Electron transport in nanoparticulate ZnO films

Electron transport in a nanocrystalline thin film was studied using an elec trode geometry in which the resistance was measured between two contacts wh ich are separated by a narrow gap bridged by the material of interest. This setup, which allows the direct study of electron transport in a wet nanocr ystalline thin film, was used to investigate in situ the electron mobility in ZnO films in contact with liquid electrolyte solutions under accumulatio n conditions. The setup is also suitable for widely different experimental conditions and materials. Nanocrystalline ZnO films with 5 nm particle size were prepared from a washed and concentrated ethanolic dispersion. Charact erization by optical transmission and scanning electron microscopy revealed a porous homogeneous structure with the same particle size as in the origi nal sol. The mobility ranged from 10(-3) to 10(-1) cm(2)/Vs for an electron density between 5 x 10(18) and 1 x 10(20) cm(-3). The mobility depended on the electron density and the solvent (aqueous or nonaqueous), but was not affected by the type or the concentration of the electrolyte ions, or the d ielectric constant of the solvent. Interparticle electron transfer is very likely the slow step in electron transport. The importance of the surface c hemistry of the particles and the film porosity and heterogeneity is outlin ed.