Combined microscopy and spectroscopy method achieves atomic resolution in directional bond spectral analyses
Combined microscopy and spectroscopy method achieves atomic resolution in directional bond spectral analyses lead image
When it comes to understanding the properties of materials, measuring the anisotropy of chemical bonding at ever smaller scales is becoming increasingly important. Techniques have drawn on transmission electron microscopy (TEM) to investigate the momentum-resolved spectra needed to understand this anisotropy. TEM methods, however, often yield spectral analyses with low spatial resolution. Yamaguchi et al. demonstrate a new method to study the anisotropy of chemical bonds with atom-level resolution.
The authors report a technique to detect the anisotropy of chemical bonding using a combination of scanning electron microscopy and electron energy-loss spectroscopy (STEM-EELS). They use the method to achieve atomic resolution in measurements of specific atoms within samples of strontium titanate, a well-understood material, that were perpendicular to the electron beam. Previous attempts to obtain momentum-resolved spectra using STEM-EELS have been hampered by the large convergence angle of the incident electron probe.
By spatially selecting specific oxygen atomic columns and using an off-axis collection aperture to measure the momentum-selected spectra, the group was able to clearly detect the directionality of sigma bonding between oxygen and titanium atoms. They observed different energy-loss near-edge structures depending on the directionality of the sigma bond between the oxygen and titanium atoms.
The approach proved to yield a higher spatial resolution than other techniques examining orientation dependence of near-edge fine structures, like angular-resolved EELS and X-ray linear dichroism.
The group stated that their method might pave the way for exploring how such high-resolution directional measurements can be applied to anisotropic crystals and interface regions. In the near future, they hope to produce two-dimensional maps showing the directionality of chemical bonding of materials.
Source: “Probing directionality of local electronic structure by momentum-selected STEM-EELS,” by A. Yamaguchi, M. Haruta, T. Nemoto, and H. Kurata, Applied Physics Letters (2018). The article can be accessed at https://doi.org/10.1063/1.5040312 .
