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Innovation with Integrity
Analysis of inhomogeneous samples and trace element detection in alloys using QUANTAX Micro-XRF on SEM Bruker Nano Analytics, Berlin, Germany Webinar, June 02, 2016
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Presenters
Stephan Boehm
Product Manager Micro-XRF on SEM, Bruker Nano Analytics, Berlin, Germany
Birgit Hansen
Application Scientist EDS & Micro-XRF on SEM, Bruker Nano Analytics, Berlin, Germany
Overview
1st Part • Why is Micro-XRF on SEM useful? (Comparison between Micro-XRF
and EDS) • Instrument design • Working principle of Micro-XRF on SEM
2nd Part • Esprit 2 software • Trace element detection in aluminum alloy • Inhomogeneous sample analysis - copper alloy example • Summary
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Why is Micro-XRF on SEM useful? Comparison EDS – Micro XRF
SEM/EDS
• Is best suited for light elements with X- rays energies below 2 keV
• High spatial resolution 20 nm to 3 µm
• Sensitivity of EDS is limited due to the overlap of fluorescence lines with the bremsstrahlung background
• Can detect most elements that are present in amounts 0.1 wt% (1000 ppm)
SEM/XRF
• Photon excitation produces spectra with little or no background better P/B- ratio
• For X rays above 2 keV XRF can detect elements below 100 ppm (depends on the matrix)
• The spatial resolution is lower µm range
• Higher information depth
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Complementary advantages:
• Electron beam excitation
• is better suited to imaging and
• quantitative compositional analysis of particles and maps
• Photon beam excitation
• increases the detectability of peaks from elements at low concentrations that otherwise might lost in the background
• is better suited to quantify trace elements but over a much larger area
• Delivers information from deeper layers inside the sample
Why is Micro-XRF on SEM useful? Comparison EDS – Micro XRF
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LOD for Micro-XRF are significantly better for elements with Z > 20 but depend strongly on analyzed element and matrix composition! Trace elements in a light matrix: LOD 100 ppm down to even 10 ppm Trace elements in a heavier matrix: LOD range 100 ppm to 200 ppm
0,000
0,001
0,010
0,100
1,000
0 10 20 30 40 50 60 70 80 90 100
Dete
ctio
n lim
it in
[wt%
]
Element [Z]
Estimated detection limit X-ray exitationElectron exitation
K L
K L
M
Fe = 26 Rh = 45 Pb = 82
Comparison between EDS and XRF Improved Limits of Detection
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Advantages of X-ray excitation:
• X-rays penetrate deeper into the sample
• Examination of thicker layers / coatings and of multiple layer structures
• Information depth depends on the sample matrix
Comparison between EDS and XRF XRF Information depth
Spectra of a multiple layer system: Au 3 µm, Ni 2 µm / Cu (EPMA: blue; µ-XRF: red)
Differences in the spectra:
• Spectral background is different due to bremsstrahlung
• Upper layers are very well excited by electrons but deeper layers can excited by X-rays only
• Thicker layers or even multiple layer systems can analyzed with XRF only
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Comparison between EDS and XRF XRF Information depth
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Micro-XRF on SEM X-ray tube added to the SEM
• Contains a micro - focus X-ray tube with a target spot size of 50 x 50 µm
• Target material according to analytical requirements: Rh, Mo preferred due to limited overlaps with lines of typical analyzing elements
• Source includes an integrated shutter allows an continuously X-ray beam even if the chamber is opened
• Tube radiation is captured by a polycapillary optics and concentrated on the sample surface down to spot sizes of either 10 or 35 µm
• X-ray detection will be done by a (existing) EDS (Bruker XFlash®) detector
X- ray tube with housing
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sample
e- beam
EDS Z – adjustment
Filter wheel
X - Y adjustment
Z – adjustment
X - Y adjustment
Primary filter wheel
Warning lamps for HV and X-ray beam
Micro-XRF on SEM Instrument design
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Rh-Ka
Rh-L Rh-Kb
• Emission of electrons from the filament by electrical heating • Acceleration of electrons to the anode by HV • De-acceleration of electrons on the anode • Emission of continuous bremsstrahlung and characteristic
fluorescence radiation of the anode material
Working principle of Micro-XRF for SEM X- ray tube (Physical principles)
Working principle of Micro-XRF for SEM Polycapillary X-ray optics
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SEM image of a polycapillary structure. Inner diameter in the range of 2 µm
Images courtesy of IfG GmbH, Berlin
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XTrace Alignment Approach
sample
EDS
WD: 10 mm
X-ray optics (the focused X-ray beam) has to be adjusted to match the location where the e-beam hits the sample (at the respective WD of the EDS detector)
Thus, whenever the WD of the SEM is changed consequently the X-ray optic has to be realigned
WD: 12 mm
EDS detector
e-beam
Polycapillary optics
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XTrace Alignment Glass sample
Misaligned Xray spot
Glass makes the X-ray spot visible
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ESPRIT 2 analytical software suite Integrated user interface
• All devices integrated under one user interface
• Use EDS and XRF alone or together
• In case of EDS measurement X-ray beam shutter is closed (HV on)
• In case of single XRF measurement e-beam is blanked
Hardware Device Boxes
ESPRIT 2 - modes of operation Combining EDS + XRF analysis
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• Integrated user interface for EDS and Micro-XRF including:
• Spot mode
• Object analysis
• Line scan
• Stage map
• Quantitative XRF analysis
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Trace element detection Aluminum alloy - comparison EDS - XRF
XRF (50 kV, 600 µA) 200 sec, ICR: 10.7 kcps EDS (20 kV) 200 sec, ICR: 9.5 kcps
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600 ppm 100 ppm
100 ppm
300 ppm
Trace element detection Aluminum alloy - comparison EDS - XRF
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BSE image
Inhomogeneous sample analysis Copper alloy
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EDS (25 kV) 300 sec, ICR: 8.5 kcps
Inhomogeneous sample analysis Copper alloy – EDS analysis
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BSE image
Inhomogeneous sample analysis Copper alloy – XRF analysis
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180 ppm
160 ppm
XRF 50 kV, 600 µA 300 sec ICR: 5 kcps
Inhomogeneous sample analysis Copper alloy – XRF analysis
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XRF (50 kV, 600 µA) 300 sec, ICR: 44 kcps
Inhomogeneous sample analysis Copper alloy – sample tilting
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Inhomogeneous sample analysis Copper alloy – Ti filter
XRF (50 kV, 600 µA) 300 sec, ICR: 5 kcps
Summary
• XTrace is attached to an inclined SEM port
• XTrace excitation radiation can be concentrated to spot sizes down to 35 µm
• Existing (Bruker) EDS detector for spectra acquisition
• 2 types of analysis on SEM (electron + photon excitation)
• One integrated user interface for EDS + Micro-XRF
• Improved limit of detection compared to EDS
• High sensibility of trace element detection
• Micro-XRF can be used for inhomogeneous sample analysis
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Q&A
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More Information
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For more information, please contact us:
https://www.bruker.com/quantax-micro-xrf
Innovation with Integrity
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