Accurate and fast analysis using a TTM equipped with EDS

19^th April 2024 | Author: Anthony Hyde

The TableTop SEM has come a long way since its introduction in 2005. The first systems were imaging only and appealed to users outside the electron microscopy community because of the small footprint and ease of use. With the addition of EDS and performance improvements, the TTM is now regarded as an invaluable tool in an EM department.

To discover what we mean by ‘Accurate and fast analysis,’ we really need to start with the basics. For the uninitiated, there are various signals produced when a sample is irradiated with an electron beam (electrons, X-rays and light). From these signals, it is possible to determine microstructure, composition and crystal structure. The TTM will have various detectors to collect:

• Backscattered and Secondary Electrons for imaging.
• Characteristic X-rays to obtain elemental information

These characteristic X-rays have a specific energy value for each element. This means the presence of the elements in the sample can be identified in a few seconds, via a spectrum (qualitative analysis).

The intensity of the characteristic X-rays can also be used to measure the content of each element (quantitative analysis).

To see where these elements are distributed within a field of view, we use X-ray mapping.

The next thing to address is the question of which EDS system you choose to collect this data. But I hear you ask, “All EDS systems are the same… aren’t they?" Well, they all do the same basic job, that’s true, in the same way different types of cars do the same basic job. We all want a car we can rely on, but some cars have a better reputation than others.

Why is it important that your EDS system is Accurate, Repeatable, Reliable, Easy to Use and Informative? Whether you are new to EDS, an infrequent user or something of an expert, you still want to know that the results you get are correct and that the software you use to get those results is simple and straightforward to use. You need to know that you’ll get the same result tomorrow as you did today. Above all, the results presented to you by the EDS system must help you solve the problem you purchased it for.

Any EDS manufacturer should use the latest technology, innovative design, robust algorithms and follow quality production processes to deliver an EDS system that doesn’t require an expert to get expert results.

The next thing is to take this ethos, which works extremely well for our standard detectors like the Ultim Max, and make it work for a detector that must work in the confines of a TTM enclosure. With some innovative design, we introduced the XploreCompact.

So what does this quality system give the user? Looking at the most fundamental requirement of an EDS system, it needs to detect the elements in your sample correctly. Poor EDS system quality can

• Result in poor peak shapes and positions
• Make the seemingly simple process of peak identification problematic
  • Resulting in the possibility that at best, some elements are not identified or at worse they are misidentified

Automatically detecting elements in a spectrum and quantifying them is only the beginning of your sample characterisation. Knowing where the elements are distributed in your sample is the next stage. This is achieved by collecting ‘X-ray Maps’, but there are also potential pitfalls here too. Normal EDS mapping utilises energy windows to construct a 2D image showing the distribution of an element. Unfortunately, there are many element combinations where their peaks are either very close or overlap each other in the spectrum. This results in potential errors in the X-ray Maps.

In this example, the energy windows for Pb and S overlap, so their respective X-ray Maps look very similar.

The way to correct for this is to use a software option live AZtec TruMap, which is a real-time mapping mode that automatically separates the signals from overlapping elements to give the real element distributions.

Now we have accurate results we can rely on, but how do we take all the information in a field of view and present in a way it can be easily interpreted? Using AutoLayer, we identify and combine the elements that vary in a sample into a single image that helps visualise both phases and element distribution in a field of view.

Having a system that can deliver accurate and reliable results gives the opportunity to create an innovative product like ‘Live Chemical Imaging’. Instead of carrying out the classic stop/start sequential investigation of your sample, LCI enables you to move around your sample with a live Layered Image. Until now, this hasn’t been possible on a TTM because the large count rates required. With the introduction of the XploreCompact 65 LCI on a TTM, this is now a reality. The video below shows how you can navigate around your sample using a live layered image with useful chemical information. Then, whenever you find an interesting feature, just stop; and the information automatically accumulates to reveal even more detail. You can then either acquire a full SmartMap or move on to a different area.

To Summarise:

• To quickly analyses your samples and get accurate and reliable results, you need an innovative EDS system that has been manufactured under quality processes.
• Oh, and perhaps not all EDS systems are the same.

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