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©Oxford Instruments 2005 Oxford Instruments Developments & Limitations in GSR Analysis Jenny Goulden Oxford Instruments NanoAnalysis ENFSI Working Group Meeting June 2006

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©Oxford Instruments 2005

Oxford Instruments

Developments & Limitations in GSR Analysis

Jenny GouldenOxford Instruments NanoAnalysis

ENFSI Working Group Meeting June 2006

©Oxford Instruments 2005

Oxford Instruments

Overview

• Introduction• Developments in GSR Software• Importance of EDS Hardware • Particle detection

©Oxford Instruments 2005

Oxford Instruments

• 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

©Oxford Instruments 2005

Oxford Instruments

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

©Oxford Instruments 2005

Oxford Instruments

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

©Oxford Instruments 2005

Oxford Instruments

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

©Oxford Instruments 2005

Oxford Instruments

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

©Oxford Instruments 2005

Oxford Instruments

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:

©Oxford Instruments 2005

Oxford Instruments

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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Oxford Instruments

• 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

©Oxford Instruments 2005

Oxford Instruments

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

©Oxford Instruments 2005

Oxford Instruments

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

©Oxford Instruments 2005

Oxford Instruments

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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Oxford Instruments

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

©Oxford Instruments 2005

Oxford Instruments

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

©Oxford Instruments 2005

Oxford Instruments

Detector Performance

©Oxford Instruments 2005

Oxford Instruments

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

©Oxford Instruments 2005

Oxford Instruments

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

©Oxford Instruments 2005

Oxford Instruments

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

©Oxford Instruments 2005

Oxford Instruments

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

©Oxford Instruments 2005

Oxford Instruments

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

©Oxford Instruments 2005

Oxford Instruments

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

©Oxford Instruments 2005

Oxford Instruments

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

©Oxford Instruments 2005

Oxford Instruments

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

©Oxford Instruments 2005

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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?

©Oxford Instruments 2005

Oxford Instruments

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

©Oxford Instruments 2005

Oxford Instruments

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

©Oxford Instruments 2005

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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

©Oxford Instruments 2005

Oxford Instruments

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,

©Oxford Instruments 2005

Oxford Instruments

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

©Oxford Instruments 2005

Oxford Instruments

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

©Oxford Instruments 2005

Oxford Instruments

Spot or Area Analysis •INCAGSR option:

•Spot analysis - centre of the longest chord•Scan over entire particle

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Oxford Instruments

• 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

©Oxford Instruments 2005

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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

©Oxford Instruments 2005

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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

©Oxford Instruments 2005

Oxford Instruments

•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

©Oxford Instruments 2005

Oxford Instruments

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

©Oxford Instruments 2005

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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

©Oxford Instruments 2005

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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)

©Oxford Instruments 2005

Oxford Instruments

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

©Oxford Instruments 2005

Oxford Instruments

Conclusion• Particle Detection critical• Influenced by a number of parameters• Will differ from system to system• Difficult to standardise on set of conditions

that will work on every system