Post on 04-Jun-2018
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Developments & Limitations in GSR Analysis
Jenny GouldenOxford Instruments NanoAnalysis
ENFSI Working Group Meeting June 2006
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Overview
• Introduction• Developments in GSR Software• Importance of EDS Hardware • Particle detection
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• Accurate particle detection• Accurate particle analysis• Correct identification of Unique particles• Relocation of specific particles for
‘confirmation’• Compliance to ASTM Standard - (E 1588)
GSR Analysis by SEM/EDS
What do we want to achieve with GSR
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Requirements for GSR• Accurate - MUST give the right answer
• Particle detection/Element Identification /Quantification & Classification
• Flexible • ammunition types/ different sample preparation / different
environments
• Fast • critical for laboratories dealing with casework
• Ease of reporting• Data Integrity
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Particle Detection and Measurement
• For ALL the particles to be detected and measured correctly :
• Area & Field layout must be accurate• Particle detection criteria must be
suitable• Beam relocation must be accurate• Spectrum Processing must be correct
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GSR Software
• INCAGSR provides:• Automated analysis• Flexible detection criteria, which can be
optimised for SEM and particle type• Analysis conditions stored in a recipe for
reuse• Easy and fast data reprocessing• Straightforward reporting
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INCAGSR• INCA Navigator: Data is acquired
through a series of logical steps• Enter sample details• Define area layout• Grey scale calibration• Define parameters for particle detection
and quantification• Automatically acquire data from whole
area or selected fields• Data classification• Data reporting
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Automated particle analysis
• Analysis achieved by dividing the sample into rectangular fields of equal area
• Relocate any selected area under the beam
• Define up to 48 areas in any one run
Sample areas are defined with the aid of a stage mimic. The positions are stored and recalled for future use:
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Progress monitoring• Motorised microscope stage is driven to
each field position in turn• Detected particles are displayed during and
after acquisition • By predefining the
position of standards monitor microscope/system stability during a run
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• GSR particles are typically seen as bright particles on a dark background in the BSE image.
• Detection of inclusions in a typical field:
Particle Detection
(a) BSE Image (b) Grey level thresholding (c) Feature detection
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Particle Detection Criteria• Signal Source - BSE / SE• Magnification / Minimum required particle size• 2 pass imaging technique.
• Pass 1 scans entire field quickly• Pass 2 scans over detected
particles slowly• If no particles detected pass
2 is skipped• Guard Zone
• user defined enforced field overlap to correct for particleswhich occur at the field boundaries
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Particle Relocation• User selects optimum conditions, • SE image may be collected
in addition to BSE • Morphology and
chemistry are measured
• New data may be saved
Example shows a relocated GSR particle, analysed at a high
magnification
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Data Analysis• Plot all data or selected classes
Identify the particle number of any point on the graph
• Histograms• Ternary plots - select up to
4 elements/oxides at eachcorner
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Data Review
• By class or selection of classes• Select a particle from the list
or the field of view • Select individual samples or
groups of samples from a batchrun for data review
• Particle can be relocated under the microscope beam automatically
• By class or selection of classes• Select a particle from the list
or the field of view • Select individual samples or
groups of samples from a batchrun for data review
• Particle can be relocated under the microscope beam automatically
•The data for each particle can be reviewed instantly
•The data for each particle can be reviewed instantly
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Importance of EDS Hardware • INCAx-sight detector• INCAx-stream pulse processor
• Combine to give superior resolution and stability
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Detector Performance
• Two main indicators of detector performance:•Resolution - FWHM of an element line
• typically measured MnKα
• ISO15632:2002 recognises the importance of light element detection
•Stability • Peak stability with count rate
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INCAx-sight & INCAx-stream count rate stability guaranteed
•Many systems claim no variation with count rate, we can prove it…
•Our specification is:•Between 1,000 and 10,000cps peak position and resolution will change by less than 1eV
•Measured on MnKa at Process Time 5
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Why is this important for GSR Analysis?
• When peaks are well separated small changes in resolution and position can be easily compensated
• When peaks are close together, the position and resolution must be known for the areas of the constituents to be correctly proportioned
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Why is this important for GSR Analysis?
• This is important in GSR analysis where there are some well documented overlaps:• Ba & Ti• Pb & S• Ca & Sb
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GSR Overlaps - Ba/Ti
Ti K line overlaps with Ba L
BaBaSb
Sb
Pb Sb
Sb
Ba
TiSb
Ba
Sb
TiBa
Sb
3 3.5 4 4.5 5 5.5 6 6.5keVFull Scale 637667 cts Cursor: 6.628 (39406 cts)
particle 1
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GSR Overlaps - Pb/S
S K lines overlap with Pb M
SbPb SbPb
Sb
S SSb
Pb
1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4keVFull Scale 939559 cts Cursor: 1.031 (57702 cts)
particle 1
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GSR Overlaps - Sb/Ca
Ca K lines overlap with Sb L
SbPb Sb BaSb
Ba
Sb
Ba
Sb
2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 5 5.2keVFull Scale 856256 cts Cursor: 5.376 (46895 cts)
particle 1
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BaSbBa
BaPb Pb
Sb
BaSb
Ba
Pb
2 3 4 5 6 7keVFull Scale 247 cts Cursor: 7.221 (7 cts)
22
GSR Spectrum
• 20kV• PT 4• approx 7kcps• 5 seconds livetime
Peak and resolution stability are key if the peaks are to be correctly resolved and the elements correctly identified
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Pulse Processor Performance• Peak position must be reproducible for:
• peak shape and area to be correctly resolved,• element to be correctly identified and quantified
• Accurate analysis requires:• when count rate changes, peaks must not shift or
change in resolution• Key for GSR applications:
• possibility of peak overlaps, • relatively high count rates are often used• coupled with a short analysis time
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Benefits of Peak Stability•Accurate & Reliable AutoID at productive count rates
• even for spectra containing difficult overlaps results do not change with count rate
• reliable AutoID at high count rates and with the short livetimes typical for GSR analysis
• No need to know the elements in your sample• Unexpected / Unusual ammunitions will not be
overlooked
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Benefits of Peak Stability
•Accurate & Reliable Quantification • Correct elements are identified then the quant will
be accurate•Accurate & Reliable Classification
• whatever your ammunition
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Particle Detection • Requirements for particle detection are increasing to
the sub-micron range for many applications• The use of SEM with field emission sources has
made the imaging of samples on the nano-scale at allkVs a reality
• Plano standard now includes particles in sub-micron range
• In GSR is the routine analysis of sub-micron particles is becoming a more common requirement?
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Particle Detection & Analysis• Factors that control the particle detection:
• Beam conditions - kV, spot size, beam current (W-SEM or FEG-SEM)
• Spot or raster beam for analysis• Stage reproducibility and calibration
• Detection System & Sample• BSE detector solid state 2 Segments or 4 Segments• Background of GSR sample e.g. carbon tape or cloth
• Optimum time for analysis
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Spatial Resolution of Interaction Volume at Different kVs
12 keV 7 KeV 3 keV
Material: Fe
800 nm 300 nm 100 nm
550 nm
200 nm
80 nm
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Spatial Resolution of Interaction Volume at Different kVs
• Higher kV larger interaction volume• X-ray signal from background as well as
particle• The smaller the particle - the greater the X-
ray signal from the background
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Spatial Resolution of Interaction Volume at Different kVs
• For some particle analysis applications a lower kV is used
• For GSR applications kV of 20 or 25kV is typical • To excite the Pb L line• Achieve adequate backscatter contrast
for particle detection
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Conventional W- SEM100nm
1
2 3 4
5 6
77 88
99
1010
100n
m
6 full &4 partial hits of the beam
on the particle
1nA; ~ 80nm Spot Size; 100nm Pixel Size,
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Hot Field Emission SEM
11 12
2
4 5 6
7 8 9 10
11
33
100nm
100n
m
12 hits of beam on the particle
1nA; < 8nm Spot Size ; 100nm Pixel Size
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Effect of Spot Size on Particle Detection
•Larger Spot size• higher count rate• poorer image quality • smallest particles may be missed
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Beam Conditions• Effect of kV & spot size on image,
• 20kV 4nA -> • good statistics (spectrum)• poor quality image with W - SEM• better image with FEG SEM
• 25kV 1nA -> • acceptable statistics • image acceptable on both W and FEG SEM
• 20kV 0.5nA -> • analytical statistics poor - possibly use a large
detecting crystal (30mm²), • good quality image
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Spot or Area Analysis •INCAGSR option:
•Spot analysis - centre of the longest chord•Scan over entire particle
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• When detecting small particles accuracy of stage calibration and stage movement are critical
• The scanned raster and the stage movements must be orthogonal • i.e. The sides of the image area must be parallel with
the stage X and Y axes
Stage and Beam Calibration
correctly tiled fieldscorrectly tiled fields
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particles doublecounted
particles missed
Stage and Beam Calibration• If the image and stage are not
orthogonal the fields will not be properly tiled• Gaps where particles are missed• Overlapping fields were
particles are counted twice
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System Calibration & Validation
• GSR a measure of confidence in your system is required
• INCAGSR dedicated stage and beam calibration
• This is then validated using a supplied particle standard
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•Regular arrays•Regular grid of Au particles with a known size and position
System Validation
• Au particles 5,10,15,20 µm• Used to validate
•field tiling• particle detection• particle measurement
• Au particles 5,10,15,20 µm• Used to validate
•field tiling• particle detection• particle measurement
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•Random arrays -• e.g.Plano series of standards which are
specifically designed for GSR validation • Particle positions and chemistry known• For example Plano SPS 521C with 43 Sb/Pb
particles precipitated onto the surface of a silicon chip
• 6, 2.5 and 1.2µm size• Additional Fe, Cu and Pb particles
System Validation
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System validation - Standards
•Conditions of analysis
• 20kV, 1nA probe current• 2048x2048 image
resolution• 5 seconds live time• minimum size 0.5µm
43 unique particles detected and measured correctly
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Detection System• Range of BSE-detectors are available, for
example:• Solid state detectors ( 2 quadrants , 4
quadrants)• Robinson type detectors• Scintillator based systems • Micro channel detectors
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e.g. 4 quadrant solid state detectors
Detection System
•BSE detector must be:• fast response• high signal/noise
ratio
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Particle detection
• Find “global” dynamic range for BSE detector using a suitable standard e.g Mn/Rh or Cu/C
• Test this on known particles, of a suitable size• Verify your system on a real particle
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Analysis Time• Any system can detect and measure all
particles correctly•slow scan speed•high magnifications•high magnification
• All result in an overall increase in analysis time
• Optimum conditions, for time and quality of data (e.g. 98% of particles detected and measured correctly)
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Conclusion• Software developments have created
powerful and sophisticated tools for GSR applications •easy of use•powerful data processing
• Hardware is at least as important as software