| Combining the properties of individual and collective properties of coupled nanocrystals, granular metal films exhibit rich physical properties different from the bulk materials, which make them to be good potential applications ranging from novel electronics devices to high-end photovoltaic cells. One the other hand, granular metal films with tunable disorder, electronic structure and electronic correlations in the processes of preparation, offer a good model system for studying some fundamental physical problems. In this thesis, series of Mox(SnO2)1-x granular films, two-dimensional (2D) and3D Agx(SnO2)1-x granular films, and Agx(SnO2)1-x films deposited at different substrate temperatures were fabricated by the co-sputtering method. The microstructure and electrical transport properties for these films were studied systematically.For Mo-SnO2granular films in the insulating regime, a σ-exp[-(T0/T)1/2] dependence of conductivity is observed. The results are explained in terms of the hopping conductance of granular metals proposed by Sheng and co-workers in which the structural effects of metal particles are considered, but incompatible with Efros Shklovskii’s variable range hopping conduction and co-tunneling conduction due to unrealistic values of the relevant parameters are inferred. And the function form of conductivity at higher temperatures can be best described by fluctuation-induced tunneling (FIT) conduction. When x increases, the FIT remains valid till very low temperature in metallic films.We have observed the lnT dependence of Hall coefficient (RH) and conductivity (σ) in both3D and2D Ag-SnO2granular films, the behaviors exist in films with gT from strong intergrain coupling (the dimensionless tunneling conductance gT>>1) to quite close to critical conductance gc (still in the metallic regime), which derive from the quantum correction due to electron-electron interaction (EEI). For the films at gT>>1regime, the influence of EEI effect is quite small that can be treat as perturbation as theoretical prediction. When x decreases, the influence of EEI effect would rise to bring about larger enhancements of RH and σ, until the films with gT quite close to gc, the enhancement increases to～60%for3D films, at this point, the EEI effect cannot be considered perturbatively. However, the theoretical expressions derived in the strong coupling limit gT>>1still can well describe the△RH∝lnT and△σ∝lnT behaviors for films at gT'gc regime, which requires to be further studied and calculated theoretically. Moreover, when the substrate temperature for3D Ag-SnO2films increases from573K to673K, the mean-grain size for films with the same gj would increase by～2nm, and the lowest temperature above which the△σ∝1n T law holds reduces by a factor of-1/2, which is consistent with theoretical estimation.We have observed the giant Hall effect (GHE) in Mo-SnO2granular films, and the Hall mobility is enhanced by about one order of magnitude near the quantum percolation threshold. On the other hand, in all the Ag-SnO2granular films with thickness～500nm,～28nm and～9nm, GHE and the peak of Hall mobility near the quantum percolation threshold are not observed. The distinct behaviors of Hall effect and mobility observed in the two granular systems derive from their different microstructures. There are many Mo and SnO2substructures exist in Mo-SnO2films, resulting in quantum percolation governs the electrical transport properties. While in Ag-SnO2films, there is no substructure, in contrast, distinctly spherical Ag grains are formed, and the transport properties are dominated by classical percolation. However, the inherent physics needs to be further studied theoretically. |
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