Water-Dispersible Small Monodisperse Electrically Conducting Antimony Doped Tin Oxide Nanoparticles

We describe the fabrication of crystalline electrically conducting antimony-doped tin oxide (ATO) nanoparticles highly dispersible in polar solvents such as water and ethanol without any stabilizing agents. Nonagglomerated monodisperse ATO nanoparticles with different doping levels are obtained by a facile solvothermal reaction in tert-butanol, leading to the formation of monodisperse nanocrystals with a size of about 3 nm directly after synthesis. Electrical conductivity of ATO nanoparticles strongly increases due to the substitutional doping with antimony, reaching 6.8 x 10(-2) S cm(-1) for the as-synthesized nanoparticles prepared with 35 mol % Sb. This increase stems from transition from hopping in the undoped samples to band-like conduction in the doped samples as revealed by terahertz (THz) spectroscopy measurements describing transport on nanometer distances. The dc conductivity of the doped nanoparticles increases by about 3 orders of magnitude up to 62 S cm(-1) after annealing in air at 500 degrees C. The electrical conductivity, crystallinity, small size, and high dispersibility in polar solvents make the obtained ATO nanoparticles promising building blocks for the direct assembly of more complex conducting architectures using polymer templates that could be damaged in organic solvents. We illustrate the benefits of the water-dispersible ATO nanoparticles by their assembly to periodic macroporous electrodes using poly(methyl methacrylate) (PMMA) beads as the porosity templates. Aqueous dispersion of ATO nanoparticles can be directly combined with PMMA beads that are easily removed by calcination, enabling a facile deposition of 3D-macroporous ATO electrodes featuring optical transparency and a large periodically ordered conducting interface.