Dr. Sophie Yan, Applications Engineer, EDAX
The new year is here. And with it, we look for ways to start our research on the right foot.
Over the past two years, I’ve traveled less and been fortunate to spend more time supporting customers online and working in the lab analyzing samples. Whether it’s a customer’s sample or my own, my goal is to push the limit by using different conditions across various samples to get the best results. Using this approach, I can always get good Electron Backscatter Diffraction (EBSD) indexing results when analyzing challenging samples. It is the highlight of my day when I see the colorful Inverse Pole Figure (IPF) maps and feel that my hard work has paid off.
On the other hand, my experience in technical support provides me with some tips. After all, most people’s mistakes are similar. I want to take this opportunity to discuss this.
In many cases, analysis results are sub-optimal because experimental details are not well controlled and are not a reflection of the product age or technology. Recently, I have seen many papers (such as the deformed Ti on the cover of Science) where they did not use the latest hardware/technology, but the results are excellent. If you take EBSD as a whole process and properly deal with all influencing factors, then any shortcomings will affect the final result. Many factors need to be accounted for, such as the preparation of the sample, sample mounting, the input signal strength or weakness, and then it comes to the EBSD operation itself.
Figure 1. September 17, 2021 issue of Science magazine featuring an EBSD orientation map of cryoforged Titanium.
Since I have a Gatan Ilion® II (model 697) in my sample preparation room, I no longer worry about the sample preparation process. Ion polishing is the best method, and it can achieve the requirements most of the time. Of course, vibration or electrolytic polishing is also a suitable method; just pay attention to the choice of parameters.
Figure 2. Gatan Ilion II System
Often it is attention to the small details that pay the biggest dividends. When mounting the sample for EBSD, we want to eliminate sources of physical sample drift due to the effects of a 70° sample tilt. I use a mechanical method or choose a liquid glue when performing this step. This becomes more important as the sample size and mass increase. Also, use an appropriate beam current selected for EBSD. Beam currents used for high-resolution SEM imaging are often lower than required for traditional EBSD detectors. Make sure the image is in focus and is properly stigmated. I once demonstrated the effect of focus on EBSD Image Quality (IQ) values, and the people present were astonished. When needed, use the dynamic focus correction on the SEM to keep the focus constant across the tilted surface.
Be aware of the different parameters that can be set for the EBSD system as well as the SEM. From my personal experience, the selection and optimization of these parameters can easily increase the speed and quality of your data.
Once you get to this point, the process is almost complete. The EBSD parameters are pretty simple, as long as the signal can be reached. Think about the number of grains to analyze and the SEM magnification required for this field of view. Then select a step size appropriate for the average grain size and type of analysis. Selecting this requires thinking about our desired acquisition time, the speed of the detector, and the details of the microstructure, and the APEX software can recommend different values. If every step is done well, then this process should be perfect. Then, just do it.
In the end, these proven approaches can be applied to your existing or new instrumentation to achieve your best results. I hope these thoughts are helpful to ensure your work goes smoothly in the new year.