# Robust valley polarization of helium ion modified atomically thin MoS$_{2}$

## TL;DR

This study demonstrates that helium ion bombardment can modify atomically thin MoS₂ to create nanoscale valleytronic devices with preserved valley polarization, crucial for future optoelectronic applications.

## Contribution

It reveals that helium ion irradiation induces controlled defects in MoS₂, enabling nanoscale valleytronic device fabrication without significant loss of valley polarization.

## Key findings

- Interdefect distance correlates with disorder-related luminescence.
- Valley polarization remains robust until defects reach a few nanometers.
- Helium ion modification enables sub-10 nm valleytronic device writing.

## Abstract

Atomically thin semiconductors have dimensions that are commensurate with critical feature sizes of future optoelectronic devices defined using electron/ion beam lithography. Robustness of their emergent optical and valleytronic properties is essential for typical exposure doses used during fabrication. Here, we explore how focused helium ion bombardment affects the intrinsic vibrational, luminescence and valleytronic properties of atomically thin MoS$_{2}$. By probing the disorder dependent vibrational response we deduce the interdefect distance by applying a phonon confinement model. We show that the increasing interdefect distance correlates with disorder-related luminescence arising 180 meV below the neutral exciton emission. We perform ab-initio density functional theory of a variety of defect related morphologies, which yield first indications on the origin of the observed additional luminescence. Remarkably, no significant reduction of free exciton valley polarization is observed until the interdefect distance approaches a few nanometers, namely the size of the free exciton Bohr radius. Our findings pave the way for direct writing of sub-10 nm nanoscale valleytronic devices and circuits using focused helium ions.