I do a lot of research for my PhD, and some of that research is painstaking and tedious. But some aspects of research are just downright fun! Today I’m going to talk about one of my favorite parts of my research: taking very high-resolution and close-up images of my fossil plankton, foraminifera!
Because the fossils I work with are so small (about the size of a grain of sand), we need a very unique system to take high-quality and close-up images of them. To do this, people who take images of microfossils use scanning electron microscopes, or SEM for short. An SEM uses electrons reflected off the surface of the fossils to create an image. To do this, the interior of the SEM is a vacuum, and the fossils need to be coated with a conductive material. At our university, we use platinum to coat our fossils.
The first thing I do before I can take images of my fossils is to pick out specimens that I want to photograph. These are then placed onto a small, round piece of double-sided sticky tape. The fossils are so tiny, I can fit tens onto one small piece. This sticky piece is then placed onto a glass slide. We call the fossils, tape, and glass a ‘stub’. Once all the fossils are in place, I then put the stub into a coating machine. This machine coats all the fossils with a very thin layer of platinum while in the presence of xenon gas. The entire process is very quick (about 30 minutes at most). Once the specimens are coated, they’re ready for imaging in the SEM!
The SEM itself is a rather large contraption, but incredibly amazing! The entire machine is operated from a computer that sits on a desk beside the SEM, so everything is pretty self-contained and right there. The first thing I do after coating is to mount the stub on the stage within the SEM. This is simple: it involves taping the stub to a metal piece, which in turn fits snugly onto the stage element of the SEM.
Once in place, I then slide the door to the SEM shut and vent the machine. Venting means I push a button on the computer, which tells the machine to begin creating a vacuum inside its chamber. This process takes about ten minutes or so.
After the chamber inside the SEM is under vacuum, I can then begin the process of photographing my fossils! Everything from this point forward is operated using software on a desktop computer that talks to the SEM. Just like a camera, the images have to be focused before taking the actual picture. This can be either very easy, or very tedious. There are several factors to determining how the image looks on the screen: are the levels balanced, is there charging on the fossils that’s causing a disturbance, the distance of the stub fro’m the camera, etc. There are controls on the computer program that allow the user to make changes and adjustments as necessary.
I find that the best way to focus the image is to zoom in very close to the fossil I want to photography. In this case, ‘very close’ means zooming in more than 2,000 times or more, so I’m really getting up close and personal with the fossils! I use a technique where I select a small window of the entire image, and use the tools in the program to tweak and focus the image in that smaller box. This is a faster way to focus, and when I’m happy with the results, I can apply the changes made to the small area to the entire image.
Once the settings are adjusted and correct for my fossils, I can then get through taking images pretty quickly! Each image includes a scale bar to indicate the size of the fossil and the magnification, which is helpful and necessary to include with each fossil picture. For this project, I was very interested in taking close-up images of the surface of my specimens, and also taking a side-view of the shells (quite unfortunately, this means I had to break open some foraminifera shells once placed on the stub and before coating).
Once all the images are taken, I can then download them onto a thumb drive and work with them on my own computer. This involves using other photography programs such as Adobe Photoshop to crop the fossil images and place them onto a black background.
Although the process of taking SEM images of fossils is incredibly fun, it’s also vastly important for research. I will include images of all my fossils in a publication. This way, other researchers will know how I tell one species apart from another, and the different characteristics of each plankton species. Ideally, I’ll have pages and pages of fossil images, called plates, included with my publications!