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Probe for EPMA / Re: Questions about MAN background use
« Last post by John Donovan on September 23, 2023, 08:41:34 AM »
Note that if you have these two options checked in the Analytical | Analysis Options menu dialog:

you will see the MAN fit details for the optimized Z fraction exponent, "ZEXP:" parameter:

St  310 Set   2 SM Fayalite, Results in Elemental Weight Percents
ELEM:       Si      Al      Ca       K      Ti      Cr      Fe      Mn
BGDS:      MAN     MAN     MAN     MAN     MAN     MAN     MAN     MAN
MAN1:  .165963 2.59049 -.08976 -.10492 -.36600 -1.2218 -.18728 .109394
MAN2:  .196322 -.22066 .068148 .119022 .255554 .312196 .102628 .039946
MAN3:  .000000 .012323 .000000 -.00014 .000000 -.00291 .000000 .001477
ABS%:   -27.70  -39.15   -3.56   -5.55   -1.30    -.28     .18     .00
ZEXP:      .64     .63     .69     .68     .70     .72     .73     .73
TIME:    40.00   40.00   40.00   20.00   20.00   40.00   25.00   25.00
BEAM:    19.97   19.97   19.97   19.97   19.97   19.97   19.97   19.97

Assuming the MAN Z Fraction exponent is set to zero...
Another change we made earlier this summer:

07/31/23   Add output of variable Z fraction exponent for MAN parameters. Add two more references to AnalyzeTypeReport.
v. 13.4.5   Add variable exponent to Z fraction backscatter exponent code. Add new
      Z fraction backscatter parameter to GetZAF form and code.

07/30/23   Modify MAN Z fraction zbar calculation to accept a zero for dynamically calculated
v. 13.4.4   Zbar exponents based on emission line energy.

These two changes are slightly related.

The variable exponent in the MAN Z-bar calculation allows the user to have a "optimized" Z fraction exponent based on each MAN element's emission line energy.  For example, see this topic for more details:

The variable exponent for the Donovan and Moy (DAM) backscatter correction is discussed here in more detail:

Probe for EPMA / Re: Donovan and Moy (DAM) backscatter correction
« Last post by John Donovan on September 23, 2023, 08:30:42 AM »
We've also now added the ability to specify a variable exponent for the Donovan and Moy (DAM) backscatter calculation as shown here:

The calculated "optimized" exponent is based on the electron beam energy from PENEPMA Monte Carlo modeling of pure elements and compounds at various electron beam energies.

If all your elements are run at the same beam energy you could just specify the exponent explicitly. The optimized exponent is calculated as shown here by Aurelien Moy:

Probe for EPMA / Re: Questions about MAN background use
« Last post by John Donovan on September 23, 2023, 08:19:56 AM »
Here is the new Z fraction average Z calculation using a fixed exponent as described in our recent paper this summer:

Here the Z fraction exponent is fixed at 0.7 for all MAN elements.  However, starting with v. 13.4.4 of Probe for EPMA you can now change this exponent to a zero and the program will automatically calculate the optimized exponent based on the emission line energy (as described in the paper linked above).

Here we've entered a zero for the Z fraction exponent and clicked the Update Fits button. We can can now see the calculated "optimized" Z bar exponent is 0.67 which produces a better Rel % Deviation fit to the MAN standards:

Probe for EPMA / Re: Donovan and Moy (DAM) backscatter correction
« Last post by John Donovan on September 21, 2023, 02:36:07 PM »
Re-processing all 826 binary k-ratios in the Pouchou2.Dat file, we obtain this error distribution using the Armstrong/Love-Scott matrix correction:

Not too bad, but now using the Armstrong/Donovan and Moy (BSC) correction we obtain this error distribution:

A significant improvement (take a look at the y axes)!
EPMA Standard Materials / Re: Standard Samples from Micro to Nano
« Last post by Probeman on September 21, 2023, 02:28:55 PM »
Hi friends,

Does anyone have any experience using standards from the supplier Micro to Nano?

A colleague is considering them.


Well, I for one have a problem with these "standard" materials, because first of all many of these so called "standards" are not actually standards, they are simply various materials that someone has obtained from various sources by various means. I quote from their web site:

The stoichiometric compositions of these natural minerals are nominal; other impurities or small inclusions may be present. Intended as reference standard for quantitative EDS and WDS micro-analysis applications.

So they are "nominal compositions" but intended as "reference standard [sic] for quantitative EDS and WDS micro-analysis applications"?  I can't think of any statement more self contradictory.    >:(
EPMA Standard Materials / Standard Samples from Micro to Nano
« Last post by SteveSeddio on September 21, 2023, 07:30:32 AM »
Hi friends,

Does anyone have any experience using standards from the supplier Micro to Nano?

A colleague is considering them.

Cameca / Re: Diffusion pump on SX100
« Last post by sem-geologist on September 21, 2023, 01:21:26 AM »
But how do I know what DC voltages SX vacuum logical board expects for corresponding vacuum? I did reverse engineering scanning of it. (No one would expect anything less from me I guess  ::)). I fed coaxial cable of secondary gauage with different voltages while watching vacuum values shown in GUI. The setup was simple 20k potentiometer, two 9V batteries (two connected in series, so I could cover with scanning voltages up to 10V), SMB coaxial connector, small breadboard to make some T junctions to attach the voltmeter for V measurement. By changing potentiometer I scanned from 0 to 10V and wrote down corresponding vacuum values. It seems that up to 9V the relation between log(P) and U is pretty linear. Actually in normal circumstances the gauge is engaged with better vacuum so below 9V. Thus that low vacuum range (9V-10V) can be ignored, and then looking for offset and scaling values I was looking that it would cover 0.5-9V range of expected values. The attached spreadsheet contains these recalculations with estimated gain and offset values for DC. tables has two offset values, mathematical and InAmp offset (InAmp - instrumentation amplifier). Mathematically we see no difference between these two equations:

Usx = Ugauge*G + O


Usx = (Ugauge+O/G)*G

where Usx is expected voltage, Ugauge is voltage output of gauge, G is gain and O is offset.

However, first equation is not possible to implement in OPAMPS which would saturate at gain, where second is easier to implement. So the offset which will be need to be set by potentiometer is InAmp ref (pin) offset or O/G. Gain is then applied at next stage (the G). Attached spreadsheet shows and presents gains and offests for different kind of gauges.
Cameca / Re: Diffusion pump on SX100
« Last post by sem-geologist on September 20, 2023, 10:14:47 AM »

We have the turbo on our SX100, but to quote the person I learnt from: "Never trust the gauge!".

Yes, I started to understand such narrative. But is the situation still the same as decades ago and can't we have anything better?

At first, Alcatel Penning gauge (gauge installed on early models of SX100) is indeed hard to trust - there is whole pipeline of things where stuff can go wrong... I dig up through piles of old emails (my late predecessor had printed all communications and emails, which I could look through and learn the whole history of repairs of our SX100), and learned that indeed the problems with vacuum measurements were re-emerging again and again and again... Not only gauge but also cable was changed many times. Investigation of complete construction had revealed major weaknesses of this type of gauge.

1) High Voltage is sent through coaxial cable. That is about 4kV which is constant. If dielectric material weakens somewhere in the cable it start to leak  and generates some current at HV source side. The whole vacuum measuring is based on precise current measurement through shunting resistor at returning path of HV generator, so such additional cable leakage current will sum up with current generated at gauge and worsen the displayed value of vacuum. But, in case of a huge leak in cable there will be no possibility to start penning gauge at all, as there will be significant voltage drop at gauge (leakage in cable will form something like voltage divider). Even if it will be clean gauge - bad cable will hinder its functioning. As for alcatel gauge cables - these are no more produced - all available at second hand shops are of questionable quality! Making new cable (DIY) from scratch is also hindered by requirement of HV reliable cable terminations (tools, expertise), and proper cable availability on the market (There are cables more think, and expensive).

2) Penning gauge, while being in simple construction, can give easily wrong idea about vacuum when not striking. Its lack of current (no strike event) could be compensated with small leak and final reading would look as good properly working gauge value. Experienced user knows that reading is wrong - but only if user tracks vacuum readings closely after the moment the vacuum valve is opened, and tracks the vacuum value response to that event. If vacuum suddenly just goes to 5E-5Pa from very rough vacuum - that is clearly unrealistic. However, if user leaves pumping unattended, and gets back to instrument after 10 min (and cable is leaky a bit), he can see the i.e. 4E-4Pa, even if gauge had not strike. Also Penning gauge needs constant high voltage, that have tendency to deteriorate the weakened isolation material in the cable and progress the problem(s).

Thus I came up with initiative, to make a replacement card which would interface modern gauges to SX100 (giving-up alcatel penning). That would be not jumping one tier in technology (like SXFive's used Agilent IMG) but two tiers. The next technological tier, IMG (inversed magnetron gauge), is more advantageous compared to Penning, but still requires the high voltage cabling and its correct termination and custom made current sensing circuits are difficult to do properly. Interfacing stock controlers of gauges is also hard as it would require changing firmware and finding some serial port on Cameca SX100 vacuum logical board. (That is rather completely out of equation).
Inside SX100 vacuum supply box, there is small board interfacing Alcatel gauge. It produces HV supply, measures the return current and sends the calculated vacuum as log10(P) as DC signal from 0 to 10V (10V roughting, 0V -ultimate vac) through coaxial cable to Vacuum logical board.

Thus naturally my attention got stolen by active gauges, which is higher tier than normal IMG. Active gauges work with low voltage cables, and produce all required HV for integrated IMG inside the gauges integrated electronics and send out only low voltage 0-10V signals (see the pattern?). Such gauges are also flexible as they can be powered from 14.5 to 40V, and such supply is already present in the Vacuum supply box. Also it looks that few different vendors have very similar connection based on 8C8P (or FCC68, or well known RJ45 ethernet cable/sockets), with same basic pin configuration: at least I found out few such gauges from Edwards, Curt J. Lesker and Inficon with such connections.

But what are advantages?
1) No HV cable. Basically simple Ethernet cable will do the job, as only 2W +15V is required to power such gauge, and signal is 0 to +10V. Replacement cable can be easily made or bought. (but it should not age at all, differently to high voltage cables).
2) These active gauges have builtin microcontrollers and LED(s) which show(s) status of gauge (i.e. if strike was successful) - the meaning of vacuum reading is clear. Situation then strike failed, and we have low current and very low vacuum reading is easily to catch. Also Active Gauges reduce high voltage to minimum after strike - this means less contamination of gauge - longer exploitation time between need of cleaning.
3) Edwards gauges (i.e. AIM200) has special multi-strike geometries which guaranties striking even in dirty environments.

How it will work?
My idea is to translate the voltage from such modern gauge to corresponding expected DC voltage by logical vacuum board of SX100. Basically my design is few OPAMPS for DC offset, scale and clip (values out of expected range). Two potentiometers will allow to easily recalibrate board to different kind of gauges from different vendor. It would be possible even to use WRG from Edwards (albeit pirani range would not be seen). The idea is to have seamless replacement (no firmware or software changes).

So how many people would be interested in such design?

I have schematics alreadynearly finished (see the attachement), and now I am at stage of PCB design.
I won't produce and sell the boards, the EU laws and handicaps are too enormous for me (Basically RoHS3 forbids me to make and sell reliable electronics). But I could share the design, gerber files, bill of materials and notes for proper assemblage at site overcoming RoHS hindrances. PCB when having these is possible to order in most of the world. Buying parts and assembling them on PCB should be not too difficult, board is designed to be hand solder-able (no surface mounted parts, everything "though hole" parts). Albeit design could be updated with surface mounted parts if someone would decide to produce and sell larger batch of such boards.
Probe for EPMA / Donovan and Moy (DAM) backscatter correction
« Last post by John Donovan on September 19, 2023, 02:02:05 PM »
Based on our recent paper:

Aurelien Moy and I have a developed a new backscatter correction (which we call the DAM backscatter correction, get it?), which utilizes Z fraction averaging as opposed to traditional mass fraction averaging. This new backscatter correction is especially important for situations with large atomic number effects, particularly when compounds contain elements with different A/Z ratios as discussed in the above paper.

Here is the new ZAF/Phi-rho-z dialog:

We're basically using the Armstrong/Brown absorption correction and replaced the mass based Love/Scott backscatter correction with our new Z fraction based correction. Here's a good example of what this new BSE correction can do, where we've analyzed PbS using FeS2 as a sulfur standard, first using the default Armstrong/Brown/Love-Scott correction:

St  731 Set   4 Galena U.C. #7400, Results in Elemental Weight Percents
ELEM:       Fe       S      Pb
BGDS:      LIN     LIN     EXP
TIME:    60.00   60.00   60.00
BEAM:    29.88   29.88   29.88

ELEM:       Fe       S      Pb   SUM 
   440   -.001  14.229  87.048 101.276
   441    .003  14.258  86.510 100.771
   442    .010  14.303  86.553 100.867
   443    .020  14.216  86.300 100.535
   444    .005  14.307  86.617 100.930

AVER:     .007  14.263  86.606 100.876
SDEV:     .008    .042    .275    .269
SERR:     .004    .019    .123
%RSD:   107.77     .29     .32

PUBL:     n.a.  13.400  86.600 100.000
%VAR:      ---    6.44   (.01)
DIFF:      ---    .863   (.01)
STDS:      730     730     731

STKF:    .4276   .5015   .8698
STCT:   319.56  459.23   72.26

UNKF:    .0001   .1520   .8697
UNCT:      .07  139.21   72.25
UNBG:     4.07    1.28     .90

ZCOR:    .8501   .9383   .9958
KRAW:    .0002   .3031   .9999
PKBG:     1.02  109.75   81.62

Note the 6.4% relative error in the sulfur value when extrapolating from FeS2. Now the same material, using the DAM backscatter correction:

St  731 Set   4 Galena U.C. #7400, Results in Elemental Weight Percents
ELEM:       Fe       S      Pb
BGDS:      LIN     LIN     EXP
TIME:    60.00   60.00   60.00
BEAM:    29.88   29.88   29.88

ELEM:       Fe       S      Pb   SUM 
   440   -.001  13.138  86.989 100.126
   441    .003  13.167  86.467  99.636
   442    .010  13.209  86.515  99.734
   443    .019  13.128  86.257  99.404
   444    .005  13.213  86.577  99.795

AVER:     .007  13.171  86.561  99.739
SDEV:     .008    .039    .268    .263
SERR:     .003    .018    .120
%RSD:   107.77     .30     .31

PUBL:     n.a.  13.400  86.600 100.000
%VAR:      ---   -1.71  (-.05)
DIFF:      ---   -.229  (-.04)
STDS:      730     730     731

STKF:    .4266   .5045   .8526
STCT:   319.56  459.23   72.26

UNKF:    .0001   .1529   .8525
UNCT:      .07  139.21   72.25
UNBG:     4.07    1.28     .90

ZCOR:    .8246   .8612  1.0154
KRAW:    .0002   .3031   .9999
PKBG:     1.02  109.75   81.62

Note that the relative error is now only ~1.7% using this new Z fraction based backscatter correction method.  Now let's look at the Pouchou k-ratio dataset for compounds with larger than 10% atomic number corrections. The traditional Armstrong/Brown/Love-Scott method shows this error distribution for the Armstrong/Brown/Love-Scott correction:

And with the new DAM backscatter correction we obtain this error distribution:

A considerable improvement for large atomic number corrections.

We believe this correction can be further improved by calculating the optimized average Z BSE exponent based on the electron beam energy and we are modeling this now and will implement it soon.
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