x-ray fluorescence analysis a.somogyi (esrf) a.iida (kek-pf) k.sakurai (nims, tsukuba) t. ohta...
TRANSCRIPT
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)