-Fundamental knowledge of EDS -Basic functions in INCA and EDAX EDS analysis software

1. References:
Oxford Instruments website
“Scanning Electron Microscopy and X-Ray Microanalysis” by Joseph Goldstein et al
“ Energy Dispersive Spectroscopy on the SEM: A Primer ” by Bob Hafner
“Transmission electron microscopy IV Spectrometry” by David B. Williams et al
EDS softwares: INCA (SEM)and EDAX (TEM)
Dr. Yina Guo
Materials & Surface Science Institute
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Distances depend strongly on
material and beam energy.
Note SEM X-ray resolution,
typically about 1 mm, TEM X-
ray resolution ~ width of
beam
Interaction volume for
electrons in a bulk sample.
Distances are for 20 kV
electrons in Cu, for Al
multiply by 3.
Interaction volume

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The important point is that the voltage pulse produced is
proportional to the energy of the incoming X-ray photon.
Operator control
:

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Things under your control:
• Geometry of the Detector (working distance)
• Accelerating voltage
• Process time
• Duration of signal acquisition (to obtain a statistically significant
number of counts and thus good peak/backgound ratios)
• Probe current (changing probe currents will necessitate realignment
of the microscope)
The important point is that the voltage pulse produced is
proportional to the energy of the incoming X-ray photon.
Operator control

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The X-Max Silicon Drift Detector
Detector size: 50mm2
EDS system in Hitachi-SU70 SEM

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36
4
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INCA acquisition process

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INCA acquisition process_Microscope Setup
Input rate: This shows the approximate
rate of photons striking the detector.
As you adjust the microscope beam
current, the input rate or the approximate
rate of X-rays entering the detector will be
in direct proportion to the beam current.
Acquisition rate: This shows how fast the
system is accumulating spectrum counts.
Spectrum counts determine statistical
precision and limits of detection. Since it
takes time to measure photon energy, there is
a chance that second photon will arrive while
the pulse processor is measuring the first. If
this happens, the measurement is rejected
and the acquisition rate is therefore less than
the input rate.
Beam current setting

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INCA acquisition process_Microscope Setup
Process time:
The signal (voltage step) from the preamplifier is transformed into a voltage pulse that is suitable for
the multi channel analyzer. Shaping and noise reduction of the signal are achieved by digital
computation. The noise on the voltage ramp from the detector is effectively filtered out by averaging
the signal. The time over which the waveform is averaged is called the process time (Tp). Tp is under
control of the operator. The longer the Tp, the lower the noise. If noise is minimized, the resolution of
the peak displayed in the spectrum is improved, and it becomes easier to separate or resolve, from
another peak that is close in energy.
However, there is a trade-off between the process time that is used, and the speed at which data can
be measured. The longer the process time, the more time is spent measuring each X-ray, and the fewer
events that can be measured.
Dead time-time during which pulses are not measured
Deadtime = (1 – Output rate/Input rate) x 100.
Deadtimes of 30-60% will tend to maximize output.
The operator can and should maximize output rates
for a given sample and process time by controlling
probe current/spot size.

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2
INCA acquisition process_Quant Optimization
• For a given X-ray pulse the X-ray energy it is
assigned to depends on the gain of the
amplifier which can drift over time.
• Thus the system must be calibrated by
acquiring a spectrum from a known
element such as Co or Cu.

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Microscope setup
3
INCA acquisition process_Acquisition setup
EDS Setting
WDS Setting

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4
INCA acquisition process_Confirm elements

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INCA acquisition process_Confirm elements
1. Ensure that the incident beam energy is high enough.
Beam energy > 2 × Highest peak energy.
2. Ensure that the spectrum is reliable.
Repeat the spectrum from the same area, ensure there are enough
counts
3. Use prior knowledge of the sample to know which elements are
likely to be present and which are unlikely to be present.
4. Confirm elements by looking for other peaks from that element.
5. Work from high energy to low energy identifying peaks.
At high energy, there are fewer peaks - and it is easier to resolve
neighbouring peaks.

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INCA acquisition process_Quant setup
5

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INCA acquisition process_Spetrum comparison

15. EDS line scan analysis (Aghada)
15
MX (VX)
Vanadium
Chromium
Iron
M= Nb or V, X = C and/or N*
Czyrska-Filemonowicz, A., Zielinska-Lipiec, A., Ennis, P.J. (2006) 'Modified 9% Cr Steel for Advanced Power
Generation: Microstructure and Properties' Journal of Advancements in Materials and Manufacturing
Engineering, 19(2), 43-48.

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21. Wt% MoL V K CrK FeK NbK At% MoL V K CrK FeK NbK
multipoint1 13.49 0.63 65.3 20 0.58 multipoint1 7.93 0.7 70.82 20.2 0.35 M23C6
multipoint2 13.68 0.61 62.57 22.59 0.54 multipoint2 8.06 0.68 68.05 22.88 0.33 M23C6
multipoint3 11.31 0.45 63.88 23.86 0.5 multipoint3 6.59 0.49 68.72 23.9 0.3 M23C6
multipoint4 8.31 69.2 11.55 0.94 10 multipoint4 4.83 75.82 12.4 0.94 6.01 V-rich MX
multipoint5 3.06 73.84 16.97 1.07 5.07 multipoint5 1.69 77.04 17.34 1.02 2.9 V-rich MX
multipoint6 2.69 71.87 15.88 4.13 5.43 multipoint6 1.49 75.18 16.27 3.94 3.11 V-rich MX
multipoint7 13.27 0.6 64.87 20.47 0.79 multipoint7 7.8 0.66 70.38 20.68 0.48 M23C6
EDAX-EDS example 1_Multi-point analysis

22. SE image
V Fe
Cr
EDAX-EDS example 2_Elemental mapping

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Series2
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EDS/X identifying element