Lead sulfide (PbS) nanocrystals are chemically tunable, high-extinction near-infrared absorbers and emitters, but, as synthesized, are coated in long organic ligands and therefore form electrically insulating films. Here, we optimize the interparticle ordering and particle density of films treated with a series of short organic ligands. We find that the types and densities of defects in the film depend on the chemical structure of the binding headgroup, and the length and rigidity of the ligand.

Electron microscope images of single PbS nanocrystals (left) and monolayers of PbS nanocrystals treated with formic acid at the liquid-air interface (top) or solid-air interface (bottom)