Shelf Life

Dr. Bruce Scruggs, XRF Product Manager, EDAX

Recently, we had a customer request to see a demonstration on the Orbis micro-XRF system. As we talked about what they would like to see, he mentioned that he had made some test XRF measurements on table salt, and he couldn’t measure the iodine content. I agreed to measure the iodine content in table salt. Initially, I thought this would be a very straightforward exercise, as table salt is just NaCl with some iodine added, but this was anything but straightforward.

The iodization of salt in the United States began about a century ago. Iodine is an important micronutrient for thyroid gland health. Certain portions of the American population had diets deficient in iodine and the iodization of table salt was chosen as a method to increase the level of iodine in the average American diet. The salt iodization process was inexpensive; salt does not spoil and estimates of table salt consumption were available.

Some weeks before the customer demo, I bought some iodized table salt from the local grocery store. The ingredients list showed iodine in the form of potassium iodide at about 45 ppm iodine. This concentration was consistent with my web searches. I pressed a pile of salt grains onto a piece of carbon tape and measured it with the Orbis system using a 2 mm spot size (the system was equipped to measure down to a 30 μm spot size, small enough for individual grains, but I wanted to avoid any potential issues with grain to grain variations). It was easy enough and I could measure the I(L) lines with I(Lα) at 3.937 keV (Figure 1).

(A): Salt spectrum with peak deconvolution, not including I(L) series; Fig 1(B): The same salt spectrum as in (A) with peak deconvolution including I(L) series.

Figure 1. (A) Salt spectrum with peak deconvolution, not including I(L) series. (B) The same salt spectrum as in (A) with peak deconvolution including I(L) series.

Some weeks later, during the actual customer demonstration, we measured a variety of customer supplied samples and the customer asked to measure table salt near the end of the demo. I put my table salt sample into the Orbis and was astonished to find that the iodine signal disappeared (Figure 2). Peak fitting and quantification results showed no detectable iodine. After a discussion with the customer, I began to suspect that the salt iodization level was not stable, given that solid I2 is known to undergo sublimation at room temperature. I spoke to the customer again and in his previous attempts, he measured table salt (from shakers) in the company cafeteria. I often wonder how long that salt has been in the shaker!

The same salt sample, as Figure 1, measured on the Orbis a few weeks later without the presence of iodine.

Figure 2. The same salt sample, as Figure 1, measured on the Orbis a few weeks later without the presence of iodine.

Further web searches indicated that indeed, the iodization level of salt has a certain shelf life depending on many factors, including temperature, humidity, impurities in the salt, the chemical form of the iodine bearing additives, and product packaging. For example, potassium iodide is oxidized by contact with oxygen and atmospheric moisture and the resulting iodine then undergoes sublimation. In various regions of the world, iodized table salt is formulated to improve its shelf life with regard to iodine retention based on the characteristics of the table salt and the general environment, e.g., desert, tropical. Based on this loss mechanism, I suspect that there must also be a significant loss of iodine during cooking depending on whether salt is added while cooking or directly applied before consuming.

In my case, the iodine level had dropped below detectable limits in about three weeks of being left out on the table. The grains of salt ranged in size from about 100 – 500 μm in characteristic dimensions, and I was curious to what characteristic depth XRF was measuring. Was there possibly any iodine left in the largest crystals? This depth can be estimated based on the fluorescent signal energy as the exciting X-ray energy always has to be greater than the fluoresced photons (The physics are a bit different for electron excitation where the answer is determined by electron penetration depth into the sample).

XRF measurement depth can be estimated from the Beer-Lambert equation for the absorption and transmission of light:

Equation 1

Equation 1.

The mass absorption coefficient (MAC) describes how readily the I(Lα) signal line at 3.937 keV will be absorbed by the NaCl matrix. It can be described as follows:

Equation 2

Equation 2.

For NaCl, we have two MACs describing how Na and Cl each absorb the 3.937 keV photon. The easiest way to get the full matrix MAC is to back-calculate it from the Beer-Lambert equation and any web-based calculator describing X-ray absorption/transmission characteristics modeling the fluoresced photon traversing the sample matrix to the detector. I prefer the website, http://henke.lbl.gov/optical_constants/filter2.html. By inputting the sample matrix formula (including trace elements if desired), and an arbitrary path length, one can get the calculated result for I/Io and then rearrange Equation 1 to solve for the NaCl matrix MAC by inputting the previously used path length and the known density of table salt. The result is: μNaCl(3.937 keV) ~ 540 cm2/g.

Rearranging Equation 1, one can solve for the signal path length through the sample traversed by the fluoresced photon to the detector as a function of I/Io:

Equation 3

Equation 3.

The XRF Emission Depth, D, would typically be defined as normal to the sample surface, and you should also consider the take-off angle (TOA) of the detector defined from the sample surface, as shown in Equation 4.

Equation 4

Equation 4.

Table 1 shows the XRF Emission Depth as a function I/Io with a nominal detector TOA of 50ᵒ.

I/Io [%] Path Length, x [μm] Emission Depth, D [μm]
10 20 15
1 39 30
0.1 59 45

Table 1. XRF Emission Depth as a function of the signal transmission ratio, I/Io.

The definition of the characteristic XRF path length and emission depth is somewhat arbitrary, as it depends on the value assigned to the signal transmission ratio, I/Io. Typically, the characteristic path length is defined as the length over which 99% of the signal is absorbed. Hence:

Equation 5

Equation 5.

It is interesting to note from Table 1, that at 50% of the critical emission depth, the XRF signal is undergoing 90% absorption.

Coming back to the original analysis, it is possible that iodine was still present at the core of the larger 500 μm grains of salt. Further analyses could be done on cross-sectioned grains or pulverized grains to make that determination. It would be possible to measure cross-sectioned grains of NaCl using the 30 μm spot size on the Orbis to study how readily iodine is lost as a function of depth into the NaCl grain, but that is a study for another day.

Colorful Language

Dr. Stuart Wright, Senior Scientist EBSD, EDAX

As some of you may know, I dabble in woodworking. Over the years, I’ve built several things for our home. I’m embarrassed to admit that when things don’t go right on these projects, I’ve also been known to use some colorful language to express my frustration. I’m a little prouder that color maps have been the language of EBSD since the inception of the automated systems. Figure 1 shows one of the first color maps I created with the help of Karsten Kunze, who was a Post-Doc at Yale University while I was working on my PhD. The colors are associated with prominent peaks in the ODF. Namely the ideal copper orientation {112}〈111〉 in blue and its statistically symmetric variant (i.e. arising from the processing symmetry – rolled sheet in this case) in red, the ideal brass orientation {011}〈211〉 in green and its statistical variant in orange. The ability to illuminate the crystallographic orientation aspects of the microstructure using such color maps took off quickly. I’ve always thought such maps have an aesthetic beauty to them. As the New Mexico based artist, Georgia O’Keeffe said “I found I could say things with color… that I couldn’t say any other way.”

Orientation distribution function (ODF) plotted in Euler space and an orientation map from rolled aluminum (November 1991). Colors correspond to the copper and brass texture α-fiber components for rolled FCC materials.

Figure 1. Orientation distribution function (ODF) plotted in Euler space and an orientation map from rolled aluminum (November 1991). Colors correspond to the copper and brass texture α-fiber components for rolled FCC materials.

I remember a conversation in the lab with Karsten and my advisor, Professor Brent Adams, arguing whether we could see some patterns in the arrangement of the different “colored” orientations. We found each of us were predisposed to seeing patterns for certain colors over other colors. This led to one more chapter in my PhD thesis focused on orientation correlation. In this chapter, I tried to confirm the presence of patterns in the arrangement of orientations within the microstructure with some statistical rigor. In the end, there didn’t appear to be much correlation for any of the colors.

There has been some recent work on improving color mapping. There are two parts to this, to try and get (1) more “perceptually uniform” color maps1 and (2) better color maps for showing crystallographic orientation particularly for low symmetry materials2,3. I’ve implemented these ideas into OIM Analysis™ v8.5. This version will hopefully be ready early this year – we are currently in the testing/bug fixing phase. The reason for “perceptually uniform” color maps (PUCM) is that we can see variations within some colors but not others. For example, Figure 2 shows a GROD map for a steel sample after 10% tensile strain. The mapping has been done using our standard “rainbow” color gradients and with a PUCM version of the rainbow gradient.

Grain Reference Orientation Deviation (GROD) maps for steel tensile specimen deformed in-situ. The first row is displayed using the standard OIM “rainbow” color gradient and the second using a perceptually uniform color map (PUCM). The first column of maps are GROD-angle maps, the second column of maps are GROD-angle maps overlaid on gray scale image quality (IQ) maps.

Figure 2. Grain Reference Orientation Deviation (GROD) maps for steel tensile specimen deformed in-situ. The first row is displayed using the standard OIM “rainbow” color gradient and the second using a perceptually uniform color map (PUCM). The first column of maps are GROD-angle maps, the second column of maps are GROD-angle maps overlaid on gray scale image quality (IQ) maps.

You will notice in the color gradient that it is difficult to see subtle color variations for blue, green and red in the standard rainbow gradient, whereas the PUCM color gradient shows a more consistent variation in the colors across the full range of colors. The variations at the top of the color scales are 10%. From a purely aesthetic point of view, I like the vibrancy of the colors in our standard rainbow color mapping. However, I can also see that the standard color gradient can be somewhat misleading as to the degree of color variation. I noted in my thesis, “This visualization of the microstructure is a useful technique for coupling the morphological and orientation aspects of microstructure into a discrete picture. … Orientation correlation calculations can be made to statistically quantify this apparent structure. This is discussed in the following chapter.” In other words, the colors are nice and helpful. They can serve as a guide for further quantitative analysis, but without that subsequent chapter on the “further quantitative analysis”, our microstructure characterization report will end up as a picture book for the coffee table.

Here is another way to look at the benefits of perceptually uniform color mapping. Figure 3 shows a series of IPF maps where I have rotated the data to show the large grain at the center in several ideal orientations. The top row uses our standard color triangle, whereas the bottom row uses the PUCM color triangle. Note that the subtle color variations in the large grain are more evident in some colors than in other colors.

Inverse Pole Figure (IPF) maps for the same grain in seven different orientations displayed using the standard OIM color mapping scheme (top row) and the PUCM scheme (bottom row).

Figure 3. Inverse Pole Figure (IPF) maps for the same grain in seven different orientations displayed using the standard OIM color mapping scheme (top row) and the PUCM scheme (bottom row).

It is interesting to note that, in general, the PUCM maps show less color variation than our standard IPF maps. Also note that the degree of color variation is more consistent across the full range of colors. Consistency is good, but the results are not as dramatic as I had originally anticipated. PUCM does not alleviate the need to extend our analysis beyond pretty pictures to a thorough quantitative examination of the orientation data.

For the lower symmetries, the PUCM color mapping schemes are quite different from our standard color mapping schemes and include both white and black to extend the available color palette. As can be seen in Figure 4, for rhodochrosite, the extended PUCM color palette works well for standalone IPF maps, but does not work as well when the IPF maps are overlaid on a gray scale map, such as an IQ map. So once again, the PUCM maps have some advantages and disadvantages over the standard maps. Certainly, having more views of the same data is helpful. But another chapter on quantitative analysis is needed.

IPF maps for a mineral specimen containing rhodochrosite, barite, quartz and pyrite. The left column of maps are displayed using the standard OIM color mapping scheme and the right column using the PUCM scheme. The top row of maps are standalone IPF maps, the second row of maps are IPF maps overlaid on gray scale IQ maps.

Figure 4. IPF maps for a mineral specimen containing rhodochrosite, barite, quartz and pyrite. The left column of maps are displayed using the standard OIM color mapping scheme and the right column using the PUCM scheme. The top row of maps are standalone IPF maps, the second row of maps are IPF maps overlaid on gray scale IQ maps.

A phase map for the rhodochrosite mineral specimen.

Figure 5. A phase map for the rhodochrosite mineral specimen.

OK, probably a few too many references about the need to go beyond pictures to quantitative analysis, so let me end on a fun anecdote about color from the “Microscale Texture of Materials” Symposium at the joint ASM/TMS Meeting in Cincinnati, OH in October 1991. At this meeting, I gave our first presentation on results obtained using fully automate EBSD. My presentation was short leaving time for an energetic discussion. One point of discussion was the bit depth needed for image processing to detect the bands in the patterns. My advisor, Professor Adams, said something along the lines of “the human eye can only differentiate 32 colors” (he meant 32 gray levels). I remember Professor Dr. Robert Schwarzer chimed in after Brent with “I don’t know about the American eye, but the European eye can certainly see more than 32 colors!” Of course, we all got a big laugh 😊. Perhaps my European friends can get by with the color maps and can skip the extra “chapter” on quantitative analysis!

1 Peterkovesi.com/projects/colourmaps/index.html
2 G. Nolze and R. Hielscher (2016) “Orientations–perfectly colored” Journal of Applied Crystallography, 49: 1786-1802.
3 William C. Lenthe & Marc De Graef (2018), “Perceptually Uniform Color Maps for the Disk, Sphere, and Ball”, preprint

What a Difference a Year Makes

Jonathan McMenamin, Marketing Communications Coordinator, EDAX

EDAX is considered one of the leaders in the world of microscopy and microanalysis. After concentrating on advancements to our Energy Dispersive Spectroscopy (EDS) systems for the Scanning Electron Microscope (SEM) over the past few years, EDAX turned its attention to advances in Electron Backscatter Diffraction (EBSD) and EDS for the Transmission Electron Microscope (TEM) in 2019.

After the introduction of the Velocity™ Plus EBSD camera in June 2018, which produces indexing speeds greater that 3,000 indexed points per second, EDAX raised the bar further in 2019. In March, the company announced the arrival of the fastest EBSD camera in the world, the Velocity™ Super, which can go 50% faster at 4,500 indexed points per second. This was truly a great accomplishment!

EBSD orientation map from additively manufactured Inconel 718 collected at 4,500 indexed points per second at 25 nA beam current.

EBSD orientation map from additively manufactured Inconel 718 collected at 4,500 indexed points per second at 25 nA beam current.

Less than three months later, EDAX added a new detector to its TEM product portfolio. The Elite T Ultra is a 160 mm2 detector that offers a unique geometry and powerful quantification routines for comprehensive analysis solutions for all TEM applications. The windowless detector’s geometric design gives it the best possible solid angle to increase the X-ray count rates for optimal results.

EDAX Elite T Ultra EDS System for the TEM

EDAX Elite T Ultra EDS System for the TEM.

Just before the annual Microscopy & Microanalysis conference, EDAX launched the OIM Matrix™ software module for OIM Analysis™. This new tool gives users the ability to perform dynamic diffraction-based EBSD pattern simulations and dictionary indexing. Users can now simulate EBSD patterns based on the physics of dynamical diffraction of electrons. These simulated patterns can then be compared to experimentally collected EBSD patterns. Dictionary indexing helps improve indexing success rates over standard Hough-based indexing approaches. You can watch Dr. Stuart Wright’s <a href=”https://youtu.be/Jri181evpiA&#8221; target=”_blank”>presentation from M&M</a> for more information.

Dictionary indexing flow chart and conventional indexing results compared with dictionary indexing results for a nickel sample with patterns collected in a high-gain/noisy condition.

Dictionary indexing flow chart and conventional indexing results compared with dictionary indexing results for a nickel sample with patterns collected in a high-gain/noisy condition.

EDAX has several exciting product announcements on the way in early 2020. We have teased a two of these releases, APEX™ Software for EBSD and the Clarity™ Direct Electron Detector. APEX™ EBSD will give users the ability to characterize both compositional and structural characteristics of their samples on the APEX™ Platform. It gives them the ability to collect and index EBSD patterns and EBSD maps, as well as allow for simultaneous EDS-EBSD collection. You can learn more about APEX™ EBSD in the September issue of the Insight newsletter and in our “APEX™ EBSD – Making EBSD Data Collection How You Want It” webinar.

EBSD of a Gibeon Meteorite sample covering a 7.5 mm x 6.5 mm area using ComboScan for large area analysis.

EBSD of a Gibeon Meteorite sample covering a 7.5 mm x 6.5 mm area using ComboScan for large area analysis.

The Clarity™ is the world’s first commercial direct electron detector (DeD) for EBSD. It provides patterns of the highest quality and sensitivity with no detector read noise and no distortion for optimal performance. The Clarity™ does not require a phosphor screen or light transfer system. The DeD camera is so sensitive that individual electrons can be detected, giving users unprecedented performance for EBSD pattern collection. It is ideal for analysis of beam sensitive samples and potential strain applications. We recently had a webinar “Direct Electron Detection with Clarity™ – Viewing EBSD Patterns in a New Light” previewing the Clarity™. You can also get a better understanding of the system in the December issue of the Insight newsletter or the .

EBSD pattern from Silicon using the Clarity™ detector.

EBSD pattern from Silicon
using the Clarity™ detector.

All this happened in one year! 2020 looks to be another great year for EDAX with further improvements and product releases to offer the best possible tools for you to solve your materials characterization problems.

Those People and Things

Dr. Sophie Yan, Applications Engineer, EDAX

Click here to read the post in Chinese.

The end of the year is my conference season. I have been to various conferences since October and I have seen many new faces. Recently, I realized that several young people I trained have stepped into the electron microscopy and microanalysis world. Their reasons seemed to be similar: want a life like Sophie’s. I felt deeply honored but also frightened. Did I give the young people a good example or fantasy?

A couple of us who used to study and/or work at Shanghai Institute of Ceramics have organized an annual meetup at the Chinese Electron Microscopy Society Conference. This year the number of participants reached 19, indicating more and more people have joined this field. As time passes, I have been able to recognize some of the big names in microscopy, and I am overwhelmed at how quickly young scientists have become those big names. Indeed, when more and more new faces have become major players in this field, it indicates the prosperity of this field. I am very fortunate to be a witness of this booming industry.

Once at SEMICON, a participant from Taiwan couldn’t believe my decision to step out after he/she realized that I was no longer in the semiconductor industry. At that time, I didn’t care about his/her words, but right now I figured out why he/she felt so sorry for me. It is very fortunate to love a job you choose. The semiconductor industry was a little down at the time I left, but it has been developing incredibly fast afterwards and I have found the job I love. It is so good to see that my breakup with semiconductor made both of us happy.

Mr. Yang from The University of Science and Technology Beijing (the author of the first Chinese EBSD book you’re supposed to read in China) used to tell me that “I felt you have been attending a lot of conferences and got much more resources than other people.” So I really got lucky.

My EBSD mentor, European applications specialist, René de Kloe, has traveled all around the world. He is very knowledgeable and humble but shows his expertise when questioned. He always promptly and fully replies to my emails and is always ready to help. Although we meet often, every time I am impressed by his expertise and like him more.

Dr. Sophie Yan and Dr. Stuart Wright

Dr. Sophie Yan and Dr. Stuart Wright

EDAX EBSD experts at a meeting in Draper, UT.

EDAX EBSD experts at a meeting in Draper, UT.

And Dr. Stuart Wright, he is a legend in the EBSD world. His name appears in textbooks and references to all kinds of EBSD papers. He took René and I to the west coast of the United States the first time I met him. René said that his toes finally touched the water of the Pacific Ocean again and for the first time in 3 years. He said that his feet high fived each other from the last time he dipped his feet in Tokyo Bay. In 2017, ICOTOM was held in the small city where Stuart lives. As a conference organizer, he took care of everything by himself. That was the most successful conference that considered both academic atmosphere and hospitality. (Well, I must attend the next ICOTOM in Osaka in September 2020).

With lots of luck, I have been to many places and gotten in touch with big names in this field. The cost is I travel more than 50%, on mainly domestic trips with more than 100,000 kilometers every year. I have seen everything there is to see in the Beijing and Shanghai airports. In contrast, the streets of every city look common to me. A kind of common that you can’t figure out their meanings at a glance.

Beijing Daxing International Airport

The new Beijing Daxing International Airport opened in September 2019.

But when people ask what exactly is EDAX’s direct electron detection? I can finally calm down and keep the conversation going, although I just know a little about it. René and Stuart patiently explained it to me when I knew nothing about it, and now it is my turn to spread the word. This is a brand-new field, and EDAX is the first player. What can we do with direct electron detection? Just wait and see. For a sneak preview, take a look at René’s recent webinar, “Direct Electron Detection with Clarity™ – Viewing EBSD Patterns in a New Light”.

Look Closer

Dr. René de Kloe, Applications Specialist, EDAX

All our senses are aimed at observation. We feel, see, hear, smell and taste things to experience the world around us. We are relying on our senses to make many of our day-to-day decisions and choices. And especially in the upcoming holiday season, shops and companies in the business of selling things cleverly use shiny advertisements, brochures, fragrances, and unbeatable product descriptions to entice us to select their wares. All the time hoping that we will succumb to our senses that focus on the superficial appearance of products before thinking things through.

We must be very careful not to let this very successful marketing strategy subconsciously guide us when analyzing materials as well. During our work as microscopists we are continuously selecting samples, cutting and preparing them to expose a feature of interest, and then choosing the analytical tool and actual analysis area. How sure can we be that we really get representative and objective information?

Dr. René de Kloe's PhD thesis

Dr. René de Kloe’s PhD thesis.

As a geologist, I was taught to take your distance from a rock outcrop and look it over before going into any detail, knowing that the context of your observations is crucial in your interpretation. Then I would go in close to look, feel, and yes sometimes actually taste the rock in order to try to identify what I was actually looking at and how the overall structure fit in the geological setting of the area.

Observing this distance is crucial for your understanding of structures, but in some cases, you cannot get out far enough to see the bigger picture and then you must make do with what you can see.

Perhaps an extreme example is what I did for my PhD research. I have studied the occurrence and distribution of nm-scale films of amorphous material along grain boundaries in experimentally deformed rocks that originate deep inside the Earth. In total I may have characterized a few cubic microns of material but based on that I tried to draw conclusions on the effects of these melt layers on the movements of entire continents!

In microanalysis, we are suffering from the same problem. Microscopy inherently means that you cannot look at the wider picture and when you are looking at extremely small-scale features, their size combined with a practical image resolution may limit the observable surface even further. And one of the most difficult questions you then must ask yourself before starting an analysis is, if the analysis area is representative. And that can be a really tricky question. How objective are we all when browsing the sample surface to find a spot to collect the data? Don’t we all tend to preferentially pick an area that looks promising? I am not so sure that that would always be the most representative region.

It is not that long ago that the acquisition limits in EDS and EBSD were caused by the detector technology. For EDS mapping, we were quite happy if you could collect your data with 50,000 input counts per second and a 50% dead time. This meant that when you were collecting a 512 x 400 pixel map where you wanted to have, say 1000 X-ray counts per pixel, it would take you a few hours. And after that time someone else would be hovering behind you, eager to use the microscope. This seriously limited the sample area that could be analyzed and as a researcher you needed to think carefully about your analysis strategy to get representative information.

Single field EDS map of FeSi sample with REE phases

Single field EDS map of FeSi sample with REE phases.

The area that can be analyzed has changed dramatically with the introduction of the latest EDS detector technology. These detectors are capable of processing more than two million input counts and get maximum throughputs of 850,000 counts per second. You can now get the same area analysis in a matter of minutes, which allows you to analyse more samples or simply more areas on your sample. Alternatively, you can choose to get a wider view and collect large area mosaic maps to minimise the risk of unintended preferential area selection and get more representative data.

120 field multi-field EDS map of an igneous rock showing merged ROI maps of Si (red), Fe (yellow), and O (green) on a backscatter SEM image. Total image resolution 6144 x 4000 points ~ 5.4 x 3.5 mm

120 multi-field EDS map of an igneous rock showing merged ROI maps of Si (red), Fe (yellow), and O (green) on a backscatter SEM image. Total image resolution 6144 x 4000 points ~ 5.4 x 3.5 mm.

A similar dramatic improvement has occurred in EBSD technology. When I started as EBSD application specialist at EDAX in 2001, my first EBSD demo system could collect at least two points per second when it was not raining and the moon was in the right quarter (or perhaps more realistically, if I was really lucky to have a good sample with strong patterns). The map below was one of my first maps that I collected when getting to know the system and I still use it today as an example to show different typical EBSD mapping features, such as grain boundaries, subgrain boundaries, twins, and slip planes. This map contains “only” 124,405 points but took an 8.5-hour overnight scan to collect.

EBSD IPF on IQ map of Ni alloy

EBSD IPF on IQ map of Ni alloy.


49 field EBSD comboscan IPF on PRIAS™ center map of an Fe alloy

49 multi-field EBSD comboscan IPF on PRIAS™ center map of an Fe alloy.

The same map today would take less than half a minute to collect with a Velocity™ EBSD detector. Or when you would like to take a little wider view you can combine beam and stage movements to collect a 2.5 million point scan of an entire sample in about 15 minutes.

These technological improvements allow you to be more efficient with your time and collect the same data much faster. But alternatively, it can effectively open our eyes and allow us to investigate much larger areas to see the bigger picture. Just be careful when you look at things from a bit further away, sometimes at the end of the day it may seem that these things start looking back at you!

Large area EDS map of FeSi sample with REE phases – look who’s watching!

Large area EDS map of FeSi sample with REE phases – look who’s watching!

Coming Up To Speed

Eric Rufe, U.S. Northeast Sales Manager, EDAX

“Dad, do you want to see someone cut an arrow in half with a sword?”

That is the sort of question I’ve come to expect from my 13-year old son. Lately, he and his friends watch a YouTube show where two intrepid scientists conduct all sorts of crazy experiments, record with a high-speed camera, and play the results back in slow motion. In this case, one guy shot an arrow at the other, who managed to cut it in half in mid-flight on his first attempt. In other videos, they burst water balloons and spin flaming steel wool to create cascades of sparks. All these experiments are recorded with a high-speed camera and played back in slow motion. It is really a lot of fun to watch. And, I noticed the camera they use is made by AMETEK!

I have been paying attention to AMETEK high-speed cameras lately, in a tangential way. Let me explain. I joined EDAX just over one year ago as Northeast Sales Manager. At EDAX, I handle the EDS, WDS, EBSD and µ-XRF products. Although I used some of these products as a student, that was a long time ago. During most of my career I worked with other types of microscopy techniques, and the EDAX technology has advanced dramatically during that time. For example, silicon drift detectors with thermoelectric cooling had replaced the SiLi detectors form my student days, which mean no more filling up a LN2 dewar (Figure 1). Joining EDAX meant that I had a lot to learn and I had to learn it quickly.

Very old stock photo of a scientist filling a LN2 dewar for the old SiLi detectors.

Figure 1. Very old stock photo of a scientist filling a LN2 dewar for the old SiLi detectors.

Fortunately, EDAX has a lot of resources to bring me up to speed. EDAX does a good job of presenting webinars on new techniques and recent developments. These are all archived on the EDAX website, along with videos of presentations recorded at different meetings and workshops. I counted 94 different presentations dating back to 2014 and quickly set to work watching and learning. EDAX also has a lot of literature available through the website: product brochures, data sheets, articles, presentations, and essential knowledge briefings. Somewhere over 120 pieces of literature.

One of the benefits of the Northeast territory is that the EDAX headquarters is in my territory, located in Mahwah, NJ. This proximity makes it easy for me to bring customers to Mahwah for demonstrations. As you enter the demonstration area in Mahwah, you are greeted by a group of signs showing all of the different companies within AMETEK’ s Materials Analysis Division (MAD) (Figure 2). EDAX is one of several companies in MAD, along with CAMECA, Amptek, SPECTRO, Forza Silicon and Vision Research. There is some cross-pollination among these different companies, and I like to tell the story that EDAX is part of a larger group of related technologies. So, I made it a point to also learn something about each of these different companies and set about examining their websites.

Canvas signs on the wall outside the demo labs in Mahwah, NJ showing some of the companies in the AMETEK Materials Analysis Division.

Figure 2. Canvas signs on the wall outside the demo labs in Mahwah, NJ showing some of the companies in the AMETEK Materials Analysis Division.

Now we come back to the high-speed cameras. One of the sister companies makes high-speed cameras for a variety of applications. They have many great slow motions videos on their web page, including ballistics tests, water droplets, flying insects, and an exploding strawberry (yes, an exploding strawberry).

Collaboration with this sister company resulted in the Velocity™ EBSD camera, with collection speeds up to 4,500 indexed points per second. This is the fastest EBSD camera available, and it has been fun to demonstrate the speed to customers. Large maps that may require an overnight run can now be completed in minutes. The first generation of the Velocity™ EBSD Systems was launched in June 2018 with speeds up to 3,000 fps. This release date was shortly before I joined EDAX. The faster Velocity֭™, the Velocity™ Super EBSD Systems, were launched in March 2019. Only 9 months later, the new Velocity™ has a 50% increase in speed (Figure 3).

EDAX Velocity™ Super EBSD Camera EBSD orientation map from an additively manufactured Inconel 718 collected at 4,500 indexed points per second at 25 nA beam current
Figure 3. EDAX Velocity™ Super EBSD Camera (left) and an EBSD orientation map from an additively manufactured Inconel 718 collected at 4,500 indexed points per second at 25 nA beam current (right).

There has been a rapid release of new and improved products since I joined, in addition to the developments in the Velocity™ camera. EDAX released a 160 mm2 EDS detector for TEM, the Elite T Ultra. APEX™ software development has continued, and now APEX™ is available on the Element, Octane Elect, and Octane Elite EDS Systems. We are on the verge of releasing APEX™ for EBSD as well. New EBSD software (OIM Matrix™) has been released, which includes dynamic pattern simulation and dictionary indexing. In November, we will host a webinar on EBSD using a Direct Electron Detector.

The challenge I have been facing over the past 12 months is that no matter how fast I read, and watch, and learn, it seems there is always something new. I am reminded of the Red Queen, in Through the Looking-Glass, explaining to Alice:

“Now, here, you see, it takes all the running you can do, to keep in the same place”.

Things That Change The Way We Use EDS

Dr. Shangshang Mu, Applications Engineer, EDAX

I got into the EDS world about 10 years ago, when I started my PhD study at Boston University. In my first project, I needed to quantify the elemental composition of my experimental samples. My advisor told me that ideally, we should use an electron microprobe and that the nearest one was at MIT, which is literally on the other side of the Charles River. But after we heard of the hourly fee and estimated the number of samples I would need to analyze, we started to plan an alternative. We found out that there was a field emission SEM equipped with an EDS detector in our own Photonics Center, just across the street and most importantly it was free of charge. At that time, I knew neither microprobe nor EDS and decided to give EDS a try first. Even if it did not work, I had nothing to lose except wasting some time. Graduate students have plenty of time to waste. So finally, I didn’t cross the beautiful Charles River but Commonwealth Avenue for the EDS.

As a result, I was introduced to the EDS world by the EDAX Apollo 40 SDD detector and EDAX was the only EDS manufacturer I knew as a beginner. It is such a good brand name standing for Energy Dispersive Analysis of X-rays so in the first couple of years I was under the impression that it was the term of this technique. For quantitative analysis, I used known standards that were close to my experimental samples in composition to standardize and got pretty good results fast and easy. In the subsequent projects, I collected a lot of EDS maps and the Apollo 40 never disappointed me. Since the EDS detector worked well for my PhD projects, I no longer considered other techniques. By the way, although I missed the opportunity to learn how to use the microprobe across the river due to the budget issue, my first full-time job in the states was to manage a much fancier microprobe acquired by a former user of the MIT’s microprobe. He received his PhD in geochemistry from MIT and I got most of my microprobe skills from him.

As an entry level EDAX user in graduate school, I had no way to imagine that I turned myself into an EDAX applications engineer and right now I am celebrating my one-year anniversary. After I joined EDAX, I got to know that the Apollo was the first generation SDD detector series of EDAX and our current EDS detectors have much better all-around performance. At the beginning of my second year with EDAX, I looked back into the EDS data I collected in graduate school and noticed that they were collected at a much slower amp time (the time the detector processes one X-ray count) compared to current ones and the EDS maps looked kind of noisy in comparison to my current perspective. Prompted by these findings, I wanted to initiate the discussion with how advancements in detector technology shaped the way we use EDS.

Apollo 40 SDD at Boston University
EDAX Octane Elite SDD in Draper, UT
Figure 1. The EDAX Apollo 40 SDD attached to the SEM I used at Boston University (left) and the EDAX Octane Elite SDD I am currently using (right).


I believe all EDS users have heard of this rule of thumb: keep the dead time between 20% and 40%, or something like this. At least I was taught to keep the percentage within this range and as far as I know a lot of EDS users are following this rule. This is a traditional perspective that came out in the past when detector amp times were much slower. The dead time is all about throughput and affected by the amp time. Historically, if the dead time is below 20%, it means the detector either doesn’t receive enough X-ray counts per second to ensure high data quality or the amp time is too fast to maintain an optimal detector resolution. On the other hand, if the dead time is over 40%, the Input Counts Per Second (ICPS) is too high to be handled optimally by the current amp time and may lead to excessive summed peaks. We can get the dead time back in the range by either decreasing the beam current to lower the count rate or choosing a faster amp time.

In the past, we usually did not consider the second option since it would sacrifice the detector resolution a lot for throughput. However, the current generation of EDAX EDS detectors is equipped with CMOS based pre-amplifiers that allow much faster amp times ranging from 0.12 μs to 7.68 μs, while keeping very good resolution and high throughput. For example, if I have the EDAX Octane Elite detector in my lab, I can run eight times faster by moving the amp time from the slowest 7.68 μs to the intermediate 0.96 μs, the resolution is only decreased by roughly 4 eV (from 124 eV to 128 eV). This intermediate amp time can handle at least 80% of the job, however under this condition it is hard to make the dead time go over 20% unless the detector is receiving over 100K ICPS. Even if I use the fastest amp time at 0.12 μs, the resolution is still below 150 eV, which is not a significant decrease in resolution if you know that the detector resolution for those equipped with traditional JFET pre-amplifiers is about 250 eV at this fastest amp time. Since resolution is no longer a limiting factor, feel free to open your aperture to increase the count rate and choose a faster amp time to lower the dead time. In return, you will get a higher throughput, which means more statistics and higher quality of data. Although we can go below 20% dead time to have a throughput improvement, it still makes sense to apply the 40% upper bound since the detector will not convert X-rays efficiently once the dead time is beyond this maximum percentage.

When do we want to hit hundreds of thousands of ICPS and take advantage of the fast amp time and high throughput brought by current EDS detectors? While I was using the Apollo 40 at Boston University to collect EDS maps, I stuck to 12.8 μs amp time believing the higher the detector resolution, the better the map quality. Now, I have realized that the major limitation to the quality of EDS maps is not the detector resolution but the limited statistics at the pixel level. Not to mention for our current detectors, the degradation in resolution when running fast is very little. The quality of peak deconvolution is primarily determined by the level of statistics, even when dealing with tricky peak overlaps.

I did a quick study on a piece of floor tile in my lab that contains both calcium phosphate and zirconium silicate, so P and Zr are in distinct phases. P K and Zr L peaks are heavily overlapped with only 29 eV of energy difference. I used the Octane Elite detector to do a quick five-minute net intensity map on this floor tile at 26 nA beam current and 0.96 μs amp time. This combination gave me 160K ICPS and 28% dead time. For the purpose of comparison, I used the slowest amp time at 7.68 μs to yield the highest detector resolution and recollected the maps for 6.5 minutes. To keep the dead time at 28% I had to lower the beam current to 3.2 nA to constrain the ICPS at 20K. Obviously, in the first run Zr and P were separated out nicely in the sharp images (Figure 2 left), as it built up eight times more statistics than the second run in roughly the same amount of time. In the second run at the highest detector resolution, the separation was not quite as good (Figure 2 right). As we can see, the images are kind of pixelated and the coral pixels are mixed within the green in the overlay, so the slightly better detector resolution did not help at all. If I were able to know this trick as a rookie, I would be able to get higher quality maps in the same amount of time or get the same quality of maps faster.

Net intensity maps of P/Zr overlay and P collected at 0.96 μs amp time (left) and 7.68 μs amp time (right) for roughly 5 minutes.
Figure 2. Net intensity maps of P/Zr overlay and P collected at 0.96 μs amp time (left) and 7.68 μs amp time (right) for roughly 5 minutes.

From my point of view, the advancements in detector technology, the experience we gain, or a combination of the two change the way we use EDS.

Texture on the Greens

Matt Nowell, EBSD Product Manager, EDAX

For better or worse, I am a golfer. The story of how I became a golfer helps explain my love for EBSD, and evolution as a material scientist. While I was at the University of Utah trying to decide on a major, I enjoyed fishing. Here in Utah, we have lovely access to many rivers, streams, and lakes with great fishing potential. When I started investigating Materials Science and Engineering as a degree, I thought it would be interesting to learn about the graphite used in fishing rods, and how the different processes used improved the performance of the rods. With this interest, I enrolled in the Materials Science department. Fortunately (for the fish I like to think), two things happened that changed my recreational and professional focus.

Tate Nowell catching a Utah trout

My son catching a nice Utah trout.

First, I enrolled in Organic Chemistry. Memorizing different molecules was not something that I excelled at. This dampened my enthusiasm for all things polymer-based, like composite fishing rods. Second, I was hired to work in the Electron Microscopy lab for the Materials Science department. This gave me lots of direct exposure to SEM, TEM, EDS, and even XRD instruments. It also helped to build a strong appreciation for sample preparation, but that’s the topic for another blog. All these things pushed me in the direction of materials characterization, and when I graduated, it led me to TSL, EDAX, and EBSD.

How does all this relate to golf? Soon after I started working, I played a round of golf with some friends. I had played a few casual rounds over the years, but nothing serious. Looking back, I consider myself lucky because the parking lot for the EM characterization facility was also the parking lot for the University golf course, and if I had been bitten by the golf bug at that point, things might have occurred differently. After this round, which I greatly enjoyed, I went to the local golf store thinking about different golf clubs. I found a set where the shafts of the club were manufactured by the same company that made my favorite fishing rod. This seemed like a sign to me, so I bought the clubs and jumped right into becoming a golfer.

It was great timing. EBSD scans were slow. To collect a 20,000-point scan, which was our typical target at the time, took 5-6 hours. It was easy to fit in 9 holes during some of these scans. Today, with our new Velocity™ cameras, it takes about 5 seconds to collect this data. Sometimes there is barely enough time to hit a practice putt down the hall in the lab. Many of us in the office enjoyed playing together. We even commissioned an annual tournament called the Burrito Open, where we combined golf with Mexican food. If you examine the picture of the 2008 tournament closely, you may notice it is an International event, with participants from Europe (Rene de Kloe) and Japan (Suzuki-san).

2008 Burrito Open

2008 Burrito Open

This tournament also allowed us to indulge and combine golf with work a little bit. The first trophy was constructed from an old port cover we no longer needed. The second trophy was of course a crystal trophy. As you might imagine, there was some discussion over what crystal structure would be most appropriate.

Burrito Open Trophies

Burrito Open Trophies

There is plenty of time to think during a round of golf, and one of the things I’ve thought about is how the club heads are produced. When thinking about this, we are considering either woods (or more accurately metal woods) or irons. Irons are typically either cast or forged. Forged clubs are generally positioned for the better players, but what caught my eye is that some manufacturers started marketing the idea of microstructure and the role of grains in the material. One brand even pushes what they call Grain Flow Forged.

Grain Flow Forged Iron

Grain flow forged iron

Of course, just like the fishing rods, the processing of the club affects the properties. The key link is that the processing changes the microstructure, and the microstructure defines the properties. With that in mind, it’s a fun experiment to compare the microstructure of cast clubs versus forged clubs. Stuart Wright and I first did this experiment about 20 years ago for a conference on Materials in Sports, but given the increases in capability, it would be fun to reevaluate.

I sectioned and prepared EBSD samples from both forged and cast irons. These were both made with an unknown steel alloy and prepared with my standard metallographic preparation approach. Enough coarse-grained polishing was used to remove plating from the club surface. The resulting Image Quality + Orientation Maps (IPF relative to the surface normal direction) are shown below. These were collected from the face of the golf club. I prepared cross-sections for further analysis. I was a little surprised by both microstructures. The cast iron had a dual-component microstructure, with both generally equiaxed grains and needle shaped grain constituents. It looks a lot like a dual phase Ferrite-Martensite microstructure, but with martensite being tricky to directly identify with EBSD relative to ferrite, I indexed both regions with a BCC Ferrite material file. The local misorientations were higher in the needle shaped regions, and there were also some austenitic grains present in these regions. The forged iron microstructure has a bimodal grain size distribution, with larger equiaxed grains decorated and intermixed with smaller equiaxed grains. A second scan was collected at higher magnification and with a finer step size to better resolve these fine grains.

IQ and IPF ND Orientation Map from cast golf club

IQ and IPF ND Orientation Map from cast golf club

IQ and IPF ND Orientation Map from forged golf club

IQ and IPF ND Orientation Map from forged golf club

Higher magnification IQ and IPF ND Orientation Map from forged golf club

Higher magnification IQ and IPF ND Orientation Map from forged golf club

As expected, the microstructures of the forged and cast clubs are different. As a Materials Scientist and EBSD guy, I tend to think forging is a more interesting materials processing option. In this case though, both casting and forging have produced interesting microstructures that could use further investigation. I once bought a set of forged clubs, and it was with this set I made my only hole-in-one. I’m pretty sure there is a direct correlation, and when I buy my next set, I’ll continue my experimentations.

Celebrating Nearly 60 Years of Materials Analysis Expertise with EDAX

Arjun Dalvi, Regional Sales Manager – Southeast Asia and India, EDAX

During a recent trip to Bangkok, Thailand I visited a customer and was very happy to see that two EDAX DX-95 units were installed at his location. The units are a piece of history because EDAX hasn’t sold liquid nitrogen cooled detectors or systems anywhere in the world in quite some time.

When I asked the customer when this system was installed, he said it was installed more than 30 years ago, at a time when I was still in elementary school! EDAX was one of the first companies to produce liquid nitrogen cooled detectors for microanalysis.

EDAX DX-95 EDAX SiLi Detector
EDAX DX-95 (left) and SiLi detector (right) used over 30 years ago.

Since its origin in 1962, EDAX has provided customers with reliable, accurate microanalysis systems. The company has benefitted from its stellar reputation, as well as its, name recognition. The name EDAX almost has a generic trademark, because many people throughout the world refer to their Energy Dispersive Spectroscopy (EDS) systems as “EDAX” systems.

EDAX, a big name in microanalysis and microscopy, has a vast history in research and development of new technology and product improvements. The company has been a part of the AMETEK corporation since 2011. Since joining the well-respected organization of AMETEK, EDAX has been able to pursue new developments in the fields of EDS, EBSD and WDS analysis. After AMETEK acquired a company that produced silicon nitride windows, EDAX gained a great advantage by having an inhouse supplier for its new SDD window. This was a big revolution for EDAX’s EDS products. Now, EDAX is the only manufacturer that has a unique silicon nitride window with vacuum encapsulation technology. EDAX has become one of the top manufacturers of EBSD systems, providing solutions to various applications in the fields of microstructure and formation and deformation of new materials. The new CMOS-based Velocity™ EBSD Camera is the fastest EBSD camera on the market for high-speed EBSD mapping. In India, we have many users that have EBSD systems and are doing research in the fields of steel and metals.

Today, EDAX has a complete range of products with all the latest developments and inhouse raw materials needed to help us maintain quality and add to our customers’ confidence in our products.

I feel EDAX will come up with new developments for years to come. Maybe 30 years or more down the road, we will see the Element, Octane Elect, Octane Elite or Orbis at one of our customers sites, much like the DX-95, which is still in use today.

Saying What You Mean and Meaning What You Say!

Shawn Wallace, Applications Engineer, EDAX

A recent conversation on a list serv discussed sloppiness in the use of words and how it can cause confusion. This made me consider that in the world of microanalysis, we are not immune. We are probably sloppiest with two particular words. They are resolution and phase.

Let us start with how we use the word phase and how phases are commonly defined in microanalysis. In Energy Dispersive Spectroscopy (EDS), we use phase for everything, for example, phase mapping, phase library. In Electron Backscatter Diffraction (EBSD), the usage is a little more straightforward.

So, what is a phase? Well to me, a geologist, a phase has both a distinct chemistry and a distinct crystal structure. Why does this matter to a geologist? Two different minerals with the same chemistry, but with different structures, can behave in very different ways and this gives me useful information about each of them.
The classic example for geologists is the Al2SIO5 system (figure 1). It has three members, Kyanite, Sillimanite, and Andalusite. They each have the same chemistry but different structures. The structure of each is controlled by the pressure and temperature at which the mineral equilibrated. Simple chemistry tells me nothing. I need the structure to tease out that information.

Figure 1. Phase Diagram of the Al2SiO5 system in geological conditions. Different minerals form at different pressures and temperatures, letting geologists know how deep and/or the temperature at which the parent rock formed.**

EDS users use the term phase much more loosely. A phase is something that is chemically distinct. Our phase maps look at a spectrum pixel by pixel and see how they compare. In the end, the software goes through the entire map and groups each pixel with like pixels. The phase library does chi squared fits to compare the spectrum to the library (figure 2).

Figure 2. Our Spectrum Library Match uses as Chi-squared fit to determine the best possible matches. This phase is based on compositional data, not compositional and structural data.

While the definition of phase is relatively straight forward, the meaning of resolution gets a little murkier. If you asked someone what the EDS resolution is, you may get different answers depending on who you ask. The main way we use the term resolution when talking about EDS is spectral resolution. This defines how tight the peaks in a spectrum are (figure 3).

Figure 3. Comparison of EDS vs. WDS spectral resolution. WDS has much higher resolution (tighter peaks) than EDS, but fewer counts and more set-up are required.

The other main use of resolution, in EDS is the spatial resolution of the EDS signal itself (figure 4). There are many factors which determine this, but the main ones are the accelerating voltage and sample characteristics. This resolution can go from nanometers to microns.

Figure 4. Distribution of the electron energy deposited in an aluminum sample (top row) and a gold sample (bottom row) at 15 kV (left column) and 5 kV (right column). Note the dramatic difference in penetration given by the right hand side scale bar.

The final use of resolution for EDS is mapping resolution. This is by far the easiest to understand. It is just the step size of the beam while you are mapping.

Luckily for us, the easiest way to find out what people mean when they use the terms resolution or phase, is just to ask. Of course, the way to avoid any confusion is to be as precise as possible with your choice of words. I resolve to do my part and communicate as clearly as I can!

** Source: Wikipedia