In support of the goals of The Rensselaer Plan, the Institute made a commitment to acquire an environmental scanning electron microscope (ESEM) in 2013. Through the gift of Adjunct Professor George Pearsall ’55, the capabilities of the microscope have been further expanded to include ion imaging capabilities, and the instrument is now installed and operational in the Materials Research Center.
Robert Hull
According to Professor Robert Hull, head of the Department of Materials Science and Engineering, it will support research throughout the university, enabling ultra-high resolution imaging across a broad spectrum of materials, in both the physical and biological sciences.
When first commercialized in the 1960s, electron scanning microscopes could only image conductive samples within a vacuum. An environmental electron scanning microscope makes it possible for vapors at relatively high pressure to be maintained around the sample during imaging. In particular conditions, it can be maintained where water remains in its liquid state. This represents a huge advance, allowing for remarkable investigation in the biological sciences, as samples can remain hydrated during imaging.
The state-of-the-art microscope can image samples—wet or dry—to a resolution of about one nanometer. The sample environment can vary widely as well, from life science samples in situ, to materials and nano-structures at different pressures, temperatures, and gaseous compositions. The ESEM can image samples at pressures as high as 50 Torr and is compatible with such dynamic processes as tension, compression, heating, degradation, freezing, melting, hydration, and dehydration.
An environmental electron scanning microscope makes it possible for vapors at relatively high pressure to be maintained around the sample during imaging. This represents a huge advance, allowing for remarkable investigation in the biological sciences, as samples can remain hydrated during imaging.”
The electron imaging uses voltages as high as 30,000 volts to accelerate electrons in a focused beam down a column, through a series of lenses, where they collide with the sample. The signals generated on the surface of the specimen correlate to its morphology or texture, chemical composition, and crystalline structure. While the electrons don’t modify the sample substantially, the ion beam does, eroding the surface continuously, imaging as it erodes, and supplementing the electron’s two-dimensional image capabilities with a tomographic, three-dimensional image. This dual electron and ion, surface and depth imaging, will allow for fundamental understanding of a wide range of materials.
In situ imaging shows dissolution of NaC1 by the FEI Versa 3-D environmental scanning electron microscope.
Pearsall, an adjunct professor of materials science and engineering, remembers that it was in a Rensselaer metallurgy class that he first looked through a microscope. Torn at the time between a career in art and science, he continued with engineering, getting his doctorate and teaching at MIT, and Duke University, where he is professor emeritus, with a research specialty in materials failure analysis. “I’m fascinated with what advanced optics can do to interpret what we can’t see with our eyes,” he said.
Open training sessions on the electron and ion environmental scanning microscope began a few weeks ago. “We are grateful for the coordination and support of Claude Rounds, vice president for administration, for his support in the installation, and to George Pearsall for his generous enhancement of the equipment,” noted Professor Hull. And in reference to this final stage of a long process, he said, “I am personally thrilled and delighted by this tremendous example of the Institute’s support of faculty and student research endeavors.”
