Electronic localization and optical activity of strain-engineered transition-metal dichalcogenide nanobubbles

TL;DR

This study uses ab initio methods to analyze strain-engineered transition-metal dichalcogenide nanobubbles, revealing how their structure influences electronic and optical properties, with implications for quantum device design.

Contribution

It provides the first detailed theoretical link between nanobubble strain, electronic structure, and optical activity in TMDs, guiding future quantum material engineering.

Findings

Strain induces tunable geometries and apex-concentrated strain.

Valence states become non-dispersive and composition-dependent.

Transitions from apex-localized valence states are predominantly dark.

Abstract

Strain-engineered transition-metal dichalcogenide nanobubbles are promising platforms for quantum emission, as revealed by recent experimental observations. In this work, we present an \textit{ab initio} investigation of MoS$_2$, WS$_2$, MoSe$_2$, and WSe$_2$ nanobubbles, linking their structural and electronic properties to predictions of their optical activity. Inflating forces yield tunable geometries with non-uniform, apex-concentrated strain, which is sensitive to material rigidity. Strain modifies band gaps and universally induces non-dispersive valence states, exhibiting composition-dependent wave-function character, as revealed by an in-depth analysis of band structures and orbital contributions. Crucially, transitions from these apex-localized valence states are predominantly dark. This characteristic is attributed to their localization at the $\Gamma$-point, inhibiting transitions to the lowest unoccupied states that reside at the K-valley. While revealing that the herein considered sub-10-nm nanobubbles fall short as single-photon emitters, our findings provide essential understanding of the structure-property relations in emerging quantum materials, providing robust design rules to optimize their characteristics for novel quantum applications.