Ultra Localized Optoelectronic Properties of Nanobubbles in 2D Semiconductors

TL;DR

This study combines advanced microscopy and spectroscopy techniques to reveal how nanobubbles in 2D semiconductors create highly localized electronic and optical states, significantly altering their properties at the nanoscale.

Contribution

It provides the first detailed experimental correlation between local electronic structure and emission properties in nanobubbles of 2D semiconductors, supported by self-consistent simulations.

Findings

Localized electronic states exist at bubble edges independent of defects.

The bandgap varies continuously over ~20 nm at the bubble edge.

Nano-PL shows a redshift of interlayer excitons within bubbles.

Abstract

The optical properties of transition metal dichalcogenides have previously been modified at the nanoscale by using mechanical and electrical nanostructuring. However, a clear experimental picture relating the local electronic structure with emission properties in such structures has so far been lacking. Here, we use a combination of scanning tunneling microscopy (STM) and near-field photoluminescence (nano-PL) to probe the electronic and optical properties of single nano-bubbles in bilayer heterostructures of WSe2 on MoSe2. We show from tunneling spectroscopy that there are electronic states deeply localized in the gap at the edge of such bubbles, which are independent of the presence of chemical defects in the layers. We also show a significant change in the local bandgap on the bubble, with a continuous evolution to the edge of the bubble over a length scale of ~20 nm. Nano-PL measurements observe a continuous redshift of the interlayer exciton on entering the bubble, in agreement with the band to band transitions measured by STM. We use self-consistent Schr\"odinger-Poisson (SP) simulations to capture the essence of the experimental results and find that strong doping in the bubble region is a key ingredient to achieving the observed localized states, together with mechanical strain.