Isotopes represent a degree of freedom that might be exploited to tune the
physical properties of materials while preserving their chemical behaviors.
Here, we demonstrate that the thermal properties of two-dimensional (2D)
transition-metal dichalcogenides can be tailored through isotope engineering.
Monolayer crystals of MoS2 were synthesized with isotopically pure 100Mo and
92Mo by chemical vapor deposition employing isotopically enriched molybdenum
oxide precursors. The in-plane thermal conductivity of the 100MoS2 monolayers,
measured using a non-destructive, optothermal Raman technique, is found to be
enhanced by ∼50% compared with the MoS2 synthesized using mixed Mo isotopes from
naturally occurring molybdenum oxide. The boost of thermal conductivity in
isotopically pure MoS2 monolayers is attributed to the combined effects of
reduced isotopic disorder and a reduction in defect-related scattering,
consistent with observed stronger photoluminescence and longer exciton lifetime.
These results shed light on the fundamentals of 2D nanoscale thermal transport
important for the optimization of 2D electronic devices.