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 analysis

mm=> m

•Total reflection analysis

1015atoms/cm2=>108atoms/cm2

•Non-destructive •multi-elemental analysis

•environmental condition •high accuracy

•wide dynamic range

Advantages of XRF elemental analysis

SR

5 10 15 20 25

0.0

0.5

1.0

R

efle

ctiv

ity

Glancing Angle (mrad)

101

102

103Penetration D

epth (nm)

Si ( Li )Detector

Sample

CriticalAngle

CriticalAngle

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

Detector

R

SR (horizontally polarized beam)

IS

IF

r

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

42

22 sincos2

R

r

R

rI scat

2

R

rI 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 X-Ray FluorescenceHow to analyze X-Ray FluorescenceWavelength-dispersive vs. energy-dispersiveWavelength-dispersive vs. energy-dispersive

Wavelength-dispersive

solar-slit solar-slit

crystal

gas/scintillation detector

Energy

2dsin=

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 lines

Double-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

nsi

ty (

nor

mal

ised

)

Energy ( eV ) ( + 5860 eV )

KMnO4

K2MnO4

Mn greenMnO2

Mn2O3

MnO

MnK

MnK

Chemical Shifts and Profile ChangesHigh resolution X-ray spectrometryHigh resolution X-ray 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 view

top view

ICIC

sample

Synchrotron X-Ray Microbeam

Beam size 5~6 m2 (1m 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 SPring-8 Plan View of Beamline 40XU at SPring-8

Experimental hutchExperimental hutch Optics hutchOptics hutch

K-B mirrors

Spectrometer

HALL

RING

SR

10000 20000 30000

1016

1017

1018

1019

1020

Bri

llian

ce (

phot

ons/

sec/

mra

d2 /mm

2 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 Energy-dispersive to Wavelength-dispersive SpectrometerFrom Energy-dispersive to Wavelength-dispersive Spectrometer To further upgrade signal to background ratio To further upgrade signal to background ratio

Energy-dispersive TXRFEnergy-dispersive TXRFEnergy-dispersive TXRFEnergy-dispersive TXRF

Sample

Si(Li)Detector

Substrate

X-ray

Wavelength-dispersive TXRFWavelength-dispersive TXRFWavelength-dispersive TXRFWavelength-dispersive 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-efficiency Low detection-efficiency

DisadvantagesDisadvantages

AnalyzingCrystal

(Johansson)

Sample

Substrate

X-ray

Scintillatordetector

Design ConsiderationsDesign ConsiderationsFlexibility and feasibility for practical analytical applicationsFlexibility and feasibility for practical analytical applications

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 X-ray Fluorescence SpectrometerCompact Johansson X-ray Fluorescence Spectrometer

Detector

Ionizationchamber

SR

Crystal analyzerGe (220) Johansson

He gas

Sample

Sample positioning stagesSample positioning stages

Vac. chamber

6380 6400 6420

0

5000

10000

15000

20000

MnK1,3

MnK1,3

K2

FeK1

X-R

ay I

nten

isty

(co

unts

)

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

100m

Glass Capirally

Lily Pollen (20 particles.)

5850 60000

5000

10000

LaL

2

BaL

4

Cr K

1,3

BaL

3BaL

2

LaL

1

Mn K2

Mn K1

X-R

ay In

tens

ity (

Cou

nts)

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 6450

0

5000

10000

15000

20000

25000

30000

FeK1

FeK

2

Inte

nsity

(co

unts

)

Energy (eV)

NiK2

FeK

1,3

CoK1

CoK

2

////

// //

CoK1,3

NiK1

Substrate

X-ray

SampleFe, Ni, Co 20ppb

0.1l

FWHM5.71eVFWHM5.71eV

FWHM6.62eVFWHM6.62eV

FWHM7.06eVFWHM7.06eV

　 5 sec/point　　 5 sec/point　

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

1 10 100 1000

103

104

105

106

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

X-R

ay I

nten

sity

(cp

s)

Concentration (ppb)

Performance of Wavelength-Dispersive TXRFPerformance of Wavelength-Dispersive TXRFppt level detection limit with less than 10eV energy ppt level detection limit with less than 10eV energy

Concentration of solution of 0.1l

Detection LimitDetection Limit

Ni

Absolute amount

0.31fg 3.1pptNi in 0.1 l solutionNi in 0.1 l solution

7420 7440 7460 7480 7500 7520

0

200

400

600

800

Inte

nsity

(cp

s)

Energy (eV)

13536counts　　 /20sec

196counts　　 /20sec

Ni 1ppb-0.1lliquid drop

Ni 1ppb-0.1lliquid drop

FWHM7eV

Calibration curveCalibration curve

SummarySummaryTowards ppt chemistry Towards ppt chemistry

Con

cent

rati

on (

g/

g )

AAS

ICP-MS

ConventionalXRF

ConventionalXRF

Conventional TXRF

Conventional TXRF

10-12

(pg)10-6

(g)10-9

(ng)10-15

(fg)

10-12

(ppt)

10-9

(ppb)

10-6

(ppm)

10-3

Absolute amount ( g )

Trace chemical characterization using K 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 0.1l

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 en

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

(XRD, XANES and EXAFS)