place photo here
Quantrainx50 7.2
EDS Basic
3-2010
Confidential
EDS
• Universal applications
• Elemental analysis
• 1% Accuracy
• Beam Control / Imaging
• Repeatable
2
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)
3
• *(Many thanks to Dr. Bob Anderhalt for graphics and
Example of Quantax50/EDAX Integration
OUT DATED IMAGE !!!
4
Your Basic Bohr Atom


5
N shell
M shell

L shell

K shell
Inelastic Collision
N shell
Primary Beam Electron
M shell
Secondary Electron
L shell
K shell
Forward Scattered Electron
6
Inelastic Collision
Emitted X-ray
N shell
M shell
Secondary Electron
L shell
K shell
Forward Scattered Electron
7
X-ray Transitions

N shell
g Transition

M shell

L shell

K shell
β Transition
α Transition
9
K α Transition


N shell
M shell
K α Transition
10

L shell

K shell
K β Transition


K β Transition
11
N shell
M shell

L shell

K shell
L
α Transition

L α Transition
12

N shell
M shell

L shell

K shell
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
13
Continuum X-rays -(Background
Radiation)
Incident
Electron Beam
Ejected
Electron
White radiation
(Continuum)
14
Characteristic
X-ray
Emission Depth of X-rays of KV Vs.. Z (in
Microns)
SIMPLIFIED VALUES
Z
4
5
11
12
13
14
19
20
22
24
24
26
27
28
29
30
32
38
40
42
46
47
79
15
SYMBOL
Be
C
Na
Mg
Al
Si
K
Ca
Ti
Cr
Mn
Fe
Co
Ni
Cu
Zn
Ge
Sr
Zr
Mo
Pd
Ag
Au
ELEMENT
Beryllium
Carbon
Sodium
Magnesium
Aluminum
Silicon
Potassium
Calcium
Titanium
Chromium
Maganese
Iron
Cobalt
Nickel
Copper
Zinc
Germanium
Strontium
Zirconium
Molybdenum
Palladium
Silver
Gold
5KV
.5
.4
.9
.5
.3
.3
.5
.2
.01
10KV
1.7
1.2
3.1
1.7
1.1
1.2
2.9
1.6
.5
.25
.2
.2
.1
.09
.06
.02
20KV
5.3
3.9
10.0
5.6
3.6
4.1
10.8
5.9
2.0
1.2
1.2
1.0
.9
.85
.8
1.0
1.2
1.2
.2
30KV
10.5
7.7
19.2
11.1
7.1
8.2
21.9
12.2
4.1
2.6
2.4
2.2
2.0
1.9
1.9
2.3
3.0
4.8
1.7
.9
.5
.4
.2
EDS Hardware
SEM
Column
Monitor (MCA Display)
Dewar
FET
Preamp
Pole
Piece
Detector
Analyzer
SCSI
Window
Collimator
16
Sample
Stage
X-section of Window & Crystal
-500 to 1000 volts
+,charges
Detector
Vacuum
Detector
Window
8u Be or 0.3u Polymer
17
Detector
SiLi
to
preamplifier
(FET)
X-section of Window & Crystal
-500 to 1000 volts
+,charges
Detector
Vacuum
Detector
Window
8u Be or 0.3u Polymer
18
Detector
SiLi
to
preamplifier
(FET)
3.8 eV for each
charge pair
X-section of Window & Crystal
-500 to 1000 volts
AlKa X-ray=
1.48KeV in
+,charges
Detector
Vacuum
Detector
Window
8u Be or 0.3u Polymer
19
Detector
SiLi
to
preamplifier
(FET)
389 charge
pairs out
@ 3.8 eV each=
1.48KeV
How a Spectrum Grows
Kα
Kb
Lα
Counts
.938
20
Energy
8.044
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)
21
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
22
• Heavy elements will produce K
Qualitative analysis - Peak ID
Manual ID (Z- Z+) steps along elements
Auto ID
EPIC table
Peak Identification chart)
(Element
HPD : halographic peak deconvolution
Peak Fit / (to check overlapping elements)
Display possibilities
Marker options : ESC - SUM
23
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
24
What Affects Quantitative Analysis
• K Ratio
• Atomic Number (Z)
Accelerating Voltage
• Absorption (A)
Take-Off Angle
• Fluorescence (F)
Atomic Matrix/Topography
25
What Affects Quantitative Analysis
• K Ratio
Unknown / Known ratio or
Unknown Intensity / Pure Element Intensity
26
What Affects Quantitative Analysis
• K Ratio
• Atomic Number (Z)
Accelerating Voltage
1.5 to 10 Times excitation energy
Or 2 times the highest energy peak
27
Why should the overvoltage be less than 10
to 20 times the lowest energy peak?
High overvoltage means a high absorption
condition and a small peak and poor
statsitics (again)
X-Ray
Generated
Volume
28
Why should the overvoltage be at least 1.5
for the highest energy element?
X-Ray Vol.
Low overvoltage means a small, poorly excited peak and poor
statistical quality in the spectrum
Electron Volume
29
What Affects Quantitative Analysis
• K Ratio
• Atomic Number (Z)
Accelerating Voltage
• Absorption (A)
Take-Off Angle
30
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
31
Normal Take-Off Angle
EDS Detector
35 º T-O
Normal take -off Angle Allows Low Energy X-rays to
Become Absorbed in Specimen
32
Greater Take-Off Angle
EDS Detector
Greater T-O
Greater Take-Off Lets Low Energy X-rays Escape
33
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
34
Ideal (Set-up) Detector Geometry
Scale =50, EA = 35, Azimuth=45, ID= 10 (5)
Intersection
Distance/
Working Distance
Elevation
Angle
35
Various Detector Geometries
ID
EA
WD > ID
TOA > EA
36
WD < ID
TOA < EA
Tilt > 0
TOA > EA
• Intersection
Distance
• Elevation
Angle
• Working
Distance
• Take-Off
Angle
What Affects Quantitative Analysis
• K Ratio
• Atomic Number (Z)
Accelerating Voltage
• Absorption (A)
Take-Off Angle
• Fluorescence (F)
Atomic Matrix/ Topography
37
Fluorescence
EDS Detector
35 º T-O
High Energy X-ray Excites a Lower Atomic
Number Atom
38
Other Issues with Quantitative
Analysis
BSE-image useful to determine if sample homogeneous
SE-image
39
BSE-image
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
40
• Glasses and minerals : Si absorption edge
Quantitative analysis - Background
Subtraction
41
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
42
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
43
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
44
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)
45
•
Quantitative
analysis
standard
less
2 different methods
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
46
• Mainly used for light elements- can be dangerous!!!
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)
47
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
48
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)
49
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
50
Effects of Specimen Surface on X-ray
Emission
EDS Detector
Electron Beam
Backscatter
electrons
Fluorescence
X-rays
Specimen Matrix
Absorption of x-rays
51
Interaction
volume
Directionality Is a Major Effect
Detector
Direction
A B C
sample
stage/mount
Topography has a significant effect on spectrum count rate
and on composition (take-off angle and absorption effects)
52
The Effect of Topography
A= Lower low end peaks
B= Normal
C= Higher low end peaks
A
Take-off angle is
highest at C and
lowest at A.
53
B
C
3 different spectra at
3 locations on the
same particle with a
uniform
composition.
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).
54
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
55
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%)
56
Spectral artifacts - Sum peaks
Sum peak Cr Ka = 2 x 5.411 = 10.822 KeV
2 times line energy
57
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
58
Artifacts- Escape Peaks
Si @ 1.74
SiLi
crystal
59
Spectral artifacts - overview
Artificial spectrum of Fe, showing background shape, escape
and sum peaks and the absorption edge
60
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.
61
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
62
Calibration of EDS






63
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 %
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)
64
Calibration Control page
X-ray lines of Al (1) and Cu(2)
Maximum full scale counts
Number of attempts
detector resolution
(Mn Ka line)
65
Spectral artefacts - Warming of the detector
Two type of dewars : 2.5 litre and 10 liter
66
•
Spectral artefacts - Warming of the
Large dewar (10 L):detector
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
67
present anymore
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
68
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
69
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
70
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
71
-
How to perform an analysis?










72
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
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)
74
2
1
3
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)
75
EDS Geometry With and Without Cone
Working Distance (WD) vs. Beam Gas Path Length (BGPL)
Electron
beam
Electron
beam
EDX
EDX
Detector
Detector
10mm WD
10mm WD
Sample
Cone
76
No Cone
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
77
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)
78
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)
79
Mapping and Linescans
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
81
EDX Multi Element Mapping :
Image collection and display
Imaging:
•
•
•
82
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
Region of Interest Control
Page
Element with region of interest
(keV window)
Activated ROIs
+ is enabled (= activated)
83
Mapping – Windows or ROI
84
EDX Multi Element Mapping
85
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)
•
•
•
•
86
•
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
EDX Fast Mapping
Fast X-ray mapping:
Continuous update
during collection
87
EDX Multi Element Mapping Quantitative Mapping
Quantitative X-ray
mapping: true element
distribution in samples with
overlapping peaks
PbM = 2.35 KeV
S K = 2.31 KeV
88
EDX Multi Element Mapping - Line
Scan
(EDAX advanced class )
Line scan in combination
with Quant map also
collection of quantitative
line scans
89
EDX Particle/Phase Analysis
(EDAX
advanced
class)
Rapid, automated
detection and
characterisation of
particles
Chemical and
morphological data
Automated
multifield run
Classification in
user defined classes
Automated area distribution and X-ray classification
90
Microanalysis with Sirion
Collimator with magnets
W and ESEM-FEG instruments only
SUTW or UTW Window
with magnets
to deflect BSE
92
If BSE reach the detector they will produce
background anomalies --a hump in the
background at high energies.
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)
93
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
•
Minimum magn. 130x (easy navigation)
•
Full range of kV at 5 mm WD Best EDX results
94
No skirt effect
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
95
End of Quantrain 7.1 Options EDS
96
Title slide
sub-title
Confidential