

Emission from Mn excited above the K edge

U. Bergmann et al. CPL 302 (1999), 119.

Kα1 and Kα2 transition from 2p levels: fair chemical sensitivity

Kβ1,3 and Kβ’ transition from the 3p statesKβ2.5 and Kβ’’ transitions from the valence band

Chemical sensitivity !



Mn Kβ fluorescence

Variation of the Kβ lines for various Mn compounds. Excitation well above the edge. (Tsutsumi et al. PRB 13 (1976), 930.)

•Simple chemical characterization

•Data collection currently done with Crystal analyzers•Possible use of LTD detectors if ∆E=few eV•Advantage in using LTD detectors: parallel acquisition, no mechanical movement



Spin selective XAS

G. Peng et al. JACS 116 (1994), 2919

•In MnII compounds it can be shown that Kβ1,3 originates from a spin down electron, Kβ’ from a spin up electron

•XAS spectra can be collected by separately monitoring the two lines

•Differences are observed that reflect the different DOS for the two spin configurations.

•Peak separation 16 eV at 6500 eV.

ConventionalXAS

1s->3d



Resonant Inelastic X-ray Scattering (RIXS)

•1) Promotion of a K electron above Ef by photon absorption (virtual state, no energy conservation).•2) Filling of the K hole with an L electron•3) Emission of a photon

•The energy of the global process is conserved Ein-Eout = ε - EL•The process is resonant, i.e. enhanced near the (K) edge•Access to the electronic structure

K

L

Ef

1

2

ε



RIXSDallera & Grioni STUC 14 (2003), 57

•Data collected with grating spectrometer

•Evidence of a Charge Transfer peak for an excitation energy on the white line

•The CT peak disappears for higher excitation energies

Peak separations 5-20 eV at 835 eV



(Non resonant) X-ray Raman Scattering, XRS

νi, ki

ν f, k f

Q=kf-kiΘ

( ) [ ] ( )[ ]fiif hEEirQifw ννδ −−−•Θ+∝ 22 expcos1 rr

Transition probability w

Same operator as XAS



XRS

C K edge, graphite 6 keV

XRS

XAS

U. Bergmann et al.Microchem. J. 71 (2002) 221

•Useful for obtaining bulk information on light atoms: experiment is done at high energy.

•1eV energy resolution is OK for data collection.

•Signal significantly smaller than Elastic / Compton



Energy Dispersive X-ray Diffraction (EDX)

Bragg law: λ=2dsin Θ

•Normally λ is fixed and Θ is varied•In EDX Θ is fixed and λ is varied



EDX

Typical EDX spectra

Used in the early days of SRfor experiments needing small sized beams (HighPressure).Limitations•Energy resolution•Count Rate

Application of LTDdetectors to small beams



Conclusion

• High resolution LT-detectors match the requirements for X-ray absorption spectroscopy &

fluorescence analysis ⇓

Rise the maximum count rateExtend to hard X-rays

• Possible use for X-ray emission spectroscopy & Raman scattering

⇓Improve the energy resolution down to 1 eV.

• EDX ?

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