Surface evolution of thermoelectric material KCu₄Se₃ explored by scanning tunneling microscopy

Novel two-dimensional thermoelectric materials have attracted significant attention in the field of thermoelectric due to their low lattice thermal conductivity. A comprehensive understanding of their microscopic structures is crucial for driving further the optimization of materials properties and developing novel functional materials. Here, by using in situ scanning tunneling microscopy, we report the atomic layer evolution and surface reconstruction on the cleaved thermoelectric material KCu₄Se₃ for the first time. We clearly revealed each atomic layer, including the naturally cleaved K atomic layer, the intermediate Se²⁻ atomic layer, and the Se⁻ atomic layer that emerges in the thermodynamic-stable state. Departing from the majority of studies that predominantly concentrate on macroscopic measurements of the charge transport, our results reveal the coexistence of potassium disorder and complex reconstructed patterns of selenium, which potentially influences charge carrier and lattice dynamics. These results provide direct insight into the surface microstructures and evolution of KCu₄Se₃, and shed useful light on designing functional materials with superior performance.