multielement spectrum multielement spectrum evaluted · 2012-08-06 · denver x-ray conference 2012...

1

Workshop on Trace Analysis

IntroductionInstrumentation

TXRF

Peter Wobrauschek

Denver X-Ray Conference 2012Email: [email protected]

X-ray source X-ray detector

sample

Interaction:

Photoeffectelastic scatteringinelastic scattering

X-ray tubeSynchrotron radiation

energy dispersive

E(keV)C.Streli 2002

Principle of EDXRS

X-ray tube

Synchrotron radiation

Multielement spectrum Multielement spectrum evaluted

2

xx+dx

x = d

x = 0

dx

Detektor Anregungsquelle

ϕ

dž 1

dž 2

ψ

I (E Kα

i ) =x=0

x=d∫ I0 (E)

E =Eabsi

E =Emax

∫ ⋅ G1 ⋅ρ

sin ϕ⋅

τKi (E )

ρ⋅ωK

i ⋅pαi ⋅ci ⋅ V i (E ) ⋅

⋅e−

μ (E)ρ⋅sin ϕ

+μ(EKα

i )ρ⋅sin ψ

⎛

⎝ ⎜

⎞

⎠ ⎟ ⋅ρ⋅x

⋅ G2 ⋅ f (EKαi ) ⋅ ε(E Kα

i ) ⋅dx ⋅ dE

Quantitative XRF fundamental equations I

SourceDetectorConcentration

Simple Net peak area and Background calculation

Nb=Y(a)+Y(b) * [xb-xa+1]/2

Number of background countsNb

NbNgross = sum (i) y(i) i=xa,xb

Nnet = Ngross - Nb

Nnet

Software for background stripping and deconvolution of overlapping peaks

LLD =3⋅ NB

NN⋅msample =

3⋅ IB / t

S(cps / ng)

Definition of detection limit

Reduction of detection limits:

increase in intensityreduction of background

increase of measuring time

The lower the detection limits the better you can do trace analysis

Aim of all spectral modification elements:Reduction of background due to scattering

Physical reasons: elastic and inelastic scattering on sample and substrate

Detector reasons:Detector shelf

Incomplete charge collectionCompton backscatter from detector crystal

Intensity

Energy

3

Influence on sensitivity

•Physical strategies:

•choice of the anode material

•selective excitation -• characteristic E slightly

above absorption edge E

•spectral distribution of the source

• tuning monoenergetic• high-energy cutoff• selected filters for low-energy

photons suppression

•Total reflection of x-rays ⇐ 2·S

•Technical strategies:

•distance reduction source-sampledetector

•detector area larger

•X-ray optics

•source-power increase

• 2 kW standing anode• 18 kW rotating anode

•synchrotron radiation•multiple tube (future idea)

Reduction of the Background

• Modify primary spectrum (high energy cut off) by glassreflector adjusting total reflection conditions

• Multilayer monochromator purely monoenergetic beam

• Linear polarized beam - Barkla or Bragg polarizer in triaxial geometry (90°-90°-90°)

• Optimum conditions – monochromatic synchrotronradiation

X-ray Sources

Standing Anodes – Fluorescence and Diffraction tubes

Anode Materials: Cr,Cu,Mo,W, Ag

Special for light element W-M line or Si anode

Focal size 0.04x12mm² line 0.4x0.8 mm² point

Power from few W to 3 kW

Special tubes. Thin window transmission of low E photons – Transmission anode tubes end window

Windowless tubes W- Si anode light element excitation

Rotating anode up to 90 kW


Femtosecond pulsed laser induced x-rays

high harmonics or plasma source andLiquid Metal Jet

X-ray tube and housing

4

Low power tube

Product Neptune - Water Cooled) XTF6000 XTF5011/75Max kV 50.0 kV 60 kV 50.0 kVMax mA 5.0 mA 1.0 mA 1.5 mAMax Power 100 Watts 50 Watts 75 WattsFocal Spot size (nominal)* 100 microns* (W) <80 microns* (W) <85 microns* (W)Target types W, Mo,Cu W,Rh W,Rh,Mo,Cr,Pd +Exit window type Beryllium Beryllium BerylliumExit window thickness 75 µm to 254 µm 80 µm to 254 µm 75 µm to 254 µmCone angle 25 degrees 20 degrees 25 degrees

www.oxfordxtg.com

Rotating anode X-ray tubes

www.rigaku.com/protein/ruh3r.html

1515

Conventional Target Technology

• Solid target close to melting• Possible Improvements

• More efficient cooling• Smaller spots• Fast rotation

• Unfortunately now very close to fundamental limits

Rotating anodeSolid anode

1616

Key Concept – The Metal Jet Anode

~ 200 µm

~ 75 m/s

5

1717

Brightness Comparison

Approximately 10× brightness compared to a solid anode in the ~5 – 40 µm focal-spot-size range

1818

Power Limitation of MetalJet

Metal vapour

1919

Window Vapour Mitigation

127 µm Beryllium vacuum window

20 µm heated carbon foil that re-evaporates contamination. 2020

Available Alloys and Their X-ray Spectra

• Alloys molten at room temperature are used in the first generation sources. Future versions may include alloys with higher melting points.

• Gallium-rich alloy has emission similar to copper• Indium-rich alloy has emission similar to silver

Element Kα1 Kα2 Lα1 Lα1

Gallium 9.25 keV 9.22 keV 1.10 keV 1.10 keV

Indium 24.21 keV 24.00 keV 3.29 keV 3.28 keV

6

2121

Acknowledgement to Bjoern Hansson EXCILLUM

Aereal view of ESRF

Synchrotron radiation ED detector LN2 cooled Si(Li)

Neue Arbeiten am Atominstitut WS07/08 | Jan.

7

Ketek Si drift detector Peltier cooling

Finger length 100 mm

High voltage, DPP,

Peltier cooling

Multichannel analyzer

USB connector

All in one small box and

Very compact

Ultimative

Source and detector in onebox HANDHELD

MANY COMPANIES

WORLDWIDE

Detector Transmittance with Ultra Thin Window

TXRF 2009, Gothenburg, Sweden | | Seite 26

Light element detector

Gresham Sirius Detector

TXRF 2009, Gothenburg, Sweden | | Seite 28

8

High ThroughputAMPTEK

Filtered radiation

Background Reduction

DetectorDetector

XX--Ray Ray SourceSource

Source FilterSource Filter

Simple effective

Scheme polarization plane - detectorposition

E-vector

linearpolarizedx-rays

plane of polarization

detector

atomicdipolessample

anisotropicdipoleemissioncharacteristic

isotropic emission offluorescence radiation

EDXRF with linear polarized radiation

Polarized radiation

www.panalytical.com

Epsilon 5

detektor

sample

polarizer

source

9

Polarizer materials

• Light elements – pressed pellets• Boron Carbide B4C• Alu• Plexiglass• Graphite• Al2O3

• Bragg crystals for 45° Bragg angle • Cu (113) for Cu Ka radiation• HOP-G highly oriented pyrolithic graphite

Polarization

Direct excitation (2-dimensional) Polarised excitation (3-dimensional)

Effect of using linear polarization

From:

Vert:: detdownlooking

Hor: detsidelooking

A. Knöchel et al Fresenius 1990

Pol planebeam

Detector

beam


Secondary target

Improved Fluorescence and lowerbackground

Sample

X-Ray TubeDetector

Secondary Target

ENERGY (keV)

Tube Target peak

With Zn Secondary Target

FeRegion

Continuum Radiation

Comparison of optimized direct-filtered excitation with secondary target excitation for minor elements

10

37Trace element workshop 2012

Polarization and selective excitation

From: handbook of X-ray spectrometry, Marcel Dekker 1993, 2002

unfiltered

Mo sec.targ.

HOPG Bragg polarizer

White(left) versus monoenergetic excitation (right)

White excitation Monoenergetic excitation

0 5 0 0 0 1 0 0 0 0 1 5 0 0 0 2 0 0 0 0 2 5 0 0 0 3 0 0 0 0

0 . 0

0 . 2

0 . 4

0 . 6

0 . 8

1 . 0

ar

bi

tr

ar

yu

ni

ts

D O R I S I I I L

C u t O f f S i O2

M L W\

C 4 0

S i 1 1 1

E n e r g y [ e V ]

Crystal versus Multilayer monochromator

COMPARISON OF SPECTRAL MODIFICATION

Selective Excitation:

Ti-K 4.96keV

Ba Liii 5.24keV

Cu-K 8.98keV

11

Panalytical Epsilon 5

• Commercial EDXRF Spectrometer

• X-ray Tube: W-Sc Anode• 9 Secondary Targets• Ge-Detector• Permanent vacuum during

measurements• Generator: max. 100kV,

24mA, 600W3D optical path(www.panalytical.com)

Sample Cup

X‐ray Tube

Secondary Targets

Detector

Epsilon 5 and Angelika Maderitsch

Sample measured and operating conditions

• Sample Pellet: 2g Soil 7 + 1g HWC (Wax-Binder)

• Measured with Panalytical Epsilon 5

• Dual anode: Sc/W 100kV/6mA 600 W

• Used secondary targets: Al2O3, Zr, Ge

• Detector: Ge(HP) 30mm² x 5mm, Be window 8 µm

• Measuring time: 1020 s

Soil 7- Al2O3

12

Pb - Zr sec target compared with Barkla Al2O3 Fe - Ge-, Zr - sec target compared with Barkla Al2O3

Peak to Background Ratio for Pb

Secondary Target

Netto Counts (cps)

Background (cps) Ratio

Al2O3 4,93 3,5 1,41

Zr 43,8 13,28 3,42

Peak to Background Ratio for Fe

Secondary Target

Netto Counts (cps) Background (cps) Ratio

Al2O3 586,56 8,556 68,55

Zr 3785,79 86,36 43,84

Ge 7720 73,31 105,30

13

Peak to Background Ratio for Ti

Secondary Target

Netto Counts (cps) Background (cps) Ratio

Al2O3 11,78 6,0 1,96

Zr 23,97 123,53 0,19

Ge 180,06 16,16 11,14

Triaxial Geometry polarizing primary radiation

x-ray tube Rh-anode

50kV 1.5 mA

SecondaryTarget:

2mm Mo

sample

Si drift detector

Vortex50mm²

Scheme of triaxial geometry

X-ray properties of combination Rh anodeMo secondary target

•Rh K-alpha 20.165 keV K-beta 22.72keV

• plus bremsstrahlung excitation

•Mo K- absorption edge 20.001 keV highest photo cross section

•Mo K-alpha 17.48 keV K-beta 19.6 keV

•Pb LIII edge 13.04 keV LII edge 15.2 keV

•Source Oxford XTF 50kV 1.5 mA Rh target US$ 3700

•Matusada HXR x-ray generator + PC controller US$ 4600

•Portable system - air cooling

Final Setup

detector

Tube Al holder

shieldingsample

14

Animal Bone Sample

Animal Bone Standard Reference Material IAEA (H-5)(3.1 µg/g Pb) powder pressed to a pellet

0 2 4 6 8 10 12 14 16 18 20

100

1000

10000

Pb Lβ

Pb Lα

cts

/ 100

0s

Energy [keV]

animal bone Excitation:Rh anode material49.5 kV / 1.5 mA1000s livetime

Detector:Radiant VORTEX50 mm2 SDD

LLD: 0.7 µg/g Pb

Orchard Leaves Sample

Orchard Leaves Standard Reference Material NIST SRM 1571(45µg/g) powder pressed to a pellet

0 2 4 6 8 10 12 14 16 18 20100

1000

10000

100000

Pb Lβ

Pb LαAs Kα

cts

/ 100

0s

Energy [keV]

orchard leavesExcitation:Rh anode material49.5 kV / 1.5 mA1000s livetime

Detector:Radiant VORTEX50 mm2 SDD

LLD: 0.4 µg/g Pb

CONCLUSIONS

• Using x-ray physical effects as:• Filters – polarizers – monochromators and

secondary targets• Background conditions are improvesd• Increase of primary flux by power or x-ray optics

improves sensitivity• Detector and electronics allow high countrate

processing• All ideas are perfectly applied for trace element

analysis to achieve improved detection limits

Acknowledgement• Nina Cernohlawek• Bernhard Pemmer• Angelika Maderitsch• Team of Atominstitut X-ray group

15

TXRF – A VERSATILE TOOL FOR TRACE ELEMENT ANALYSIS

A REVIEW

Peter WobrauschekAtominstitut, TU Wien

[email protected]

OUTLINE• TXRF: fundamentals of total reflection X-ray fluorescence analysis• Chemical analysis at pg levels by tube excitation• Chemical analysis at fg levels by synchrotron radiation excitation

• GI-XRF: grazing incidence XRF• Layered structures above surface: thickness, density, element• Implants: concentration profiles, element

• SR-TXRF: synchrotron radiation induced TXRF

• Low Z element determination

E D X R F

Standard XRF Micro XRFµ-XRF

Total Reflection XRFTXRF

Absorption Spectroscopyin fluorescence mode (XAS)

EDXRF at the Atominstitut

Advantages

• background reduction

• double excitation of sample

• small distance sampledetector (~1mm) large solid angle

• angle dependence of fluorescence signal

information about type of sample (bulk, particle, film, implantation)

ρδ ⋅≈⋅≈ΦEcrit

7.202

φcrit [mrad], E [keV], ρ [g⋅cm-3]

)()(

2

1

EfKEfK

⋅=⋅=

βδδ ~ 10-6 … dispersion:

β ~ 10-8 … absorption:

fi … atomic scattering factorr0 … classical elektron radiusλ … wavelength of incident beamNA … Avogadro‘s constantA … atomic weigthρ … density [g⋅cm-3]

ρπλ

⋅⋅⋅

=A

NrK A

2

20

Fundamentals of TXRF

Total (external) reflection of X-Rays

ϕ critical(Si, 17.5 keV) ≈ 0.1° ≈ 1.75 mrad(Si, 500 eV) ≈ 3.7° ≈ 64.6 mrad(Si,12.2 keV) ≈ 0.15° ≈ 2.6 mrad

βδ in −−= 1X-rayrange:

16

βδ in −−= 1

ρδ ⋅≈⋅≈ΦEcrit

7.202

φcrit [mrad], E [keV], ρ [g⋅cm-3]

Transmission / Reflection Coefficient17.5 keV, Si-reflector

0,001

0,01

0,1

1

0 0,5 1 1,5 2

T R

φ/φcrit

Penetration depth (nm)17.5 keV in Si

1

10

100

1000

10000

0 0,5 1 1,5 2 2,5 3 3,5 4angle(mrad)

pene

trat

ion

dept

h(n

m)

φ

crit

Fundamentals of TXRF Principle of XRF and TXRF

© Siegfried Pahlke 06.2004

Comparison between Conventional XRF and TXRF shows Difference in the Geometric Grouping of Excitation and Detection Units.

X-Ray Tube Wafer Detector

Fluorescence radiation

X-Ray-Fluorescence (XRF)

X-Ray Tube Wafer

Detector

total reflected beam

Fluorescence radiation

Total-Reflection X-Ray-Fluorescence (TXRF)

Principle of TXRF

NativeSiO2

Silicon Wafer !

Penetration Depth about 5 to 10 nm

1 mrad incident angle of beam

In Total Reflection Conditions

© Siegfried Pahlke 06.2004

X-ray intensity in the proximity of the surface

λ

φ

I0 IR

D

)sin(2 ϕλ

⋅=D

-100

-50

0

50

100

01234

airsilicon

X-Ray Intensity

dist

ance

from

surfa

ce[n

m]

ϕ = ϕcrit/2

ϕ = ϕcrit

ϕ = 2ϕcrit

Long and transv. Coh restricts volume

17


0 1 2 3 4 50.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

fluore

scence

inte

nsi

ty [

a.u.]

incidence angle [mrad]

residueon surface surface layer

bulk

Angle dependence of fluorescence signal information about type of sample:

• bulk

• particle (residue on surface)

• film, implantation (surface layer)

Analytical features

• only small sample volumes required (ng some µl)

• detection limits in the pg range (for medium Z elements using X-Raytubes)

• Simple quantification ( thin film approximation) by adding an internal standard


Environment:

water: rain, river, sea, drinking water,

waste water.

air: aerosols, airborne particles, dust,

fly ash.

soil: sediments, sewage sludge.

plant material: algae, hay, leaves, lichen, moss,

needles roots, wood.

foodstuff: fish, flour, fruits, crab, mussel,

mushrooms nuts, vegetables, wine,

tea.

various: coal, peat.

Medicine / Biology / Pharmacology:

body fluids: blood, serum, urine, amniotic fluid.

tissue: hair, kidney, liver, lung, nails, stomach,

colon.

various: enzymes, polysaccharides, glucose,

proteins, cosmetics, bio-films.

Industrial/Technical applications:

surface analysis: Si-wafer surfaces,

GaAs-wafer surfaces

implanted ions depth and profile variations

thin films single layers, multilayers

oil: crude oil, fuel oil, grease.

chemicals: acids, bases, salts, solvents.

fusion/fission research: transmutational elements in

Al + Cu, Iodine in water

Mineralogy:

ores, rocks, minerals, rare earth elements.

Fine Arts / Archeological / Forensic:

pigments, paintings, varnish.

bronzes, pottery, jewelry.

textile fibers, glass, cognac, dollar bills, gunshot residue,

drugs, tapes, sperm, finger prints.

C.Streli 2003

Applications of TXRF


TXRF• TXRF for chemical analysis using internal standard for quantification

• TXRF of wafer surface analysis using external calibration and absolute quantification

•GI-XRF (changing angle of incidence) for depth profiling and thin layer analysis

• Synchrotron radiation induced TXRF (SRTXRF) for ultra trace analysis

• SRTXRF-XANES for speciation at trace levels

18


Kapton window

Fine focusX-ray tube

entrance slit50 µm

multilayermonochromator

beam exitwindow

detector

sample reflector

Pb-shielding

vacuum chamberpump

Scheme of the Atominstitut standard vacuum TXRF spectrometer

schema stanford chamber 70Trace element workshop 2012

Measurements with TXRF Aerosol on Si wafer

Experiments with Mo anode tubeML monochromator, 80mm² Si(Li)50kV 40 mA 1000sDet Lim: pg range


WOBISTRAX:Schematic view


WOBISTRAX

19


Detection limits: AXIL deconvolution

0

200

400

600

800

1000

1200

0 5 10 15 20

S9RBV1~1.txt

cts/

chn

Energy(keV)

Si

Rb

LLD= 0.7 pg

Mo/50/40/100900 pg Rb

Standard : Mo-tube

Mo anode

50 kV, 40 mA, 100 s

900 pg Rb

Analysis of tap water


Low Z performance

0

500

1000

1500

2000

2500

3000

0 1 2 3 4 5 6

AL1_01.txt

cts/

chn

Energy(kev)

Al

Si

K

Ca

Sc

Cr-scatter

Cr/30/50/100Jamcham75 ng Al, 3 ng Sc

LLD(Al) = 42 pg

0

500

1000

1500

2000

2500

3000

3500

0 1 2 3 4 5 6AL1_01.txt

cts/

chn

Energy(kev)

MgSi

K Ca

Sc

Cr-scatterCr/30/50/100Jamcham75 ng Mg, 3 ng Sc

LLD(Mg)= 156 pg

0

1000

2000

3000

4000

5000

0 1 2 3 4 5 6AL1_01.txt

cts/

chn

Energy(kev)

Na

Si

ClCa

Sc

Cr-scatter

Cr/30/50/100Jamcham90 ng Na, 3 ng Sc

S

LLD( Na) = 900 pg

E lem en t S (cp s/n g) L LD ( p g ) N a 0 .3 900 M g 1 156 A l 2 42

Cr- anode X-ray tube, 30 kV, 50 mA

KETEK 10mm2 8um Be window

• Straight TXRF – no sample preparation– Inspected area: 0.5 cm2– Mapping of wafer surface possible– Surface layer response of contamination– LLD: E10 atoms/cm2

• VPD ( vapor phase decomposition)- TXRF– Decomposition of native oxide layer with HF vapor and collection

of impurities in one drop – inspected area: wafer size!– LLD: E8 atoms/cm2

• VPT (vapor phase treatment) –TXRF– Decomposition of native oxide layer with HF, no collection – leads to residue response of contamination– Mapping still possible– LLD: 2E9 atoms/cm2

Wafer analysis with TXRF

20

Straight TXRF- VPD- VPT

Shimazaki, A.; Ito, S.; Miyazaki, K.; Matsumura, T.;

Semiconductor Manufacturing, 2005. ISSM 2005, IEEE International Symposium on 13-15 Sept. 2005 Page(s):456 - 459

Digital Object Identifier 10.1109/ISSM.2005.1513404

Wafer mapping

TXRF spectrometers• Chemical analysis:

– Picofox: www.bruker-axs.de/s2picofox.html?&L=1– TX2000: www.italstructures.com/tx2000.htm– WOBISTRAX: www.ati.ac.at/index.php?id=142&L=1– Nanohunter: www.rigaku.com/xrf/nanohunter-show.html– Handy-type TXRF: int.icc.kyoto-u.ac.jp/?p=924,

www.ourstex.co.jp/product.html– Fisichem-TXRF: www.fisichem.com

• Wafer analysis:– Rigaku: www.rigaku.com/semi/txrf-v300.html

THANKS FOR YOUR

ATTENTION

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multielement spectrum multielement spectrum evaluted · 2012-08-06 · denver x-ray conference 2012...

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