Electrical and Plasmonic Properties of Ligand‐Free Sn⁴⁺‐Doped In₂O₃ (ITO) Nanocrystals

Abstract

Sn⁴⁺-doped In2O3 (ITO) is a benchmark transparent conducting oxide material. We prepared ligand-free but colloidal ITO (8 nm, 10 % Sn⁴⁺) nanocrystals (NCs) by using a post-synthesis surface-modification reaction. (CH₃)₃OBF₄ removes the native oleylamine ligand from NC surfaces to give ligand-free, positively charged NCs that form a colloidal dispersion in polar solvents. Both oleylamine-capped and ligand-free ITO NCs exhibit intense absorption peaks, due to localized surface plasmon resonance (LSPR) at around λ=1950 nm. Compared with oleylamine-capped NCs, the electrical resistivity of ligand-free ITO NCs is lower by an order of magnitude (≠35 mΩ cm^-1). Resistivity over a wide range of temperatures can be consistently described as a composite of metallic ITO grains embedded in an insulating matrix by using a simple equivalent circuit, which provides an insight into the conduction mechanism in these systems