Electrical and optical properties of thin films consisting of tin-doped indium oxide nanoparticles -: art. no. 155410

Electrical transport and optical properties were investigated in porous thin films consisting of In(2)O(3):Sn (indium tin oxide, ITO) nanoparticles with an initial crystallite size of similar to16 nm and a narrow size distribution. Temperature dependent resistivity was measured in the 77<300 K temperature interval for samples annealed at a temperature in the 573less than or equal tot(A)less than or equal to1073 K range. Samples annealed at 573less than or equal tot(A)less than or equal to923 K exhibited a semiconducting behavior with a negative temperature coefficient of the resistivity (TCR). These data were successfully fitted to a fluctuation induced tunneling model, indicating that the samples comprised large conducting clusters of nanoparticles separated by insulating barriers. Samples annealed at t(A)=1073 K displayed a metallic behavior with no signs of insulating barriers; then the TCR was positive at t>130 K and negative at t<130 K. Effects of annealing on the ITO nanoparticles were investigated by analyzing the spectral optical reflectance and transmittance using effective medium theory and accounting for ionized impurity scattering. Annealing was found to increase both charge carrier concentration and mobility. The ITO nanoparticles were found to have a resistivity as low as 2x10(-4) Omega cm, which is comparable to the resistivity of dense high quality In(2)O(3):Sn films. Particulate samples with a luminous transmittance exceeding 90% and a resistivity of similar to10(-2) Omega cm were obtained.