Ligand exchange based molecular doping in 2D hybrid molecule-nanoparticle arrays: length determines exchange efficiency and conductance

Effective control of ligand exchange is important in the emerging field of nanoparticle-based meta-materials; controlling both the separation and electronic coupling between nanoparticles impacts the electrical, optical, chemical, and thermal properties of these materials. However, methods to evaluate exchange efficiency are generally lacking for solid state devices. In this paper, it is shown that controlling the initial ligand length determines the efficiency of the secondary ligand's substitution into the nanoparticle array. Controlling this ligand exchange efficiency determines the post-exchange conductance in a manner akin to doping in conventional semiconductor systems. For a series of initial ligand lengths the distribution of nanoparticle separations in the array is determined, and the ligand exchange efficiency is extracted using a bond percolation model. Finally, Monte Carlo simulations of charge transport in the arrays agree with the experimental conductance data for each molecular state and support the determination of the corresponding exchange efficiencies. This analysis provides a general framework for maximizing the efficiency of ligand exchange that will benefit the use of nanoparticle films in electronic, optoelectronic, plasmonic, and sensing systems. Controlling the initial ligand length determines the efficiency of the secondary ligand's substitution into the nanoparticle array. This determines post-exchange conductance in a manner akin to doping.