Controlling Stoichiometry in Ultrathin van der Waals Films: PtTe₂, Pt₂Te₃, Pt₃Te₄, and Pt₂Te₂

Abstract

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.

A van der Waals Heterostructure with an Electronically Textured Moiré Pattern: PtSe2/PtTe2

“…At higher growth temperatures an intermixing of the PtSe 2 with the PtTe 2 substrate is observed. The relatively low thermal stability of these phases has also been reported for pure PtTe 2 , which results in easy loss of Te and transformation into different compositional phases upon vacuum annealing …”

“…The relatively low thermal stability of these phases has also been reported for pure PtTe 2 , which results in easy loss of Te and transformation into different compositional phases upon vacuum annealing. 31 Interface States. PtSe 2 exhibits strong layer-dependent electronic properties.…”

Highly Selective Synthesis of Monoclinic-Phased Platinum–Tellurium Nanotrepang for Direct Formic Acid Oxidation Catalysis

“…To obtain insights into the amazing activity of the different phases of m -PtTe NT, r -Pt 2 Te 3 NT, and t -PtTe 2 NT, the DFT calculations were employed to study the mechanism of the FAOR on different catalysts and their excellent CO tolerance . Owing to their structural characteristics, the potential energy profiles of possible formic acid oxidation pathways and the optimized structures of the intermediates (HCOO*, COOH*, and CO*) for m -PtTe NT (001), r -Pt 2 Te 3 NT (001), and t -PtTe 2 NT (001) have been shown in Figure a–c, respectively.…”

“…Obviously, the m-PtTe NT/C can not only largely impede the formation of the CO intermediate originating from the dehydration pathway, improving the tendency of DRP, but also effectively weaken the adsorption of the CO intermediate on the surface of Pt sites, accelerating the CO* oxidation and promoting the dehydrogenation of the formic acid molecule. Hence, m-PtTe NT/C can be used as an outstanding FAOR catalyst, even under the operating DFAFC device condition.To obtain insights into the amazing activity of the different phases of m-PtTe NT, r-Pt 2 Te 3 NT, and t-PtTe 2 NT, the DFT calculations were employed to study the mechanism of the FAOR on different catalysts and their excellent CO tolerance 54. Owing to their structural characteristics, the potential energy profiles of possible formic acid oxidation pathways and the optimized structures of the intermediates (HCOO*, COOH*, and CO*) for m-PtTe NT (001), r-Pt 2 Te 3 NT (001), and t-PtTe 2 NT (001) have been shown in Figure5a−c, respectively.…”

Unraveling the mechanism of vanadium self-intercalation in 1T-VSe2: atomic-scale evidence for phase transition and superstructure model for intercalation compound

“…However, this route will become readily achievable in layered TMDCs materials in which defects particularly point defects like chalcogen vacancies and transition metal interstitials are frequently observed due to their relatively lower formation energies and thus are easily triggered by treatments such as thermal/laser annealing and energetic particle irradiation [25,26]. So far, knowledge about the self-intercalation in TMDC materials, such as the occupation site for intercalant and the structure and thus stoichiometry of self-intercalated compounds have been successfully obtained using different tools such as low-energy electron diffraction [27,28], scanning tunneling microscopy [28][29][30][31], transmission electron microscopy (TEM) [31][32][33],…”