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Tech Intelligence S/TEM Platforms
AL AL by Mike May
To understand the properties of a material, scientists often examine it with an electron microscope, sometimes using diff erent levels of magnifi ca- tion. It can also be useful to combine similar imaging techniques that can distinguish details of the sample for comparison, and that’s what scien- tists get from S/TEM—a platform that allows materials to be imaged with transmission electron microscopy (TEM) and scanning TEM. “TEM blasts high-energy electrons through the sample to get information about the internal structure of the material,” says Thomas Isabell, director of the TEM product division at JEOL USA (Peabody, Mass.). “STEM focuses electrons to a fi ne point and scans them across the sample.” This combination of imaging modalities provides new opportunities. “You usually just have TEM or STEM,” says Brian Van Devener, surface scientist at the University of Utah’s Surface Analysis and Nano-Scale Imaging Lab in Salt Lake City, “but S/TEM can be operated in either mode.”
The option to use TEM or STEM off ers greater fl exibility. “Having the capability to do both in one instrument provides a robust tool,” says Van Devener. “You don’t always know which mode will give you the informa- tion that you need the most.” So a scientist can image a sample in TEM or STEM, all without moving the sample between diff erent instruments.
“S/TEM can provide critical information—images, chemical spectra, mechanical, electrical, magnetic, structural—about a very wide variety of materials from the micron scale right down to the sub-atomic scale,” says David Foord, director of marketing at FEI (Hillsboro, Ore.). “The range of applications is pretty diverse,” Van Devener says. Chemists, engineers, material scientists and biologists benefi t from the versatility of this dual- mode technology.
Seeing the never seen This combined platform helps scientists see and understand things that
they could not without it. At the University of Utah, Zak Fang, professor of metallurgical engineering, used S/TEM to explore hydrogen storage in magnesium hydride, says Van Devener. With this material, a transition- metal catalyst drives the cycle from hydrogenated to dehydrogenated,
AMERICAN LABORATORY 38
Three-dimensional EDS tomography of silver-platinum core-shell nanoparticles. The silver cores are shown in the false color of red, cov- ered by green-colored silver shells, only a few nanometers in thickness. This tomography makes visible the pores that partially expose the cores. (Sample courtesy of Professors Yi Ding and Jun Luo, Center for Electron Microscopy, Institute for New Energy Materials and Low-Carbon Technologies, School of Materials Science and Engineering, Tianjin University of Technology, China.) (Image courtesy of FEI.)
MAY 2016
which allows the storage and release of energy. Fang wanted to see if the transition metals lie on the surface or inside the material. Van Devener combined energy-dispersive spectrometry (EDS) with S/TEM, but he still needed more. So he collected imaging data, tilted the sample and collected data again and continued this process. He then combined the data tomographically to get a 3-D image. “We showed that after succes- sive hydrogenation/dehydrogenation cycles, the transition metals move toward the surface,” Van Devener explains. “This verifi ed some theoretical
by author
Combining imaging capabilities for high-resolution spatial and chemical characteristics
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