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

## TL;DR

The paper introduces a new nanoscopy technique to study defects in multi-layered MoSe2 at the nanoscale and femtosecond time scale, revealing how these defects affect optoelectronic properties.

## Contribution

A novel hyper-temporal transient nanoscopy technique is developed to map nanoscale spatiotemporal defects in multi-layered MoSe2 with high precision.

## Key findings

- Nanoscale strain-induced defects in MoSe2, such as nano-bubbles, reduce exciton-exciton annihilation rates due to strain-induced band distortion.
- Topographically hidden defects like lattice mismatches create mid-gap states that trap charge carriers and slow recombination processes.
- The new technique enables subwavelength mapping of spatiotemporal inhomogeneities in van der Waals materials.

## Abstract

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.