I'm starting a new topic here on the FIGMAS k-ratio consensus measurements. This topic is related to the Open Letter to the Microanalysis Community on the effort to develop high purity, high accuracy synthetic silicates and oxides in ~kilogram quantities for global distribution to the microanalysis community as discussed here:
https://smf.probesoftware.com/index.php?topic=1415.0
The initial effort involves small amounts of synthetic materials obtained by John Donovan and Will Nachlas, specifically synthetic MgO, Al2O3 and MgAl2O4. Clearly for high accuracy measurements on such different materials the instrument at least needs to have properly calibrated dead time constants. Especially for modern instruments at moderate beam currents and with large area crystals with higher count rates. And especially Cameca instruments with their typically higher dead time constants!
Have you all actually measured the dead time constants on your instruments or are you simply using the "factory defaults"? It's important for accuracy and it's not hard! Much helpful information is found here for JEOL instrument dead time calibrations:
https://smf.probesoftware.com/index.php?topic=394.0
Here for Cameca instrument dead time calibrations:
https://smf.probesoftware.com/index.php?topic=33.0
And here is found general information on dead time calibrations (also using the StartWin application for an automated dead time data acquisition):
https://smf.probesoftware.com/index.php?topic=1160.0
Of course other instrument calibrations are also very important. For example, have you checked the accuracy of your high voltage power supply using the Duane-Hunt limit test?
https://smf.probesoftware.com/index.php?topic=1063.0
Or the tilt on your stage (most important for SEMs)! Or the effective takeoff angle on your spectrometers? Or the simultaneous k-ratio test on multiple WDS (or EDS!) spectrometers?
https://smf.probesoftware.com/index.php?topic=369.msg1948#msg1948
These are all important things to check especially as the instrument ages over time. In any event, I wanted to share my own efforts to measure k-ratios on these materials and discuss the effect of the dead time calibration on such k-ratio measurements...
So here are my Mg Ka and Al Ka measurements at 10 nA using element setups that I had (unthinkingly) loaded from 2015 that were using somewhat outdated dead time constants of 3.0 and 2.9 us respectively:
St 3100 Set 3 MgAl2O4 FIGMAS, Results in Elemental Weight Percents
ELEM: Mg Al O
TYPE: ANAL ANAL SPEC
BGDS: EXP EXP
TIME: 40.00 40.00 ---
BEAM: 10.06 10.06 ---
ELEM: Mg Al O SUM
141 17.399 38.789 44.985 101.174
142 17.300 38.787 44.985 101.073
143 17.244 38.544 44.985 100.772
144 17.250 38.722 44.985 100.958
145 17.329 38.724 44.985 101.038
AVER: 17.305 38.713 44.985 101.003
SDEV: .064 .100 .000 .150
SERR: .029 .045 .000
%RSD: .37 .26 .00
PUBL: 17.084 37.931 44.985 100.000
%VAR: 1.29 2.06 .00
DIFF: .221 .782 .000
STDS: 3012 3013 ---
STKF: .4740 .4353 ---
STCT: 582.29 753.61 ---
UNKF: .1341 .2700 ---
UNCT: 164.74 467.49 ---
UNBG: .67 .73 ---
ZCOR: 1.2904 1.4336 ---
KRAW: .2829 .6203 ---
PKBG: 247.22 639.60 ---
As one can see the values compared to ideal stoichiometry aren't too bad, but both are a little high. Of course one could look at different matrix corrections to double check the accuracy, because the matrix correction effects are quite large at 30% and 43% respectively, as seen here:
Summary of All Calculated (averaged) Matrix Corrections:
St 3100 Set 3 MgAl2O4 FIGMAS
LINEMU Henke (LBL, 1985) < 10KeV / CITZMU > 10KeV
Elemental Weight Percents:
ELEM: Mg Al O TOTAL
1 17.305 38.713 44.985 101.003 Armstrong/Love Scott (default)
2 17.213 39.034 44.985 101.232 Conventional Philibert/Duncumb-Reed
3 17.276 38.986 44.985 101.247 Heinrich/Duncumb-Reed
4 17.307 38.887 44.985 101.179 Love-Scott I
5 17.301 38.704 44.985 100.990 Love-Scott II
6 17.248 38.500 44.985 100.733 Packwood Phi(pz) (EPQ-91)
7 17.451 38.831 44.985 101.267 Bastin (original) Phi(pz)
8 17.333 39.217 44.985 101.535 Bastin PROZA Phi(pz) (EPQ-91)
9 17.318 39.096 44.985 101.400 Pouchou and Pichoir-Full (PAP)
10 17.303 38.915 44.985 101.203 Pouchou and Pichoir-Simplified (XPP)
AVER: 17.305 38.888 44.985 101.179
SDEV: .062 .211 .000 .225
SERR: .020 .067 .000
MIN: 17.213 38.500 44.985 100.733
MAX: 17.451 39.217 44.985 101.535
So they all look a little high, so what could be the problem? Well to me this indicates that there may be a problem with a too low dead time correction since the pure oxide (primary) intensities will be lower than expected if the dead time constants are too low (and your spectrometer dead times will only get longer over time as the instrument ages!). And when I looked at the dead time constants in the PFE Elements/Cations window, sure enough they were from a 2015 dead time calibration I had done 7 years ago of 3.0 us and 2.9 us respectively!
(https://smf.probesoftware.com/gallery/395_16_03_22_12_41_06.png)
So, one could edit the dead time constants for each element in each sample but that would be tedious. If only there was an easier way, and yes there is. Just go to the Analytical | Update Dead Time Constants menu and open the dialog and select all samples (standards and unknowns) and edit the dead time value for that spectrometer (and crystal) as seen here:
(https://smf.probesoftware.com/gallery/395_16_03_22_12_18_09.png)
By the way, this Update dead Time Constants dialog automatically loads the current dead time constants from the SCALERS.DAT file (it's almost as though it were exactly designed for such a situation!). ;D
So using the new calibrated dead time constants (from 2019!) of 3.8 us and 3.5 us respectively for Mg and Al, we obtain the following results:
St 3100 Set 3 MgAl2O4 FIGMAS, Results in Elemental Weight Percents
ELEM: Mg Al O
TYPE: ANAL ANAL SPEC
BGDS: EXP EXP
TIME: 40.00 40.00 ---
BEAM: 10.06 10.06 ---
ELEM: Mg Al O SUM
141 17.343 38.710 44.985 101.038
142 17.244 38.708 44.985 100.938
143 17.188 38.464 44.985 100.637
144 17.194 38.643 44.985 100.823
145 17.273 38.645 44.985 100.903
AVER: 17.248 38.634 44.985 100.868
SDEV: .064 .100 .000 .150
SERR: .028 .045 .000
%RSD: .37 .26 .00
PUBL: 17.084 37.931 44.985 100.000
%VAR: .96 1.85 .00
DIFF: .165 .703 .000
STDS: 3012 3013 ---
So now we have relative variances of 0.96% and 1.85% respectively, which really isn't too bad at all for extrapolating from pure MgO and Al2O3 to MgAl2O4. But since that 2019 dead time calibration is now about 3 years old, I going to re-run it as soon as I get a chance. Because if I look at a test run at 6 nA (compared to the previous run at 10 nA) I obtain these results:
St 3100 Set 8 MgAl2O4 FIGMAS, Results in Elemental Weight Percents
ELEM: Mg Al O
TYPE: ANAL ANAL SPEC
BGDS: EXP EXP
TIME: 40.00 40.00 ---
BEAM: 6.03 6.03 ---
ELEM: Mg Al O SUM
216 17.123 38.535 44.985 100.643
217 17.230 38.581 44.985 100.797
218 17.053 38.557 44.985 100.595
219 17.219 38.757 44.985 100.961
220 17.199 38.502 44.985 100.686
AVER: 17.165 38.587 44.985 100.737
SDEV: .075 .100 .000 .146
SERR: .034 .045 .000
%RSD: .44 .26 .00
PUBL: 17.084 37.931 44.985 100.000
%VAR: .47 1.73 .00
DIFF: .081 .656 .000
STDS: 3012 3013 ---
Now we are even closer with relative variances of 0.47% and 1.73% respectively. So I suspect the dead times have increased slightly since 2019 and so I will run a new dead time calibration and report the new results as soon as Julie let's me have some time on the instrument! 😁
My experience creating QC systems for multi-laboratory systems is that even "simple samples" identify shortcomings in laboratory procedures. Part of what excites me about the k-ratio project is that it will allow laboratories to compare their results with other labs in a non-judgemental yet rigorous manner. EPMA is subtle. There are many possible ways to introduce small errors that are hard to identify when you don't have a "correct result" to compare against. Every time I've been involved in one, I've learned something new that improves my procedures.
Having clean stuff isn't the whole story. I learned from doing quarterly round robins of 20 labs, to ask a lot of picky questions. The most frequent issue was overdue maintenance of the conducting surface. The numbers told us to overhaul some labs' equipment and that greatly improved their data.
(I don't have access to FIGMAS)
These questions are intended only to collect useful facts:
What about Faraday cups? In fact the exact Faraday Cup used should be a required entry in the k values database. Is it an aperture in a well or a separate FC? Is it mounted in the sample holder as opposed to the actual mount? How is it maintained?
Another required entry should be the COATING ELEMENT, and its COLOR if on steel. "Carbon coat" ranges in practice from a gold film to a solid shiny black layer. Other coatings like Os and Au impact data.
Anyway, there are already about 400 mounts out there that have the following high purity synthetic materials and a FC. The mounts are laid out in a distinctive pattern of 53 materials and were sold under several brand names. There should be at least 400 entries for k values in your database right now using the following:
Periclase MgO, "quartz" SiO2, "rutile" TiO2, "calcite" CaCO3, "cuprite" Cu2O, "fluorite" CaF2, Cr2O3, Y Al garnet Y3Al5O12. BUT note that in these mounts, "cassiterite" SnO2 is SINTERED.
Of the sulfides in these mounts, "sphalerite" ZnS, "galena" PbS, "stibnite" Sb2S3 are high purity synthetics. Cinnabar HgS might be really good or might be porous, I guess you would use the S k value from the known synthetics to verify.
Teaching labs should assign the measurement and calculation of k-values to all courses of "instrumental analysis of minerals" to every student. Getting people into the habit is important.
For a list of suppliers here is https://smf.probesoftware.com/index.php?topic=1223.msg9443#msg9443
I was able to run a new dead time calibration this weekend on the SX100.
Remembering the last dead time calibration from several years ago is shown here:
3.8 3.8 3.5 3.5 3.5 "deadtime in microseconds"
The new dead time calibration from this weekend is shown here:
3.9 4.2 3.7 3.6 2.6 "deadtime in microseconds"
So it appears that 4 of the detectors showed increases in dead time since the last calibration, hence the importance of re-running these dead time calibrations every few years or so. The last detector (spectrometer 5) using a PET crystal had a lot of scatter in the plot (see attached spreadsheet below), so I want to re-run the calibration again, this time maybe using the Ti Ka line on Ti metal (PET and LiF crystals).
Eventually, I will edit the SCALERS.DAT file on the probe computer, but in the mean time let's review the last quantitative results from the MgO, Al2O3 and MgAl2O4 FIGMAS mount using a beam current of 10 nA and the dead time constants from 2015:
St 3100 Set 3 MgAl2O4 FIGMAS, Results in Elemental Weight Percents
ELEM: Mg Al O
TYPE: ANAL ANAL SPEC
BGDS: EXP EXP
TIME: 40.00 40.00 ---
BEAM: 10.06 10.06 ---
ELEM: Mg Al O SUM
141 17.343 38.710 44.985 101.038
142 17.244 38.708 44.985 100.938
143 17.188 38.464 44.985 100.637
144 17.194 38.643 44.985 100.823
145 17.273 38.645 44.985 100.903
AVER: 17.248 38.634 44.985 100.868
SDEV: .064 .100 .000 .150
SERR: .028 .045 .000
%RSD: .37 .26 .00
PUBL: 17.084 37.931 44.985 100.000
%VAR: .96 1.85 .00
DIFF: .165 .703 .000
STDS: 3012 3013 ---
Where we see relative variances for Mg and Al of 0.96% and 1.85%. After using the handy dandy Analytical | Update Dead Time Constants menu dialog for the new dead time constants, from this weekend, for spectrometers 1 and 4, we now obtain:
St 3100 Set 3 MgAl2O4 FIGMAS, Results in Elemental Weight Percents
ELEM: Mg Al O
TYPE: ANAL ANAL SPEC
BGDS: EXP EXP
TIME: 40.00 40.00 ---
BEAM: 10.06 10.06 ---
ELEM: Mg Al O SUM
141 17.336 38.698 44.985 101.020
142 17.238 38.696 44.985 100.919
143 17.181 38.452 44.985 100.619
144 17.188 38.632 44.985 100.804
145 17.266 38.633 44.985 100.885
AVER: 17.242 38.622 44.985 100.849
SDEV: .064 .100 .000 .150
SERR: .028 .045 .000
%RSD: .37 .26 .00
PUBL: 17.084 37.931 44.985 100.000
%VAR: .92 1.82 .00
DIFF: .158 .691 .000
STDS: 3012 3013 ---
So now we have slightly smaller variances of 0.92% and 1.82%, so not a significant difference, but again an accuracy improvement in the right direction.
Why isn't any other lab posting theirs?
It may be useful to separate the two goals articulated in the Open Letter.
The collection of a k-values database absolutely does not require the creation and distribution of a new materials collection. Mount makers have been selling high-purity synthetic oxides for over 50 years and there should be something like 2,000 mounts worldwide that have adequate documentation of purity and supplier. Use google to get links to at least 10 different former and present manufacturers (not resellers).
The highest uptake of a database would be for NIST or a parallel body to set this up formally as a NIST effort.
An online table with space to make entries about k-value with material, known provenance and purity, instrumentation, Faraday cup used for data collection, software used, etc could be created. The manager would have to back up such a data-entry table daily to prevent deletions. Other ideas about security don't need to be public.
The data should be collated into a second anonymous table for public distribution. Absence of identification is necessary to secure widespread participation.
Chemistry and physics societies could help greatly to engage universal participation in a k-values project because this science is part of their mission. The increase of international linking of physics societies to the American Institute of Physics has promoted open access to even archival material that is searchable in English as well as the original language.
In contrast, participation in FIGMAS requires paid membership to a limited list of microscopy societies PLUS a membership fee to FIGMAS itself.
And to those who purchase materials for any distribution, please consider a more efficient process of material verification. For example:
Polarized light microscopy of batches of pieces immersed in a petri dish of water or isopropanol is essential.
Powder XRD on one subsample passing PLM is more than enough to confirm the phase.
SEM examination of one polished/mounted subsample will confirm whether the material is sintered—in case the PLM fails to catch this.
If the prior steps show evidence that the manufacturer's certificate is unreliable then NO further effort should be made.
Batch XRF-WDX on 50-100 grams of 2mm loose pieces is the best way to determine trace contaminants. NO you are not trying to assay the major component, just the level of contamination.
Wet chemistry that is performed under conditions that guarantee the absence of contamination during dissolution is so expensive that it is really not a priority. Some good EPMA materials simply do not dissolve easily.
LA-ICP-MS is absolutely not a batch technique. Neither is EPMA.
No one is posting consensus k-ratios here. I'm just sharing my surprise and pleasure with some quant results. Related to this I'm also collecting k-ratios at different beam currents for the possible purpose of a better dead time calibration procedure. More on this soon.
In the meantime the FIGMAS group is working with the initial participants and is collating results returned to them for the specific materials currently being distributed. More materials are "in the pipeline". I'm as impatient as you are... :D
Indeed there are many synthetic oxides "out there", but we want to utilize materials that we know are currently available in bulk quantities, so we are starting afresh working with various suppliers.
The characterization of high purity synthetic materials is indeed a separate process from the k-ratio data collection. Your suggestions for bulk purity characterization are helpful. Thanks.
We added a new feature to Probe for EPMA to assist in the accurate acquisition of consensus k-ratios.
If you're like some people and utilized element setups from the SETUP.MDB element database or loaded a sample setup from a previous Probe for EPMA run, you probably loaded the element setups, then peaked the spectrometers, checked the PHA settings and maybe even re-ran a wavescan sample to check on your off-peaks, but that might not be enough.
Recently Probeman contacted us to let us know that although he did all of the above, when loading the element setups from previous runs, he neglected to note that the dead time constants for his WDS spectrometers had since been re-calibrated. Therefore that the stored elemental setups still referenced the old dead time constants, from prior to the dead time re-calibration. And they should of course since they are a record of that calibration! ::)
But to prevent this from happening again, in the latest version of Probe for EPMA, if one has updated the dead time constants in the SCALERS.DAT file since those element setups were saved, Probe for EPMA will now check for this and provide the following user dialog, if it finds that the dead time constants have been updated since then:
(https://smf.probesoftware.com/gallery/1_15_05_22_5_43_55.png)
Therefore this new PFE update will allow one to utilize older element setups but with the new dead time calibrations from the SCALERS.DAT file.
Of course one can always manually update these dead time constants "after the fact" using the Analytical | Update Dead Time Constants menu dialog as described here:
https://smf.probesoftware.com/index.php?topic=1442.msg10641#msg10641
I wanted to mention that the new consensus k-ratio export/import format agreed by Nicholas Ritchie and myself is now documented in the Probe for EPMA User Reference manual and is described here in case anyone else wants to write a script for those using JEOL or Cameca OEM software.
This format (which could change I guess) currently consists of 12 header lines which are pretty self explanatory:
"RegistrationName
"RegistrationInstitution
"Instrument Type (make and model)
"Data File Name"
"User Name"
"File Title"
"File Description"
"Nominal Beam: "
"Database Created:
"Last Updated: "
"Last Modified: "
"Current Date and Time: "
These are followed by the data lines which contain 39 column labels as shown here:
"Sample Name"
"Line Number"
"Date/Time"
"X-pos"
"Y-pos"
"Z-pos"
"Element"
"X-ray"
"Spectro Num"
"Crystal"
"Spectro Orientation"
"Takeoff"
"Kilovolts"
"Nano-amps"
"Beam Size"
"Beam Current"
"Background Type"
"Off Peak Bgd Type"
"On-Peak Pos"
"Hi-Peak Pos"
"Lo-Peak Pos"
"Baseline (volts)"
"Window (volts)"
"Gain"
"Bias (volts)"
"Inte/Diff"
"Detector Type"
"Dead Time (usec)"
"On-Peak Time (sec)"
"Hi-Peak Time (sec)"
"Lo-Peak Time (sec)"
"Unknown Counts (cps/nA)"
"Standard Name"
"Standard Counts (cps/nA)"
"K-Raw"
"Raw On Counts"
"Raw Hi Count"
"Raw Lo Count"
"Raw Off Count"
All these data columns are tab delimited for easy import into Excel. Most of these are pretty self explanatory, but a couple of notes. First the "Spectro Orientation" column is referenced to *North* being zero degrees and proceeds clock-wise around the instrument looking down from the top.
EDS detectors should be given the spectrometer number zero (even if you have more than one), and the spectrometer orientations will differentiate them. The column "Crystal" is just a text string so for EDS detectors it could be SDD (10 sq) or SDD (30 sq) or whatever to further facilitate differentiating them.
The on and off-peak positions for EDS systems could simply refer to the emission energy, and the off-peaks could document the range of the ROI fit, or just leave blank for filter methods.
Here is an image loaded into Excel:
(https://smf.probesoftware.com/gallery/1_07_08_22_8_48_00.png)
This picture was taken pre-Covid but here is a snapshot (by who?) of Nicholas and myself which showed up in my Google "OneDrive" feed this morning:
(https://smf.probesoftware.com/gallery/1_07_08_22_9_11_28.png)
Of course I should hasten to add that if you are using Probe for EPMA to acquire your consensus k-ratios, you can simply use the string selection tool in the Analyze! window to select the samples to output (typically the secondary standards), and then right click the sample list to output those selected samples to the consensus k-ratio output format that Nicholas Ritchie and I have come up with:
(https://smf.probesoftware.com/gallery/1_08_08_22_10_03_40.png)
Or you can output all sample to the consensus k-ratio format using the Output | Save Custom Analysis Output menu...
This is the FIGMAS export/import format that we should be sending our k-ratio data to Will Nachlas and Aurelien Moy.
Of course if you think of anything in this format that you think should be modified, please chime in here!
While at M&M last week we (of course) discussed issues of accuracy in EPMA.
One metaphor I utilized was what I called the "holy trinity of microanalysis". That is standards, k-ratios and physics.
Standards because of course if our standard compositions are not what we think they are, we will introduce inaccuracy in our analytical results. This is true whether we utilize high purity synthetic standards or natural matrix matched standards:
https://smf.probesoftware.com/index.php?topic=1483.msg11084#msg11084
K-ratios because that is what we measure, at least on (WDS) EPMA/SEM instruments. And to obtain accurate k-ratios we need to correct not only for beam current and count time, but also dead time, background, standard intensity drift, spectral interferences, time dependent intensity effects (TDI) and even sometimes peak shift/shape effects (APFs).
It is worth mentioning that in Probe for EPMA the reported k-ratios (KRAW) are corrected for all the above items. This comes in very handy when performing further evaluation and analysis using k-ratios exported from PFE. But as we have been discussing recently we need to make sure that our k-ratios agree not only with all the spectrometers on our own instrument (simultaneous k-ratios), but also with k-ratios measured on other instruments (consensus k-ratios).
And finally physics, because we need to deal with matrix effects of absorption, energy loss, backscatter and fluorescence. Today we still have some issues with matrix corrections, e.g., backscatter corrections for high Z compounds containing elements disparate A/Z ratios, but matrix corrections have come a long way over the last 30 years.
Now it is my working hypothesis that we have, as a community, tended to drift towards (or remain fixated on) matrix matched standards for several reasons:
Historically our matrix corrections did not model the physics of electron-solid interactions very well, but this has dramatically improved in recent decades. If you are utilizing a modern phi-rho-z method today (with accurate mass absorption coefficients), you are probably in very good hands for most (not all!) matrix situations.
Second, our instruments are not as well calibrated as they ought to be, For many reasons, but particularly the reasons mentioned above: dead time and effective takeoff angles (which by the way, includes sample tilt!). The good news is that using measurements such as the constant k-ratio method we can perform these instrument calibrations and improve our accuracy.
https://smf.probesoftware.com/index.php?topic=1466.msg11075#msg11075
And of course we need to properly correct our k-ratios for background, spectral interferences, TDI effects, etc. using software tools that can handle these issues when they arise.
So, let's start making consensus/constant k-ratio measurements on our instruments and see how well they actually perform. I'll end with noting that I've attached my M&M presentation of quant mapping below (login to see attachments), because it ends with a few slides regarding the points above.
I'm sure this has already occurred to Will Nachlas and Aurelien Moy, but I'll mention it anyway just to get it off my mind.
When performing the consensus k-ratio measurements on the mounts being distributed by Will Nachlas (e.g., the MgO-Al2O3-MgAl2O4 mounts), I suggest that we measure our k-ratios at several electron beam energies. At the very least we should perform these k-ratio measurements at 10, 15 and 20 keV as this additional information will be helpful to build our consensus k-ratio database with Nicholas Ritchie.
Those wanting additional information can find more at this early topic started by Nicholas Ritchie in 2019:
https://smf.probesoftware.com/index.php?topic=1239.0
Also here is the "Open Letter to the Microanalysis Community" started by Probeman on the importance of global standards:
https://smf.probesoftware.com/index.php?topic=1415.0
And also this post from the "constant k-ratio" topic, which stresses the importance of performing k-ratio measurements at multiple beam currents (count rates):
https://smf.probesoftware.com/index.php?topic=1466.msg11166#msg11166
This is to ensure that our:
1. Dead time constants are well calibrated
2. Our picoammeter is well calibrated
3. Our spectrometers (EDS and WDS) produce k-ratios that are consistent with each other.
See also starting here for more details on using the constant k-ratio method to calibrate your instrument:
https://smf.probesoftware.com/index.php?topic=1466.msg11100#msg11100
Finally a quick reminder that the current version of Probe for EPMA now contains an easy to use menu to export your consensus k-ratio measurements to an external file, for import into the consensus k-ratio database that Nicholas Ritchie is building:
https://smf.probesoftware.com/index.php?topic=40.msg10835#msg10835
Andrew Ducharme and I decided to re-run the FIGMAS MgO, Al2O3, MgAl2O4 mount again (I apologize that when I ran it previously I had not taken sufficient care to calibrate my dead times). So better late than never? 🙂
Yesterday, we ran at 15, 20 and 25 keV (20 nA). Even with dead time corrections of ~8% on the large TAP, all the results are surprisingly accurate (relative to assumed stoichiometry of the synthetic spinel MgAl2O4). The k-ratios are also very close to my 200k sec PENEPMA modeling which I will be presenting more on. Here is one of the 15 keV results run using all matrix corrections in Probe for EPMA:
Summary of All Calculated (averaged) Matrix Corrections:
St 3100 Set 1 MgAl2O4 FIGMAS
LINEMU Henke (LBL, 1985) < 10KeV / CITZMU > 10KeV
Elemental Weight Percents:
ELEM: Mg Al O TOTAL
1 16.981 38.020 45.066 100.067 Armstrong/Brown/Scott-Love (prZ)
2 16.869 38.321 44.633 99.823 Philibert/Duncumb-Reed
3 16.940 38.282 44.775 99.997 Heinrich/Duncumb-Reed
4 16.987 38.193 45.095 100.275 Love-Scott I
5 16.982 38.013 45.148 100.143 Love-Scott II
6 16.915 37.809 44.828 99.552 Packwood Phi(prZ) (EPQ-91)
7 17.153 38.161 45.442 100.756 Bastin (original) (prZ)
8 17.032 38.532 45.346 100.910 Bastin PROZA Phi (prZ) (EPQ-91)
9 17.013 38.410 45.309 100.733 Pouchou and Pichoir-Full (PAP)
10 16.987 38.225 45.126 100.338 Pouchou and Pichoir-Simplified (XPP)
11 16.978 38.032 45.073 100.083 PAP/Donovan and Moy BSC/BKS (prZ)
AVER: 16.985 38.182 45.076 100.243
SDEV: .072 .206 .249 .417
SERR: .022 .062 .075
MIN: 16.869 37.809 44.633 99.552
MAX: 17.153 38.532 45.442 100.910
Percent Variances:
ELEM: Mg Al O
PUBL: 17.084 37.931 44.985
STDS: 3012 3013 3012
ELEM: Mg Al O
1 -.60 .23 .18 Armstrong/Brown/Scott-Love (prZ)
2 -1.26 1.03 -.78 Philibert/Duncumb-Reed
3 -.84 .92 -.47 Heinrich/Duncumb-Reed
4 -.57 .69 .24 Love-Scott I
5 -.60 .22 .36 Love-Scott II
6 -.99 -.32 -.35 Packwood Phi(prZ) (EPQ-91)
7 .41 .61 1.02 Bastin (original) (prZ)
8 -.31 1.59 .80 Bastin PROZA Phi (prZ) (EPQ-91)
9 -.41 1.26 .72 Pouchou and Pichoir-Full (PAP)
10 -.57 .78 .31 Pouchou and Pichoir-Simplified (XPP)
11 -.62 .27 .20 PAP/Donovan and Moy BSC/BKS (prZ)
AVER: -.58 .66 .20
SDEV: .42 .54 .55
SERR: .13 .16 .17
MIN: -1.26 -.32 -.78
MAX: .41 1.59 1.02
Note first that the average variance from the "published" compositions are all well within 1% relative accuracy and close to 1 standard deviation. Note also that these matrix corrections are NOT small (~30 to ~80%):
ZCOR: 1.2946 1.4343 1.8239
Yet they all agree quite well as one can see above. Maybe a 2nd round of FIGMAS runs are called for with more stringent protocols where we first check our spectrometers using the constant k-ratio method:
https://smf.probesoftware.com/index.php?topic=1466.msg11173#msg11173
for dead time calibrations, and Bragg order k-ratios for spectrometer alignment testing:
https://smf.probesoftware.com/index.php?topic=1739.0
I think this quick test clearly demonstrates that with sufficiently calibrated instruments, not only are these materials useful as global standards, but that we can make accurate extrapolations from pure oxides to other matrices.
Continuing with the testing of the MgO, Al2O3, MgAl2O4 mount from the previous post, we have for 20 keV:
Summary of All Calculated (averaged) Matrix Corrections:
St 3100 Set 2 MgAl2O4 FIGMAS
LINEMU Henke (LBL, 1985) < 10KeV / CITZMU > 10KeV
Elemental Weight Percents:
ELEM: Mg Al O TOTAL
1 17.082 37.706 45.421 100.209 Armstrong/Brown/Scott-Love (prZ)
2 16.923 37.719 44.915 99.558 Philibert/Duncumb-Reed
3 16.995 37.697 45.056 99.748 Heinrich/Duncumb-Reed
4 17.099 38.209 45.415 100.722 Love-Scott I
5 17.117 37.953 45.692 100.762 Love-Scott II
6 17.006 37.385 45.197 99.587 Packwood Phi(prZ) (EPQ-91)
7 17.249 38.001 45.816 101.066 Bastin (original) (prZ)
8 17.144 38.350 45.773 101.266 Bastin PROZA Phi (prZ) (EPQ-91)
9 17.134 38.352 45.783 101.268 Pouchou and Pichoir-Full (PAP)
10 17.091 37.965 45.566 100.621 Pouchou and Pichoir-Simplified (XPP)
11 17.080 37.725 45.435 100.240 Armstrong/Donovan and Moy BSC/BKS (prZ)
AVER: 17.084 37.915 45.461 100.459
SDEV: .086 .304 .304 .636
SERR: .026 .092 .092
MIN: 16.923 37.385 44.915 99.558
MAX: 17.249 38.352 45.816 101.268
Percent Variances:
ELEM: Mg Al O
PUBL: 17.084 37.931 44.985
STDS: 3012 3013 3012
ELEM: Mg Al O
1 -.01 -.59 .97 Armstrong/Brown/Scott-Love (prZ)
2 -.94 -.56 -.16 Philibert/Duncumb-Reed
3 -.52 -.62 .16 Heinrich/Duncumb-Reed
4 .09 .73 .96 Love-Scott I
5 .19 .06 1.57 Love-Scott II
6 -.46 -1.44 .47 Packwood Phi(prZ) (EPQ-91)
7 .97 .18 1.85 Bastin (original) (prZ)
8 .35 1.10 1.75 Bastin PROZA Phi (prZ) (EPQ-91)
9 .29 1.11 1.77 Pouchou and Pichoir-Full (PAP)
10 .04 .09 1.29 Pouchou and Pichoir-Simplified (XPP)
11 -.02 -.54 1.00 Armstrong/Donovan and Moy BSC/BKS (prZ)
AVER: .00 -.04 1.06
SDEV: .50 .80 .68
SERR: .15 .24 .20
MIN: -.94 -1.44 -.16
MAX: .97 1.11 1.85
Again, very small variances from the published values. Now again, but at 25 keV:
Summary of All Calculated (averaged) Matrix Corrections:
St 3100 Set 3 MgAl2O4 FIGMAS
LINEMU Henke (LBL, 1985) < 10KeV / CITZMU > 10KeV
Elemental Weight Percents:
ELEM: Mg Al O TOTAL
1 17.150 37.445 45.275 99.871 Armstrong/Brown/Scott-Love (prZ)
2 16.964 37.149 44.858 98.970 Philibert/Duncumb-Reed
3 17.035 37.139 44.994 99.167 Heinrich/Duncumb-Reed
4 17.154 38.191 45.125 100.470 Love-Scott I
5 17.223 38.065 45.702 100.989 Love-Scott II
6 17.081 37.087 45.150 99.318 Packwood Phi(prZ) (EPQ-91)
7 17.311 37.880 45.710 100.901 Bastin (original) (prZ)
8 17.221 38.190 45.682 101.093 Bastin PROZA Phi (prZ) (EPQ-91)
9 17.218 38.366 45.714 101.297 Pouchou and Pichoir-Full (PAP)
10 17.171 37.796 45.539 100.506 Pouchou and Pichoir-Simplified (XPP)
11 17.151 37.474 45.297 99.923 Armstrong/Donovan and Moy BSC/BKS (prZ)
AVER: 17.152 37.707 45.368 100.228
SDEV: .097 .470 .316 .826
SERR: .029 .142 .095
MIN: 16.964 37.087 44.858 98.970
MAX: 17.311 38.366 45.714 101.297
Percent Variances:
ELEM: Mg Al O
PUBL: 17.084 37.931 44.985
STDS: 3012 3013 3012
ELEM: Mg Al O
1 .39 -1.28 .64 Armstrong/Brown/Scott-Love (prZ)
2 -.70 -2.06 -.28 Philibert/Duncumb-Reed
3 -.29 -2.09 .02 Heinrich/Duncumb-Reed
4 .41 .69 .31 Love-Scott I
5 .81 .35 1.59 Love-Scott II
6 -.02 -2.22 .37 Packwood Phi(prZ) (EPQ-91)
7 1.33 -.13 1.61 Bastin (original) (prZ)
8 .80 .68 1.55 Bastin PROZA Phi (prZ) (EPQ-91)
9 .78 1.15 1.62 Pouchou and Pichoir-Full (PAP)
10 .51 -.36 1.23 Pouchou and Pichoir-Simplified (XPP)
11 .40 -1.20 .69 Armstrong/Donovan and Moy BSC/BKS (prZ)
AVER: .40 -.59 .85
SDEV: .57 1.24 .70
SERR: .17 .37 .21
MIN: -.70 -2.22 -.28
MAX: 1.33 1.15 1.62
Again, excellent average variances, though the individual corrections will differ somewhat..
And please note that at 20 and 25 keV beam energies, these are very large matrix corrections. So my conclusion is that our modern matrix corrections are pretty darn good. Although sure, this example is not exactly pushing the Z correction much at all.
On the other for hand, for large extrapolations in average Z, the Donovan and Moy (DAM) backscatter correction does a pretty darn (damn!) good job:
https://smf.probesoftware.com/index.php?topic=1809.msg13858#msg13858
But let's look at all the quant data graphically in the next post...
By plotting the concentration values for multiple beam energies, we should see a consensus of concentration values (unlike k-ratios which would be different for each accelerating voltage). Because Andrew Ducharme and I acquired data at 15, 20 and 25 keV, here are some results...
I think we might call this test the multi-voltage concentration consensus. But what does this test actually test, well for these emission lines of low energy (Mg Ka, Al Ka and O Ka), we are testing both the accuracy of our spectrometer alignment, checked using the Bragg order k-ratio test:
https://smf.probesoftware.com/index.php?topic=1739.0
That is essentially the effective take off angle of our spectrometers:
https://smf.probesoftware.com/index.php?topic=1569.0
and also the accuracy of our absorption matrix correction (and MAC values), given that for these compounds (MgO, Al2O3 and MgAl2O4) there is basically no atomic number correction as they are all close to ~10.5 average atomic number, and the fluorescence correction is also minimal (output from PFE using DebugMode):
ELEMENT ABSCOR FLUCOR ZEDCOR ZAFCOR STP-POW BKS-COR F(x)u Ec Eo/Ec MACs STDNUM uZAF/sZAF
Mg ka 1.7237 .9778 1.0106 1.7034 1.0209 .9899 .4160 1.3050 19.1571 1472.73 3012 1.0596
Al ka 1.9233 1.0000 1.0423 2.0047 1.0606 .9827 .3927 1.5600 16.0256 1614.04 3013 1.3835
O ka 2.8605 .9985 .9618 2.7471 .9470 1.0156 .1633 .5317 47.0190 3962.09 3012 1.1049
ELEMENT K-RAW K-RATIO ELEMWT% OXIDWT% ATOMIC% FORMULA TAKEOFF KILOVOL
Mg ka .26929 .10101 17.206 ----- 14.343 .000 40.00 25.00
Al ka .51280 .18730 37.548 ----- 28.193 .000 40.00 25.00
O ka 1.03468 .16520 45.382 ----- 57.464 .000 40.00 25.00
TOTAL: 100.136 ----- 100.000 .000
Of course we could alternatively stress test the average atomic number (and/or the fluorescence matrix correction) using these multiple beam voltages, while simultaneously lowering our sensitivity to the absorption matrix correction (and spectrometer effective take off angle), by selecting emission lines that are high energy, yet have significant differences in average atomic number, e.g., Zn Ka in ZnO and ZnTe:
Effective K-Ratios for Primary Standard: 30 ZnO synthetic
Secondary Standard: 658 ZnTe (synthetic)
Emission line: zn ka at 15 keV
Absorption Correction Method: Phi(pz) Absorption of Armstrong/Packwood-Brown 1981 MAS
MAC File: LINEMU Henke (LBL, 1985) < 10KeV / CITZMU > 10KeV
Absolute k-ratio change per degree at 40 degrees: .000250
Percent (relative) k-ratio change per degree at 40 degrees: .049771
Takeoff Angle: 35.0000, K-Ratio: .499680
Takeoff Angle: 35.5000, K-Ratio: .499844
Takeoff Angle: 36.0000, K-Ratio: .500003
Takeoff Angle: 36.5000, K-Ratio: .500158
Takeoff Angle: 37.0000, K-Ratio: .500308
Takeoff Angle: 37.5000, K-Ratio: .500454
Takeoff Angle: 38.0000, K-Ratio: .500595
Takeoff Angle: 38.5000, K-Ratio: .500733
Takeoff Angle: 39.0000, K-Ratio: .500867
Takeoff Angle: 39.5000, K-Ratio: .500997
Takeoff Angle: 40.0000, K-Ratio: .501123
Takeoff Angle: 40.5000, K-Ratio: .501246
Takeoff Angle: 41.0000, K-Ratio: .501366
Takeoff Angle: 41.5000, K-Ratio: .501482
Takeoff Angle: 42.0000, K-Ratio: .501595
Takeoff Angle: 42.5000, K-Ratio: .501706
Takeoff Angle: 43.0000, K-Ratio: .501813
Takeoff Angle: 43.5000, K-Ratio: .501918
Takeoff Angle: 44.0000, K-Ratio: .502020
Takeoff Angle: 44.5000, K-Ratio: .502119
Takeoff Angle: 45.0000, K-Ratio: .502216
Anyway, here are the multi-voltage concentration results for Mg Ka in MgAl2O4 at 15, 20 and 25 keV:
(https://smf.probesoftware.com/gallery/395_10_02_26_12_50_53.png)
There's definitely a positive slope trend with beam energy but close to within 3 sigma errors. Though interesting that 20 keV gave the most accurate results.
Here's the same for Al Ka in MgAl2O4:
(https://smf.probesoftware.com/gallery/395_10_02_26_12_51_12.png)
Note the larger accuracy errors though still close to statistics. Though worth noting that the matrix correction for Al Ka is significantly larger than for Mg Ka:
ELEM: Mg Al O
ZCOR: 1.2946 1.4343 1.8239 15 keV
ZCOR: 1.4841 1.6944 2.3015 20 keV
ZCOR: 1.7031 2.0049 2.7475 25 keV
Still for matrix corrections (Armstrong/Brown pr-z) these large, that's still pretty impressive. And finally for O Ka in MgAL2O4:
(https://smf.probesoftware.com/gallery/395_10_02_26_12_51_26.png)
Here we see something different. The different accelerating voltages all give similar concentrations, but slightly high, though still close to within 3 sigma.
My preliminary hypothesis is that there is a small but significant APF (Area Peak Factor) shape/shift effect here for O ka in this material relative to MgO (or Al2O3):
https://smf.probesoftware.com/index.php?topic=536.0
Andrew and I will perform some careful wavescans of these three compounds to check on this. Next I will share our PHA and background settings as they might surprise some of you...
OK, let's look at some of the PHA and background settings Andrew and I used to get these quite decent quant results above.
To start, let's assume that you've peaked up your spectrometers and run your initial PHA scans. On a Cameca instruments we run PHA scans after adjusting the gain, and on the JEOL instruments we run either PHA scans or bias scans after adjusting the bias.
The key thing here is to tune your PHA settings so that at the highest peak intensity (measuring the highest concentration of the element in your std, at the highest beam current you will be utilizing), the PHA peak is well above the baseline filter level. In addition, you will generally (always?) want to run your PHAs in Integral mode, not Differential mode. Setting your PHA baseline too tight simply produces non-linear response in your counting electronics and makes accurate quant impossible.
https://smf.probesoftware.com/index.php?topic=1466.msg11636#msg11636
What about spectral interferences? If there are higher order interferences, it is better to allow them in and quantitatively correct for the interferences in software:
Donovan, John J., Donald A. Snyder, and Mark L. Rivers. "An improved interference correction for trace element analysis." Proceedings of the Annual Meeting-Electron Microscopy Society of America. San Francisco Press, 1992.
PHA filtering of higher order interferences isn't very helpful anyway, and it doesn't help at all for same order interferences! This is discussed here by SEM Geologist and others:
https://smf.probesoftware.com/index.php?topic=1466.msg11636#msg11636
So here is an initial PHA scan of Mg Ka for the measurements shown in the previous reply above:
(https://smf.probesoftware.com/gallery/395_11_02_26_9_17_03.png)
Obviously we need more gain (or bias in the case of JEOL instruments) and after a few iterations we get this:
(https://smf.probesoftware.com/gallery/395_11_02_26_9_17_21.png)
This PHA tuning will produce a nice linear response from your highest count rates to your lowest count rates (as the PHA peak shifts to the right at lower count rates).
We see pretty much the same for Al Ka, but here is for O Ka. First the default PHA settings:
(https://smf.probesoftware.com/gallery/395_11_02_26_9_32_18.png)
After adjusting the oxygen PHA settings (on our highest concentration std) we see this:
(https://smf.probesoftware.com/gallery/395_11_02_26_9_32_33.png)
Now this might not look correct, but it is! With these settings, we obtain the full (integrated) photon count because we are in Integral mode and as we go to lower concentrations of oxygen (or lower beam currents) and the PHA peak shifts to the right, we will still obtain a nice linear response which is essential for quantitative WDS analysis.
Next we will look at our background settings, which admittedly aren't as important for major elements:
https://smf.probesoftware.com/index.php?topic=1535.msg12121#msg12121