Electron Microscopy and Spectroscopy of Low-Dimensional Materials at the Single Atom Level
Written by Aditi Risbud
On Thursday afternoon, Kazutomo Suenaga of the National Institute of Advanced Industrial Science and Technology in Japan gave the last Symposium X presentation of the week. His talk focused on single-atom spectroscopy and single-molecule imaging of low-dimensional (1D, 2D) materials.
Suenaga uses electron microscopy and spectroscopy to characterize materials atom by atom. What began as his “science dream from a long time ago” has now become a set of analytical tools to understand the physical and chemical properties of single atoms.
In particular, Suenaga and his team use electron energy-loss spectroscopy (EELS) to discriminate between individual atoms in low-dimensional materials, whether they are different atoms, or identical atoms in excited states or with different spin properties.
Unlike in 3D or bulk materials, defects have significant impact on the properties of low-dimensional materials. Without accurate characterization techniques, the behavior of devices based on low-dimensional materials such as graphene cannot be understood or controlled.
During his talk, Suenaga outlined several examples in various carbon nanostructures using EELS to examine structural imperfections such as defects, impurities, edges, or boundaries. EELS provides an “atomic size probe” to image a material and if the sample is thin enough, obtain some optical absorption information as well.
There are challenges to single-atom spectroscopy, including weak inelastic scattering from electrons, localized signals, and specimen damage. To overcome these difficulties, Suenaga has designed a high-resolution, low-voltage electron microscope that produces high-quality images without destroying a sample. This microscope can resolve a carbon–carbon bond at 30 keV and generate spectroscopic data from individual molecules or atoms.
“Low-voltage microscopes are very good for low-dimensional materials characterization because we can identify each element, even lighter elements such as lithium,” Suenaga concluded.
Symposium X lectures are aimed at a broad audience to provide meeting attendees with an overview of leading-edge topics.