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Such close examination allows scientists to design and make new materi- als and then analyze the structure to see if it came out as expected and if the material behaves as desired. If not, scientists can use the information from S/TEM to figure out what went wrong and how to fix it.
A team from Oak Ridge National Laboratory (Oak Ridge, Tenn.) and the University of California San Diego used STEM to study lithium-ion batter- ies.1
The authors noted: “Lithium-ion batteries are a leading candidate for
electric vehicle and smart grid applications. However, further optimiza- tions of the energy/power density, coulombic efficiency and cycle life are still needed, and this requires a thorough understanding of the dynamic evolution of each component and their synergistic behaviors during bat- tery operation.” By exploring the structure and chemistry at the atomic level with this technology, they concluded: “[Many] of the previously formidable tasks, such as visualizing the distribution of light elements, unraveling the interface structure and chemistry at the atomic scale, prob- ing the [solid-electrolyte interface] layers and so on, are now achievable.”
S/TEM-HAADF (high-angle annular darkfield) image of a palladium– rhodium bi-metallic nanoparticle during the early stages of its formation. The five distinct regions are indicative of its fivefold rotational symmetry, colorized for easy viewing. (Image courtesy of Moon Kim’s group [Ning Lu, Jinguo Wang], University of Texas at Dallas. Sample provided by Younan Xia, Georgia Tech, Atlanta.)
predictions from Fang’s group and complemented some other work that showed that these metals move to the surface.”
By adding capabilities such as EDS, scientists can get even more from this platform. “Spectroscopic capabilities like EDS show you the elemental distribution in materials,” Van Devener explains. “Crystallographic tech- niques can also be used to get direct crystallography at small scales, and other accessories are available, too.” So the breadth of an S/TEM can be expanded with add-on technology, and the range depends on the instru- ment being used.
Adding new options As this technology advances, more features enhance the images. Using
a smaller probe focuses electrons on a finer point. Combining that with an improved detector improves the resolution. Isabell says that such advances make a platform that is “more efficient at exploring a material’s chemistry.”
The high-resolution of S/TEM lets scientists explore materials in new ways. As Foord points out, “S/TEM reveals sub-nanometer material defects or distribution of strengthening or weakening mechanisms, such as pre- cipitates, grain boundaries or dislocations, which are atomic level–local rearrangements of atoms that can be either advantageous or detrimental to a material’s properties depending on the material or use case.”
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S/TEM technology promises even more advanced applications. At FEI, says Foord, new technology allows “more sensitive experiments over longer time periods, such as large-area chemical mapping and 3-D imaging and chemical tomography.” He adds that advances in EDS X-ray detection provide “fast chemical mapping to increase throughput for our industrial customers that may have to control industrial processes by characterizing manufactured structures at the near atomic level.”
Getting up to speed It takes some operator knowledge to use an S/TEM, says Van Devener, especially to switch between modes. “This is something that you’d learn by a course instead of a quick standard operating procedure,” he says. “Once trained, it’s not difficult to switch between modes, and it usually takes only a couple [of] minutes.” The University of Utah runs a seven-week course on using S/TEM, and other universities offer similar training.
Sample preparation requires training, too. “When looking at the atomic level,” says Isabell, “the sample has to be prepared very well. There are a lot of techniques to do that.” Some institutions, including Stanford University, offer special training in sample preparation for S/TEM.
Getting the preparation right and then combining it with S/TEM offers new opportunities for scientists interested in the characteristics of a mate- rial. As Van Devener concludes, “It’s a powerhouse of an instrument.”
Reference 1. Qian, D.; Ma, C. et al. Advanced analytical electron microscopy for lithium-ion batteries. NPG Asia Materials 2015, 7, e193.
Mike May is a freelance writer and editor living in Ohio. He can be reached at
mikemay1959@gmail.com.
MAY 2016
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