AFM-IR of EHD-Printed PbS Quantum Dots: Quantifying Ligand Exchange at the Nanoscale

TL;DR

This study uses AFM-IR nanospectroscopy to quantify ligand exchange in PbS quantum dots at the nanoscale, demonstrating rapid, controllable exchange and providing insights into structural stability for device fabrication.

Contribution

It introduces a nanoscale infrared spectroscopy method to analyze ligand exchange in colloidal quantum dots, enabling precise control and understanding of surface modifications.

Findings

Approximately 90% ligand exchange achieved in ~60 seconds

Prolonged exposure causes degradation of microstructures

Method enables quantitative analysis of ligand exchange at the nanoscale

Abstract

Colloidal quantum dots (cQDs) recently emerged as building blocks for semiconductor materials with tuneable properties. Electro-hydrodynamic printing can be used to obtain sub-micrometre patterns of cQDs without elaborate and aggressive photolithography steps. Post-deposition ligand exchange is necessary for the introduction of new functionalities into cQD solids. However, achieving a complete bulk exchange is challenging and conventional infrared spectroscopy lacks the required spatial resolution. Infrared nanospectroscopy (AFM-IR) enables quantitative analysis of the evolution of vibrational signals and structural topography on the nano-metre scale upon ligand substitution on lead sulphide (PbS) cQDs. A solution of ethane-dithiol in acetonitrile demonstrated rapid (~60 s) and controllable exchange of approximately 90% of the ligands, encompassing structures up to ~800 nm in thickness. Prolonged exposures (>1 h) led to the degradation of the microstructures, with a systematic removal of cQDs regulated by surface-to-bulk ratios and solvent interactions. This study establishes a method for the development of devices through a combination of tuneable photoactive materials, additive manufacturing of microstructures, and their quantitative nanometre-scale analysis.