EBSD sensors have changed as camera technologies have evolved. They began as intensified video cameras, then improved to scientific grade CCD cameras. These have provided both the high pixel count and high speed needed for EBSD acquisition requirements. Typical sensor sizes exceed 1M pixels at 10 fps for pattern quality applications and high-binning sensors are used for 1,500+ fps mapping applications at beam currents <=10 nA.
Newer technologies are appearing from imaging research labs that have similar pixel resolutions but significantly higher fps values. Unfortunately, the 1st generation of these devices do not have quite the sensitivity of the older devices, but each journal publication shows improvements.
R N Clough, et al, “Direct Detectors for Electron Microscopy”, 2014 J. Phys.: Conf. Ser. 522 012046
R. Clough, et al, “Direct Digital Electron Detectors” in Advances in Imaging and Electron Physics, Volume 198 # 2016 Elsevier Inc. ISSN 1076-5670
Angus J. Wilkinson, et al, “Direct Detection of Electron Backscatter Diffraction Patterns”, PRL 111, 065506 (2013)
S. Vespucci, et al, “Direct electron imaging of EBSD patterns using a CMOS hybrid pixel detector”, RMS-EBSD Workshop 2013
K.P. Mingard, et al, “Practical Application of Direct Electron Detectors to EBSD Mapping in 2D and 3D”, Ultramicroscopy (2017)
Angus Kirkland, “A Detector Revolution: Direct Silicon Detectors for Electron Microscopy”, EMAS 2017
Recent devices under test are providing binned patterns at 3,000 indexed fps, which provide 99% indexing quality but require a higher beam current of 40 nA. When performing higher resolution imaging at low beam energies (<=5 keV), less than 1 nA is required, which is significantly lower than previous devices, for full camera resolution at 100 fps.
5 kV EBSD pattern at 100 pA
OIM map collected at 3,000 fps and 40 nA providing 99% indexing quality
Many interesting developments are occurring with EBSD sensors. My colleagues will be reporting on those findings in the coming months.
One of the interesting aspects of being in applications is the wide variety of interesting samples that you come across and this one came up when I was looking for a sample for an upcoming webinar, where I needed some ‘pretty’ maps. Our US EBSD applications engineer Shawn Wallace was previously at The Department of Earth and Planetary Sciences at the American Museum of Natural History in New York and consequently he knows quite a bit about space rocks. He handed me a thin section of a meteorite labeled NWA 10296 (more information at https://www.lpi.usra.edu/meteor/metbull.php?code=62421) and it did not disappoint.
There were a lot of interesting features in the sample, but I ended up concentrating on one of the large chondrules shown below.
Figure 1. BSE image
The primary composition of the sample is olivine (magnesium iron silicate) and the maps below show a high concentration of the Mg internal to the chondrule with an outer perimeter low in Mg and Si. The iron within the chondrule is forming particulates with low content of O and some veins of Al is also seen while the outer perimeter is an iron oxide.
Figure 2. Mg, Si and O maps (left to right).
My astronomy classes are long behind me and I can’t claim to be able to extract deep insight as to the formation and origin of this meteor but regardless, there’s something fascinating about looking at some of the early matter of the universe. As I heard Emma Bullock phrase it at the Lehigh Microscopy School, “It might just be an old rock, but it’s an old rock from outer space!”.