Ultrafast exciton dynamics in chemical heterogenous WSe2 monolayer

We investigate the exciton emission and transient absorption properties in size-dependent WSe2 monolayers using photoluminescence and pump-probe microscopy techniques. As the size of the WSe2 monolayer increases, the exciton emission presents nonlinear behavior and exhibits concentric fluorescence triangles with dark and bright bands in their fluorescence microscope images. The optical property of this special WSe2 monolayer is facilitated by the chemical heterogeneity in the growth of the WSe2 monolayer. The bright and dark regions with different band structures construct 1D interfaces, which play important roles in carrier scattering, trapping, and transporting. As a result, the saturable absorption of the monolayer is enhanced and a much longer exciton recombination process occurs.