Friction Tuning of Interlayer Exciton Recombination in Van der Waals Heterostructures

Van der Waals heterostructures combine low friction with excellent optoelectronic properties, making them suitable for opto-nano-electromechanical systems. While the long lifetime of interlayer excitons in these materials helps reduce energy loss, friction in mechanical systems is unavoidable and can shorten the exciton recombination lifetime, undermining the low-friction benefits. Despite its importance, the fundamental mechanism underlying friction-induced changes in exciton recombination remains unexplored, mainly due to the difficulty of probing long-lifetime exciton recombination at friction interfaces. Here, time-resolved photoluminescence combined with an atomic force microscope is used to detect exciton recombination at the friction interface of MoS₂/WS₂ heterostructures. The findings show that friction generates defects, which trap electrons and create additional recombination pathways, shortening exciton recombination lifetimes. This, in turn, increases friction by altering charge density evolution and raising the friction sliding barrier. Density functional theory calculations confirm this mechanism. These results reveal how friction influences exciton recombination, paving the way for advancements in low-friction nano-opto-electromechanical devices.