Dipolar ligands tune plasmonic properties of tin-doped indium oxide nanocrystals

Surface functionalization with dipolar molecules is known to tune electronic band alignment in semiconductor films and colloidal quantum dots. Yet, the influence of sur- face modification on plasmonic nanocrystals and their properties remains little explored. Here, we functionalize tin-doped indium oxide nanocrystals (ITO NCs) via ligand ex- change with a series of cinnamic acids with different electron withdrawing and donat- ing dipolar characters. Consistent with previous reports on planar and nanocrystalline semiconductors, we find that withdrawing (donating) ligands increase (decrease) the work function, which we ascribe to an electrostatic potential shift across the molecular layer. Quantitative analyses of the plasmonic extinction spectra reveal that varying the ligand molecular dipole affects the near-surface depletion layer, with an anticorrelated trend between electron concentration and electronic volume fraction, factors that are positively correlated in as-synthesized NCs. Electronic structure engineering through surface modification provides access to distinctive combinations of plasmonic prop- erties that could enable optoelectronic applications, sensing, and hot electron-driven processes.