Confidential Quantrainx50 7.2 EDS Basic 3-2010 place photo here

Confidential

Quantrainx50 7.2EDS Basic

3-2010

place photo here

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EDS

• Universal applications

• Elemental analysis

• 1% Accuracy

• Beam Control / Imaging

• Repeatable

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References (“the Book” --Highly Recommended)

• Scanning Electron Microscopy and X-Ray Microanalysis A Text for Biologists, Materials Scientists, and Geologists, Joseph I. Goldstein, Dale E. Newbury, Patrick Echlin, David C. Joy, A.D. Romig, Jr., Charles E. Lyman, Charles Fiori, Eric Lifshin, Plenum Press, New York, 1992. (ISBN -- 0-306-44175-6)

• *(Many thanks to Dr. Bob Anderhalt for graphics and advisement)

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Example of Quantax50/EDAX Integration

OUT DATED IMAGE !!!

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Your Basic Bohr Atom

K shell

L shell

M shell

N shell

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Inelastic Collision

K shell

L shell

M shell

N shell

Secondary Electron

Primary Beam Electron

Forward Scattered Electron

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Inelastic Collision

K shell

L shell

M shell

N shell

Secondary Electron

Forward Scattered Electron

Emitted X-ray

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X-ray Transitions

K shell

L shell

M shell

N shell

g Transition

β Transition

α Transition

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K shell

L shell

M shell

N shell

K α Transition

K α Transition

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K β Transition

K shell

L shell

M shell

N shell

K β Transition

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L α Transition

K shell

L shell

M shell

N shell

L α Transition

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Inelastic Collision Summary

• Primary beam electron interacts with atom

• There is an energy transfer

• An electron from the atom is liberated

• Creates a secondary electron (SE)

• SE has low energy

• The atom is excited and wants to return to a relaxed state

• Characteristic X-ray is emitted

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Continuum X-rays -(Background Radiation)

White radiation(Continuum)

CharacteristicX-ray

EjectedElectron

Incident Electron Beam

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Emission Depth of X-rays of KV Vs.. Z (in Microns)

SIMPLIFIED VALUES

Z SYMBOL ELEMENT 5KV 10KV 20KV 30KV

4 Be Beryllium .5 1.7 5.3 10.55 C Carbon .4 1.2 3.9 7.711 Na Sodium .9 3.1 10.0 19.212 Mg Magnesium .5 1.7 5.6 11.113 Al Aluminum .3 1.1 3.6 7.114 Si Silicon .3 1.2 4.1 8.219 K Potassium .5 2.9 10.8 21.920 Ca Calcium .2 1.6 5.9 12.222 Ti Titanium .01 .5 2.0 4.124 Cr Chromium .25 1.2 2.624 Mn Maganese .2 1.2 2.426 Fe Iron .2 1.0 2.227 Co Cobalt .1 .9 2.028 Ni Nickel .09 .85 1.929 Cu Copper .06 .8 1.930 Zn Zinc .02 1.0 2.332 Ge Germanium 1.2 3.038 Sr Strontium 1.2 4.840 Zr Zirconium .2 1.742 Mo Molybdenum .946 Pd Palladium .547 Ag Silver .479 Au Gold .2

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EDS Hardware

Monitor (MCA Display) Dewar

Preamp

SEMColumn

Pole Piece

SampleStage

Detector

Window

Collimator

FET

Analyzer

SCSI

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to preamplifier

(FET)

Detector Vacuum

DetectorWindow

8u Be or 0.3u Polymer

+,-charges

Detector

SiLi

-500 to 1000 volts

X-section of Window & Crystal

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to preamplifier

(FET)

Detector Vacuum

DetectorWindow


+,-charges

Detector

SiLi

-500 to 1000 volts


3.8 eV for each charge pair

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to preamplifier

(FET)

Detector Vacuum

DetectorWindow


+,-charges

Detector

SiLi

-500 to 1000 volts


AlKa X-ray=1.48KeV in

389 charge pairs out@ 3.8 eV each=1.48KeV

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How a Spectrum Grows

Energy

Counts

8.044.938

L α

K α

Kb

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Qualitative analysis - Peak ID• Identification of all

possible peaks

• Auto or Manual Peak ID

• Do not trust system : it is not 100% reliable

• Be aware of : - spectral artefacts

- skirt effects

(low vacuum systems)

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Qualitative analysis - Peak ID

• Identification of an element

• Place cursor exact on the top of the peak (expand scale)

• L and M line can show shift due to poor separation of /ß line

• First check main lines such as L or M lines

• Check the other lines of the same element

• Heavy elements will produce K and L radiation

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Qualitative analysis - Peak ID

Manual ID (Z- Z+) steps along elements

Auto ID

EPIC table (Element Peak Identification chart)

HPD : halographic peak deconvolution

Peak Fit / (to check overlapping elements)

Display possibilities

Marker options : ESC - SUM

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Qualitative analysis - Deconvolution• Deconvolution = peak strip

method

• Requires well calibrated system

• Check deconvolution for overlapping elements and missing elements

• Press HPD / Peak Fit button

• Check other lines

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What Affects Quantitative Analysis

• K Ratio

• Atomic Number (Z)Accelerating Voltage

• Absorption (A)Take-Off Angle

• Fluorescence (F)Atomic Matrix/Topography

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• K Ratio

Unknown / Known ratio or

Unknown Intensity / Pure Element Intensity

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• K Ratio


1.5 to 10 Times excitation energy

Or 2 times the highest energy peak

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High overvoltage means a high absorption condition and a small peak and poor statsitics (again)

X-Ray Generated

Volume

Why should the overvoltage be less than 10 to 20 times the lowest energy peak?

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Low overvoltage means a small, poorly excited peak and poor statistical quality in the spectrum

Electron Volume

X-Ray Vol.

Why should the overvoltage be at least 1.5 for the highest energy element?

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• K Ratio



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Take-off Angle

• The take-off angle is the angle between the x-ray trajectory and the sample surface.

• The angle is a combination of detector angle, its position, sample working distance, and sample tilt.

• Typical angles will range from 25 - 40 degrees

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Normal Take-Off Angle

Normal take -off Angle Allows Low Energy X-rays to Become Absorbed in Specimen

EDS Detector

35 º T-O

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Greater Take-Off Angle

Greater Take-Off Lets Low Energy X-rays Escape

Greater T-O

EDS Detector

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Sample position is extremely important• Working distance is very

important

• Optimum sample position eucentric position = 10 mm

(Sirion = 5 mm)

• Field of view of the EDX detector : 9 -12 mm

(Sirion : 5 - 6 mm)

• Below 12 mm : inhomogeneous “illumination” of the field at low magnification

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Ideal (Set-up) Detector Geometry

ElevationAngle

scale setting

IntersectionDistance/ Working Distance

Scale =50, EA = 35, Azimuth=45, ID= 10 (5)

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Various Detector Geometries

• Intersection Distance

• Elevation Angle

• Working Distance

• Take-Off Angle

EAID WD < ID

TOA < EA

WD > IDTOA > EA

Tilt > 0TOA > EA

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• K Ratio



• Fluorescence (F)Atomic Matrix/ Topography

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Fluorescence

High Energy X-ray Excites a Lower Atomic Number Atom

EDS Detector

35 º T-O

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Other Issues with Quantitative Analysis BSE-image useful to determine if sample homogeneous

SE-image BSE-image

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Quantitative Analysis- Background Subtraction• Background needs to be removed

before quantification

• Auto or Manual method

(new method Conc. Method - v3.2)

• Manual method may improve BKGD fit

• Background shape will affect the quantitative results : normally a very small effect

• Pay attention to absorption edges

• Glasses and minerals : Si absorption edge

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Quantitative analysis - Background Subtraction

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Quantitative analysis - Deconvolution

• Halographic peak fit procedure (HPD / Peak Fit)

• Suitable to separate overlapping peaks

• Sensitive to peak shift

• Requires well calibrated system

• Check deconvolution for missing elements

• In case of poor results or bad fit: choose other line

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Quantitative analysis - Matrix correction

• Remove Background

• Calculation of net peak intensity

• K-ratio calculation

• K-ratio = int. unknown peak / int. standard peak

• Matrix correction for Z - A - F

• Conc. = K-ratio / [ ZAF]

• Different correction models

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Quantitative analysis - Matrix correction

• Different correction models to calculated ZAF factors

• Two models :

- ZAF correction model

- Phi-Rho-Z correction model

• Phi-Rho-Z model very suitable for light element quantification

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Quantitative analysis - Matrix correction• Standardless analysis (normalise to 100%)

• Flexible, kV independent• System needs kV to make a matrix correction• Every identified peak will be quantified• EDAX standardless calculation :

WT% = Intensity measured /(P.E.I.F). X (SEC)______________________________

(Z.A.F)

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Quantitative analysis - standard less methods

• 2 different methods

• Standardless (normalisation to 100%) • Default SEC (standardless element co-efficient)

• All SECs are set to 1.0

• Improved Standardless : updating the SECs - User table

• Normally a few elements are updated to create more accuracy using standards

• Only the updated elements are more accurate : rest still standardless

• Mainly used for light elements- can be dangerous!!!

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Quantitative analysis: SEC

• SEC = standardless Element Coefficient

• All default SECs are set to 1.0

• SEC’s have to be changed for the lighter elements only (B, C, N, O, F)

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Poor Quantitative Analysis Conditions• Several situations where

the calculation of the ZAF factor does not apply :

- unsupported thin film

- thin film on substrate

- inclusion or particle

- biological sample

- particle on thin foil

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Quantitative analysis - Sources of errors

• Situation where the ZAF factors does not apply• X-ray interaction volume larger than phase size• Wrong coating (preferable Carbon-coating)• Poor statistics (acquisition time / countrate to low)• High count rate (high dead time)• Overlapping elements (trace elements)• Energy calibration errors• Improper background selection• Irregular specimen surfaces• Skirt effect (low vacuum SEM / ESEM)

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Quantitative analysis - Summary

• Background subtraction

• Deconvolution : needs well calibrated system

• Matrix correction models : ZAF,Phi-Rho-Z and Phi-ZAF

• Several situations where the ZAF factors do not apply

• Several errors possible

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Effects of Specimen Surface on X-ray Emission

Absorption of x-rays

EDS Detector Electron Beam

Fluorescence

X-rays

Specimen Matrix

Backscatterelectrons

Interactionvolume

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Directionality Is a Major Effect

A B C

DetectorDirection

samplestage/mount

Topography has a significant effect on spectrum count rate and on composition (take-off angle and absorption effects)

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The Effect of Topography

BA C

A= Lower low end peaksB= NormalC= Higher low end peaks

Take-off angle is highest at C and lowest at A.

3 different spectra at 3 locations on the same particle with a uniform composition.

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Real Time

• Real Time = Live Time + Dead Time (Real Time = Clock Time)

• Live Time - time when detector is alive and able to receive an x-ray event

• Dead Time - time when the detector or preamplifier is unable to accept a pulse because it is busy processing or rejecting an event(s).

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X-ray Generation - Continuum radiation• Continuum radiation =

Bremsstrahlung or background radiation due to inelastically scattering

• Observed fall out at low energies due to X-ray absorption enroute to the detector

• Background needs to be removed for quantification

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Spectral artifacts - Sum peaks• Sum peaks due to pulse pile-up

effects• Two X-rays are entering detector

at the same time• Sum of the energies is seen as

one energy• Sum peaks depending on (to

high) count rates for the corresponding amplification time

• Not only pure elements : combinations possible

• Prevent sum peaks by keeping countrate in balance with the chosen Ampl.Time (Dead time 25 - 35%)

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Spectral artifacts - Sum peaksSum peak Cr Ka = 2 x 5.411 = 10.822 KeV

2 times line energy

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Spectral artifacts - Escape peaks

• Escape peak : result of losing Si K energy in the Si-dead layer of the crystal

• Si K line = 1.74 KeV

• Remaining energy is original energy minus Si K energy

• Difficult to identify

• Intensity of the escape peak belongs to the main peak

• S/w can correct for escape peaks

• Example : Fe escape peak = same position as La L peak

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Artifacts- Escape Peaks

SiLicrystalCa

@ 3

.69

Si @ 1.74

1.74

1.95

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Spectral artifacts - overviewArtificial spectrum of Fe, showing background shape,

escape and sum peaks and the absorption edge

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The Effect of Detector Time Constant

At faster time constants, the throughput is increased but the resolution broadens. Fast time constants are commonly used for mapping but not for the collection of spectra with subtle overlaps.

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Spectral artefacts - Dead time • Dead time = system is busy with pulse shaping

• Dead time = relationship of input and output count rate

• Dead time depending on amplification time (TC)

• Reasonable dead time 25 - 35 %

• High dead time : system is slow

• Result : sum peaks and peak broadening

• Use live-seconds (corrected for dead time)

• Keep dead time in balance with chosen TC

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Calibration of EDS

X-ray peaks must be located accurately on the energy axis

Therefore calibration needed Automatic s/w procedure: zero and gain

adjustments Use two elements: Al and Cu Calibrate using a countrate as under

normal operations Optimum countrate: dead time 25 -

35 %

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Calibration (cont.)

• Calibration of amplification times

• Slow ampl.time is used for quantification:

good resolution (130 - 138 eV)

• Fast ampl. time used for mapping:

poor resolution (145 - 180 eV)

• Calibration every 2 - 4 weeks (if temperature is constant)

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Calibration Control page

X-ray lines of Al (1) and Cu(2)

Maximum full scale counts

Number of attempts

detector resolution

(Mn Ka line)

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Spectral artefacts - Warming of the detectorTwo type of dewars : 2.5 litre and 10 liter

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Spectral artefacts - Warming of the detector• Large dewar (10 L): always LN2

• Not designed to run dry

• Once a year let it run dry (EDAX tip 22)

• Small dewar (2.5 L) : fill when needed

• Designed to run dry*

• When warming up : low end noise peak

• Bias light still green

• Bias light will turn red when no LN2 present

anymore

• *- when microscope is not running

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Warming Detector• As the detector warms the noise peak widens and may appear

in the spectrum as a low-end noise peak.

• All peaks will broaden and may shift in energy

• Also note large incomplete charge collection area to the left of the Cu peak

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EDS Summary

• Quick lnformation

• Consistency is a must

• Accuracy is poor but repeatability is near perfect

• Ignore multiple decimal points, round out to nearest whole number for consistency

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Spectral artefacts - Peak overlap• EDS poor resolution :

result peak overlap

• Difference at least 60 eV to separate lines

• Classical example: Pb M - S K 2.345 KeV - 2.307 KeV difference = 38 eV

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Spectral artefacts - Poor counting statistics• Low count rate results in ‘noisy’ spectrum = poor statistics• ‘Noisy’ spectrum will introduce PEAK ID errors• System will identify noise (Auto ID)

Solution• Long acquisition time

- disadvantage : limited number of specimens• High countrate in combination with appropriate ampl. time

- disadvantage : poor peak separation• Find the ideal combination for your own samples

• qual/quan work : 2000 cps (DT30%) at Amp. Time 50

• acquisition time 100 Lsec

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How to perform an analysis? Use calibrated system Choose suitable place on the sample Make an image : - SE image shows topography -

BSE image shows atomic number contrast Focus (calculation of the TOA) Acquire a spectrum (label spectrum during acquisition) Unknown sample : 30 - 15 - 5 kV to find all elements Identification of all elements (using HPD / Peak Fit) Store spectrum to HD Built library of pure elements (reference spectra) If needed : perform quantification

Microanalysis under low vacuum conditions

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Poor Vacuum Microanalysis Considerations

“Skirt” electrons have almost full beam energy: 1. X-rays from the probe spot (actual information) 2. X-rays due to the gas 3. Information of surroundings (=skirt)

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2

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Steps to reduce skirt effect

• shorten BGPL (use the cone)• lower pressure• use high acceleration voltage (25kV)• use beam stop method• correct via software Gas Compensation Module (EDAX 3.1)

(last choice)

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EDS Geometry With and Without Cone

Working Distance (WD) vs. Beam Gas Path Length (BGPL)

Cone No Cone

Electronbeam

EDX

Detector

10mm WD

Electronbeam

EDX

Detector

10mm WD

Sample

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EDS at Low Gas Pressures and Short BGPL (ESEM Configuration)

ESEM Mode: 15kV, 2mm BGPL, 10mm WD, 1 torr Water Vapor

Examples of data from Electron Flight Simulator

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Microanalysis under low vacuum conditions• Low vacuum SEM : charge is eliminated by a gas (water, air or

N2)

• High kV possible, no limitation of excitation energies

• Two major problems :

- beam damage

- beam spread (skirt effect)

• Beam damage : because of high kV heating of sample

• Beam spread :

- Electron are scattered due to gas collision

- X-ray generation outside the probe spot

- X-ray information upto 500 micron from central spot (=skirt)

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Microanalysis under low vacuum conditions• To reduce the skirt effect:

• use short gas path (EDX cone in case of ESEM)• use high acceleration voltage (25kV)• use low pressure (0.1 - 0.3 mbar)• correct via s/w module (quant.)

(Gas Compensation Module = GCM)• GCM available for ESEM in s/w version 3.1

(minimum particle size 20 um)

Mapping and Linescans

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Mapping and Line scans

• Mapping and Linescan:

via optional EDX s/w module

EDX Multi element mapping program

Linescan software covered by EDAX applications class

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EDX Multi Element Mapping : Image collection and display

• Imaging:• built-in scan generator • built-in pixel averaging

• High resolution images (8200 x 6400 pixels)

• High resolution X-ray maps (2048 x 1600 pixels)

• Up to 15 elements with simultaneous image collection

• Overlay of maps, colour or grey levels

• Full control of beam and stage

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Region of Interest Control Page

Element with region of interest

(keV window)

Activated ROIs

+ is enabled (= activated)

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Mapping – Windows or ROI

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EDX Multi Element Mapping

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Options for EDX Multi Element Mapping

• EDX Fast Mapping• Fast X-ray mapping: Continuous update

during collection• EDX Quantitative Mapping

• Quantitative mapping• True element distribution

• EDX Line Scan (by EDAX advanced class)• Digital X-ray line scan

Results must be transferred to MS Excel (EDAX advanced class)

• EDX Particle/Phase Analysis• Automated area distribution and X-ray

classification

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EDX Fast Mapping

Fast X-ray mapping: Continuous update during collection

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EDX Multi Element Mapping -

Quantitative MappingQuantitative X-ray mapping: true element distribution in samples with overlapping peaks

PbM = 2.35 KeVS K = 2.31 KeV

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EDX Multi Element Mapping - Line Scan(EDAX advanced class )

Line scan in combination with Quant map also collection of quantitative line scans

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EDX Particle/Phase Analysis(EDAX advanced class)

Automated area distribution and X-ray classification

Rapid, automated detection and characterisation of particles

Chemical and morphological data

Automated multifield run

Classification in user defined classes

Microanalysis with Sirion

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Collimator with magnets

SUTW or UTW Windowwith magnets to deflect BSE

If BSE reach the detector they will producebackground anomalies --a hump in thebackground at high energies.

W and ESEM-FEG instruments only

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EDS Operation of the Sirion

• Semi-inlens system, using strong external magnetic field

• Electron-trapless EDX detector collimator to give optimised X-ray collection (no magnets)

• Backscatter electrons “trapped” by semi-immersed lens field

• HR mode: BSEs will enter the detector

EDX detector is “blinded”No X-ray

microanalysis possible X-rays only below 5 kV (hardly any BSEs)

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EDS Operation of the Sirion(cont.)

• UHR mode :• Strong magnetic field to trap BSEs• Skirt effect caused by reflecting BSEs• X-ray microanalysis possible (skirt effect)

Minimum magnification 1100x At 5 kV

• EDX mode :Dedicated EDX-mode to trap BSEs in the field

No skirt effect• Minimum magn. 130x (easy navigation)• Full range of kV at 5 mm WD Best EDX results

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EDS Operation of the Sirion - Summary

• Three modes of operation• HR mode• UHR mode• EDX mode

• EDX only possible under UHR and EDX mode• Best results with EDX mode• SS-BSD can limit the “field of view” for EDX • optimum EDX WD around 5.5 mm

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End of Quantrain 7.1 Options EDS

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Confidential Quantrainx50 7.2 EDS Basic 3-2010 place photo here