Exploring the growth and oxidation of 2D-TaS2 on Cu(111)

Abstract

In this work, the growth and stability towards O2 exposure of two dimensional (2D) TaS2 on a Cu(111) substrate is investigated. Large area (~1cm2) crystalline 2D-TaS2 films with a metallic character are prepared on a single crystal Cu(111) substrate via a multistep approach based on physical vapor deposition. Analytical techniques such as Auger electron spectroscopy, low energy electron diffraction, and photoemission spectroscopy are used to characterize the composition, crystallinity, and electronic structure of the surface. At coverages below one monolayer equivalent (ML), misoriented TaS2 domains are formed, which are rotated up to ±13^o relative to the Cu(111) crystallographic directions. The TaS2 domains misorientation decreases as the film thickness approaches 1 ML, at which the crystallographic directions of TaS2 and Cu(111) are aligned. The TaS2 film is found to grow epitaxially on Cu(111). As revealed by low energy electron diffraction in conjunction with an atomic model simulation, the (3 × 3) unit cells of TaS2 match the (4 × 4) supercell of Cu(111). Furthermore, the exposure of TaS2 to O2, does not lead to the formation of a robust tantalum oxide film, only minor amounts of stable oxides being detected on the surface. Instead, the exposure of TaS2 films to O2 leads predominantly to a reduction of the film thickness, evidenced by a decrease in the content of both Ta and S atoms of the film. This is attributed to the formation of oxide species that are unstable and mainly desorb from the surface below room temperature. Temperature programmed desorption spectroscopy confirms the formation of SO2, which desorbs form the surface between 100 K and 500 K. These results provide new insights into the oxidative degradation of 2D-TaS2 on Cu(111).