Electrical transport and optical properties were investigated in porous thin films consisting of In2O3:Sn (indium tin oxide, ITO) nanoparticles with an initial crystallite size of 16 nm and a narrow size distribution. Temperature dependent resistivity was measured in the 77<t<300 K temperature interval for samples annealed at a temperature in the 573tA1073 K range. Samples annealed at 573t A923 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 tA = 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 2 × 10-4 cm, which is comparable to the resistivity of dense high quality In2O3:Sn films. Particulate samples with a luminous transmittance exceeding 90% and a resistivity of 10-2 cm were obtained

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Porous tungsten oxide nanoparticle films were prepared by reactive gas evaporation. The structure was studied by x-ray diffraction and scanning electron microscopy, and the oxygen nonstoichiometry was inferred by x-ray photoelectron spectroscopy, elastic recoil detection analysis, and neutron scattering. Specifically, the films consisted of WO3−x with 0.25&lt;x&lt;0.4. The optical and electrical data were consistent with the formation of small polarons having a radius of 5–6Å. The infrared optical data, used to extract information on phonon energies, were instrumental to reach this conclusion. The polaron hopping energy was about half the polaron binding energy, as expected from the theory.

Conduction noise measurements were carried out in the 0.3-45 Hz frequency range on Au films covered by a thin layer of tungsten trioxide (WO 3 ) nanoparticles. Exposing the films to alcohol vapor resulted in a gradually increased noise intensity which went through a maximum after an exposure time of the order of 15 min. The maximum noise intensity could increase by several orders of magnitude above the initial level. Longer exposure times made the noise decrease and approach its original value. This effect was not observed in the absence of WO 3 nanoparticles. The phenomenon is discussed in terms of a new 'invasion noise' model in which the noise is related to the insertion and extraction of mobile chemical species.

We extend the Mayadas and Shatkes's approach ͓Phys. Rev. B 1, 1382 ͑1970͔͒ to study the optical properties of polycrystalline metal thick films in the visible and far infrared range of the spectrum. We show that in this range grain boundary scattering can account for the experimentally observed lowering of the film reflectivity as the mean size of its constituent grains decreases.

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