LAUSR

Two-dimensional (2D) PtSe2 has potential applications in near-infrared optoelectronics because its band gap can be tuned by varying the layer thickness. There are several different platinum-selenide phases with different stoichiometries that result from high-temperature processing. In this report, we use in situ scanning/transmission electron microscopy (STEM) to investigate high-temperature phase transitions in 2D PtSe2 and observe interfacial reactions as well as the Kirkendall effect. The 2D nature of PtSe2 plays a key role in the unique one-dimensional interfaces that result during the formation of Se-poor phases (PtSe and PtSe1-x) at the edges of the PtSe2 crystals. The activation energy extracted for this formation suggests that the process is mediated by Se vacancies, as evidenced by the large strain variations in the material made via 4D STEM measurements. The observation of the Kirkendall effect in a 2D material suggests routes to engineer 1D edge chemistry for contact engineering in device applications.