Quantitative Measurement of Interfacial Adhesion of CVD Grown Bilayer WS on Various Substrates.

The interfacial adhesion between transition metal dichalcogenides (TMDs) and the growth substrate significantly influences the employment of flakes in various applications. Most previous studies have focused on MoS and graphene, particularly their interaction with SiO/Si substrates. In this work, the adhesion strength of CVD-grown bilayer WS is directly measured using the nano scratch technique on three different substrates-Sapphire, SiO/Si, and fused quartz. The scratch test is performed using a Berkovich tip of ≈100 nm radius, mounted to a 2D transducer, capable of measuring normal and lateral forces simultaneously. The critical load is calculated from the Atomic Force Microscopy (AFM) images. The critical load for delamination is lowest for the Sapphire substrate (10 µN) and highest for the SiO/Si substrate (29 µN). MD simulation has also been performed, and the results agree with experimental observations. The pull-off force, an essential indicator for the easy removal and transfer of 2D materials, shows the least pull-off force of 2.56 nN for WS on sapphire and the highest, 2.83 nN, for WS on SiO/Si.