Ultrafast Pump-Probe Microscopy on 2D Transition Metal Dichalcogenides

Although microscopic techniques have been used to characterize transition metal dichalcogenides (TMDs), direct observation of charge carrier dynamics distribution in TMDs with diverse shapes remains unexplored. Herein, ultrafast pump-probe microscopy (UPPM) is employed to reveal the carrier dynamics distribution in molybdenum disulfide (MoS2) and tungsten disulfide (WS2) monolayer of four shapes: triangular (t-MoS2), curved triangular (c-MoS2), triangular (t-WS2), and hexagonal (h-WS2). Monitoring the photon transmission T at 1.55 eV after pumping with a photon energy of 3.1 eV, a negative.T/ T occurs in t-MoS2 and c-MoS2, while a positive.T/ T is detected in t-WS2 and h-WS2 after 3-7 ps time evolution. This distinctive behavior is attributed to deep/shallow defects below the conduction band minimum (CBM) in MoS2 and WS2. Spatial-independent.T/ T is observed in tMoS2 and t-WS2, while the.T/ T in c-MoS2 has a rapid decay of photoexcited carriers at the vertices and curved edges. Additionally, a threefold symmetry of.T/ T is revealed in h-WS2, attributed to the dissimilar occupation of defect states near the h-WS2 CBM. This work paves the way for examining charge carrier dynamics of various shapes of TMDs and provides a unique microscopic method for studying the charge carrier dynamics in emerging TMDs heterostructures.