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Rethinking EDS
Keith Thompson Jan 21, 2014
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Outline
- Background on EDS detector technology
- Discussion of modern EDS detectors
- Finding the right detector for your application
Rethinking EDS Keith Thompson Jan 21, 2014 Outline Background on - - PowerPoint PPT Presentation
Rethinking EDS Keith Thompson Jan 21, 2014 Outline Background on - - PowerPoint PPT Presentation
Rethinking EDS Keith Thompson Jan 21, 2014 Outline Background on EDS detector technology Discussion of modern EDS detectors Finding the right detector for your application Proprietary & Confidential 2 EDS & WDS: 1950s
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EDS & WDS: 1950s
- The first “EDS-styled” analytical technique was actually WDS
- Based on Bragg diffraction
- First EPMA built in 1949 by Raymond Castaing
- The spectrometer looked at 1 element at a time
- The spectrometer was manually adjusted
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1960s: EDS becomes mainstream with Si(Li) detectors
Whole spectrum at once type of analysis Computing power to run the system and process the data Acceptance of EDS in the SEM community
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Drawbacks to the first Si(Li) EDS detectors
- X-ray loss in Be window
- Window required to protect Si(Li) module
- No spectrum < 1 keV with Be windows
- Poor energy resolution and count rates
- ~ 145 eV at < 2,000 X-ray stores per second
- ~ 200 eV at up to 20,000 X-ray stores per second
- Inherent limitations to active area
- The constant requirement for Liquid Nitrogen!
Despite these drawbacks, LN-cooled detectors would dominate EDS for 40 + years
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1988: First no-LN cooled detector
- Mechanical cooling with Peltier devices were used to replace Liquid
Nitrogen cooled detectors.
- No LN ever again!
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SuperDry at high count rates: 54,000 cps
- Resolution at count rate remained a challenge
- Window transmission challenges remained
- Potential reliability concerns with mechanical vibration (shaking of the
electron image) and water recirculation (water leaks)
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Modern EDS for the new Millennium
- Novel light element windows allowed transmission to Be
- PC-based acquisition and data storage
- Element mapping evolves into Spectral Imaging
- SDD – based EDS detectors commercially available
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The SDD revolution
SDD vs. LN circa 2002 Same sensitivity in one third the time! (Spectra taken at same beam current)
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SDD Benefit versus Si(Li) at High Throughput
- At high count rates, conventional Si(Li) experiences significant peak shift
and loss of sensitivity for light elements
- The UltraDry SDD maintains resolution at high count rates
Si(Li) Spectrum SDD Spectrum
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2nd generation SDD: Improved Light element
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3rd Generation Silicon Drift Detector
Si(Li)
Larger detectors for faster throughput: 10, 30, 60, 100 Improved energy resolution Improved light element
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Outstanding low energy resolution
Clear peak separation Excellent peak – background
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SDD Gen 3 vs. SDD Gen 2
60 mm2 10 mm2
10 mm2
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Large Area detectors: What does it mean to me?
256 pixel x 192 pixel resolution 20 second acquisition
CuFeS Quartz NiFeS FeS Epoxy
10 mm2 detector 15 counts/pixel 100 mm2 detector 120 counts/pixel1 Larger area detectors collect more X-rays under identical circumstances
- 1. Collection rate saturated at 300,000 stored counts per second
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Steady resolution with count rate
60 mm2 SDD detector at: 10,000 cps 100,000 cps 300,000 cps
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Light Element Detection – Li mapping
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A retrospective
- Before 2000
- LN dominated
- Slow count rates
- Poor energy resolution
- Be windows….. Poor light element
- No spectral imaging…. Pick your element and hit “Go”
- Modern detectors
- Large area detectors
- Very high count rates
- Outstanding energy resolution across the spectrum
- Light element detection to Li
- How does my detector stack up against my application?
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Spectral resolution Active area … SIZE Fast mapping Large mosaics Complex mapping at low energy Many elements over a large area Careful Quant of trace elements TEM & nanoscale Microprobe Point & shoot applications Failure analysis Quality control Defect review Light element analysis
… Lithium detection … B in glass
w/ EBSD
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Introducing: ThermoScientific UltraDry Compact EDS system
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Thermo Scientific UltraDry Compact EDS system
- What it is:
- A stream-lined, smaller and cost-effective EDS
detector
- Fixed length, standardized design that bolts easily
to the WDS port
- Who needs it?
- Those who want to perform high-quality, chemical
analysis in an electron microscope but don’t have the budget to pay for a high-end spectroscopic instrument.
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UltraDry Compact EDS
Spectral resolution Active area … SIZE Fast mapping Large mosaics Complex mapping at low energy Many elements over a large area Careful Quant of trace elements TEM & nanoscale Microprobe Point & shoot applications Failure analysis Quality control Defect review Light element analysis
… Lithium detection … B in glass
w/ EBSD
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More than adequate Spectral Performance
The overall spectral performance we expected from 2nd generation SDDs …. We still get that and more.
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Ideal for Point & Shoot analysis
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Element mapping when you need it
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Spectral Imaging: example extracted linescan
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Spectral Imaging: example area extraction
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