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Research Snapshot: New microscopy technique unveils feature that can shape applications of a class of quantum materials

Posted by on Friday, April 23, 2021 in News.

A team of researchers led by Oak Ridge National Laboratory microscopist Miaofang Chi and Vanderbilt theoretical physicist Sokrates Pantelides has used a new Scanning Transmission Electron Microscope technique to image the electron distribution in ionic compounds known as electrides— especially the electrons that float loosely within pockets and appear separate from the atomic network.

Miaofang Chi; Sokrates Pantelides (Vanderbilt University)

The new technique, Differential Phase Contrast in STEM, measures and maps electric fields and charge distributions inside a material. The study is the first time that DPC has been used in this way. By analyzing charge images of dozens of such channels, the team found that only some contain the negative charge predicted by theoretical calculations, while others have significantly less negative or even a small concentration of positive charge. Pantelides’ decades of experience with hydrogen led to the suggestion that traces of hydrogen, which are essentially impossible to eliminate, are responsible for the observed inhomogeneity, and subsequent detailed calculations confirmed the hypothesis. Neutron scattering experiments provided evidence in support of the hydrogen scenario.

Charge density map of a large area of the material showing an inhomogeneous profile across the center of the interstitial columns. Zoomed-in views of columns yield quantitative measures of the unexpected inhomogeneity across the entire dataset. Line profiles (red) across the column centers compared with the theoretically predicted charge (black, labeled DFT) show that significant deviations exist in some columns. A theoretical explanation that the deviation is caused by the presence of hydrogen traces was subsequently corroborated by neutron scattering experiments. (Zheng, et al.)

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