Controlling Nanoscale Thermal Expansion of Monolayer Transition Metal Dichalcogenides by Alloy Engineering

Two dimensional materials, such as transition metal dichalcogenides (TMDs), graphene, boron nitride (BN) are seen as promising materials for future high power/high frequency electronics. However, the large difference in the thermal expansion coefficient (TEC) between many of these 2D materials could impose a serious challenge for the design of monolayer-materials-based nano-devices. To address this challenge, alloy engineering of TMDs is used to tailor their TECs. Here, in-situ heating experiments in a scanning transmission electron microscope are combined with electron energy-loss spectroscopy and first-principles modeling of monolayer Mo_1-xW_xS₂ with different alloying concentrations to determine the TEC. Significant changes in the TEC are seen as a function of chemical composition in Mo_1-xW_xS₂, with the smallest TEC being reported for a configuration with the highest entropy. This study provides key insights into understanding of nanoscale phenomena that control TEC values of 2D materials.