Porosity dependence of electron percolation in nanoporus TiO2 layers

摘要

The electron diffusion coefficient at varying porosity has been determined in a series ofnanostructured TiO2 films of different initial thicknesses. The porosity was changed by applyingdifferent pressures prior to sintering, thereby modifying the internal morphology of the films thoughnot their chemical and surface conditions. A systematic increase of the effective diffusion coefficientwas observed as the porosity was decreased, indicating the improvement of the internal connectivityof the network of nanoparticles. The experimental results have been rationalized using percolationtheory. First of all, applying a power law dependence, the diffusion coefficient as a function ofporosity from different films collapsed in a single master curve. In addition, application of themodels of effective medium approximation EMA allows us to compare the experimental resultswith previous data from Monte Carlo simulation. The different data show a similar dependence inagreement with the EMA predictions, indicating that the geometrical effect of electron transport dueto variation of porous morphology in TiO2 nanoparticulate networks is well described by thepercolation concept