Month: April 2017

It’s a zoo in there!

Dr. René de Kloe, Applications Specialist, EDAX

For most of us EBSD users, our day to day experience is with metals, ceramics, or perhaps rocks. For man-made materials, analysis allows us to characterise the microstructure so that we can finetune the processing or fabrication of a material for a specific application. Another common use of EBSD data is for failure analysis where the crystallographic information can be coupled to external characterisation data and deformation structures such as cracks, welds, or ductile deformation features.

Figure 1. IPF map of partially recrystallized steel (left); IQ map of quartzite rock from the Pilbara region in Australia (right).

For natural materials like rocks, the questions start to get a bit trickier as we typically do not know exactly how a rock has come to exhibit the structures that it has. In combination with other tools, EBSD can then be an invaluable tool to add crystallographic and phase information to the puzzle. This allows researchers to piece together the deformation, temperature, and pressure history of the rock. This way tiny samples can provide insight in processes on a global scale like mountain building and the motion of the continents.

A third group of materials that gets a bit less attention in EBSD analysis are biominerals, materials that are formed with a certain degree of biological control to become part of an organism. In these biomaterials, the question is not how we have produced it, or how it could be finetuned to its intended application. Here the question is how biological processes have been able to optimise a material to such a remarkable degree and the EBSD analysis is used to try to understand the biological use and control of crystallisation. Unfortunately, we rarely get to look at structures that are produced by living organisms, except possibly fossils. One of the reasons that “fresh” biomineral structures are rarely studied with EBSD is that they often contain an organic fraction that makes electron microscopy samples susceptible to beam damage. To analyse such materials, the researcher must be very careful. A single pass with the electron beam is often all you get as the structure is easily damaged. In fossilised remains of animals, the organic component has been lost or replaced by solid crystals which make its analysis somewhat easier. For example, in recent years, papers have been published on crystalline lenses in the eyes of long extinct trilobites which were formed of calcite [1] and EBSD has also been used to estimate which areas of dinosaur eggs are most likely to represent the original microstructure such that the isotope ratios from these grains can be used to estimate the crystallisation temperature of the eggs [2].

A bit closer to us is perhaps the analysis of hydroxyapatite in bones. In the SEM image this cross section of a bone consists of a fibrous framework with brighter areas containing individual hydroxyapatite grains. What is not clear from such an image is if the grain orientations in these areas are all identical or perhaps exhibit random orientation. EBSD analysis clearly shows that the apatite grains occur in small clusters with similar IPF colours or equivalent orientations, which indicates that these smaller clusters are connected in the 3rd dimension in the material.

Figure 2. BSE image cross-section of bone (left); Hydroxyapatite IPF map on a single hydroxyapatite region in bone (right).

The recent introduction of the easy recording of all EBSD patterns during a scan and performing NPAR (neighbour pattern averaging and reindexing) during EBSD post-processing have allowed dramatic improvements in the analysis of beam sensitive materials. You still have to use gentle beam currents and relatively low kV to obtain the EBSD patterns. These patterns are then very noisy and the initial maps often show poor indexing success rates, but once these have been collected you are free to find the optimum way to analyse these patterns for the best possible results. For example, beam sensitive materials like the aragonite in the nacre of shells can be successfully analysed.

Figure 3. Calcite-aragonite transition the inside of a shell: original measurement (left); after NPAR reprocessing (right).

The aragonite-calcite phase map above on the left shows the initial results of an EBSD map of the inner surface of a shell over a transition zone from the calcite “framework” on the right to the smooth nacre finish on the left of the analysis area. Directly at the interface the EBSD pattern quality is so poor that it is difficult to interpret the microstructure. The phase map on the right is after NPAR reprocessing. Now the poorly indexed zone at the transition is much narrower and the map clearly shows how the aragonite starts growing in between the calcite pillars, then forms a thin veneer on top of the calcite until it gets thick enough to create euhedral planar crystals that form the smooth nacre surface at the inside of the shell.

Figure 4. Aragonite structure from pillars to nacre: original measurement (left); after NPAR reprocessing (right).

Figure 4 shows another shell structure which is now completely composed of aragonite. In cross section the structure resembles that of the calcite pillars with the nacre platelets on top, but the initial scans do not reveal any structure in the pillars. This could be taken as evidence that the crystal structure might be damaged and cannot be characterised properly using EBSD. However, after NPAR reprocessing the crystal structure of the pillars becomes clear and a feather-like microstructure is revealed.

These fascinating biological structures don’t appear often to the average materials scientist or geologist, but if you keep an open mind for unexpected structures you can still be treated to beautiful virtual creatures in or on your samples. For example, dirt is not always just in the way. Here it poses as a micron sized ground squirrel overlooking your analysis. And this magnetite duck is just flying into view over a glassy matrix.

Figure 5. Dirt patch in the shape of a ground squirrel (left); crystal orientation map of a magnetite duck flying through glass (right).

And what to think of these creatures, a zirconia eagle that is flying over a forest of Al2O3 crystals and this micron sized dinosaur that was lurking in a granite rock from the highlands of Scotland. Perhaps we finally found an ancestor of Nessie?

Figure 6. Zirconia EDS Eagle: in zirconia -alumina ceramic (left); on PRIAS bottom image (right).

Figure 7. Ilmenite-magnetite dinosaur in a granite rock.

It is clear that “biological” EBSD can occur in many shapes and sizes. Sometimes it is literally a zoo in there!

[1] Clare Torney, Martin R. Lee and Alan W. Owen; Microstructure and growth of the lenses of schizochroal trilobite eyes. Palaeontology Volume 57, Issue 4, pages 783–799, July 2014
[2] Eagle, R. A. et al. Isotopic ordering in eggshells reflects body temperatures and suggests differing thermophysiology in two Cretaceous dinosaurs. Nat. Commun. 6:8296 doi: 10.1038/ncomms9296 (2015).

My New Lab Partner Part 2 (East Coast Edition)

Jens Rafaelsen, Applications Engineer, EDAX

During a recent trip to our Draper lab in Utah for a training class, I got a first-hand look at Matt’s new lab partner (https://edaxblog.com/2017/02/14/my-new-lab-partner/). I must admit that I am a little envious of his new microscope and how easily you get great looking images (even at low acceleration voltage or high beam current) compared to the systems we have in our Mahwah lab. However, I must also admit that he needed an upgrade a lot more than we did. While his old XL has been very reliable (and still seems to be, even after moving it to another room), it was always a bit of a worry conducting a training class with only one microscope available and one that was at end of service life at that.

Around the time when Matt got his new microscope we also had an addition to our Mahwah lab as seen in the picture below:

OK, it’s definitely not an ARM or a TITAN, it only goes to 120kV, it’s not quite as new and fancy as Matt’s microscope, and the firmware might read 1994 when you hit the ON button, but it’s still good to have a TEM in the building once again. One of the things that’s great about older scientific instruments is that they often include full vacuum and wiring diagrams, schematics, and troubleshooting directions. Not so great: pressure readings in arbitrary numbers… I did some creative plumbing and mounted extra gauges on the line of the microscope gauges so now I know that a pressure reading in the buffer tank of 26 corresponds to roughly 10-1 mbar and that the camera chamber goes down to the mid 10-5 mbar. As an added bonus, several people in the building have been around long enough to have experience with the CM12 both as users and service and have had their memories jogged for how to run and align it. This also spurred the comment: “That’s right, this is why I decided to get out of field service…”.

Having had very limited TEM experience it’s been a bit of a learning curve for me but I think it’s getting there. There’s still a lot to learn when it comes to fine tuning of the instrument, diffraction, and aligning for dark field imaging, but at least I am able to get bright field images at over 500k magnification without spending too much time. And some of the images actually have somewhat decent resolution and recognizable features at that:

Holey carbon at 660.000x magnification

Of course, a lot of what we do at EDAX doesn’t really require great resolution or the newest instruments. While it’s always nice to have pretty pictures to go along with things, the X-rays don’t really care much about your astigmatism or spot size (unless you are trying to map of course). But there’s a significant difference in what you see in your spectra whether your electrons are hitting the sample with 15 kV or 120 kV. There are also very different considerations and limitations between a SEM and a TEM when it comes to actually mounting the detector, designing collimators, and even what materials can be used. With that being said, I hope that with my “new” lab partner we will move things along so that we can show you new applications, software, and hardware specifically for the TEM in the near future.