Resolving Elements at Atomic Scale in Metal Alloys with Synchrotron X-ray Scanning Tunneling Microscopy*

Scanning tunneling microscopy (STM) is a powerful tool in characterizing novel materials with topographic and electronic information at the atomic scale. However, it typically cannot distinguish between different types of elements. Using synchrotron X-ray scanning tunneling microscopy (SXSTM), we collect photo-ejected electrons due to the X-ray absorption at elemental adsorption edges with the STM tip, which provides elemental information at the nm scale. It has been demonstrated that the elemental resolution in SXSTM can be at the 2 nm scale. In this work, by using an Fe₂Cr₉₈ crystalline alloy, we demonstrate that the elemental resolution can reach the 1 nm scale. With this spatial resolution, nm scale X-ray absorption spectrum (XAS) can be achieved. This result indicates that SXSTM could be a promising technique to reveal the elemental distributions at the surfaces of multi-principal element alloys (MPEAs) and other high entropy materials, such as high entropy perovskite oxides and high entropy TMDs, at the atomic scale.