Tunable Electronic Properties by Ligand Coverage Control in PbS Nanocrystal Assemblies
It is well-known that controlling the electronic properties of nanocrystal (NC) assemblies can be achieved by the usage of various types of ligands on the NC surface. However, the ligand coverage, which could also tune electronic properties, is always ignored. It is due to the lack of accurate evaluation methods of ligand amounts on the surface of NCs and the difficulty of ligand binding control in nanoscale. Here, we demonstrate a precise ligand (oleic acid) coverage control of PbS NCs through a modified liquid/air assembly technique. By this way, both the assembly structures and electronic properties can be tuned by ligand coverage at the same time. In particular, the medium oleic acid coverage (2.1 ligand/nm2), which forms a square lattice of PbS NCs, shows best electronic properties. Especially, when it is compared with the full coverage (2.4 ligand/nm2) and the sparse coverage (0.7 ligand/nm2) of oleic acid on NC surface. This ligand coverage controlled electronic properties of NC films will give new insights for finely tuning the properties of electronic devices based on NCs.