Improved Strain Engineering of Monolayer Transition Metal Dichalcogenides via Van der Waals Epitaxy on Graphene/SiC(0001).

Engineering thermal strain is crucial for tuning the properties and functionalities of transition metal dichalcogenides (TMDs). Thermal strain arises from the thermal expansion coefficient (TEC) mismatch between TMDs and substrates, but conventional substrates often induce inhomogeneous broadening in the electronic structure, mainly due to surface roughness and charged impurities. Here, we demonstrate uniform thermal strain in monolayer WSe via van der Waals epitaxy on graphene/SiC(0001) substrates. Compared to WSe grown on graphite, its photoluminescence peaks show a redshift and line width narrowing of about 30%. These results suggest that uniform tensile strain is introduced to WSe due to the small TEC of SiC, and interfacial graphene suppresses the inhomogeneous broadening. Furthermore, tensile-strained monolayer MoS grown on graphene/SiC exhibits enhanced catalytic activity for the hydrogen evolution reaction. Our findings highlight the potential of the graphene/SiC substrate as a platform for improved strain engineering in TMDs, enabling future applications in electronics, optoelectronics, and electrocatalysis.