Distinguishing Elements at the Sub-Nanometer Scale on the Surface of a High Entropy Alloy.

Materials in crystalline form possess translational symmetry (TS) when the unit cell is repeated in real space with long and short range orders. The periodic potential in the crystal regulates the electron wave function and results in unique band structures, which further define the physical properties of the materials. On the other hand, amorphous materials lack long range order TS due to the randomization of distances and arrangements between atoms, causing the electron wave function to lack a well-defined momentum. High entropy materials provide another way to break the TS by randomizing the potential strength at periodic atomic sites and provide unique physical and chemical properties. The configuration of the elemental distribution has a great impact on catalytic behavior and magnetic interactions in high entropy materials. Thus, it is critical to distinguish elements at the sub-nanometer scale to uncover the detailed correlations between the configuration of the elemental distribution and the material's properties. Here, we demonstrate the use of synchrotron X-ray scanning tunneling microscopy (SX-STM) with sub-nm scale resolution in identifying elements on the surface of a HEA. By examining the elemental fingerprints of X-ray absorption spectroscopy (XAS) with a STM tip to enhance the spatial resolution, the elemental distribution on the surface of a HEA at a sub-nm scale was extracted. The results shown here open a pathway towards a quantitative understanding of high entropy materials and their correlated material properties. This article is protected by copyright. All rights reserved.