Seeing More @ UBC

One of the challenges we have in Materials Engineering is to view, and ultimately understand, the structure of our materials. Typically, these structures exist at the atomic (i.e. sub-nm) to mm length scale, and control the properties of the final material or component. As materials engineers, we often try to change or influence the formation of this so-called “microstructure” by varying the manufacturing route.

It’s therefore really exciting to share that we have a new piece of equipment in the Department of Materials Engineering, at the University of British Columbia (Vancouver-campus, Canada) that will help us image and measure the structure of materials — a table top scanning electron microscope.

The table top scanning electron microscope (SEM) — a Thermo Fisher Scientific Phenom XL GL2, equipped with energy dispersive X-ray spectroscopy (EDX), as well as secondary & backscatter electron detectors.

Our table top SEM is a Thermo Fisher Scientific Phenom XL GL2 instrument, and it is equipped with a large area stage (100 x 100 mm, accepting 36 stubs) with an integrated optical microscope to aid finding your samples quickly.

The integrated optical microscope — NavCam — enables us to find our samples quickly for further study.

In brief, a scanning electron microscope enables us to image and measure a sample by scanning a focused beam of electrons across the surface of our sample. At each point, we measure the signal and for this instrument we can collect backscatter (sensitive to topography, chemistry, crystal phase, and/or crystal orientation), secondary (surface topography) and chemical information.

Example backscatter electron (BSE) micrograph showing the presence of a large precipitate within an iron-nickel meteorite (sample prepared by Graeme Francolini, microscopy by Ben Britton)

The Phenom platform has been engineered to make it really easy to use and collect data, and we can usually train people to start collecting their own data within an ~hour of having not used one of these instruments before. In addition to these features, we’re quite lucky to have a few extra ‘tricks’ that helps us get useful and informative data quickly.

ChemiSEM

To measure the local chemistry in a sample, typically we will collect characteristic X-ray spectra from a sample while we point the electron beam at a feature using the technique “energy dispersive X-ray spectroscopy” (EDX/S). To get enough signal to noise, for a typical system this can take quite a while (often 30 seconds per spectra) so that we can get enough counts to understand the feature of interest.

Now what makes our system really interesting for a first ‘look’ is the extension of the ChemiSEM technique to the Phenom platform, where a hierarchical strategy is used to perform fast and informative EDX-informed analysis of where different elements are located. When we turn on the ChemiSEM mode, we get a very quick overlay of the different chemistries within our material in just a few additional seconds. In this iron-nickel meteorite, we can see the presence of three phases: iron-rich (matrix), nickel-rich (red, half the precipitate), and iron-phosphor rich (yellow, left-half of the precipitate).

ChemiSEM reveals the precipitate chemistries within this iron-nickel meteorite (sample prepared by Graeme Francolini, microscopy by Ben Britton)

Large Area Mapping

Often in our multi-scale characterization approach, as materials engineers, we want to have an overview of the microstructure across a large area but also we want to ‘zoom-in’ to features to find out more. This is kind of like how you might use Google Maps to understand the relationship between holiday-destination and the local countryside.

Meteorite sample just after scanning, showing the map as collected and if you look carefully you can see each of the individual tiles in the micrograph (sample prepared by Graeme Francolini, microscopy by Ben Britton).

Our Phenom is equipped with the MAPS platform and this enables layer of micrographs from multiple different instruments, as well as large area online mapping and good quality stitching. In this example, I’ve optimized the imaging of a single tile with a resolution of 1920 x 1200 pixels with a 130 nm pixel size and the contrast was set to reveal different phases and also grain-contrast within the iron-nickel matrix.

A single tile as captured from the sample — the horizontal field width for this tile is 0.26 mm with a pixel size of 135 nm (sample prepared by Graeme Francolini, microscopy by Ben Britton).

Once my tile was optimized, I drew a grid around my sample in the NavCam optical micrograph. The MAPS software does the rest, and it breaks down the area I want to study into a subset of a 32 x 22 tiled region, with 10% overlap per tile. In total, 656 tiles were captured in under 3 hours of scanning with no further intervention from me.

Overview micrograph of the Nantan meteorite, capturing using backscatter electron imaging (sample prepared by Graeme Francolini, microscopy by Ben Britton). The horizontal field is approximatly 7 mm wide.

Now, you might think that’s the end of the story — but if you got this far, you are in for a treat. You can view this micrograph, and zoom in, by heading to the public version of the micrograph here.

If you are interested in materials characterization in the Department of Materials Engineering at UBC, please see our website: https://emlab.mtrl.ubc.ca/equipment/

If you are interested in Undergraduate Study with us, see: https://mtrl.ubc.ca/undergraduate/

If you are interested in Graduate Study with us, see: https://mtrl.ubc.ca/graduate/

If you are interested in the technical specifications of the instrument, see the data sheet provided by Thermo Fisher Scientific.

If you are interested in working with us, please get in touch with me: https://mtrl.ubc.ca/ben-britton/

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