Metal configurations on 2D materials investigated via atomic resolution HAADF stem

Abstract

The behaviour of palladium and nickel deposited on mechanically exfoliated samples of 2D transition metal dichalcogenides (MoS₂ , WS₂ and WSe₂ ) via e-beam evaporation was investigated. Sputtering of metals on the 2D flakes allowed for interaction of the metal and TMD to be investigated on the Å scale in an aberration-corrected transmission electron microscope. Through low energy sputtering, metals can be deposited on 2D materials without causing damage to the thin flakes. The material's interaction is investigated on the atomic scale via high resolution scanning transmission electron microscopy in high angle annular dark-field imaging. Initially, the effect of thermal annealing on the stability of the Pd-2D interaction was investigated, revealing the remarkable difference in particle stability between the 2D materials. Nickel deposition however only resulted in oxidised amorphous particles. The oxide particles' cross-sectional area and circularity were independent of the TMD substrate thickness, type, or deposition rate. LAY DESCRIPTION: Understanding the interaction between metals and 2D materials is imperative for future device functionalisation. Palladium and nickel were deposited on samples of 2D transition metal dichalcogenides (MoS₂ , WS₂ and WSe₂ ) via e-beam evaporation. Low energy introduced metal to the 2D materials without causing damage to the thin flakes. The metal-2D interaction was investigated on the Å scale via high resolution scanning transmission electron microscopy in high angle annular dark-field imaging. The interaction between the Pd and the 2Ds was investigated to see whether Pd is a viable contact solution for TMD materials and to study the metal-2D interaction at the atomic level. Effect of annealing and heat on the stability of the Pd-2D interaction was investigated, showing Pd-WSe₂ to have high particle stability up to 200 °C. In contrast, the Pd-MoS₂ and Pd-WS₂ had lower particle stability when heated, revealing particle agglomeration and changes. Nickel was found to oxidise into amorphous oxide particles quickly after deposition. The oxide particles' characteristics were independent of the TMD substrate thickness andtype, and independent of the rate at which metal was deposited.

Keywords: 2D materials; HAADF STEM; MoS2; WS2; WSe2; metal nanoparticles.