There are 3 main drivers in specifying an EDS detector: • Energy resolution @ Mn k-alpha • Sensitivity • Solid angle How relevant are these specifications in determining the performance of an EDS detector? How do I choose the right detector for your lab?

1. Choosing the right
EDS detector
Keith Thompson
April 7 2014

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EDS and SEM go hand-in-hand
Electron Microscopy provides the imaging
EDS provides the “chemistry”

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EDS provides a look at material composition
Point & Shoot, Line Scan and Mapping

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Electron Microscopes
• Material Science
• Electronics
• Petrochemical
• Mining
• Metals
• Semiconductor
• Life Science
Many options for
electron microscopes
Many options for EDS

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EDS detector advances
Larger active areas
Various tube size… even oval tubes
Faster Acquisitions

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• There are 3 main drivers in specifying an EDS
detector
• Energy resolution @ Mn k-alpha
• Sensitive to
• Solid angle
• How relevant are these specifications in determining
the performance of an EDS detector?
• How do I choose the right detector for my lab?

7. Energy Resolution
Which detector is right for my application?

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Energy resolution
Measured:
Width of the Mn k-alpha peak @
half the peak height
- Why does this spread occur?
- What is good enough?
- Is this a valuable metric?

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How x-ray detection works:
X-rays generate a small current of e- – hole pairs
Next stage: charge-sensitive pre-amplifier stage
Next stage: Pulse processor measures the amplitude

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Signal
Time
Function of Silicon Drift Detector
Charge
Collection:
Event 1 signal 1
Event 2 signal 2
Event 3 signal 3
1
2
3

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0
5
10
15
20
25
30
35
0 100 200 300 400
Voltage
Time
0
0.2
0.4
0.6
0.8
1
1.2
50 60 70 80 90 100 110 120 130 140 150
Energy (keV)
Counts
Peaking time
X-ray induced
voltagestep
Every system has noise. This noise drives energy resolution

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Sources of uncertainty: Noise
• Internal or “system”
• Inherent in the system: SDD module, wire bonding, cabling, electronics and
other overall architecture design
• Measured in the factory in a “golden” environment.
• External or “Environmental”
• Any external noise source: motors, old equipment, switching circuits, EM
interference, UPS, poor power, ground-loops and so forth

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System noise
• In a SiLi-based EDS, the capacitance is directly related to the active
area of the device.
• Capacitance starts as BIG
• As active area increases, capacitance increases
Needs LN

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Get much smaller
And have potential to get smaller still.

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Move averaging, less uncertainty, better resolution
Less averaging, more uncertainty, worse resolution

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Longer integration times result in superior energy resolution
Shorter integration times are required for high count rates

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What does high count rate resolution look like?
123 eV @ 6.4 sec
183 eV @ 0.2 sec
EDS detectors are routinely specified @ 2,000 – 3,000 cps

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Take-away points
• Energy resolution
• Laboratory noise impacts performance
• speed matters: faster acquisition = worse resolution
• Detectors are specified at slow rates

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What does high count rate resolution look like?
Often-times 185 eV is just fine
2000 eV
peak-to-peak
2000 eV
peak-to-peak

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What does high count rate resolution look like?
Sometimes we need 4 eV

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Take-away points
• Energy resolution
• Laboratory noise impacts performance
• speed matters: faster acquisition = worse resolution
• Detectors are specified at slow rates
• Sometimes poor resolution is just fine
• Other times the resolution will never be good enough

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What does high count rate look like?
128 eV @ 6.4 sec
160 eV @ 0.4 sec
How about down here?
(input cps)
Standard EDS

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What does high count rate look like?
Difficult to even define resolution
@ 1,000,000 cps
(input cps)
Standard EDS

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Can we improve on this?
It is possible to design an SDD with excellent low energy performance
76 eV
78 eV
114 eV
66 eV
67 eV
90 eV
55 eV
61 eV
114 eV
(input cps)
Extreme EDS

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Can we improve on this?
It is possible to design an SDD with excellent low energy performance
57 eV
67 eV
50 eV
62 eV
50 eV
62 eV
(input cps)
Extreme EDS

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Take-away points
• Energy resolution
• Laboratory noise impacts performance
• speed matters: faster acquisition = worse resolution
• Detectors are specified at slow rates
• Sometimes poor resolution is just fine
• Other times the resolution will never be good enough
• Low energy part of the spectrum is affected more dramatically than the
moderate to higher part of the spectrum

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• High quality light element energy resolution
• Low quality light element energy resolution
• Can we quantify the difference between these two
detector designs?

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A look at the numbers
Group 1 = Standard EDS
Group 2 = Extreme EDS

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A look at the numbers
All “129 eV” detectors~ 10 eV difference in light element
Group 1 = Standard EDS
Group 2 = Extreme EDS

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How much of an impact?
Extreme detector, 10 kcps
Standard detector, 10 kcps
Standard detector, 1 Mcps

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Take-away points
• Energy resolution
• Laboratory noise impacts performance
• speed matters: faster acquisition = worse resolution
• Detectors are specified at slow rates
• Sometimes poor resolution is just fine
• Other times the resolution will never be good enough
• Low energy part of the spectrum is affected more dramatically than the
moderate to higher part of the spectrum
• Energy resolution specifications up at Mn –ka (5.9 keV) are not
reflective of the performance in the low energy spectrum.

34. Light element sensitivity
“Sensitive to ”
Which detector is right for my application?

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Light element sensitivity: “Sensitive to”
•EDS detectors often carry a light element
sensitivity specification termed as:
•“Sensitive to”
•Why this specification?
•What does it really indicate?

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Light element sensitivity: “Sensitive to”
• The detector system absorbs x-rays
• Window between SEM chamber and crystal
• Thin metal layer on detector crystal to avoid cathodoluminescence
• Some detectors use N2 backfill
window
detector
crystal
pre-amp
cold finger
insulator
X-rays
liquid Nitrogen

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X-ray absorption in windows
Na
OB

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X-ray absorption in windows
O
BLi Be
Li detection is not possible with a window and has challenges well beyond
window technology

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Light element sensitivity: “Sensitive to Be”
Extreme EDS

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Light element sensitivity: “Sensitive to BN”
Extreme EDS

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Light element sensitivity: “Sensitive to B”
Compact EDS
Pure B metal

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Compact EDS detector

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Light element sensitivity: “Sensitive to B”
8x sensitivity Extreme EDS
Compact EDS

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Light element sensitivity: “Sensitive to B”
0
1000
2000
3000
4000
5000
6000
0
200
400
600
800
1000
1200
1400
1600
1800
2000
80 180 280 380 480
EDScounts
WDScounts
Energy eV)
B - WDS
B - EDS
Trace B (2% B in Fe-Cr) is harder
B
C
0
2000
4000
6000
8000
10000
0
20000
40000
60000
80000
100000
120000
80 180 280 380 480
EDScounts
WDScounts
Energy eV)
B - WDS
B - EDS
B metal is easy for EDS/WDS
B

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Take-away points
• Energy resolution
• Laboratory noise impacts performance
• speed matters: faster acquisition = worse resolution
• Detectors are specified at slow rates
• Sometimes poor resolution is just fine
• Other times the resolution will never be good enough
• Low energy part of the spectrum is affected more dramatically than the
moderate to higher part of the spectrum
• Energy resolution specifications up at Mn –ka (5.9 keV) are not reflective of the
performance in the low energy spectrum.
• Sensitivity
• Detection to B isn’t always detection to B

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•Is light element sensitivity just
about my detector and window
technology?

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Light element sensitivity: Variable pressure mode

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Light element sensitivity: Variable pressure mode

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Light element sensitivity: Variable pressure mode
C Cu-L
Pure B metal

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Light element sensitivity: Variable pressure mode
No VP
50 Pa
200 Pa
No VP
Extreme detector
Compact EDS detector

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Take-away points
• Energy resolution
• Laboratory noise impacts performance
• speed matters: faster acquisition = worse resolution
• Detectors are specified at slow rates
• Sometimes poor resolution is just fine
• Other times the resolution will never be good enough
• Low energy part of the spectrum is affected more dramatically than the
moderate to higher part of the spectrum
• Energy resolution specifications up at Mn –ka (5.9 keV) are not
reflective of the performance in the low energy spectrum.
• Sensitivity
• Detection to B isn’t always detection to B
• Variable pressure mode has a major impact on light element detection

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Light Element Detection – Li mapping
Windowless Extreme EDS detector

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Take-away points
• Energy resolution
• Laboratory noise impacts performance
• speed matters: faster acquisition = worse resolution
• Detectors are specified at slow rates
• Sometimes poor resolution is just fine
• Other times the resolution will never be good enough
• Low energy part of the spectrum is affected more dramatically than the
moderate to higher part of the spectrum
• Energy resolution specifications up at Mn –ka (5.9 keV) are not
reflective of the performance in the low energy spectrum.
• Sensitivity
• Detection to B isn’t always detection to B
• Variable pressure mode has a major impact on light element detection
• The technology for light element detection exists today. You need to
specifically ask & plan for it.

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Light element sensitivity: “Sensitive to”
•Determine what you need
•Is it important to your application?
• Light element detection? Or mapping?
• Transition metals?
• Do you work in VP mode?
• How critical is quant?
•Be specific & avoid ambiguity.

55. What detector is best for my
application?

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Point & Shoot analysis of geological
Compact EDS detector

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Spectral Imaging Map: Geological

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Example – Multiphase sample with peak overlaps
• Detector: UltraDry 10mm2 SDD
• Resolution: 129eV MnK FWHM
• Accelerating Voltage: 7kV
• Magnification: 500x
• Map resolution: 256x192
• Storage Rate: 107,000cps
• Acquisition Time: 5 minutes

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Example – Multiphase Sample – Raw Count Maps
Si_K
Ta_M
W_M
Ni_L
Cu_L

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Multiphase Sample – Net Count Maps

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Multiphase Sample – Net Count Maps
Si_K
Ta_M
W_M
Si, Ta, W: No detector can separate these peaks
Peak deconvolution algorithms cleanly separate the peaks

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Example – Mo, S, Ba Multiphase Sample
• Detector: UltraDry 10mm2 SDD
• Resolution: 129eV MnK FWHM
• Accelerating Voltage: 7kV
• Magnification: 500x
• Map resolution: 256x192
• Acquisition Time: 3 minutes

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Example – Mo, S, Ba – Raw Count Element Maps

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Example – Mo, S, Ba – Net Count Maps

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Example – Mo, S, Ba – Phase Maps
 Distinguishing the three main phases is
not possible without robust peak
deconvolution
2100 2150 2200 2250 2300 2350 2400 2450 2500
eV
MoL SK

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Take-away points
• Energy resolution
• Laboratory noise impacts performance
• Speed matters: faster acquisition = worse resolution
• Detectors are specified at slow rates
• Sometimes poor resolution is just fine
• Other times the resolution will never be good enough
• Low energy part of the spectrum is affected more dramatically than the moderate to higher part of the
spectrum
• Energy resolution specifications up at Mn –ka (5.9 keV) are not reflective of the performance in the
low energy spectrum.
• Sensitivity
• Detection to B isn’t always detection to B
• Variable pressure mode has a major impact on light element detection
• The technology for light element detection exists today. You need to specifically ask & plan for it.
• Post-processing algorithms
• Peak deconvolution, background subtraction and matrix correction algorithms are critical to high quality
mapping
• Phase mapping is even more powerful than these element mapping algorithms

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• EDS detector have made many advances over the last several years
• 3 main drivers in specifying an EDS detector
• Energy resolution @ Mn k-alpha
• Sensitive to
• Solid angle
• Actually important
• Energy resolution in low energy
• Actual sensitivity of light element
• Actual throughput
• Most important: Peak deconvolution and net counts mapping
• The most important factor is careful discernment of the EDS detector and
the overall EDS system