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.