Author Topic: EPMA and large area SDD detectors  (Read 33 times)


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EPMA and large area SDD detectors
« on: June 12, 2019, 11:38:19 am »
On our SEM we have an SDD EDS detector which is 30 sq. mm. On our EPMA we have a 10 sq. mm. The idea being that the SEM tends to operate at lower beam currents, while the EPMA tends to operate at higher beam currents. And we don't want to saturate the detector on our EPMA when running at high beam currents.

Though it's worth mentioning that we have modified the EDS aperture wheel on our Cameca SX100 to reduce the geometric efficiency of the 10 sq. mm detector for very high beam currents, as discussed here:

Though generally we leave it "wide open". It should also be mentioned that utilizing a smaller aperture works just fine when performing standards based EDS analysis, because both the standards and unknowns are measured using the same EDS aperture.

But here's my question: does anyone have a 30 sq. mm SDD detector on their EPMA instrument?  If so, at what beam currents (with a fully open aperture) does one see deadtimes increase beyond 60-80%?

That is, is it a good idea to install a 30 sq. mm SDD EDS detector on an EPMA instrument?
UofO MicroAnalytical Facility

Karsten Goemann

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Re: EPMA and large area SDD detectors
« Reply #1 on: June 12, 2019, 04:06:00 pm »
We have a Thermo UltraDry Extreme 30mm2 on our 8530F plus. I think it's great to have. I was even considering 60mm2 but that's probably too large for our current setup. The 30mm2 gives us great EDS count rates when we use lowish beam currents like 10nA or less for beam sensitive materials. If the dead time gets too high at higher beam currents we can always switch to a smaller aperture.
Count rates obviously also depend a lot on the distance of the detector chip to the sample surface. Haven't tried to measure/compare that for different EPMA/EDS combinations.