AFM-IR of Electrohydrodynamically Printed PbS Quantum\nDots: Quantifying Ligand Exchange at the Nanoscale

Colloidal quantum\ndots (cQDs), semiconductor materials with widely\ntunable properties, can be printed in submicrometer patterns through\nelectrohydrodynamic printing, avoiding aggressive photolithography\nsteps. Postprinting ligand exchange determines the final optoelectronic\nproperties of the cQD structures. However, achieving a complete bulk\nexchange is challenging, and the conventional vibrational analysis\nlacks the required spatial resolution. Infrared nanospectroscopy enables\nquantitative analysis of vibrational signals and structural topography\non the nanometer scale upon ligand substitution on lead sulfide cQDs.\nA solution of ethanedithiol led to rapid (∼60 s) exchange of\n≤90% of the ligands, in structures up to ∼750 nm thick.\nProlonged exposures (>1 h) caused the degradation of the microstructures,\nwith a systematic removal of cQDs regulated by surface:bulk ratios\nand solvent interactions. This study establishes a method for the\ndevelopment of devices through a combination of tunable photoactive\nmaterials, additive manufacturing of microstructures, and their quantitative\nnanometer-scale analysis.