Synthesis of 2D-NiPtTe₂ by topotactical surface reaction of PtTe₂ with Ni

Topotaxy of 2D materials by reacting a van der Waals-material with a transition metal is a potential approach for accessing compositional 2D variants. Here, the synthesis of a 2D-NiPtTe₂ alloy is demonstrated by incorporating Ni into PtTe₂. The Pt-telluride system exhibits two 2D phases, a di-telluride (PtTe₂) and mono-telluride (Pt₂Te₂). By reacting PtTe₂ with Ni the system transforms into a NiPtTe₂, i.e. the monotelluride phase with two transition metals per unit cell in an ordered alloy structure. The samples are grown by molecular beam epitaxy and characterized by low energy electron diffraction, X-ray photoemission spectroscopy, and scanning tunneling microscopy. Studies are performed on both multilayer PtTe₂ films as well as monolayer samples. On multilayers the transformation is more complex and different phases can coexist. In monolayers a phase separation into pure PtTe₂ and the Ni-modified NiPtTe₂ phase is observed, indicating that both are low energy configurations. The formation energy of various structures with different Ni-composition is also evaluated by density functional theory calculations confirming that the mixed NiPtTe₂ phase is favored over other configurations, particularly the intercalation of Ni in between PtTe₂ layers is shown to be less favorable.