# Including surface ligand effects in continuum elastic models of nanocrystal vibrations

## TL;DR

This paper develops a continuum elastic model incorporating surface ligand mass-loading effects to accurately predict quantum dot vibrational energies and infer ligand elastic properties, improving upon traditional models especially for small QDs.

## Contribution

The authors introduce a novel elastic continuum model that accounts for surface ligand effects, enabling accurate vibrational predictions and ligand property inference.

## Key findings

- Model accurately predicts $l=0$ phonon energies across various QDs.
- Model performs well even in small QD regimes.
- Raman measurements combined with the model infer ligand elastic properties.

## Abstract

The measured low frequency vibrational energies of some quantum dots (QDs) deviate from the predictions of traditional elastic continuum models. Recent experiments have revealed that these deviations can be tuned by changing the ligands that passivate the QD surface. This observation has led to speculation that these deviations are due to a mass-loading effect of the surface ligands. In this article, we address this speculation by formulating a continuum elastic theory that includes the mass-loading effects of the surface ligands. We demonstrate that this model is capable of accurately reproducing the $l = 0$ phonon energy across variety of different QD samples, including cores with different ligand identities and epitaxially grown CdSe/CdS core/shell heterostructures. We highlight that our model performs well even in the small QD regime, where traditional elastic continuum models are especially prone to failure. Furthermore, we show that our model combined with Raman measurements can be used to infer the elastic properties of surface bound ligands, such as sound velocities and elastic moduli, that are otherwise challenging.