X-ray Fluorescence Analysis

A.Somogyi (ESRF)A.Iida (KEK-PF)

K.Sakurai (NIMS, Tsukuba)

T. Ohta (U.Tokyo)

What happens by core hole creation?What happens by core hole creation?

KL

M

X-ray Fluorescence

KL

M

Auger electron emission

How can we create core holes?

• X-rays, Electrons, Ions which have higher energy than the core electron ionization energies.

• Electrons and ions produces many peaks with multiple excitations. X-ray excitation is preferable.

• Now, X-ray fluorescence analysis by X-ray excitation is a standard technique for trace element alalysis.

How is the Trace Characterization important?

Bio-medical

?

Social

?

Industrial

LSI

Environmental

?

Why synchrotron radiation x-rays ?

• Higher intensity higher sensitivity• Energy tunability Make the analysis

easier, chemical state analysis• Polarizablity Reduce background• Directionality applicable to tiny sample• Spectromicroscopy, Imaging

Synchrotron Radiation excited X-ray fluorescence Analysis

•High sensitivity

ng=>fg, ppm=>ppb

•Chemical state analysis

•Micro-beam analysismm=> µm

•Total reflection analysis1015atoms/cm2=>108atoms/cm2

•wide dynamic range•high accuracy•environmental condition

•multi-elemental analysis•Non-destructive

Advantages of XRF elemental analysis

SR

5 10 15 20 25

0.0

0.5

1.0Re

flect

ivity

Glancing Angle (mrad)

101

102

103

Penetration Depth (nm

)

Si ( Li )Detector

Sample

CriticalAngle

Total-refection X-Ray Fluorescence ( TXRF )Reduction of scattering background from the substrate(1)

Detector

R

SR (horizontally polarized beam)

IS

IF

φ

r

Total-refection X-Ray Fluorescence ( TXRF )Reduction of scattering background from the substrate (2)

42

22 sincos2

+

∝

Rr

RrIscat φφ

2

∝RrI fluo

Fluorescent X-rays

Scattered X-rays

Sample: chelete resin beads

Monochromatic excitation

Laboratory source

Continuum excitation

Refl./Trans. MirrorsComparison of S/N and S/B ratios

How to analyze XHow to analyze X--Ray FluorescenceRay FluorescenceWavelengthWavelength--dispersive vs. energydispersive vs. energy--dispersivedispersive

Wavelength-dispersive

solar-slit solar-slit

crystal

gas/scintillationdetector

Energy

2dsinθ=λ

Energy-dispersive

electronic signal

processing

MCA

Energy

semiconductor/superconductor

detector

Qualitative and quantitative analysisin terms of XRF

Intensity changes

Chemical shifts

Profile changes and other fine structures

Satellite linesDouble-crystal spectrometer

Single-crystal spectrometer

Si ( Li ) detector

Chemical Characterization by X-ray Fluorescence Spectra

0 10 20 30 40 50

0.1

0.2

0

Inte

nsity

( no

rmal

ised

)

Energy ( eV ) ( + 5860 eV )

KMnO4K2MnO4Mn greenMnO2Mn2O3MnO

MnKα1

MnKα2

Chemical Shifts and Profile ChangesHigh resolution XHigh resolution X--ray spectrometryray spectrometry

Prof. Y. Gohshi

Fe2O3

FeO

EHEL

Selectively Induced X-Ray Emission Using Edge Shifts Use of tunable monochromatic synchrotron sourceUse of tunable monochromatic synchrotron source

K.Sakurai~1988

Kirkpatrick-Baez Optics

sample

SRSlit 1

Double crystalmonochromator

Multilayer monochromator

Slit 2

side viewtop view

ICIC

sample

Synchrotron X-Ray Microbeam

Beam size 5~6 µm2 (1 µm min)

Photon Flux(Max) 1010 (Multilayer) 108 (DXM)

Application to criminology

• A serious case of murder happened in a small town in Japan in 1999.

• White arsenic(arsenic oxide) was mixed in curry and 5 kids died of arsenic poisoning.

• No wittness and no confession, only presumptive evidence

• XFS technique works effectively.

XFS of white arsenic produced in various countries

Sb

China

Mexico

X-ray energy(keV)

As

Ag SbBi

Korea

Spectral patterns from two samples agree with each other!

Plan View of Beamline 40XU at SPringPlan View of Beamline 40XU at SPring--8 8 Experimental hutchExperimental hutch Optics hutchOptics hutch

K-B mirrors

Spectrometer

HALL

RING

SR

10000 20000 30000

1016

1017

1018

1019

1020

Brill

ianc

e (p

hoto

ns/se

c/m

rad2 /m

m2 in

0.1

% b

.w.)

Photon Energy (eV)

ID Gap 12mm

S S

N N

Helical Undulator Helical Undulator

40m45m50m55m

(Distance from the source)

35m

From EnergyFrom Energy--dispersive to Wavelengthdispersive to Wavelength--dispersive Spectrometerdispersive SpectrometerTo further upgrade signal to background ratio To further upgrade signal to background ratio

EnergyEnergy--dispersive TXRFdispersive TXRF

Sample

Si(Li)Detector

Substrate

X-ray

WavelengthWavelength--dispersive TXRFdispersive TXRF

Large solid angle (High detection efficiency)

Collecting whole XRF spectra simultaneously

Large solid angle (High detection efficiency)

Collecting whole XRF spectra simultaneously

Low energy-resolution

Limitation of counting-rate

Scattering background

Low energy-resolution

Limitation of counting-rate

Scattering background

AdvantagesAdvantages

DisadvantagesDisadvantages

High energy-resolution

Good signal to background ratio

High energy-resolution

Good signal to background ratio

AdvantagesAdvantages

Low detection-efficiencyLow detection-efficiencyDisadvantagesDisadvantages

AnalyzingCrystal

(Johansson)

Sample

Substrate

X-ray

Scintillatordetector

Design ConsiderationsDesign ConsiderationsFlexibility and feasibility for practical analytical applicationFlexibility and feasibility for practical analytical applicationss

Detector

SR

Entrance Slit

Curved Crystal Johansson Ge (220)

Receiving Slit

Sample

Rowland CircleR=120mm( flexible )

Rowland CircleR=120mm( flexible )

Vac. chamber

4 axes for scanning X-ray energy4 axes for scanning X-ray energy

4 axes for alignment and positioning of the sample4 axes for alignment and positioning of the sample

Compact Johansson XCompact Johansson X--ray Fluorescence Spectrometerray Fluorescence Spectrometer

Detector

Ionizationchamber

SR

Crystal analyzerGe (220) JohanssonHe gas

Sample

Sample positioning stagesSample positioning stages

Vac. chamber

6380 6400 6420

0

5000

10000

15000

20000

Kα2

FeKα1

X-R

ay In

teni

sty (c

ount

s)

Energy (eV)

Performance of the SpectrometerPerformance of the SpectrometerFeasibility for the analysis of trace elements in small samplesFeasibility for the analysis of trace elements in small samples

100µm

Glass Capirally

Lily Pollen (20 particles.)

5850 60000

5000

10000

LaLγ2

BaLγ4

Cr Kβ1,3

BaLγ3Ba

Lγ2LaLγ1

Mn Kα2

Mn Kα1

X-R

ay In

tens

ity (C

ount

s)

Energy (eV)

(300 ppm)

(5800 ppm)

Coal Fly Ash (NIST SRM-2690)

(67 ppm)

Capillary

Powders adhered to glue sphere (~0.5mm)

35mm

FWHM7.2eV

6900 7000 7100 7400 7500 7600 77006350 6400 64500

5000

10000

15000

20000

25000

30000

FeKα1

FeKα

2

Inte

nsity

(cou

nts)

Energy (eV)

NiKα2

FeKβ

1,3

CoKα1

CoKα2

////

// //

CoKβ1,3

NiKα1

Substrate

X-ray

SampleFe, Ni, Co 20ppb

0.1µl

FWHM5.71eVFWHM5.71eV

FWHM6.62eVFWHM6.62eV

FWHM7.06eVFWHM7.06eV

5 sec/point5 sec/point

WDWD--TXRF Spectra for Trace Elements in Micro DropTXRF Spectra for Trace Elements in Micro DropSignificant enhancement of signal to background ratioSignificant enhancement of signal to background ratio

1 10 100 1000103

104

105

106

Log(Y) = 2.93(4) + 1.01(2) * Log(X)(r=0.99908)

X-R

ay In

tens

ity (c

ps)

Concentration (ppb)

Performance of WavelengthPerformance of Wavelength--Dispersive TXRFDispersive TXRFpptppt level detection limit with less than 10eV energy level detection limit with less than 10eV energy

Concentration of solution of 0.1µl

Detection LimitDetection Limit

Ni

Absolute amount

0.31fg 3.1pptNi in 0.1 µl solution

7420 7440 7460 7480 7500 7520

0

200

400

600

800

Inte

nsity

(cps

)

Energy (eV)

13536counts/20sec

196counts/20sec

Ni 1ppb-0.1µlliquid drop

FWHM7eV

Calibration curve

SummarySummaryTowards Towards pptppt chemistry chemistry

Con

cent

ratio

n ( g

/g )

AAS

ICP-MS

ConventionalXRF

ConventionalXRF

ConventionalTXRF

ConventionalTXRF

10-12

(pg)10-6

(µg)10-9

(ng)10-15

(fg)

10-12

(ppt)

10-9

(ppb)

10-6

(ppm)

10-3

Absolute amount ( g )

Trace chemical characterization using Kβ spectra

Reducing scattering background as well as parasitic X-rays due to contamination is extremely important.

Downsized wavelength depressive XRF spectrometer is effective to enhance both detection efficiency and energy resolution.

Present detection limit(SR-WD TXRF)

~10-16g~10-12(ppt)For 0.1µl

Conclusions SR-X-ray XRF technique is very powerful.

• Low detection limit down to fg, ppt level• applicable to samples of limited size• well analyzed due to energy tunability and high

energy resolution• Development of XRF imaging• Combination with different micro techniques

(XRD, XANES and EXAFS)