Recent Posts

Pages: [1] 2 3 ... 10
1
Probe for EPMA / Re: Correction of negative result in quant
« Last post by Probeman on Today at 09:07:43 AM »
Here's a slide from my recent webinar on improving accuracy and sensitivity of trace element analyses:

https://www.youtube.com/watch?v=9KM5lU403VY&t=1478s



This slide is based on a slide sent to me by one of our commercial EPMA colleagues who asked to remain anonymous, but I think it makes the point well, that we should not be zeroing our negative intensities when measuring trace elements close to zero. If you are seeing consistently negative intensities, instead figure out what is wrong with your analytical approach. Maybe you have:

1. a spectral interference on one (or both) of your off-peak positions (check a wavescan and adjust your off-peak positions)
2. a curved background and you are using a linear interpolation (switch to a curved background model, e.g., exponential or polynomial)
3. perhaps you have a "hole" in your background under your on-peak position (apply a blank correction)

Regarding the last point, note that there are two types of "holes" in the continuum. One is due to an instrumental artifact, e.g., the hole under the Ti Ka peak position on some PET crystals, the other is due to an absorption edge in the sample, e.g., measuring Au Ma in iron sulfides.  The latter requires a zero blank sample that (roughly) matches your unknown matrix, the former could be any high purity material since the artifact will show up in all materials (though in the case of Ti Ka, high purity SiO2 is readily available).

The discussion of this issue is found at time stamp: 47:05 in the webinar video.
2
EPMA Standard Materials / Re: Standards for meteorite samples
« Last post by Probeman on May 17, 2024, 11:10:05 AM »
Quote from: EPMA_Gremlin on May 14, 2024, 08:05:33 PM
we are analysing some meteorite samples and have encountered a nickel phosphide (Fe,Ni)3P mineral want to use Fe3P as a standard.  Can anyone help with getting a single crystal of this material, synthetic for preference.  I have tried all the usual crystal growers and have not identified any.  We did at one stage try and purchase a Fe3P MAC standard but this is no longer available?

I note this PhD thesis published in 2010 by John William Howard, University of Nevada Las Vegas on testing of Fe3P, on page 35:

"The samples used were obtained from Alpha Aesar chemical supply company; samples of single crystal F e3P were selected and examined prior to experimental runs to test for crystal integrity..."

I also note a group at Ames growing synthetic sulfide and phosphide single crystals published in 2023:

https://www.mdpi.com/2075-163X/13/3/429

Might be worth contacting...
3
Discussion of General EPMA Issues / Re: EPMA Events (Meetings, Workshops, Seminars...)
« Last post by John Donovan on May 17, 2024, 10:24:53 AM »
The video recordings of our Probe Software webinar held last Wednesday, are now available on our Probe Software YouTube channel:

https://www.youtube.com/@ProbeSoftware

Using PictureSnap and PictureSnapApp for advanced sample navigation and documentation by Dr. Anette von der Handt, University of British Columbia, Vancouver:

https://www.youtube.com/watch?v=Q6tzYdyOJmE

High sensitivity, high accuracy trace element analysis by John J. Donovan, University of Oregon/Probe Software:

https://www.youtube.com/watch?v=9KM5lU403VY

Comments and questions are more than welcome!
4
EPMA Standard Materials / Re: Standards for meteorite samples
« Last post by Probeman on May 17, 2024, 10:20:09 AM »
Quote from: Mike Jercinovic on May 16, 2024, 08:14:19 AM
Up until the day he passed, Joe Goldstein used a natural Schreibersite included in a nickel iron meteorite as a P standard for meteoritic phosphides.  He maintained that the P was stoichiometric in Schreibersite, so just knowledge of the Fe,Ni ratio was the only thing that needed to be determined (not a very big effect anyway).  I don't know which meteorite he used, but it was (and still is) in his own mount along with Fe, Ni, and Co pure metals.  As PKa originates from a transition involving the valence band, the peak position changes substantially compared to phosphates.  Probably a peak shape effect too, so using an actual (FeNi)phosphide is undoubtedly a little better than just using a phosphate standard and then updating the peak position on the unknown phosphide.  I know the community is throwing a lot of shade on these sorts of 'internal' laboratory standards, but one might say that Joe did okay.

We've know for over 300 years why "internal standards" are not our best course of action:

“by Standards kept by each particular workman, without any agreement or reference to one another”
-Edmond Halley, 1693
5
EPMA Standard Materials / Re: Standards for meteorite samples
« Last post by Probeman on May 16, 2024, 06:20:12 PM »
Quote from: sem-geologist on May 16, 2024, 01:15:27 AM
Quote from: EPMA_Gremlin on May 14, 2024, 08:05:33 PM
Hi;
we are analysing some meteorite samples and have encountered a nickel phosphide (Fe,Ni)3P mineral want to use Fe3P as a standard.  Can anyone help with getting a single crystal of this material, synthetic for preference.  I have tried all the usual crystal growers and have not identified any.  We did at one stage try and purchase a Fe3P MAC standard but this is no longer available?

Why not use highly available GaP as standard for P?

I agree that GaP is worth a try. But also worth checking the differences in the absorption correction relative to Fe3P.
6
General EDS Issues / Re: Duane-Hunt limit
« Last post by Probeman on May 16, 2024, 10:23:36 AM »
Quote from: Probeman on April 15, 2024, 07:52:14 AM
And here is the dataset for Ge Ka:



This plot causes me to suspect that the electron beam energy on my Cameca SX100 at ~11 kV is slightly higher than the nominal value would indicate...  what do you all think?

Again, both the Ti and Ge pure metals were freshly polished and uncoated (though well grounded).

Somebody asked about the counting times and beam current for these over voltage curve measurements and so I checked and they were 120 seconds on-peak and and 120 seconds off-peak at 100 nA.

Note that I used freshly polished pure metal standards for these tests, but in case ones samples are carbon coated, one can calculate the electron beam energy loss with a 20 nm carbon using the CalcZAF app and here is is for 5 keV:



So we're losing about 14 volts out of 5 KV. And here at 12 KV:



So only about 8 volts at 12 KV.  But I would still stick with freshly polished pure metals for these over voltage curve tests...
7
PictureSnapApp / Re: PictureSnapApp version 1.8.9
« Last post by John Donovan on May 16, 2024, 09:06:21 AM »
New version of PictureSnapApp fixes a small bug that didn't properly handle when the user removed more than a single image from the Image Locator list at a time.

Also we added the new JEOL EPMA models as seen here:



It's exactly the same interface as the previous 8230/8530 models, but just so it's clear.
8
EPMA Standard Materials / Re: Standards for meteorite samples
« Last post by Probeman on May 16, 2024, 08:43:53 AM »
Quote from: Mike Jercinovic on May 16, 2024, 08:14:19 AM
Up until the day he passed, Joe Goldstein used a natural Schreibersite included in a nickel iron meteorite as a P standard for meteoritic phosphides.  He maintained that the P was stoichiometric in Schreibersite, so just knowledge of the Fe,Ni ratio was the only thing that needed to be determined (not a very big effect anyway).  I don't know which meteorite he used, but it was (and still is) in his own mount along with Fe, Ni, and Co pure metals.  As PKa originates from a transition involving the valence band, the peak position changes substantially compared to phosphates.  Probably a peak shape effect too, so using an actual (FeNi)phosphide is undoubtedly a little better than just using a phosphate standard and then updating the peak position on the unknown phosphide.  I know the community is throwing a lot of shade on these sorts of 'internal' laboratory standards, but one might say that Joe did okay.

You just identified one of the many problem with using "internal standards".    They are difficult if not impossible to reproduce!   How is Colin to obtain Joe's standard? 

I'm sure that Joe did a great job using this standard and I might even accept his assurance that the P is stoichiometric, but then there's the issue you mentioned with the Fe/Ni ratio, so yet another problem!

I think Colin is exactly correct to seek a high purity synthetic that matches the valence of his sample.  Come on people, let's go global and source these high purity synthetics...

Well deserved shade perhaps!    :D
9
EPMA Standard Materials / Re: Standards for meteorite samples
« Last post by Mike Jercinovic on May 16, 2024, 08:14:19 AM »
Hi Colin,
Up until the day he passed, Joe Goldstein used a natural Schreibersite included in a nickel iron meteorite as a P standard for meteoritic phosphides.  He maintained that the P was stoichiometric in Schreibersite, so just knowledge of the Fe,Ni ratio was the only thing that needed to be determined (not a very big effect anyway).  I don't know which meteorite he used, but it was (and still is) in his own mount along with Fe, Ni, and Co pure metals.  As PKa originates from a transition involving the valence band, the peak position changes substantially compared to phosphates.  Probably a peak shape effect too, so using an actual (FeNi)phosphide is undoubtedly a little better than just using a phosphate standard and then updating the peak position on the unknown phosphide.  I know the community is throwing a lot of shade on these sorts of 'internal' laboratory standards, but one might say that Joe did okay.

Mike J.
10
EPMA Standard Materials / Re: Standards for meteorite samples
« Last post by sem-geologist on May 16, 2024, 01:15:27 AM »
Quote from: EPMA_Gremlin on May 14, 2024, 08:05:33 PM
Hi;
we are analysing some meteorite samples and have encountered a nickel phosphide (Fe,Ni)3P mineral want to use Fe3P as a standard.  Can anyone help with getting a single crystal of this material, synthetic for preference.  I have tried all the usual crystal growers and have not identified any.  We did at one stage try and purchase a Fe3P MAC standard but this is no longer available?

Why not use highly available GaP as standard for P?
Pages: [1] 2 3 ... 10