Characterizing nanoscale spatiotemporal defects of multi-layered MoSe₂ in hyper-temporal transient nanoscopy

We directly characterize nanoscale spatiotemporal inhomogeneities of multi-layered molybdenum diselenide (MoSe₂) in real space and time - the nanometre-femtosecond scale, attributing to local mechanical structures such as strain and surface/subsurface defects, which are critical in semiconductor and optoelectronic applications. This remarkable precision is achieved through the development of a hyper-temporal transient nanoscopy incorporating a sideband-coupled generalized lock-in amplification technique, allowing for characterization of local spatiotemporal defects at each pixel within a subwavelength mapping region. By utilizing this technique, we characterize the nanoscale strain-induced spatiotemporal defects of multi-layered MoSe₂, including nano-bubbles that exhibit a noticeable reduction in exciton-exciton annihilation rates, which may attribute to the suppressed probability of bimolecular interaction of excitons due to the strain-induced band distortion. Moreover, we visualize topographically hidden spatiotemporal defects such as lattice mismatches, which induce mid-gap states that traps charge carriers and thereby slow down recombination process. We propose that this hyper-temporal approach to resolving intricate spatiotemporal inhomogeneities in van der Waals materials provides significant insights into their optoelectronic properties and opens new avenues for innovative material design and characterization.