The platinum−tellurium phase diagram exhibits various (meta)stable van der Waals (vdW) materials that can be constructed by stacking PtTe 2 and Pt 2 Te 2 layers. Monophase PtTe 2 , being the thermodynamically most stable compound, can readily be grown as thin films. Obtaining the other phases (Pt 2 Te 3 , Pt 3 Te 4 , Pt 2 Te 2 ), especially in their ultimate thin form, is significantly more challenging. We show that PtTe 2 thin films can be transformed by vacuum annealing-induced Te-loss into Pt 3 Te 4 -and Pt 2 Te 2 -bilayers. These transformations are characterized by scanning tunneling microscopy and X-ray and angle resolved photoemission spectroscopy. Once Pt 3 Te 4 is formed, it is thermally stable up to 350°C. To transform Pt 3 Te 4 into Pt 2 Te 2 , a higher annealing temperature of 400°C is required. The experiments combined with density functional theory calculations provide insights into these transformation mechanisms and show that a combination of the thermodynamic preference of Pt 3 Te 4 over a phase segregation into PtTe 2 and Pt 2 Te 2 and an increase in the Te-vacancy formation energy for Pt 3 Te 4 compared to the starting PtTe 2 material is critical to stabilize the Pt 3 Te 4 bilayer. To desorb more tellurium from Pt 3 Te 4 and transform the material into Pt 2 Te 2 , a higher Te-vacancy formation energy has to be overcome by raising the temperature. Interestingly, bilayer Pt 2 Te 2 can be retellurized by exposure to Te-vapor. This causes the selective transformation of the topmost Pt 2 Te 2 layer into two layers of PtTe 2 , and consequently the synthesis of e Pt 2 Te 3 . Thus, all known Pt-telluride vdW compounds can be obtained in their ultrathin form by carefully controlling the stoichiometry of the material.

Monolayer PtTe2 is a narrow gap semiconductor while Pt2Te2 is a metal. Here we show that the former can be transformed into the latter by reaction with vapor-deposited Pt atoms. The transformation occurs by nucleating the Pt2Te2 phase within PtTe2 islands, so that a metal–semiconductor junction is formed. A flat band structure is found with the Fermi level of the metal aligning with that of the intrinsically p-doped PtTe2. This is achieved by an interface dipole that accommodates the ∼0.2 eV shift in the work functions of the two materials. First-principles calculations indicate that the origin of the interface dipole is the atomic scale charge redistributions at the heterojunction. The demonstrated compositional phase transformation of a 2D semiconductor into a 2D metal is a promising approach for making in-plane metal contacts that are required for efficient charge injection and is of particular interest for semiconductors with large spin–orbit coupling, like PtTe2.

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The interlayer interaction in Pt-dichalcogenides strongly affects their electronic structures. The modulations of the interlayer atom-coordination in vertical heterostructures based on these materials are expected to laterally modify these interlayer interactions and thus provide an opportunity to texture the electronic structure. To determine the effects of local variation of the interlayer atom coordination on the electronic structure of PtSe 2 , van der Waals heterostructures of PtSe 2 and PtTe 2 have been synthesized by molecular beam epitaxy. The heterostructure forms a coincidence lattice with 13 unit cells of PtSe 2 matching 12 unit cells of PtTe 2 , forming a moirésuperstructure. The interaction with PtTe 2 reduces the band gap of PtSe 2 monolayers from 1.8 eV to 0.5 eV. While the band gap is uniform across the moiréunit cell, scanning tunneling spectroscopy and dI/dV mapping identify gap states that are localized within certain regions of the moiréunit cell. Deep states associated with chalcogen p z -orbitals at binding energies of ∼ −2 eV also exhibit lateral variation within the moiréunit cell, indicative of varying interlayer chalcogen interactions. Density functional theory calculations indicate that local variations in atom coordination in the moiréunit cell cause variations in the charge transfer from PtTe 2 to PtSe 2 , thus affecting the value of the interface dipole. Experimentally this is confirmed by measuring the local work function by field emission resonance spectroscopy, which reveals a large work function modulation of ∼0.5 eV within the moiréstructure. These results show that the local coordination variation of the chalcogen atoms in the PtSe 2 /PtTe 2 van der Waals heterostructure induces a nanoscale electronic structure texture in PtSe 2 .