Synthesis and Functionalization of PbSe Nanocrystals

Brian Ji with Andrew Mangham, Jeremy Streifer, and Dr. Bob Hamers

UW-Madison Department of Chemistry

Semiconducting PbSe nanocrystals show promise in solar technology because they can convert photons to electrons with an efficiency greater than 100%. We have discovered a method to synthesize and functionalize these nanocrystals, thereby stabilizing their semiconducting properties by inhibiting their oxidation upon exposure to oxygen and/or water. We first synthesized PbSe nanocrystals coated with oleic acid ligands. UV-Vis/near IR spectroscopy was used to probe the size and distribution of the nanoparticles and infrared absorption Spectroscopy (IRS) was used to determine the band gap of the particles, correlating to their size. We then preformed a biphase ligand exchange on the PbSe particles to coat them with mercaptopropionic acid. We also investigated a photochemically activated ligand exchange between trifluoroacetamide-protected amino-undecene (TFAAD) and the oleic acid terminated particles. The structure of TFAAD allows it to form a strong, covalent bond to the surface of other inorganic semiconductors, including PbS, and would pave the way for many other useful experiments.

Our results confirmed the existence of PbSe particles, proving a successful synthetic technique. A visible exciton peak from a near IR UV Vis spectrum confirmed that the particles were monodisperse. IRS revealed that the particles were originally capped with the oleic acid ligand. The particles capped with mercaptoproprionic acid suspended in water, signifying a successful ligand exchange. However, IRS did not confirm the attachment of TFAAD to the PbSe particles. Future TFAAD experiments will focus on adjusting variable factors such as time and eliminating contamination.