Ask the Expert: Surface Contact and Optical Metrology
During this live Ask the Expert event, we will answer pre-submitted questions from our audience regarding materials analysis with various surface contact and optical analytical techniques.
Characterization of Crystalline Structures – SEM-EBSD vs. TEM-PED
When optical microscopy cannot provide sufficient image resolution or magnification, techniques like Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) are used to provide higher resolution investigations of sample microstructure, morphology, and more.
Besides images provided by SEM and TEM, different attachments can be added to reveal crystalline information from micrometer to nanometer level, including Electron Backscatter Diffraction detector with SEM (SEM-EBSD) and Precession Electron Diffraction detector with TEM (TEM-PED).
What are SEM-EBSD and TEM-PED?
Electron Backscatter Diffraction (EBSD) is a unique technique used to characterize crystallographic properties of samples, such as grain size, shape, orientation, etc. In EBSD, a small, focused electron beam is used to raster scan the sample surface and create an electron backscatter diffraction pattern at each pixel. This can be analyzed to determine crystallographic information and is visualized with spatial coordinates of the sample.
If higher spatial resolution is needed and/or more complicated crystal structures need to be resolved, TEM-PED can be used instead. Precession Electron Diffraction (PED) differs from EBSD in that the electron probe transmits through the TEM specimen (typically smaller than tens of nanometer) and yields electron diffraction patterns. Such patterns provide a more detailed characterization of crystal structure than what can be achieved with EBSD. Although PED is capable of providing detailed visualizations of crystallographic information down to the nanometer scale, sample preparation is typically more complex than the equivalent preparation process required for SEM-EBSD.
When to use EBSD vs. PED
A good rule of thumb is that EBSD is appropriate for samples with a grain size larger than 200 nanometers, and PED is capable for samples where the grain size is less than 20 nanometers. Sample preparation for EBSD is typically easier compared to PED, and this technique provides a larger field of view at the expense of lower resolution. When EBSD does not provide enough spatial resolution, PED is the appropriate characterization technique, providing better resolution at the expense of a smaller field of view.
These two techniques can also be complimentary and have advantages and disadvantages based on your sample and use case.
EAG’s advanced microscopy group provides both the tooling and expertise to determine the best course of action for your sample analysis.
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