resolution

It’s All About Speed!

Dr. Oleg Lourie, Senior Product Manager EDS, EDAX

Different perceptions of speed can be measured differently, and yet in my opinion speed is one of those few fascinating concepts, which you are always aware of regardless of your activity. The world of speed is enriched with various emotional flavors which generate a multitude of reactions:  curiosity, when I observed the 690m/h cruising speed during my recent flight with KLM (‘are we getting close to 1Mach and when?’), or a contemplative focus when you accelerate to 170m/h on the German Autobahn near Düsseldorf.

In all circumstances speed inevitably arrests your attention, just as blazing fast EDS mapping did for me recently, when I saw a literally staggering acquisition speed below 200 us/pixel, which translated into a 512×400 pixel, fully quantifiable elemental map, which was collected in less than 1 min.

The ‘Octane’ EDS power, that ‘fueled’ this racing performance is equally remarkable – holding above 2Mcps in X-ray input counts without a single complaint  and exploding with 860Kcps for a single channel at about 50% dead time. I should admit I simply enjoyed it. It is inspiring to push the ‘limits’. The new electronics for this system will move things even further by leveling the throughput up to 1.8Mcps for a single channel – literally doubling the processing speed of the system.

1. Phase map of mineral clearly showing separation of zirconium silicate and calcium phosphate phases. 2. Spectrum of zirconium silicate

While astounded at the extreme throughput, a casual observer may wonder where this power can be applied in a ‘daily commute’ for elemental information. The answer is everywhere! It affects all your materials analysis when there are no boundaries imposed by your spectrometer on the scope of your experiment. It is indispensable for setting automated runs where sudden changes in sample composition, geometry or topography can impact acquisition. It aids in the formulation of statistics, where you need the fastest screening to acquire reliable statistical data. It is essential in ‘in situ’ studies where you rapidly change the sample compositional structure during the observation. It is useful in observing live Direct Phase Mapping and showing various phase distributions immediately after the scanned image is acquired. With more than 860 kcps ‘under the hood’, low noise CUBE electronics design and pulse processing times geared from 7.8 us to 120 ns, you can focus on driving your experiment at any speed you can imagine to achieve superior results in less time.

3. Spectrum of calcium phosphate 4. Superimposed spectra of 2 and 3 showing an complete overlap of the P and Zr peaks, which makes them undistinguishable in the RGB elemental map.

With all this ‘Octane’ power to keep your acquisition limits tunable on demand, there are many more exciting experiments further ‘down the road’. And yes, the roads can be icy and slippery in December. It is more fun to race with your fast EDS, collecting powerful, streamlined data and aiming towards the holidays with new observations, and possibly new discoveries.

When Shattering Performance Limits Makes You Think You Have Broken Your New Detector!

Tara Nylese, Global Applications Manager

The last few months have been some of the most rewarding ever throughout my time at EDAX.  In the last year or more we’ve been working on a series of new detector technology offerings, which we can now finally bring to our customers.  These detector advancements are quite literally shattering past performance limits.  And it’s not just one technology, but a combination of three technologies together which makes the Octane Elite launch one of the most exciting of my 20 year career here.

Two months ago, I sat at the system generating data that would give us an idea of the performance specifications that we could associate with the product promotion as we went to launch.  I had just achieved a never before reached input count rate of 2 million counts per second, but was slightly hesitant to promote that, since it’s variable based on SEM conditions and sample.  So, I let it sit for a bit and we went into a stellar M&M show with a strong set of performance specs from low energy performance to grid materials and spectral resolutions at high speeds.  Following the show, we had a webinar planned, which again focused on those performance limits. It’s been one of my goals this year to be very data-driven, using direct examples to let a story show itself, so a crucial piece of the webinar was to collect the applied examples that illustrate the specs, and this made a great opportunity to revisit the 2 MCPS data collection.

Being efficient (much like our detectors!) I like to try to use one sample to tell multiple stories, so I grabbed a favorite ductile iron sample, which has both carbon for low energy performance and iron for high speed mapping.  My first notable point was that I could run the count rate up to 750 K CPS input with max output at 60% deadtime and still obtain an excellent carbon peak in a spectrum extracted from a map (Figure 1).  At these high count rates, older technology detectors cannot maintain this type of performance, and we’ve even seen carbon dropping off at 500 K CPS, our previous best, which was also an industry high.  And by dropping off, I really do mean that the spectrum will no longer show a carbon peak as the spectrum no longer displays the peak at all, or in some cases, a highly distorted peak with little differentiation from the background.  So, by achieving a carbon map at one and a half times the highest count rate ever achieved before, I felt I really shattered previous limits.  I didn’t stop there, but pushed the count rate up to 1.5 M CPS input and still was able to detect the carbon peak, albeit with some degradation in the quality of the spectrum.

Figure 1 shows a clear display of the quality low energy performance even extracted extracted from a high speed map collected at 750 KCPS.

Figure 1 shows a clear display of the quality low energy performance even extracted extracted from a high speed map collected at 750 KCPS.

But why stop there?  As I was already ramping up the count rate, I figured I’d continue as far as I could, and I opened the aperture all the way on our thermal FEG.  At this point, I was running our SEM at 20 kV and max aperture, which would mean a beam current at or above 100 nA.  This is really not an achievement in itself, since most all thermal FEGs can get there, and this SEM is 15 years old, so it’s not a new type of achievement.  The steel sample was conductive, of course, making it suitable for this condition, but it was mounted in a non-conductive mount, so I had it grounded simply with carbon tape.

Once I opened the aperture, I had to do a double take at the CPS since that was a lot of numbers, and I actually counted to make sure I had it right – we were at 2.8 M CPS input!  The reason I had a hard time believing this is that normally at that count rate, the detector would saturate and this time it did not.  I was certain at that moment that I had broken our new detector and what I was seeing must be noise, because even just getting those counts without the detector turning off is a feat.  So, of course I had to collect data to see what the quality was.  And while the dead time was high at >90%, I was still able to collect a phase map (Figure 2) where both the low energy elements and higher energy steel were solved by the phase map routine in just a few passes.

These detectors have a great many additional performance enhancements with the Silicon Nitride window, vacuum encapsulation and CUBE electronics, but this example serves as a good display of the payoff of all combined, and this work would not be possible without the benefits of all of these aspects together.

To also address the windowless comments that I’ve gotten since my webinar, in summary, that’s an altogether different product.  Our Octane Elite is a mainstream, general purpose detector that has all of these performance benefits, while the windowless serves more of a niche set of applications.  I’ve had a windowless detector in my lab for years now and I’ll be very honest, it sits unused on a bench and I only mount it when I have a special requirement. My detector of choice, given my unlimited detector options, is absolutely the Octane Elite.

Figure 2 shows the highest x-ray map ever collected at EDAX at 2.8 million counts per second at 20 kV with the Octane Elite detector technology. Steel matrix is shown in red and graphite nodules are blue.

Figure 2 shows the highest x-ray map ever collected at EDAX at 2.8 million counts per second at 20 kV with the Octane Elite detector technology. Steel matrix is shown in red and graphite nodules are blue.

On a side note – we’re currently looking to fill an EBSD apps position in our NJ lab, and as I describe the job to potential candidates, I’m always drawn to some of the real highlights that an applications position offers someone in the technology field.  I hope this blog today captures it perfectly.  As an apps person, we bridge the area between commercial and development, or customer and engineering.  In fact, it’s even part of our mission statement that the applications group understands the real world customer needs and translates them into the product development process at EDAX for our future products.  This in turn, strengthens our products and services to meet the most important needs, those of our customers and those that further the technology into groundbreaking directions like this never before achieved detector performance.

Windows of Opportunity?

window in waterDr. Patrick Camus, Director of Research and Innovation, EDAX

You may have heard of a new breed of SDD that has an ultra-thin Silicon-Nitride (Si3N4) window. Its main advantage over traditional polymer windows is its significantly higher low-energy sensitivity. In addition, it is both moisture and plasma-cleaning tolerant which permits the true vacuum sensor environment to persist for the lifetime of the detector.

If you have concerns about the robustness of this new window, watch this video, which shows some informal torture tests being performed. You will come away astounded at the results.

Click here for more information on EDAX detectors using a silicon nitride window:
Element
Octane Elite

Resolving Matters

Dr. René de Kloe, Applications Specialist, EDAX

Every now and then a new critical parameter in EBSD analysis comes up. This parameter is often related to a new trend in materials science research or industrial development. One of the latest buzz-words is “nano”. Things are getting smaller and smaller and EBSD technology has to keep up to be able to provide the microstructural answers. This drive to investigate the tiniest details led, for example, to the emergence of transmission EBSD. But it seems that not everyone means the same thing when they talk about nano; Where does nano begin and where does it end? For example, is “nano” anything smaller than 1 micron, or anything below 100 nm, or perhaps only things smaller than 10 nm? The answer is of course: all of them. The feature scale really depends on your application and field of science. For example in natural geological materials, grain sizes smaller than 1 micron are not very common and such rocks could be described as nano-structures. But in semiconductor or photovoltaic applications nano may range from single atomic layers to perhaps 100 nm.

In the EBSD community the emergence of nano-analysis has sprouted the use of another buzz-word: ‘resolution’. But exactly as with nano, ‘resolution’ can have several different meanings depending on who you talk to. So let’s start with the basics, what is resolution?

resolution
Pronunciation: /rɛzəˈluːʃ(ə)n/
The smallest interval measurable by a telescope or other scientific instrument; the resolving power.
The degree of detail visible in a photographic or television image
A firm decision to do or not to do something
The action of solving a problem or contentious matter
(from http://www.oxforddictionaries.com/definition/english/resolution)

Of these definitions the first two have obvious relevance to EBSD analysis, but at the same time define something completely different. The first one deals with the feature size on the sample, whose limits are defined by the combination of SEM beam settings and physical sample properties. The second one describes the amount of detail observable in a diffraction pattern collected from an area of a sample, which is affected by the number of pixels available on the imaging sensor. These two definitions are easily confused, but are not directly related.

And of course there is a third definition of resolving something which is a well-known strength of EBSD. It is the power to resolve the difference between different phases. For example here is a geological material, a granitic rock with several minerals with low-symmetry crystal structures. In order to resolve the phase differences, the analysis of a rock like this does not require any high resolution settings. A detector resolution of only 120 pixels and step size of 0.5 micron was sufficient.

Figure 1
But things are not always what they seem at first glance as is illustrated by the sequence of images below. All these maps are collected with the same low detector resolution of only 80 pixels, but with very different spatial resolution, or step size, on the sample. The sample is a piece of the Gibeon meteorite, an iron meteorite that was discovered in Namibia in 1836. The structure is very coarse grained and the individual grains can easily be seen with the naked eye.

Field of View_2

But looks can be deceiving. My first attempt to characterize the structure resulted in a speckled map that looked pretty bad and made me doubt my polishing skills. Subsequent maps with higher and higher spatial resolution (i.e. smaller step size) started to resolve a fine-grained structure with many grains being smaller than 100 nm. So for this example, high spatial resolution maps were obtained using low resolution camera settings.

Figure 3

For phase identification and characterization of deformation microstructures the pixel resolution of the detector becomes more important, but within reason. For phase identification you want to be able to identify small details in a pattern and this is also helpful when you are looking at small orientation changes due to dislocation structures in a material. This biotite pattern displays a pseudosymmetry where the difference between similar orientations is defined by the position of some relatively weak bands in the pattern. The correct indexing result is outlined in red.

Figure 4

Left: Biotite patterns with pseudosymmetric indexing results – red pattern is correct
Right: Kernel average misorientation map in deformed iron alloy illustrating precise locations of subgrain boundaries

In such cases, what you need to identify the difference between these orientations is having enough pixels in the band pattern across the weaker and thinner bands to be able to detect them automatically. Therefore the band detection capabilties dictate the resolution that you need to resolve the difference between these two orientations and not the number of pixels that you have available on your EBSD detector. Typically a pattern of 200 pixels is sufficient on any material. And that resolution is also enough to be able to measure orientation changes down to 0.05 degrees, which allows accurate identification of subgrain structures as shown in the kernel misorientation map.

If even smaller orientation changes are the target of your analysis or if you want to measure minute shape changes of the crystal lattice due to elastic strains, the standard band detect routines are insufficient. For such analyses you would need to use a pattern with more pixels and a dedicated technique based on cross correlation of sections of the diffraction patterns. For this tool, using many more pixels would appear to be better. But keep in mind that other variables in the system geometry such as the exact detector positioning, signal-to-noise level, lens artifacts, or pattern center calibration errors can introduce uncertainties that may easily exceed the improvements gained by using more pixels. In practice, patterns with 480 pixels or more have been used successfully. What you see is not always what you get.

The above examples have highlighted a number of different uses of the word resolution and it appears that you have to be pretty careful in describing what you really want to accomplish. Going for a high resolution camera will not give you better spatial resolution in your EBSD maps. Similarly low resolution maps may be measured using a high resolution camera which shows that the number of pixels on your detector is totally independent of the spatial resolution that may be obtained on your samples.

Therefore to conclude I would like to appeal to the last definition of resolution mentioned above: The action of solving a problem or contentious matter.
With the different meanings of resolution clouding the waters and creating confusion I would like to propose the use of “high resolution EBSD ” to describe the application of mapping with small step-size to resolve the fine details in a material. “High precision EBSD” would then describe the application to map out small orientation changes in a material in order to investigate and understand the deformation mechanisms and finally “high definition EBSD” to describe the technique of investigating minute changes in pattern geometry to characterize (elastic) strains in the crystal lattice by applying cross-correlation methods.

My $0,02