EDAX and Gatan Bring You Lithium

Dave Durham, Sales Manager – U.S. Western, EDAX

It has been interesting to recently witness EDAX and Gatan working together to combine the technologies in our portfolios. Although technically, Gatan was acquired by AMETEK back in late 2019, it seems like 2021 has been a year where the integration of our two companies has really begun to hit its stride.

For example, I’ve seen how Gatan’s ion polishing instruments can dramatically improve indexing success for EDAX’s Electron Backscatter Diffraction (EBSD) users compared to the conventional methods for sample preparation. And I’ve seen EDAX’s Elite T Energy Dispersive Spectroscopy (EDS) System undergo a tremendous workflow improvement and ease-of-use overhaul with the implementation of Gatan’s Microscopy Suite user interface. It has been great stuff!

However, the most recent integration between our two companies is truly groundbreaking, and I’m thrilled to see what it will do to enhance the research being done in its field.

Hopefully, you’ve already seen the news mentioned on our website. For the first time, we’ve been able to perform quantitative mapping of lithium in the Scanning Electron Microscope (SEM) by combining the power of EDAX and Gatan detectors and software! These breakthrough results will enable a new level of lithium research that was previously never possible with the SEM.

Figure 1. EDAX and Gatan bring you lithium.

So who cares about lithium? Everyone should. Lithium compounds and alloys are very important materials with significant commercial value. The compounds are being implemented into lightweight structural alloys in the aerospace and automotive industries. They’re also utilized in lithium-ion batteries for small electronic devices and vehicles. Many governments worldwide have proposed plans to reduce dependence on legacy energy sources, which makes further development of lithium-based technologies critical to the adoption of these plans. This means significant investments are currently being made in R&D, failure analysis, and quality control of these materials.

Figure 2. (left) Lithium-ion battery cross-section prepared by Ilion II broad beam argon milling system. (right) EBSD IQ + orientation map revealing the microstructure of the heat-affected zone in a lightweight structural alloy.

So what are the issues with lithium? While electron microscopy and EDS are already essential characterization tools in this industry, there is a distinct inability to map lithium distribution in the SEM. This has presented a significant obstacle, holding back research on these tools. EDS is typically a valuable technique for material characterization, with high sensitivity and spatial resolution to allow for quantitative analysis on a wide range of sample types. But it is not possible to identify lithium in commercially important materials by EDS because:

  1. There is no guarantee that lithium X-rays will be produced from the sample. The X-ray energy and the number of photons produced from the specimen depend on the lithium bonding state. So, even if you have lithium in your sample, it does not mean that lithium X-rays will be generated.
  2. Even if a sample does generate lithium X-rays, they are easily absorbed back into the sample itself, contamination or oxidation, or by the EDS detector window before they can even reach the EDS detector.

Indeed, specialized windowless EDS detectors can detect lithium, but these have drawbacks that impede their practicality and largescale adoption. Even on samples that have a high lithium fluorescence, these special detectors have a limit of detection of about 20 wt %. This is equivalent to about half of the atoms in the sample being lithium, which restricts analysis to only metallic lithium or simple lithium compounds that may not be relevant to advanced lithium research or applications.

And having a specialized windowless EDS system potentially introduces a slew of operational issues/limitations with the detector that aren’t present with a “standard” windowed EDS system. It also restricts the detector’s utility on non- lithium -research-based applications in the lab.

So what have EDAX and Gatan done? We have solved these issues by using a patent-pending technique called the Composition by Difference Method. In this method, we quantify the backscattered electron signal to determine the mean atomic mass for all elements in a particular area of a sample. And from the same region, we collect the EDS signal to quantify the non-lithium elements. From that information, we have two data points that tell us the actual mean atomic mass from the region and a calculated value based on the EDS results — when they don’t agree with one another, it tells us we are missing something in the EDS data. That something we’re missing is lithium.

Figure 3. Data from the OnPoint and the Octane Elite Super are combined and analyzed to quantify lithium.

By using this method, and specifically by combining the EDAX Octane Elite Super EDS Detector and the Gatan OnPoint Backscattered Electron Detector to collect these two signals, we can now generate lithium maps quantitatively with single-digit mass percentages of lithium with sub-micron spatial resolution. This accuracy has been verified to ~1 wt. % lithium by an external accredited laboratory using Glow-discharge Optical Emission Spectroscopy (GDOES).

Figure 4. Secondary electron image and elemental metal fraction maps (by wt. %) of the same region of the MgLiAl alloy; white pixels are regions excluded from the analysis due to the influence of topography (identified by arrows in the secondary electron image) shown here for clarity.

This is a cutting-edge capability in the SEM, and it is a huge opportunity for anyone wanting to discover where lithium exists in their specimens. Just to reiterate, this method does not use a specially designed EDS system for lithium detection! It uses EDAX’s standard (windowed) Octane Elite Super and Gatan’s OnPoint BSE detector, along with EDAX and Gatan software. Simply amazing!

Now that EDAX and Gatan have introduced the ability to provide quantitative lithium analysis, that is:

  • A substantial improvement in limits of lithium detection
  • Insensitive to the lithium bonding state
  • More tolerant to contamination and oxidation
  • Not limited to metallic materials or simple lithium compounds
  • Free from windowless detector-related limitations on the SEM

It seems that we have helped open an avenue for our customers to expand their lithium research beyond anything previously possible. We are truly beginning a very exciting new stage in lithium analysis, and I can’t wait to see how this new capability is used and what comes next!

You can find more information on this new development in our experiment brief.

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