Scanning Electron Microscope Images: Coming to a Screen Near You

May 4, 2020

Pandemic doesn’t prevent Duke’s Materials Science of Science Fiction class from seeing images of the nano world

By Elizabeth Witherspoon

Redbud pollen under scanning electron microscope at 2500x magnification

Redbud pollen at 2500x magnification under scanning electron microscope. The micron (µm) scale at 30 indicates the portion of the image about one-third the width of a human hair.

Having dinner delivered is one thing these days; home delivery of electron microscope images is quite another. But that’s just what Holly Leddy, an electron microscope specialist at Duke’s Shared Materials Instrumentation Facility (SMIF), did via Zoom for students in Christine Payne’s undergraduate Materials Science of Science Fiction class.

With access to SMIF restricted following Duke University’s switch to online learning after spring break, Leddy delivered a live demonstration and stunning images of materials the students chose using a portable scanning electron microscope (SEM) set up in her guest bedroom. This ensured students did not miss out on the learning experience Payne had planned for the nanotechnology module.

Earlier in the semester Payne, an associate professor of mechanical engineering and materials science, arranged for her students to tour SMIF to learn about the instruments available for studying materials, including the room-size scanning electron microscope. Ordinarily, the students would then choose materials to bring back to the SMIF for scanning, obtain their elemental analyses and write lab reports. However, this has been no ordinary semester.

Azalea pollen at 400x magnificationFortunately, Leddy’s work also includes outreach to K-12 students through the Research Triangle Nanotechnology Network—a collaboration between Duke, North Carolina State University and the University of North Carolina at Chapel Hill. For that work, prior to the pandemic, she took the portable SEM to locations in the community to demonstrate its capabilities, teach and foster interest in science. To keep up this work as we all locked down, she moved the smaller portable SEM to her home.

For the stay-at-home version of Payne’s assignment, Leddy collected samples by student request of materials readily available around her home or yard—various kinds of pollens, diatoms, plus a bonus housefly she found. Diatoms are single-cell microalgae abundant in water and soil that come in a variety of intricate structures, which makes them fascinating and popular specimens for study under the microscope.

Via Zoom she demonstrated the process of loading the samples into the vacuum chamber. First, they had to be prepared with a sputter coating of an ultrathin layer of gold to make them conductive for imaging via the beam of accelerated electrons. Then she showed the controls for driving the electron beam around the small platform of samples, slowing the scanning speed to get higher resolution, how to increase and decrease levels of magnification and the scale bar indicating the size of the specimen in microns.  

Students, scattered across the country, were captivated by the amazing clarity of the images and able to ask questions as if they were all together in person.

Students, scattered across the country, were captivated by the amazing clarity of the images and able to ask questions as if they were all together in person.

As she increased magnification from 600x to 1200x on a bundle of redbud pollen, Leddy described them as looking like little deflated footballs.

“When we think about pollen allergies, is it that little deflated football that gets us, or that whole ensemble?” Payne asked Leddy.

“It is the deflated football,” explained Leddy, increasing magnification to 2500x and revealing tiny indentations on their surfaces. Next, she switched to the much larger pine pollen that annually blankets the area in yellow dust for weeks. After that, she zeroed in dandelion and azalea pollens and the foot of housefly.

“I’ve seen what seems like a million SEM images, but this was way more interesting,” Payne said at the end of the demonstration.

This class is far from simply looking at cool images under the electron microscope, however. After Leddy left the Zoom meeting, the class turned to assigned problem sets. And, in lieu of the lab report, because the portable SEM doesn’t have the feature to do elemental analysis, Payne required the students to conduct a literature review and write a proposal as if to a funding agency justifying the value of imaging a particular material using a scanning electron microscope.