Thermal- and air- stability of the compositional variants of van der Waals Pt-Telluride thin films probed by high resolution photoemission spectroscopy

Abstract

The Pt-Te compositional phase diagram consists of at least three different compositional line phases (PtTe2, Pt3Te4, and Pt2Te2) that can be described as layered van der Waals materials. This presents challenges in controlling the composition of ultrathin Pt-telluride 2D materials by physical vapor deposition methods. Here we show by temperature programmed synchrotron photoemission spectroscopy that the different phases have varying thermal stability in vacuum. This enables the synthesis of these materials by preparation of PtTe2 films at low growth temperatures and subsequent vacuum annealing to ∼ 350 °C for Pt3Te4, or ∼ 400 °C for Pt2Te2. Such prepared phases are characterized by high resolution core level spectroscopy to provide reference spectra for these materials. Moreover, the chemical stability of these materials was tested by exposure to oxygen and air. Even after prolonged air exposure only the surface Te layer was modified by oxygen chemical bonds that caused a 3-eV shift to higher binding energy of the Te-3d core levels. However, these oxygen species could be desorbed by vacuum annealing at 280 °C and pristine Pt-telluride samples can be re-established. This shows the excellent chemical stability of these materials, important for practical applications.