light element sensitivity: eds detectors are not created...

Light element sensitivity:

EDS detectors are NOT created equal Keith Thompson Aug 2014

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EDS detectors have come a long way over the past decade

Most people will tell you that all detectors are basically the same

123 eV

• Faster • Better resolution • Better sensitivity

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In the “middle – high” energy range: detector performance is mostly the same between detectors.

123 eV 129 eV

183 eV

133 eV 138 eV

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EDS map at 145 eV

In the “middle – high” energy range: detector performance is mostly the same between detectors.

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Standard detector

Extreme detector

In the “middle – high” energy range: detector performance is mostly the same between detectors.

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In the light element world: some EDS detectors just don’t hold up.

Standard detector

Extreme detector

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Why are some detectors better than others at low energies?

• Impact of the SDD Module

• Impact of the architecture

• Impact of the window

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Three main factors in SDD light element performance

Traditional – circular / symmetric vs.

Modern – tear drop, small FET

Low energy x-ray

SDD

mod

ule

Light elementwindow

Low energy x-ray

SDD

mod

ule

Light elementwindow

Traditional: N2 backed window vs.

Modern: evacuated window

Traditional: wire-bonded FET vs.

Modern: integrated, “on-chip” FET

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Light element sensitivity: “Sensitive to B”

Pure B metal

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Light element sensitivity: “Sensitive to Be”

Extreme EDS

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Impact of the module

N2 back-filled window Traditional round geometry

Evacuated window Traditional round geometry

Evacuated window Tear-drop geometry

Normalized intensity scales Stronger B peak

Smaller zero width

Better signal to noise

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Some Examples - Trace B in steel

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Mapping 2% B in Fe-Cr: Traditional detector

0

1000

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0200400600800

100012001400160018002000

80 180 280 380 480

EDS

coun

ts

WDS

cou

nts

Energy eV)

B - WDSB - EDS

Trace B (2% B in Fe-Cr) is harder

B

C

0

2000

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0

20000

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80 180 280 380 480

EDS

coun

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WDS

cou

nts

Energy eV)

B - WDSB - EDS

B metal is easy for EDS/WDS

B

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B raw counts

B Net counts (processed)

B WDS

Mapping 2% B in Fe-Cr

1. With an evacuated tear-drop detector trace B mapping is possible.

2. “Processing” the maps to remove background helps. 3. WDS still provides the best answer.

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Some Examples - Sn: Ni-Cu intermetallic

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20 kV 5 kV

EDS Ni-Cu intermetallic

The goal is to examine potential interdiffusion through a thin barrier layer.

Low kV analysis to avoid an interaction volume that may pollute the data

Cu only

1 µm

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Spectrum analysis: EDS Ni-Cu intermetallic

Cu only

1 µm

Serious overlap

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Standard module Advanced module

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Spectrum analysis: WDS vs. EDS Ni-Cu intermetallic

1

2

3

Cu only

Ni only

Cu & Ni

1 µm

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EDS vs. WDS maps – Ni, Cu, Sn

EDS element maps are confounded

WDS element maps provide complete confidence

Copper Ni Sn

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EDS vs. WDS maps – Ni, Cu, Sn – Processed!

Copper Ni Sn

WDS element maps provide complete confidence

The PROCESSED EDS element maps provide a better look

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EDS vs. WDS maps – Ni, Cu, Sn – Processed!

Raw EDS element maps

PROCESSED – Net Counts – EDS element maps

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Summary • EDS detectors are not all the same.

• The light element performance is very different based on

• SDD module type • Detector window • Overall detector architecture

• Know your application

• Mid – high energy applications: Most EDS detectors are fine • Low energy applications: Need the best possible EDS detector.

• Often post-processing algorithms can extract the correct answer even when the raw data is confounding.