Surface reaction induced transformation of 2D-Pt-ditelluride to a 2D-monotelluride*

The group 10 transition metal tellurides may exist as 2D materials with different composition. In addition to the dichalcogenide, a less stable monochalcogenide phase may form under chalcogen-deficient conditions. The synthesis of such materials, specifically in the monolayer limit, remains a challenge, however. Here we show that monolayer PtTe2 can be transformed to PtTe by reacting it with vapor-deposited Pt atoms. This approach can also be expanded by reacting PtTe₂ with another group 10 element, i.e. Ni, to form a PtNiTe 2D-alloy. This study is the first demonstration of a compositional transformation of a monolayer 2D-TMD by surface reaction into a new 2D alloy phase.  Moreover, the ditellurides and monotellurides are closely lattice-matched, which enables the formation of a defect-free between the two phases. Since the monolayer PtTe2 is a semiconductor (~0.5 eV band gap) and the monotellurides are metals, a metal-semiconductor heterojunction is formed at the phase contact. Thus, the phase transformation of PtTe2 by vapor reaction with Ni or Pt enables to form defect-free side contacts to a semiconducting 2D material.